KEY-TERMS ● Centrosome: An associated pair of cylindrical shaped protein structures (centrioles) that organize microtubules and aid in forming the mitotic spindle during cell division in eukaryotes. ● Cell membrane (plasma membrane): The part of the cell which separates the cells from the outside environment and protects the cell, as well as regulating what goes in and out of the cell. ● Cell wall: Extra layer of protection and gives structural support (only found in plant cells). ● Chloroplast: Key organelle for photosynthesis (only found in plant cells). ● Cilium: Motile structure of eukaryotes having a cytoskeleton, the axoneme. ● Cytoplasm: Contents of the main uid- lled space inside cells, chemical reactions also happen in this jelly-like substance. ● Cytoskeleton: Protein laments inside cells (micro laments, microtubules, and intermediate laments). ● Endoplasmic reticulum (rough): Major site of membrane protein synthesis. ● Endoplasmic reticulum (smooth): Major site of lipid synthesis. ● Endosomes: Vesicles that traf c membrane and intra and extra cellular contents for recycling or degradation by lysosomes. ● Flagellum: Motile structure of bacteria, archaea and eukaryotes. ● Golgi apparatus: Site of protein glycosylation in the endomembrane system. ● Lipid bilayer: Fundamental organizational structure of cell membranes. ● Lysosome: Acidic organelle that breaks down cellular waste products and debris into simple compounds (only found in animal cells). ● Microvilli: It increases surface area for absorption of nutrients from surrounding medium. ● Mitochondrion: Major energy-producing organelle by releasing energy in the form of ATP. ● Nucleus: It contains chromosomes composed of DNA, the building block of life. Nuclear Architecture is important for dictating nuclear function. ● Organelle: This term used for major subcellular structures. ● Peroxisomes: It is a very small organelle that uses oxygen to breakdown and detoxify long fatty acids and other molecules ● Pili: It is also called mbria is used for conjugation and sometimes movement. ● Ribosome: RNA and protein complex required for protein synthesis in cells. ● Starch grain: It is found in the cytoplasm of a typical plant cell, it stores chemical energy of the plant. ● Vacuole: It contains cell sap or other storage material. ● Vesicle: It is small membrane-bounded spheres inside cells which transport substances. 2 Botany INTRODUCTION This is done both on a microscopic and molecular level as it encompasses prokaryotic cells and eukaryotic cells. Knowing Cell biology is a branch of biology that studies the different the components of cells and how cells work is basic to all structures and functions of the cell and focuses mainly on the biological sciences. idea of the cell as the basic unit of life. It explains the structure, It is also essential for research in bio-medical elds such organization of the organelles they contain, their physiological as cancer, and other diseases. Research in cell biology is closely properties, metabolic processes, signaling pathways, life cycle, related to genetics, biochemistry, molecular biology, immunology, and interactions with their environment. and developmental biology.
Filamentous cytoskeleton Plasmodesmata Small emembranous Plasma membrane vesicles Cell wall Chloroplast Thylakoid membrane Starch grain Smooth endoplasmic Vacuole reticulum Vacuole Tonoplast Ribosomes Mitochondrion (mitochondria) Peroxisome
Cytoplasm Nucleus Golgi vesicles Nuclear pore Nuclear envelope Golgi body Rough Nucleolus (Golgi apparatus) endoplasmic reticulum Fig. 1. Structure of Plant Cell.
CHEMICAL AND MOLECULAR are composed of bacteria and archaea – the shapes are: spherica l (cocci ), rods ( bacillus ), curved ( vibrio ), and spirals ( spirochetes ). ENVIRONMENT Cell biology focuses more on the study of eukaryotic cells, The study of the cell is done on a molecular level; however, and their signalling pathways, rather than on prokaryotes which most of the processes within the cell are made up of a mixture is covered under microbiology. of small organic molecules, inorganic ions, hormones, and water. The main constituents of the general molecular composition Approximately 75–85% of the cell's volume is due to of the cell includes: proteins and lipids which are either free- owing water making it an indispensable solvent as a result of its polarity or membrane-bound, along with different internal compartments and structure. These molecules within the cell, which operate as known as organelles. This environment of the cell is made up substrates, provide a suitable environment for the cell to carry of hydrophilic and hydrophobic regions which allows for the out metabolic reactions and signalling. exchange of the above-mentioned molecules and ions. The cell shape varies among the different types of organisms, The hydrophilic regions of the cell are mainly on the inside and are thus then classi ed into two categories: eukaryotes and and outside of the cell, while the hydrophobic regions are within prokaryotes. In the case of eukaryotic cells – which are made the phospholipid bilayer of the cell membrane. up of animal, plant, fungi, and protozoa cells – the shapes are The cell membrane consists of lipids and proteins, which generally round and spherical, while for prokaryotic cells – which accounts for its hydrophobicity as a result of being non-polar Cell Biology 3 substances. Therefore, in order for these molecules to participate Antibodies to many cellular proteins are available in in reactions, within the cell, they need to be able to cross this the market from different rms like Amershain, Dako, Sigma membrane layer to get into the cell. etc. Primary antibodies may be monoclonal or polyclonal. They accomplish this process of gaining access to the cell Secondary antibodies are generally coupled with uorochrome via: osmotic pressure, diffusion, concentration gradients, and for immuno uorescence studies. Antibodies can be stored at membrane channels. Inside of the cell are extensive internal –70°C or at –20°C. sub-cellular membrane-bounded compartments called organelles. The main instrument needed for the immuno uorescence studies is the fluorescence microscope with automatic Techniques Used to Study Cells photomicrograph system. Confocal microscopy is being recently Cell culture is the basic technique of growing cells in a laboratory used for detailed studies of the structures in or near the nucleus independent of an organism. Cells may be observed under the and also for round cells to obtain greater resolutions at different microscope, using several different techniques; these include levels in the cell. optical microscopy, transmission electron microscopy, scanning 2. Ion-Exchange Chromatography electron microscopy, uorescence microscopy, correlative light- In this method, molecules are separated on the basis of electron microscopy, and confocal microscopy. There are several differences in charge. Many bi ological macromolecules, such different methods used in the study of cells: as amino acids and proteins, have ionisable groups. They may 1. Immuno uorescence Microscopy carry positive or negative charge. The charge showed by these compounds depend on the pH of the solution. Immunological technique is the method to lo cate an antigen to a particular position of the cell of speci c antibody for a The ion-exchange sepa rations are performed in columns particular protein to be studied. It is another slightly modi ed packed with ion-exchanger. Two types of ion-exchangers are technique used to study cells under uorescence microscopy to present like Cation and Anion exchang ers. Cation exchangers locate the distribution of the antigen in the cells. are negatively charged and so they can attract positively charged molecules. In this case the rst antibody is un-labelled and the second antibody is made against IgGs of the organisms in which the rst Anion exchangers are positively charged, so they can bind antibody is made. This secondary antibody is coupled to some negatively charged molecules. Tire commercial ion-exchangers uorochrome such as Fluorescein Isothiocyanate, Rhodamine are made of porous polystyrene beads. The co-polymerisation of styrene is made with varying proportions of divinylbenzene etc. This method is used to study cellular architecture, subcellu - and styrene. lar localisation and the localisation of speci c proteins during cellular activities and cell cycle events. The most common example is Dowex 50, Sephadex etc. Sometimes chemically modi ed celluloses are used instead of polystyrene-based exchang ers, such as DEAE-cellulose, Carboxy- methyl cellulose etc. When the samples to be separated are passed through a column, molecules with opposite charge will bind while the other molecules with the same charge of the medium used in the Negatively column and some unwanted materials will pass through (Fig. 2). changed As the desired compound is retained in the column, this matrix technique is sometimes known as Sorption chromatography. The bind molecules can be eluted by increasing the concentration of the buffer or by changing the pH of the buffer. Sometimes the unwanted molecules are also retained within the column—thus eluting the desired substances. Ion-exchange chromatography has Species to be puri ed applica tion in separating amino acids and proteins. The selection Unwanted species of strong and weak exchanger depends on the stability over pH Fig. 2. Principle of separation in chromatography. and the effect of pH on charge. Generally, cationic buffers like Tris, Pyridine and Alkyl amines are used with anion exchangers The micro laments, microtubules and intermediate laments and anionic buffers like Acetate , Barbiturate and Phosphate can be studied to have an idea about the cytoskeletal structure are used with cation exchangers. Two types of elution can be of the cell (Fig. 2). This technique is useful to study many made, i.e., by passing the single buffer throughout the separation structures at higher resolution in the electron microscope top. 4 Botany which is known as Isocratic separation . When the gradient of 4. Partition and Adsorption Chromatography buffer is passed through the column it is called Gradient elution . It is a common practice to separate many substances by The separation of amino acids is generally performed using shaking the substance in two immiscible liquid phases in a strong acid cation exchanger. Gradient elution method helps in separating funnel. When a substance is shaken in the solvent it the sequential elution of amino acids. The acidic amino acids will partition with the formation of two phases. If one phase is come out rst followed by the neutral amino acids like Glycine allowed to move the substance will also move on the basis of and Valine . its partition coef cient. The substance will move rapidly if it This is followed by basic amino acids like Arginine and likes the mobile phase while, if it prefers the stationary phase, Lysine. This principle is also followed in the Amino acid Analyser. it will move slowly. Now the mobile phase may be liquid or Proteins are separated generally through weakly acidic or basic gas and, if the substance is adsorbed on the station ary phase exchangers. The elution of proteins takes place on the basis of and starts to move along with the stationary phase, then it is their isotonic points. called Adsorption chromatography. 3. Af nity Chromatography The substance will move at a varying speed depending In this method, the property of biological in teractions on the intensity and characteristics of adsorption and solubility between the molecules is used in order to get separation and in the solvent used for separation. Adsorption chromatography puri cation. In this case some ligand molecule (i.e., substrate can be performed either in the column or on the thin layer of of an enzyme) or some antibody is bound to the matrix of the the matrix. Adsorbents may be Silica gel, Aluminum ox ide, column. Calcium carbonate, Magnesium carbonate, cellulose etc. which are used as the stationary phase. On passing the molecules through the column, only those materials that form a speci c bond or complex with the ligand will Hydroxyapatite (Calcium phosphate) is used in the column be retained and all others will pass through the column (Fig. 3). to separate proteins, nucleic acids etc. It has the unique property of binding double-stranded DNA and not single- stranded DNA. Mobile phase moves down For mobile phases, different organic solvents may be used, depending on the polarity of the compounds to be resolved. The basic principle of Adsorption and par tition chromatography is used in Paper chro matography, Thin- layer chromatography and Gas chromatography. In case of paper chromatography, the paper is the support. Water is used to Stationary phase on matrix carrier Matrix Molecules preferring mobile phase Molecule adsorbing strongly to Matrix moist the paper and this hydrated phase is the stationary phase. Molecules preferring stationary phase Molecule adsorbing weakly to Matrix The organic solvent which is used in the chromatography is the mobile phase which moves rapidly through the aqueous phase. Fig. 3. Principle of separation in (a) partition (b) absorption chromatography. In Gas chromatography , the partitioning takes place between a liquid and a gas phase. Here the gas is the mobile The main principle of this method is that the compound phase and the nonvolatile liquid that coats the matrix substances to be puri ed is passed through the column containing some of a column is the stationary phase. This partitioning depends immobilised ligand, and the desired compound will bind to the on the temperature and the gradual increase in temperature helps ligand. more and more of the substance to come out in the mobile gas The ligand is the substrate in case of enzymes. Instead of phase from the stationary phase. This method is widely used column, this method can be utilised on nitrocellulose membranes for the qualitative and quantitative analyses of large number of for the puri cation of single-stranded DNA molecules. When the compounds. The principle for the separation is the difference in enzyme is to be puri ed, the ligand used is generally the substrate the partitioning of the volatilized compounds between the liquid and, for the separation of proteins, speci c antibodies are used. and gas phases. During the passage of the substance through the The bound-molecules can be eluted by increasing the ionic column a detector is attached with a chart recorder, which scan strength of the buffer. Thus this type of chromatography is highly the peak as the substance passes through the detector. speci c and versatile. This af nity chromatography is very useful 5. Gel Filtration Chromatography for the puri cation and separation of macromolecules of very small This type of chromatographic separation takes place on the amount. The mRNA is puri ed and isolated from various types basis of the size and shape of molecules utilizing the porosity of RNA through Af nity chromatogra phy. Immobilised single- of the gel ma terials. This method is also known as exclusion stranded DNA is used to isolate complementary RNA or DNA. or permeation chromatography. Cell Biology 5
This is done by using a column full of matrix consisting of added in the solution where cells or tissues are exposed for a Sephadex, Agarose, Sepharose, Bio Gel A, Bio Gel P, Polystyrenes certain period of time, either cells are xed at regular intervals (Bio-beads S) etc. Varying properties of the matrix axe obtained or aliquots are removed at various time intervals and the by crosslinking the poly-dextran with other compounds. radioactivity is noted. Most of the gel compounds are hydrophilic in nature, The radioactivity may be measured through Liquid thus causing very little-denaturation and adsorption of sensitive Scintillation Counter or the location of the radioactivity in different biochemical sub stance. Sephade x and polyacrylamide gels are positions of the cell, can be noted through Radioactive Tracer used as swollen beads. Many gels are available in the market Technology, called Auto-radiography. In this method, labelled cells as Super ne, Fine, Medium and Coarser. are xed and squashed on a slide or can be spread on a slide. The coarser bead shows fast ow rate but with poorer Then a thin layer of Special Auto radiographic stripping lm resolution. Fine and Super ne beads are used for analytical work is placed over it and is kept in the dark for exposure. Instead of and the coarse one for preparative work. lm, sometimes the slide is coated with photographic emulsions When the molecules of different sizes and pores are passed for autoradiography and is kept in the dark. through a column, molecules larger than pores of gel will pass During storage of slides in the dark, the emission of beta through it. Molecules of small pore size will enter the beads particles from the radioactive substance activates Silver halide and ows are retarded in the column. crystals of lm or emulsion. After a few weeks, the slides are The main use of this procedure is in the pu ri cation of developed like the photographic lm, which show the activated macromolecules, viruses, proteins, enzymes, hormones, antibodies, silver crystals as black spots under the light microscope. nucleic acids, amino acids etc. It is also used for the isolation The auto radiographic technique is also applicable to of ribosomal proteins. electron microscopy where cells or tissues are placed on a grid 6. Radioactive Tracer Technique instead of a slide. Here Silver grains are found to be opaque The easiest method for monitoring cellular events and their and electron dense against the electron transparent background. localisation in the cell is the use of radioactive isotopes. The The important use of this radioactive tracer technique is to note 3 most com monly used isotopes in the biological research are H , the metabolic pathway in the cell using Pulse-chase experiment C14 , P 32 , S 35 , I 125 , I 131 . They release high energy electron or beta through some radioactive precursor. When tissues or cells are particles during their radioactive decay. exposed to some radioactive com pounds for a certain period of Radioactive decay is a spontaneous process and its rate time, it is called Pulse and then cells are kept in a radioactive varies with the source. The number of atoms disintegrating at free medium after washing is called Chase. any time is proportional to the number of atoms present in the By xing cells or taking aliquots from cell fractionation isotope at that time. Conveniently, it is expressed as half-life in different times, biochemical transformations and movement which is de ned as the time taken for the activity to fall from of the precur sor (labelling) can be observed in the cell through any value to half that value. autoradiography or through Scintilla tion Counter. According to SI system, the unit of radioactivity is Becquerel (Bq), which is one disintegration per second. But the 7. Radio-immunoassay (RIA) most commonly used unit is the curie (Ci) which is measured as This method is widely used in Biochemistry and also in the number of nuclear disintegrations per second as compared clinical elds for diagnostic purposes. The quantitative analysis to that of 1 gm of Radium, i.e., 3.7 10 10 per second. of hormones, steroids and drugs can be done with the help of In case of biological materials, the micro curie (µCi) and this method. As the name implies, it combines the method of mill curie (mCi) are used. The disintegrations measured by the immunology as well as the ra dioisotope labelling techniques. Counter are referred to as Counts. In this method labelled antigen, un-labelled antigen and For any biological research, macromolecules of the cell are xed quantity of antibody are mixed together and a calibration made radioactive by administering the radioactive compounds to curve is plotted with percentage of labelled antigen against the tissues or cells and then the fate of the radioactive compound un-labelled antigen added (Fig. 4). can be monitored. For the study of DNA synthesis in the various Un-labelled antigen is treated as samples. Then antibody- types of cells or tissues, the use of H 3 is necessary. bound antigen is separated from free antigens through ion-exchange Many organic and inorganic compounds labelled with or adsorption chromatography. Sometimes the mixture of these Tritium are available of Bhabha Atomic Energy Research Centre, antigens and antibodies are passed through Sephadex column, Mumbai. Tritiated Thymidine and Uridine are used for the study when the bound antibodies remain attached to the Sephadex of DNA and RNA, respectively. The radioactive substance is beads and the unbound antigens can be washed out. 6 Botany
100 radiation and the substance. Light, heat, microwaves, infra-red, X-rays etc. have electromagnetic waves with average speed of 3 × 10 8 m/sec. These waves are composed of two components, such as electric eld and magnetic eld which are oscillating as perpendicular to each other. Light has both properties such as waves and particles. antigen (%)
Bound Labelled Bound Labelled 0 4 8 12 Electrons of an atom remain in the lowest energy level in Unlabelled antigen added the ground state. When an atom is treated with light, then its (arbitrary units) electrons move from the ground state to the excited state with the absorption of light or electromagnetic radiation. When an Fig. 4. Calibration curve (RIA). excited electron returns to the ground state, it will emit radiation of certain speci c wavelength (energy) which is utilised in Then the bound labelled antigens are eluted from the column spectroscopic analysis. and can be quantitatively arranged through Liquid Scintillation In some substance, emission of energy takes place spon - counter. Antibodies are generally labelled with H 3,C 14 or I 131 . taneously, i.e. , without application of any exter nal radiation. When cells or tissues axe used, radiolabeled antibodies can be Besides absorption or emission of light, atoms of certain substances used with the help of autoradiography to localize the various undergo some changes in electronic or nuclear properties when components within the cell. the molecule is exposed to electromag netic radiation. 8. Enzyme Immunoassay The study of absorption or emission properties as well as This method is also known as enzyme-linked immunosorbent some changes in the nuclear structure gives many information assay or ELISA—it combines the principle of Antibody-antigen of different macromolecules. reactions as well as the spectrophotometric enzyme assays by 10. Nuclear Magnetic Resonance Spectroscopy (NMR) using antibodies or antigens conjugated with some enzymes like Alkaline phosphatase, Alcoholic dehydrogenase, etc. ELISA It is a method for detecting interaction between the nuclei of is easy to operate and the cost is also less. Hence, ELISA is an atom with the magnetic eld of the electromagnetic radiation. gradually replacing RIA It is known that protons and neutrons of the atom have spin properties, When protons and neutrons of an atom are present In this method, speci c antibodies are attached to solid in pairs in the nucleus, there will be no net spin. phase ( lter paper, polystyrene micro titration plates etc.) then a limited amount of labelled antigen (with a speci c enzyme) But if there is any unpaired protons, these protons will and excess amount of un-labelled antigen were added, incubated impart a magnetic moment which can interact with an applied and washed. magnetic eld, i.e., the nuclei will absorb the energy and may lie either in a low energy state (nuclear spin parallel with the Some un-labelled antigens will also attach with antibodies. eld) or in a higher energy state (antiparallel to the eld). The enzyme substrate is then added and the enzyme activity is measured through spectrophotometer. The amount of enzyme This interaction of unpaired proton with the magnetic eld activity is found to be directly proportional to the amount of is the main principle of NMR spectroscopy. In a magnetic eld, antigen present. The sensitivity of ELISA is greatly enhanced these nuclei absorb radiation of radio wave length showing a through enzyme ampli cation technique using double antibody phenomenon known as nuclear magnetic resonance. method. For NMR study, unpaired nuclei like H 1, C 13 , N 14 , O 17 , p 31 ELISA is used in clinical elds to mea sure any antigen, etc. are commonly used in case of biological materials. NMR immunoglobin, haematological factor, hormone, etc. It is also spectra are plotted as energy absorbed against the magnetic used in the detection of bacterial toxins, viruses, Hepatitis B eld strength. 40 MHz radio wave frequency is used to obtain surface antigen etc. and in the assay of different antibodies like resonance of H1 nucleus. The NMR spectrometer scales in tan antiviral and antifungal antibodies. (T) units. Instead of enzymes, sometimes some uorochrome is The basic NMR instrument includes: tagged with antibody to assay the-antigens and antibodies using 1. Source of radiation, uorescence system. Then this method is known as Fluorescence 2. Receiver to detect the absorption of energy, Immunoassays (FIA). 3. Magnetic eld, 9. Spectroscopy 4. Oscilloscope or Recorder. Variety of techniques are developed with the principle of NMR is used for the study of molecular struc ture of some spectroscopy, i.e., study of interac tion between electromagnetic organic molecules, action of dif ferent antibiotics and drugs on Cell Biology 7 living systems, any alteration in the structure of molecules in the Simi larly, various functional groups like methyl, carbonyl, plasma membrane, effect of cholesterol on erythrocyte membranes amide groups etc. will show different IR spectra. Hence the IR etc. High eld NMR instruments (750 MHz, qvo MHz) have spectra is useful in biochemistry, particularly for the study of been developed to explore the structure and dynamic properties macromolecules and membranes, for the iden ti cation of drugs, of proteins in solution. for the study of secondary structure of proteins, such as the 11. Optical Rotatory Dispersion and Circular Dichroism number of helical structures present in protein etc. The three-dimensional structure of macromolecules in 13. Atomic Absorption/ Flame Spectrometry solution can be studied by noting their properties of absorption When vitalization of atoms of any compound occurs either of polarised light. The plane polarised light is a type of light in a ame or electro thermally, then it absorbs or emits atoms of consisting of waves oscillating in a single plane. This is obtained speci c wavelength. Emission ame spectrophotometer measures by passing a beam of light through a Nicol prism or a polarizing the emission of speci c wavelength of atoms in a ame which is screen. used to assay differ ent elements present in any biological sample. When a plane polarised light is passed through a substance, Atomic absorption spectrophotometer detects the absorption the polarised light will rotate to a certain angle depending on of a particular wavelength by atoms of a sample when it is heated its structure. It has also been found that this depends on the either in a ame or otherwise. The ameless method is more wavelength of light. Hence, the rate of change of rotation is sensitive than ame spectrophotometer. This atomic absorption measured with wavelength of light which is known as Optical spectrophotometer is useful in measuring amount of heavy metals Rotatory Dispersion (ORD). or other toxic metals present in any biological sample. Certain optically active substances have been found to The main components of the ame are: absorb polarised light differently, i.e., differential absorption of ● Nebulizer or Atomizer which makes ve drops of the right (R) and left (L) circularly polarised light. Thus another sample in solution, and then pass these drops with a forced spectroscopy—Circular Dichroism Spectroscopy (CD)—has air pressure to the burner ( ame). been developed to investigate the interaction of polarised light ● Monochromator is used to select the wave length. and the samples. ● Detector containing a photocell. Both CD and ORD are almost same but, due to the relative In case of Atomic absorption spectropho tometer, a source of simplicity of CD spectra, CD analysis has gained its superiority. white light (cathode dis charge lamp) and a double monochromator The resolution of CD bands is also superior. are used in addition to a detector and an atomizer. Circularly polarised lights is obtained by superimposing 14. Flow Cytometer two plane polarised light of the same wavelength which come Flow cytometry is a laser- or impedance-based, biophysical through the monochromator and Nicol prism. This superimposed technology employed in cell counting, cell sorting, biomarker light can be resolved into Right (R) and Left (L) waves. Certain detection and protein engineering, by suspending cells in a stream substances absorb differentially R and L waves and show refraction of uid and passing them by an electronic detection apparatus. with elliptically polarised beam. Principle: The instrument, Flow Cytometer, is based on ORD and CD are useful in the study of the secondary the principle that single cells in suspensions axe passed through structure of macromolecules, partic ularly protein and amino acids a eld of illumination and each cell is quantitatively assayed in solution. CD spectra is also useful for the study of binding by staining cells with uorochromes or noting the scattering of of substrate and inhibitor to the enzyme. light by each cell. The helical structure of DNA and protein can be studied with Procedure: Cell suspensions are placed at rst in a ow the CD spectra. CD spectrum, is very sensitive to any structural cell tted with a device to form a liquid jet. Cells will travel changes of the macromolecule. So, any interaction of protein through the center of a liquid jet at the rate of 5-10 m/second. with nucleic acids can be studied by observing changes in the Cells are then passed through the area of intense light. If the CD spectra. The transitions between double-stranded and single- cells contain some uorochromes, uorescence emission can stranded nucleic acids can be studied with CD spectrophotometer. be detected using lens, beam splitters and photomultiplier tubes 12. Infra-red (IR) Spectrophotometry (Fig. 5). Infra-red (10 3-10 4 nm) shows vibrational spec tra, so Different uorochromes used will show dif ferent types molecules under infra-red show dif ferent vibrational levels. of uorescence emission. These signals are then quanti ed and These vibrational levels change with the bonding characteristics are kept in the memory of computers as histograms. During the ow, droplet formation is done using piezo electric crystal of the compound. For example, vibrations of C–H,–CH 2 and in the ow cell. CH 3 will differ. 8 Botany
At the end of the instrument there is a droplet de ector 3. Microscopic Magnetic Resonance Imaging (mMRI). assembly. 4. Positron Emission Tomography (PET). Giving a de nite quantitative value to the computer for In CT scan, differences in the absorption of X-ray by the collecting a speci c cell, desirable will then be collected in a brain tissue are used to construct a three dimensional image (3D microtiter plate or tube and undesirable cells will be collected image). Here the dose of X-ray needed is very low. in the waste. The principle of MRI is to use magnetic eld which shows Flow cell differences in vibration of Protons (HT) of the water molecules Sample introduction port Photomultiplier I present in the tissues of body. This vibration of water molecule Droplet charging Aperture Filter depends on the chemical surroundings of the tissue. Besides Dichroic mirror signal protons of water molecules, the vibration of other atoms like Sheath uid Flurosive, Sodium, Phosphorus, Nitrogen can also be detected. line Lens Flow coil Filter Photomultiplier II Through MRI studies, many things of the metabolic Laser Flow cell processes of brain and other organs may be investigated. Both light Laser light Droplet de ector these types of scanning help to detect the location of tumours, assembly sites of hemorrhage, intracranial bleeding etc. MRI is better Waste D r o p l e t than CT scan because it does not require X-ray. Again, all these formation modern techniques are possible only with the help of computer. Microliter plate mMRI is the most technically complex of all techniques. Fig. 5. Operation of the ow cytometer. It requires placing the specimen inside a strong magnetic eld. The advantage of mMRI is that it can image specimen which Different uorochromes are used for different types of are too large and opaque and it can also image living specimen. cells which will then help to sort the cells having two types of It can also provide digitally recording anatomical information nuclei ( heterokaryons ). from intact specimen. Unique contrast mechanism can be applied 15. Applications of Flow Cytometer and Cell Sorter to highlight the different features of specimens. This instrument has a great importance in selecting somatic PET scan is based on the use of positron, which is like hybrid and cybrid cells using uorescence labelling technique. an electron except that it has positive (+) charge. It also gives It can also be applied to know the physical and physiological 3D image where the molecules are located. It helps to measure characteristics of plant protoplasts which has a great importance the blood ow in the brain, glucose utilisation and oxygen in molecular biology and in the manipulation of plant protoplasts. consumption, and for the diagnosis of psychiatric disorders, brain This instrument is also useful in the study of the cell cycle and tumours, epilepsy and le-generative changes due to Alzheimer’s in the isolation of chromosomes. disease. This is also suitable for cell sorting. In this case, the uid- containing cells is charged temporarily and the charged cells of CELL WALL desir able particles axe de ected in the electric eld. These are Cell wall is a tough, rigid layer that Robert Hooke in collected in the tube for the collection of mitochondria, nuclei, surrounds some types of cells. Cell 1678 discovered cell chromosomes besides cells, protoplasts and pollen. wall is a characteristic feature to cells wall while observing Flow cytometer is also used to measure the DNA content of plants, bacteria, fungi, algae and a thin section of cork. of cell, chromosomes etc. for the measurement of the ploidy level some archaea. It is located outside Around the same in short time. In case of cell-fusion studies heterokaryons can the cell membrane. time an Italian doctor be rapidly sorted out in ow cytometer. In Genetic Engineering The major function of the Marcello Malphigi studies, transformed or hybrid cells can be sorted out with this cell wall is to provide rigidity, claimed cell cavities are instru ment. tensile strength, structural support, surrounded by a rm protection against mechanical stress 16. Non-invasive Scanning of Soft Tissues cell wall. Several methods are now developed to examine the soft and infection. It also aids in diffusion tissue of the body, particularly the brain, without injecting any of gases in and out of the cell. colored substance in the body. Cell wall composition varies from species to species and also depends on the developing stage of the organism. Protozoans These include: and animals do not have a cell wall. All living things are made 1. Computer Tomography Scan (CT Scan). up of cells. The structures of different types of cells are related 2. Magnetic Resonance Imaging (MRI). to their functions. Cell Biology 9
Animal cells and plant cells (shown in Fig. 6) have features A point that should fascinate any physical scientist is the in common, such as a nucleus, cytoplasm, cell membrane, degree of control that has evolved in order to achieve conditions mitochondria and ribosomes. in which both lipid and protein structures can self-assemble (not Plant and algal cells also have a cell wall, and often have to mention the sophisticated mechanisms to make use of and chloroplasts and a permanent vacuole. Bacterial and yeast cells preserve the DNA genetic code). have different structures to animal and plant cells. While the biochemical functioning of cells depends on A rst division of organisms is between those whose proteins (essentially many of a cell’s functions can be understood cells have within them a nucleus, the structure containing most as proteins performing chemical reactions), these proteins “live” of the genetic material in the form of DNA, and those whose attached to lipid membranes, or con ned by lipid compartments. cells don’t. The nucleated cells are called eukaryotic and are The physical properties of the lipids are thought to found in animals, plants, fungi, protozoa and algae. In contrast, contribute to the regulation of protein biochemistry, but this is bacteria (and the less common archaea) do not have a nucleus still not fully clear. and their DNA is spread throughout the cell. These cells are TYPES OF CELLS called prokaryotic. Eukaryotic organisms can be unicellular or multicellular while all prokaryotes are unicellular. There are two types of cell, prokaryotic (bacteria) and eukaryotic (animal, plant, fungi and protoctista (unicellular organisms)). Aside from the distribution of DNA, there are other very obvious differences between eukaryotic and prokaryotic cells. At (1) Prokaryotic cells: Prokaryotes have no nucleolus – the a coarse level the size, and at the level of molecular detail the DNA is in the cytoplasm, and it can from small circular strands of chemical detail of proteins used in the two classes of organisms is DNA called plasmids. Prokaryotic cells all have small ribosomes, whereas eukaryotic all have larger. ribosomes.Prokaryotic have quite different. (This is what allows certain antibiotics to interfere none of these organelles. Prokaryotic cells have cell walls, but at the molecular level with essential processes in bacteria, while only plant cells and fungi have walls in the eukaryotic class. not affecting the functioning of the cells of an animal.) (2) Eukaryotic cells: Eukaryotic cells all have their DNA Within the nucleated cells there are structural differences enclosed in a nucleus. Note that viruses are not cells, by DNA between animal and plant cells. In animals, cells can often secrete with a protein coating. All eukaryotic cells have a nucleus, protein bres and complex sugar molecules (polysaccharides). These mitochondria, Golgi body, vesicles and endoplastic reticulum. mesh together at the molecular scale, making an elastic material Any eukaryotic cell with a agella have a 9 + 2 microtubule known as extracellular matrix (ECM). Some cell types reside at arrangement, but prokaryotic do not have a 9 + 2 arrangement. a particular place in the organism (e.g., the epithelium) while A bacterial cell contains cytoplasm, nucleus and ribosomes. Its others are motile through the ECM (e.g., immune system cells). external structure is made up of a cytoplasmic membrane, a Animal Cell Plant Cell cell wall and a capsule, which is surrounded by pilli, which is a type of a small hair, which coats the outer body.
Cell membrane Large plant Plant cells resemble other eukaryotic cells in many ways. Ribosomes vacuole Centroles For example, they are enclosed by a plasma membrane and have ER a nucleus and other membrane-bound organelles. A typical plant Starch grain Ncleus cell is represented by the diagram shown in Fig. 7. Nucleous A plant cell contains cytoplasm, a vacuole, mitochondria, Mitochondrion Cell wall
Small vauole Golgi, smooth and rough endoplastic reticulum, a nucleus, Golgi complex Chloroplast ribosomes and a peroxisome. Its body is made of a plasma membrane and a cell wall. This wall keeps it rigid. An animal cell contains Cytoplasm, Centriols, Peroxisome, Fig. 6. Animal cell and Plant cells. Lysosome’s, Micro laments, Mitochondria, Rough and Smooth From a “materials” point of view, it is useful to distinguish Endoplastic Reticulum, a Nucleus, Chromatin, Ribosome’s, clearly structures that are essentially built and regulated by lipids: Microtubules and a Golgi apparatus. Its made of a Plasma the external bilayer (plasma membrane), the nuclear membrane Membrane with Cilia, small hairs, surrounding the entire cell. The and various other organelles in the cell, such as the Golgi Cytoplasm is what suspends all the other organelles in the cell complex and the endoplasmic reticulum, which play key roles Lysosomes are made by the smooth ER, and are used to in the assembly of proteins. In contrast, microtubules and actin destroy and recycle old organelles and microorganisms that the laments are structures assembled of proteins cell no longer needs. Mitochondria are used to produce energy (in 10 Botany the form of ATP) in the cell. The rough endoplasmic reticulum Composition of plant cell wall: In the growing cell wall is used to produce proteins, using ribosomes that cover their the carbohydrates are cellulose, hemicellulose and pectin as well surface. The proteins are normally in the form of mostly tRNA. as lignin, proteins and enzymes. The outer part of the primary The nucleus controls the whole cell, and is the largest organelle. cell wall of the plant epidermis usually forms a permeability
barrier and is known as the plant cuticle.
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Fig. 7. The structural elements of a prokaryotic cell. Plasma Membrane
Cell Wall Functions Periplasmic space Gram Positive The functions of cell wall are given below: ● It gives the cell a de nite shape and structure and provides Peptidoglycan structural support. ● Protection against infection and mechanical stress. ● It separates interior of the cell from the outer environment. ● It enables transport of substances and information from Plasma membrane the cell insides to the exterior and vice versa. ● It also helps in osmotic-regulation. It prevents water loss. Periplasmic space ● The physiological and biochemical activity of the cell wall Peptidoglycan Gram Negative helps in cell-cell communication. ● It prevents the cell from rupturing due to tugor pressure. Outer membrane ● Aids in diffusion of gases in and out of the cell. (lipopolysaccharide ● Also provides mechanical protection from insects and and protein) pathogens. Fig. 8. Gram positive and gram negative.
Plant Cell Wall Fungi Cell Wall Plant cell wall performs essential functions like providing shape, tensile strength and protection and also helps the cell develop Fungi cell wall consists of chitin and other polysaccharides. They tugor pressure to maintain the pressure of the cell contents. Plant do not have cellulose in their cell walls. Species of fungi that cell walls are primarily made up of cellulose. cellulose is the possess a cell wall have a plasma membrane and three layers most abundant macro-molecule on Earth. of cell wall material surrounding it. These layers are made up Cell Biology 11 of chitin, glucans and a layer a of mannoproteins (mannose to the uptake of nutrients and their passage from cell to cell. containing glycoproteins). Enzymes responsible for cellulose synthesis are produced in the golgi apparatus and reach the cell surface, where they Periplasm become functional, within the membranes of vesicles, Microtubules Plasma membrane beneath the plasma membrane are thought to have a role in the Peroxisome Cytosole Vacuole organization of cellulose into micro brils. ER Golgi s Following cell division the primary wall is laid down by the s s deposition of micro brils on the middle lamella. The orientation Nucleus of the micro brils differs depending on whether the cells are Mitochondrion destined to be parenchymatous or more specialized tissue. The Cell wall secondary wall normally consists of three layers laid down after cell extension is complete. The micro brils are closely packed Fig. 9. Gram positive and gram negative. and aligned in the same direction in each layer but in different directions in successive layers. Cell Wall Structure In maturing bres, the micro brils are mainly parallel to The composition of the cell wall differs from one species to the the long axis, while in developing xylem vessels they are laid down in rings or in helical strands. other. In bacteria the cell wall is made up of peptidoglycans. The Archean cell wall is made of glycoproteins and polysaccharides. The hydrated nature of the micro brils renders the wall In fungi cell walls are made of glucosamine and chitin. In elastic and permeable to water and solutes, including the soluble respiratory gases. The pressure of cell contents against the walls algae it is composed of glycoproteins and polysaccharides. The causes stretching and confers turgidity to plant tissues. This is plant cell wall is mainly composed of cellulose, hemicellulose, a major factor in the provision of mechanical support to the glycoproteins, pectins and lignin. nonwoody tissues of plants. Lipid membranes are generally soft, meaning that they easily In the cells of sclerenchyma and xylem tissues, lignin deform due to thermal uctuations, although energies greater than is deposited within the layers of the secondary walls and the the thermal kBT are needed to bend lipid bilayers. In contrast with protoplasts of these cells eventually disintegrate. lipid structures, we can identify protein structures, in particular Lignin confers considerable strength and these tissues the laments called microtubules (made of the protein tubulin, form the wood of plants . polymerised together) and actin laments (made of the protein Function of cells which animal and plant cells have in common. actin). These form the cell’s cytoskeleton and are quite stiff, in the sense that thermal energy is not suf cient to bend them Part Function signi cantly on the scale of a cell radius: they are straight rods. Nucleus Contains genetic material, which controls the activities of the cell Figure 7 shows a prokaryotic cell, which has a simpler architecture than a eukaryotic cell, but many common aspects Cytoplasm Most chemical processes take place here, in both structure and function. It compares and contrasts these controlled by enzymes two types of cell. Bacteria are probably the most important type Cell membrane Controls the movement of substances into of prokaryotic organism. and out of the cell Note in particular the absence of a nuclear membrane – here Mitochondria Most energy is released by respiration here the DNA is spread throughout the cell. All bacteria are single- Ribosomes Protein synthesis happens here cell organisms (although to understand their evolution, and how Plant cells also have extra parts: they survive, it only makes sense to consider their collective behaviour in a colony). Many bacteria, under appropriate nutrient Part Function conditions, can replicate extremely quickly (the bacterium E. coli Cell wall Strengthens the cell can duplicate every 20 minutes, in contrast with fast eukaryotic Chloroplasts Contain chlorophyll, which absorbs light division, which may only occur every 24 hours), giving rise to energy for photosynthesis an exponential increase in cell number with time. Permanent vacuole Filled with cell sap to help keep the The external covering of a plant cell composed mainly of cell turgid cellulose molecules organized into micro brils. Small quantities of proteins have also been identi ed, e.g. enzymes such as CELL PROCESSES invertase, phosphatase, and ATPase, whose functions are related Cells regulate their behaviour and their function by controlling 12 Botany the concentration (in some cases it may be small numbers) of these are ideas still under investigation. different proteins. Some proteins perform a function themselves, whereas others serve to control protein production rates. This Forces and Structures “network” of interactions is analogous to a computing machine, As discussed above, there is evidence that forces acting on a and, indeed, cells can compute. cell, and its general mechanical environment, can affect protein However, the circuit is not hard set. It is not enough to formation and hence the process of gene regulation. How this know the genetic code since the cell behaviour will also depend takes place is still not known, but the most obvious issues to most importantly on the concentration of all proteins, but also consider are whether the external force has an effect on the on other factors among which are the conformation of the DNA binding of some transcription factor, or on the production rate and the composition of lipids in the membranes. There is recent of some other important intermediate molecule. evidence that forces acting on a cell, and more generally the Much better accepted is the idea that a cell has mechanical mechanical environment around a cell, can affect the process stability and can exert forces on the surroundings. Processes of gene regulation, maybe one day offering new opportunities such as motility and adhesion to a substrate require dynamic to exploit stem cells for regenerative medicine. Before looking control of the architecture. at how this might work, it is useful to review very brie y the There are three main types of semi exible laments in essential processes that take place in a cell. eukaryotic cells, made from different proteins, and they differ Cells contain DNA, which is a sequence of amino-acid substantially in their resistance to bending. The laments have bases. The cells in a human all have the same DNA but are many roles in the cell: providing mechanical stability; facilitating clearly very different. About 200 different cell types are classi ed directional intracellular transport (they are tracks for motors); in a human (bone, skin, blood, muscle, etc.). The differences anddetermining the symmetric separation of the nucleus and cell between cells (biologists would call this the phenotype) are due during cell division, enabling cell motility. The three types of to each being in a different steady state of protein expression. protein laments present in many eukaryotic cells. Proteins are constantly being made and degraded in a cell. The rate of production is nely controlled, involving a sophisticated Adaptation to the Environment interplay between binding constants determined by detailed Making a protein is a process that takes around 60 minutes in protein structures, and statistical physics. Short sequences of an animal cell (roughly 30 minutes to transcribe a gene and 30 DNA containing the information suf cient to describe a protein minutes to translate the protein. In a bacterium, the process is sequence (a gene) are copied (by a protein machine called RNA much faster, with transcription and translation taking just a few polymerase) into RNA. This process is known as transcription. minutes each (signi cant time is “saved” by not having to cross There are subtle different functions for the RNA, but the main the nuclear membrane). The proteins can remain functional for one is for these RNA sequences (in this case called messenger- anything between a few seconds up to inde nitely (until they RNA: mRNA) to be made into proteins. This process, through are used, or diluted when a cell divides). which the RNA code is read, and “translated” into a sequence A cell might divide a few times per hour (typical of bacteria of residues to make a speci c protein, is called translation and involves a protein machine called the ribosome. in a good growth environment), or every few days (cells in an embryo and some cancer cells) or never (various cells in a Proteins are the main “workhorses” of a cell: they do things developed organism don’t divide, such as neurons). either in isolation or by assembling with multiple units of each other, or of different proteins. As a general principle, cells need Having an idea of these timescales is important because to have different proteins at different times, and also they need it shows that if a tissue needs to sustain some transient force to use the energy and materials at their disposal ef ciently. For (e.g. we press a nger on our skin), or if a bacteria colony both reasons the production of each type of protein is regulated. needs to respond to a sudden change in temperature, this will take place with the proteins available at the time, in the cells This regulation of gene expression happens most importantly (there is no time for gene expression). However, given a few at the transcription stage, since this is the rst stage and hence minutes, bacteria could have new “adequate” proteins in place, it is most ef cient to take regulating action there. The main in response to the changed conditions. process of regulation involves RNA polymerase binding to DNA in order to start transcription, and this binding af nity can be However, the assembly and interaction of proteins with controlled by certain proteins known as “transcription regulation each other inside a cell can happen over shorter timescales than factors”. So by making a few more regulation factor proteins, gene expression. Of particular importance to the structure and a cell can tune how many of various other proteins to make. dynamic behaviour of eukaryotic cells is the assembly of tubulin There is also regulation at the other stages, with subtle and actin into their respective laments, and the equilibrium but important effects, for example, on the control of noise, and between assembled and free (monomeric) protein. Many structures Cell Biology 13 inside cells are typically in a dynamic steady state – that is, they of material through a cell: kinesin and dynein are molecular are constantly being assembled/disassembled, rather than being motor machines that are able to travel (in opposite directions, permanent features. The graph of the length of one microtubule positive and negative, respectively) along microtubules, “carrying” over time shows alternating periods of growth, where tubulin cargo such as vesicles. monomers join a lament at one end, and fast depolymerisation. A cell crawling on a surface is an example of a biological This equilibrium can easily and rapidly be unbalanced by physical process that calls for a number of physical considerations, such forces, and, indeed, this is at the heart of how a cell can probe as mechanics of the cell interior (cytoskeleton) and membrane; the environment, and “decide” in which direction to migrate, forces of adhesion; and mechanisms for the extension of cell or in which direction it might “want” to exert a pulling force. protrusions (lamellipodia) in the forward direction. Observation of the buckling of microtubules provoked by polymerisation permits simultaneous measurement of force (fp) CELL MEMBRANES and mean polymerisation speed. The cell membrane (also known as the plasma membrane The bead on the left of the tube is held in an optical trap, or cytoplasmic membrane ) is a biological membrane that measuring the force on the tube. The chart on the left shows the separates the interior of all cells from the outside environment. force at buckling, for tubes growing at various speeds. Growth It is selectively permeable to ions and organic molecules and is affected by mechanical forces, and also growth determines controls the movement of substances in and out of cells. The tube strength. basic function of the cell membrane is to protect the cell from its surroundings. It consists of the lipid bilayer with embedded Cell Mechanics proteins. The behaviour of a cell is determined by the concentrations and Cell membranes are involved in a variety of cellular processes interactions of a set of proteins. It can be regarded essentially such as cell adhesion, ion conductivity and cell signalling and as a computation, the inputs for which are the levels of a set of serve as the attachment surface for several extracellular structures, proteins, and the ne tuning of their interactions. In laboratory including the cell wall, glycocalyx, and intracellular cytoskeleton. experiments on cells, it is very challenging to set or control Cell membranes can be arti cially reassembled Phospholipids these values; experimenters have to rely on observing the mean provide the basic structure of cell membranes, where they aggregate behaviour over many cells, and attempt to deduce the “algorithm” in a closed, sheet-like structure the lipid bilayer. The bilayer is through which cells determine the outcome. A typical example formed by two parallel layers of lipids oriented so that their ionic is chemotaxis – that is, how a cell responds to a gradient of head groups protrude into the aqueous environments on either concentration of some chemical. Many cells will initiate migration side of the bilayer. Their nonpolar tails cluster together in the towards the source of the chemical. middle of the bilayer where they can interact and avoid water. Micro tubules, which are typically arranged radially in When phospholipids are shaken vigorously with water, they the cell, enable control over the transport of molecules in the spontaneously form liposomes, small spherical vesicles with a cell. They are stiff enough to resist compression and they play lipid bilayer surrounding an aqueous center. a key role in moving the two copies of the genetic material to Lipid bilayer: The basic structural unit of cell membranes; opposite sides of a cell when cell division takes place. composed of two parallel sheets of membrane lipid molecules Individual actin laments are too soft to “push” effectively arranged tail to tail. against other cellular structures), but they link with each other Liposome: A spherical structure in which a lipid bilayer via other proteins that act as crosslinkers. The network formed surrounds a water droplet. 20% or more of the weight of in this way (it is a polymer gel in the language of soft matter a membrane consists of protein molecules, many of them physics) is strong enough to push out (or pull in) the external cell glycoproteins. Peripheral proteins are associated with just one membrane, and indeed actin lament gels are the key element at face of the bilayer. Integral proteins extend completely through work in cell motility. Myosin is a molecular motor that is able the cell membrane and may twist in and out of the membrane to travel in one direction along an actin lament. many times before ending on the outside with a hydrophilic Active forces are originated by particular protein assemblies, sugar group. known as molecular motors. These are complex structures that can transform chemical energy (stored as ATP molecules in CELL ORGANELLES cells) into conformational changes – that is, mechanical energy. Living things are made of cells, or biological units also referred Some motors (myosin) can pull two actin laments towards to as the building blocks of life. Some organisms consist of just each other, which is how an actin gel can exert a tensile force. one cell, while others are made of trillions of cells. Each one Other motors are used for directed (and non-random) transport of these cells functions as a tiny factory, with individual parts 14 Botany that work together to keep the cell alive and, in turn, keep the are small pieces of RNA found throughout the cytoplasm and on organism going. These parts are called organelles. some other organelles. Their only job is to assemble proteins. DNA coding tells them which proteins to make. Prokaryotic Organelles and their Functions cells can have tens of thousands of ribosomes. Eukaryotic cells The nucleus is arguably the most important organelle in the cell. can have hundreds of thousands, if not millions of them, all It is the control center, telling all of the other organelles what making proteins. to do and when to do it. Once proteins are made, they need to be moved to different The nucleus also contains all of the cell's genetic material, parts of the cell. The endoplasmic reticulum (E.R.) is a collection or its DNA. This material has all the instructions the cell needs of lipid membranes that work to move the proteins from one for making proteins and many other important molecules. The area of the cell to another. The E.R. comes in two different nucleus is surrounded by two membranes. These membranes forms — rough and smooth. Rough E.R. has ribosomes attached have many openings in them, which allow for the transport of to it. These ribosomes make proteins that are scheduled to leave materials into and out of the nucleus. RNA, proteins, and other the cell. The E.R. transports these proteins to another organelle molecules move out of the nucleus into the rest of the cell. that will package them up and ship them out. The smooth E.R. The cell's chromosomes are also found in the nucleus. does not have any ribosomes on its surface. This is where the These condensed strands of DNA are what carry all of the lipid part of the cell membrane is assembled. cell's genetic information. When the cell is in its growing Once the ribosomes on the E.R. have made the proteins phase, the DNA is elongated into very thin, hair-like structures. for exporting from the cell, they need to be packaged in such When the cell is getting ready to divide, the DNA condenses a way that they can leave the cell and be taken in by the parts into chromosomes and the material gets duplicated. Within the of the body that need them. The organelle responsible for this nucleus of eukaryotic cells is a structure called the nucleolus. is called the Golgi apparatus (or Golgi bodies), which looks This is the site of ribosome formation. like a stack of pancakes. The Golgi apparatus changes, sorts Prokaryotic cells lack a nucleus. In these organisms and packages the proteins as they leave the E.R. so they are (which include the bacteria), the genetic material is free- oating ready to leave the cell. Because it is so important to shipping within the cell membrane. The genetic material of prokaryotes things out of the cell, the Golgi apparatus is always found near is a different shape than that of eukaryotes, but it serves the the cell membrane. same function. Cell parts wear out and die. These pieces of 'garbage' need Outside of the nucleus but within the cell membrane is a to be disposed of somehow. That is the job of the lysosomes. gel-like substance called cytoplasm (also called cytosol). It is These structures are lled with digestive enzymes that break made mostly of water and dissolved salts. It bathes the organelles down those items that would become toxic if they were left and keeps them healthy. It is also the medium through which in the cell. Lysosomes also break down proteins, lipids and materials move about the cell. carbohydrates into more usable forms for the cell. Within the cytoplasm is a network of tiny tubes called the cytoskeleton. These tubes are used to give the cell structure and STRUCTURE OF THE NUCLEUS: also to support the organelles by holding them into place. Some NUCLEOLUS, NUCLEAR MEMBRANE, AND parts of the cytoskeleton also work to transport certain things NUCLEAR PORES between different parts of the cell. The cytoskeleton is made from two different components: The Nucleus microtubules and micro laments. Microtubules are hollow and made of protein. They are very important in helping to maintain Your cells are ne-tuned and well-oiled machines. For the most the cell's shape. They are also important during cell division. part, they run smoothly, like a brand-new car on a freshly-paved When this occurs, the microtubules form structures called spindle surface. Many cells have an extremely important structure that bers, which allow the chromosomes to separate. Microtubules holds all the essential information vital to their ability to perform. are also part of the different projections coming off of the cell Each of these cells comes with an owner's manual - instructions surface. These structures, called cilia and agella, assist with on how to run day to day operations and specialized functions. cell locomotion. These instructions are your DNA, which is stored in its very Micro laments are very thin threads made of protein. Like own cellular glove compartment — the nucleus. The nucleus is the microtubules, they help the cell keep its shape. a membrane-bound structure that contains the genetic material of a cell. The plural of nucleus is nuclei. Not all cells have Making proteins is a very important job for a cell. Ribosomes Cell Biology 15 nuclei, but many cells, such as those in plants, fungi, animals, In contrast, on a large-scale, the arrangement of chromosomes and protists, contain these structures. can determine their properties. Chromosomes are organised into The nucleus is not just a storage compartment for DNA . two compartments labelled A ("active") and B ("inactive"), each It's the site of some essential cellular processes. First, DNA can with distinct properties. Moreover, entire chromosomes segregate be duplicated in the nucleus. This process is called replication into distinct regions called chromosome territories . and creates an identical copy of DNA. Creating two identical The organization of chromosomes into distinct regions copies of the owner's manual is the rst step in cell division, within the nucleus was rst proposed in 1885 by Carl Rabl. where each new cell will get its own set of instructions. Later in 1909, with the help of the microscopy technology at the Second, the nucleus is the site of transcription. The central time, Theodor Boveri coined the termed chromosome territories dogma of biology states that DNA is copied into RNA, which after observing that chromosomes occupy individually distinct is then turned into protein. nuclear regions. Since then, mapping genome architecture has Transcription is the process of creating different types of become a major topic of interest. RNA from DNA. Transcription would be like making copies of Over the last ten years, rapid methodological developments individual pages of the owner's manual that can then be passed have greatly advanced understanding in this eld. Large-scale DNA out and read by the rest of the cell. organization can be assessed with DNA imaging using uorescent There are three types of RNA that are formed in the nucleus. tags, such as DNA Fluorescence in situ hybridization (FISH), mRNA, or messenger RNA, is a code that can be read by the and specialized microscopes. Additionally, high-throughput cytoplasmic structure called the ribosome during translation. sequencing technologies such as Chromosome Conformation Capture-based methods can measure how often DNA regions Translation is a process that creates proteins from mRNA. are in close proximity. At the same time, progress in genome- A ribosome, which we will discuss in future lessons, is made editing techniques (such as CRISPR/Cas9, ZFNs, and TALENs) up of proteins and a second type of RNA, rRNA or ribosomal have made it easier to test the organizational function of speci c RNA. tRNA, or transfer RNA, is also used during the process DNA regions and proteins. of translation. All three of these RNA types — mRNA, rRNA, and tRNA — are created by the process of transcription within Nuclear Membrane the nucleus. A nuclear membrane, also known as the nucleolemma or Nuclear Structure and Organization karyotheca, is the phospho lipid bilayer membrane which surrounds the genetic material and nucleolus in eukaryotic cells. The nucleus is the structure responsible for containing DNA and providing a place for replication and transcription. These The nuclear membrane consists of two lipid bilayers—the processes make sure that the instructions on how to make you inner nuclear membrane, and the outer nuclear membrane. The who you are carried out. This is obviously a very important job, space between the membranes is called the perinuclear space, so to keep the cell functioning at top speeds, the nucleus is a a region contiguous with the lumen (inside) of the endoplasmic well-organized structure. reticulum. It is usually about 20–40 nm wide. The nuclear membrane also has many small holes called nuclear pores that The nucleus is surrounded by a nuclear envelope, which allow material to move in and out of the nucleus. is a double membrane comprised of an outer membrane and an inner membrane. Nuclear Pores Nuclear organization refers to the spatial distribution of Nuclear pores are protein-based channels in the nuclear envelope. chromatin within a cell nucleus. There are many different levels They regulate the movement of molecules from the nucleus to the and scales of nuclear organisation. cytoplasm, and vice versa. In most eukaryotic cells, the nucleus At the smallest scale, DNA is packaged into units called is enclosed by this nuclear membrane in order to separate it nucleosomes. The quantity and organisation of these nucleosomes from the cytoplasm. can affect the accessibility of local chromatin. This has a knock-on Many higher eukaryotic cells have as many as 2,000 effect on the expression of nearby genes, additionally determining nuclear pore complexes in the nuclear membrane of each cell. whether or not they can be regulated by transcription factors. This membrane or envelope keeps the DNA safe, and contains At slightly larger scales, DNA looping can physically bring it within the nucleus. Despite the presence of this barrier, together DNA elements that would otherwise be separated by communication still has to take place between the nucleus and large distances. These interactions allow regulatory signals to the cytoplasm, so the nuclear pores serve as transportation and cross over large genomic distances - for example, from enhancers communication channels. to promoters. 16 Botany
This transportation and communication has to be able to cytoplasm. In mitotic division not only the chromosomes are happen quickly for cell regulation and health. Some molecules replicated but all necessary cytoplasm constituents and organelles are simply small enough to pass through the pores, but larger are precisely divided between two daughter cells. In mitosis molecules must be recognized by different signal sequences there is no change in chromosome number. before being allowed to diffuse through the nuclear pores via a Mitosis is observed in all types of cells -haploid, diploid or concentration gradient. polyploid. If a parental cell has 1000 chromosomes, or even just Some substances, like carbohydrates, lipids, and even 1 chromosome, the daughter cells have 1000 and 1 chromosomes, ribosomes are able to pass through quite easily, while RNA respectively after mitosis. Some useful terms which are used: and some proteins must be "cleared" for release through signal Chromosome: A gene is made up of DNA which codes sequences within the nucleus. for one or more polypeptides. A chromosome is made up of many genes. The DNA in the chromosome is wrapped around MITOSIS histone and non-histone proteins. Before DNA synthesis, there is only one double stranded helix of DNA in each chromosome. Mitosis is the common method of nuclear division, followed by cytokinesis (cytoplasmic division). It usually occurs in vegetative Chromatid : After DNA synthesis , there are two identical or somatic cells therefore it is known as somatic division. It DNA helices connected by a structure called the centromere. occurs in meristematic tissues - shoot, root tip. It results in the Each DNA helix is called a chromatid.These chromatids are increase of size, shape and volume of plant parts and causes called sister chromatids. growth. The pattern of mitosis is fundamentally the same in all cells.In this division the mother cell produces two genetically MEIOSIS identical daughter cells which resemble each other and also The process, during which the germ cells are generated is parent cell qualitatively and quantitatively. The separation of called meiosis. It represents nature's solution of the problem of separate sister chromatids into two new cells with exactly the chromosome doubling that would occur, if two diploid cells, same number of chromosomes and half the amount of nuclear i.e. two cells with a double set of chromosomes would fuse. DNA is known as mitosis. Accordingly meiosis produces haploid germ cells, with maternal Therefore, it is also called equational division Mitosis is and paternal germ cell fusing at fertilization and thus generating also known as indirect division because it is an elaborate process a diploid fusion product, the zygote. involving a series of important changes in nucleus as well as Meiosis is made up by two subsequent processes, both
INTERPHASE Chromatin PROPHASE Spindle Nucleus Centrosomes Chromatids of Nucleolus chromosomes Nuclear envelope Aster INTERPHASE-PROPHASE TRANSITION PROMETAPHASE Daughter chromosomes Equatorial plate
TELOPHASE
ANAPHASE METAPHASE Fig. 10. Motosis. Cell Biology 17 of which resemble mitosis. In the rst process the homologous (2). Each chromosome in a pair is similar in structure chromosomes are separated. It has an unusually long prophase (homologous), but would have come originally from different that is subdivided into different stages: leptotene, zygotene, parents. Later in prophase the homologous pairs twist round pachytene, diplotene and diakinesis. They are followed by each other and chromatids may cross over (3). Breaks occur at metaphase, anaphase and telophase. these cross-overs (or chiasmata, singular chiasma) and pieces of Upon fertilization two nuclei fuse, so that the number of chromatid are exchanged (4). Chromosome pairs line up across chromosomes does necessarily double. If this thought is spun the equator of the spindle at metaphase I (5). In anaphase I the further, an exponential growth of the number of chromosomes chromosomes separate and travel to opposite ends of the spindle. from generation to generation would have to be expected. This is The chromosomes migrate to the equators of two new spindles not the case, because the chromosomes are reduced to half their for metaphase 2 (7). Next the chromatids are pulled apart in normal number in germ cell production. This process is called anaphase 2 to form four clusters of chromosomes in telophase meiosis. It consists of two successive mitosis-like divisions: in 2. The nuclear envelopes reform around four haploid nuclei that the rst division is the number of chromosomes reduced to their will give rise to the micro- or megagametophyte. half, the second is a normal mitosis. The leptotene —This phase differs only slightly from the Each germ cell contains a complete set of chromosomes, early stages of mitosis. The cells and nuclei of meiotic tissues a haploid set. Accordingly the cells are haploid and zygotes and are usually bigger than that of their neighbouring tissues and the body cells that stem from them are diploid, because they they do often seem to be longer and are longitudinally structured. contain two equal sets of chromosomes, one from the mother At regular intervals thickenings can be found, like beads on a and one from the father. There exist, especially in plants, also string: the chromomeres. Their number, size and positioning is triploid, tetraploid...polyploid cells. We will later on also have constant in each species. A trained cytologist can infer from their a closer look at their production. structure to their identity. In 1931, J. Belling did count 1500-2000 chromomeres in the haploid chromosomal set of a lily species. At the end of the last century (1883, 1887, 1888) the Belgian zoologist E. van Beneden and the German zoologist The zygotene — During this phase the pairing of homologous T. Boveri studied meiosis.Both understood its eminent importance. chromosomes begins. It is also called synapsis and the resulting At nearly the same time E. Strasburger found that two successive structure synaptic complex. Directly after initiation of the process mitoses occur in the pollen tube of many lily species. In 1884 the pairing spreads like a zipper across the whole length of the he began to reproduce these experiments in his courses. Still, it chromosome. does not become clear, neither in the text nor in the drawings The pachytene —During the pachytene the pairing stabilizes. that the number of chromosomes is reduced to half the original The number of synaptic complexes corresponds to the number amount during the rst division. It was not before 1889 that of chromosomes in a haploid set of the respective species. The he could prove this using Allium as his specimen. In the same pairs are also called bivalents. year J. L. L. Guignard described the reduction of the number The diplotene —The bivalents separate again. During of chromosomes in Lilium martagon. Contrary to mitosis the this process it emerges that each chromosome is built of two prophase of the rst meiotic division takes unusually long and chromatids, so that the whole complex harbours four strands during can be subdivided into several phases. During this time the the separation. Normally the separation is not accomplished, but homologous chromosomes pair. The single phases as we know the homologous chromosomes stick together at certain points, the them today are shown in the following pictures. chiasmata (sing. chiasma). This state is marked by the formation of cross-like structures, single or multiple loops. The diakinesis is the continuation of the diplotene. It is usually dif cult demarcate both states. The chromosomes condense and become more compact. The metaphase —From now on the processes resemble that of mitosis again. The nuclear membrane is completely Fig. 11. Meiosis. dissolved, the mitotic spindle fully developed. The homologous chromosomes do still stay together. At the beginning of meiosis, in prophase 1 the nuclear The anaphase —During anaphase the homologous envelope disintegrates and chromosomes become visible as in chromosomes are separated from each other. It is followed by mitosis (1). The chromosomes have replicated but individual the telophase, then by interkinesis (this state corresponds to chromatids are not visible. Instead of lining up on a metaphase the so-called quiescence or interphase state). Shortly afterwards plate, as in mitosis, chromosomes come together in pairs the second mitotic division with the usual states of prophase, 18 Botany metaphase, anaphase and telophase occurs. Here the chromatids ● Schwann, Theodor (1810-82), German physiologist, are separated from each other. generally considered the founder of modern histology, the study of the structure of plant and animal tissues. Schwann FACTS TO KNOW was born in Neuss and educated at the universities of Bonn, Warzburg, and Berlin. He was (1838-48) professor ● Hertwing coined the term cytology in 1893. of anatomy at the University of Leuven in Belgium; there ● Huxley called protoplasm as physical basis of life in 1863. after until his death he was associated with the University ● Purkinje gave the term protoplasm in 1837. of Libge, also in Belgium, serving as professor of anatomy ● In 1670, Antonie van Leeuwenhoek (1632-1723) described from 1848 to 1858, when he became professor of physiology. cells in a drop of pond water using a microscope. A Dutch Schwann achieved the physiochemical nature of life by businessman and a contemporary of Hooke. He also used applying the cell theory of the German botanist Matthias microscopes and was a physicist. He made his own ne Jakob Schleiden to the evolution of animal life. quality lens for use in monocular microscopes and was ● In 1840, Albrecht von Roelliker realized that sperm cells the rst person to observe bacteria and protozoa. Some and egg cells are also cells. of his lenses could magnify objects 250X. ● In 1845, Carl Heinrich Braun Cells were rst identi ed ● In 1833, English Botanist Robert Brown discovered the as the basic unit of life. nucleus in plant cells. ● In 1855, Taking Brown's original description of nuclei and ● In 1838, Matthias Jakob Schleiden, a German botanist, observations by Karl Nägeli on cell division, the German concluded that all plant tissues are composed of cells physiologist, physician, pathologist, and anthropologist and that an embryonic plant arose from a single cell. He Rudolf Virchow was able to add a third tenet to the cell declared that the cell is the basic building block of all plant matter. This statement of Schleiden was the rst theory: Omnis cellula e cellula, or all cells develop only generalizations concerning cells. from existing cells.Virchow, Rudolf (1821-1902), German pathologist, archaeologist, and anthropologist, the founder ● In 1839, Theodor Schwann, a German biologist, reached of cellularpathology. Virchow was born in Schivelbein, the same conclusion as Schleiden about animal tissue Pomerania (now Swidwin, Poland), and educated at being composed of cells, ending speculations that plants theUniversity of Berlin. In 1843 he became prosector at and animals were fundamentally different in structure. the Charite Hospital in Berlin, and in 1847 a university Schwann described cellular strucures in animal cartilage lecturer. In 1849 he was invited to the medical school of (rigid extracellular matrix). He pulled existing observations together into theory that stated: 1. Cells are organisms and Wurzburg as professor of pathological anatomy, having been all organisms consist of one or more cells. 2. The cell is dismissed from his Berlin posts because of revolutionary the basic unit of structure for all organisms and that plants activities. In 1856 he returned to Berlin as professor and and animals consist of combinations of these organisms director of the university's pathological institute. which are arranged in accordance with de nite rules. In ● Virchow was the rst to demonstrate that the cell theory other words, the cell is the basic unit of life. This statement applies to diseased tissue as well as to healthy tissue-that is, was the second generalization concerning cells and is the that diseased cells derive from the healthy cells of normal most important in the development of biology. It became tissue. He did not, however, accept Louis Pasteur's germ known as the cell theory. theory of disease. He is best known for his text Cellular Pathology as Based on Histology (1850-1860).
SUM-UP ● Cells are a basic unit of life, sharing many common mechanisms across different classes of organisms (plants, animals, microorganisms). Between these classes there are also key differences in cell architecture. ● Cells are too small to be seen without magni cation. Cells range in size from 1 to 100 micrometers. The study of cells, also called cell biology, would not have been possible without the invention of the microscope. With the advance microscopes of today, such as the Scanning Electron Microscope and Transmission Electron Microscope, cell biologists are able to obtain detailed images of the smallest of cell structures. Cell Biology 19
● There are two primary types of cells. Eukaryotic and prokaryotic cells are the two main types of cells. Eukaryotic cells are called so because they have a true nucleus that is enclosed within a membrane. Animals, plants, fungi, and protists are examples of organisms that contain eukaryotic cells. ● Prokaryotic organisms include bacteria and archaeans. ● The prokaryotic cell nucleus is not enclosed within a membrane. Prokaryotic single-celled organisms were the earliest and most primitive forms of life on earth. Prokaryotes can live in environments that would be deadly to most other organisms. These extremophiles are able to live and thrive in various extreme habitats. ● Archaeans for example, live in areas such as hydrothermal vents, hot springs, swamps, wetlands, and even animal intestines. ● There are more bacterial cells in the body than human cells. Scientists have estimated that about 95% of all the cells in the body are bacteria. The vast majority of these microbes can be found within the digetive tract. Billions of bacteria also live on the skin. ● Cells contain genetic material. Cells contain DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), the genetic information necessary for directing cellular activities. DNA and RNA are molecules known as nucleic acids. In prokaryotic cells, the single bacterial DNA molecule is not separated from the rest of the cell but coiled up in a region of the cytoplasm called the nucleoid region. ● In eukaryotic cells, DNA molecules are located within the cell's nucleus. DNA and proteins are the major components of chromosomes. Human cells contain 23 pairs of chromosomes (for a total of 46). There are 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes. The X and Y sex chromosomes determine sex. ● Cells contain structures called organelles which carry out speci c functions. Organelles have a wide range of responsibilities within a cell that include everything from providing energy to producing hormones and enzymes. ● Eukaryotic cells contain several types of organelles, while prokaryotic cells contain a few organelles (ribosomes) and none that are bound by a membrane. There are also differences between the kinds of organelles found within different eukaryotic cell types. Plant cells for example, contain structures such as a cell wall and chloroplasts that are not found in animal cells. Other examples of organelles include: Nucleus - controls cell growth and reproduction. Mitochondria - provide energy for the cell. Endoplasmic Reticulum - synthesizes carbohydrates and lipids. Golgi Complex - manufactures, stores, and ships certain cellular products. Ribosomes - involved in protein synthesis. Lysosomes - digest cellular macromolecules. ● Different types of cells reproduce through different methods. Most prokaryotic cells replicate by a process called binary ssion. This is a type of cloning process in which two identical cells are derived from a single cell. Eukaryotic organisms are also capable of reproducing asexually through mitosis. In addition, some eukaryotes are capable of sexual reproduction. This involves the fusion of sex cells or gametes. Gametes are produced by a process called meiosis. ● Groups of similar cells form tissues. Tissues are groups of cells with both a shared structure and function. Cells that make up animal tissues are sometimes woven together with extracellular bers and are occasionally held together by a sticky substance that coats the cells. Different types of tissues can also be arranged together to form organs. Groups of organs can in turn form organ systems. ● Cells have varying life spans. Cells within the human body have different life spans based on the type and function of the cell. They can live anywhere from a few days to a year. Certain cells of the digestive tract live for only a few days, while some immune system cells can live for up to six weeks. Pancreatic cells can live for as long as a year. ● Cells commit suicide. When a cell becomes damaged or undergoes some type of infection, it will self destruct by a process called apoptosis. Apoptosis works to ensure proper development and to keep the body's natural process of mitosis in check. A cell's inability to undergo apoptosis can result in the development of cancer. 20 Botany MULTIPLE CHOICE QUESTIONS
1. Which one of the function of peroxisomes? 10 . The Chiasmata are formed during : (a) Synthesis of glyoxylate (a) Diakinesis (b) Zygotene (b) Synthesis of serine (c) Diplotene (d) Pachytene (c) Protection of cellular organelles from the toxic effects 11 . The carrier of genetic information is :
of H 2O2 (a) Ribosomal RNA (b) Transfer RNA (d) All of these (c) Ribosomes (d) DNA 2. The Centrioles have : 12 . Which of the following is NOT present in an animal cell? (a) RNA (b) DNA (a) Nucleus (b) Mitochondria (c) Microtubules (d) None of these (c) Cell wall (d) DNA 3. The nucleolus was discovered by : 13 . The protein products of tumor suppressor genes may (a) Robert Brown (b) Fontana (a) be present in non-cancerous cells (c) Leeuwenhoek (d) De Duve (b) cause signal cell-death 4. The number of Chromosomes are constant for a particular (c) Regulate the cell-cycle species was stated by : (d) All of the above are correct (a) Benden and Boveri (b) W. Waldeyer 14 . The Nuclear membrane begins to break into vesicles in (c) W. Flemming (d) Sulton and Bovery which stage ? 5. Which of the following statements is true ? (a) Telophase (b) Anaphase (a) A diploid cell produces four diploid cell in meiosis (c) Prophase (d) Metaphase (b) The chromosome number is reduced to half in daughter 15 . In which stage chromosome line up along mid line of cell? cells in mitosis. (a) Telophase (b) Anaphase (c) The chromosome number remains the same like parent (c) Prophase (d) Metaphase cell in meiosis. 16 . The fusion of a vesicle with cell-membrane and release of (d) None of the above contents to outside cell is called : 6. The term protoplasm was proposed by : (a) Osmosis (b) Facilitated diffusion (a) Purkinje (c) Exocytosis (d) Endocytosis (b) A. V. Leeuwenhoek 17 . The Secretions of cell products such as proteins is facilitated (c) Sehleiden and Schwann by : (d) Strasburger (a) Mitochondria (b) Golgi bodies 7. The Lysosome contains : (c) Endoplasmic Reticulum (d) Chloroplasts (a) Oxidative enzyme 18 . The Mitochondria is also known as : (b) Enzymes of energy conversion (a) Bioblast (b) Parabasal bodies (c) Enzymes of protein synthesis (c) Plasmosomes (d) All of these (d) Hydrolytic enzymes 19 . RNA is found in : 8. The Plasmodesmata facilitates : (a) In uenza virus (b) Poliomyelitis virus (a) Free exchange of substances between cells. (c) Plant viruses (d) All of these (b) Exchange of materials between nucleus and cytoplasm. 20 . Bacteria are included in : (c) Exchange of material between cell and outside (a) Animals (b) Plants environment. (c) Non-living (d) None of these (d) None of these 21 . The largest cell may be : 9. The function of chromosomes in transmission of heredity (a) Few mm in length (b) Few inches in length traits was described by : (c) Few cm in length (d) None of these (a) Flemming (b) Waldeyer 22 . The prokaryotic cells lack : (c) Miller (d) Morgan Cell Biology 21
(a) Plasma membrane (b) Cell-walls (c) (i) and (iii) are correct (c) Nuclear membrane (d) All of these (d) (i), (ii) and (iii) are correct. 23 . The Chromosome of a bacterial cell is known as: 33. The crossing-over during meiosis occur at four strand (a) Autosome (b) Gonophore stage. This was proved by the observation that : (c) Kinetochore (d) None of these (i) Usually only two gametes resulting from a meiotic division could be recombinants. 24 . Which of the following is the longest cell ? (ii) Chiasmata are seen only at the four strand stage. (a) Bacterial cell (b) Fibre cell (iii) Occasionally, none of the four gametes resulting from (c) Nerve cell (d) All of these meiosis could be a recombinant. 25 . The common layer present between the adjoining cells is Which of the above statements is/are correct? known as : (a) (i) is correct (a) Ca-Pectate (b) Plasmodesmata (b) (ii) and (iii) are correct (c) Secondary cell-wall (d) Middle lamella (c) (i) and (ii) are correct 26 . Which of the following is not a function of mitochondria? (d) (i), (ii), and (iii) are correct. (a) Krebs cycle (b) Electron Transport System 34. The uid mosaic model of cell-membrane postulates that: (c) Phosphorylation (d) Glycolysis (i) A lipid bilayer has proteins embedded in the surface. 27 . The Golgi complex was found in : (ii) A lipid bilayer has some embedded proteins and some (a) Nerve cells (b) Lung cells proteins on the surface. (c) Bacterial cells (d) Gland cells (iii) A lipid bilayer is coated by a layer of proteins on 28 . The energy rich compound synthesized in Mitochondria each face. is : (iv) A lipid bilayer is coated by a layer of proteins on the (a) ADP (b) AMP outer face only. (c) ATP (d) All of these Which of the above statements is/are correct? (a) (i) and (ii) are is correct 29 . The Chromoplasts : (b) (ii) is correct (a) Contain pigment and synthesized food by photosynthesis. (c) (i) and (iii) are correct (b) Are colourless, which store food materials. (d) (i), (ii), (iii) and (iv) are correct. (c) Both of these (d) None of these 35. The sequence of cell-division is : (i) Anaphase, Telophase, Metaphase, Prophase. 30 . Which of the following is a microbody? (ii) Prophase, Metaphase, Anaphase. (a) Dictyosomes (b) Sarcosomes (iii) Prophase, Metaphase, Anaphase, Telophase (c) Peroxisomes (d) All of these (iv) Prophase, Telophase, Metaphase, Anaphase. 31. Which of the following organelles is thought to had been Which of the above statements is/are correct? a free-living prokaryotic organism? (a) (i) and (ii) are correct (a) Golgi apparatus (b) Endoplasmic reticulum (b) (ii) and (iii) are correct (c) Lysosomes (d) Chloroplasts (c) Only (iii) is correct 32. "Fluid mosaic model" of Singer and Nicolson (1972) (d) (i), (ii), (iii) and (iv) are correct. assumes that cell-membrane consists of: 36. A DNA molecule in which one strand has radioactive (i) Two phospholipids layers having a mosaic arrangement thymidine, is allowed to duplicate in an environment of extrinsic and intrinsic globular proteins. containing radioactive thymidine. What will be the correct (ii) A protein layer smeared over a lipid bilayer. no. of DNA molecules containing radioactive thymidine (iii) A semi uid unit membrane, where lipids and proteins in both strands after 3 duplications? moved. (i) None of DNA molecules Which of the above statements is/are correct? (ii) Only two molecules of DNA. (a) (i) is correct (iii) Six molecules of DNA. (b) (ii) and (iii) are correct (iv) Four molecules of DNA. 22 Botany
Which of the above statements is/are correct? (c) (i), (ii), (iv) are correct (a) (i) and (ii) are correct (d) (iv) is correct. (b) (ii) and (iii) are correct 40. The four cells derived from meiosis in a normal diploid (c) (i) is correct organism differ among themselves only in the following (d) (i), (ii), (iii) and (iv) are correct. respect : (i) Number of Chromosomes. 37. A segment of DNA has the triplet base sequence GAC, CAG, AAC, CGC and GAA. Due to mutation only the (ii) Size of Chromosomes rst base got deleted. Then the likely effect of this on the (iii) Genes carried on different Chromosomes. coding of the DNA segment is that : (iv) Number and size of Chromosomes. (i) The polypeptide will have one amino acid less. Which of the above statements is/are correct? (ii) The rst amino acid will different and all others will (a) (i) and (ii) are correct be like the earlier. (b) (ii) and (iii) are correct (iii) There will be a complete change in the types and (c) (iii) is correct sequence of amino acids. (d) (i), (ii), (iii) and (iv) are correct. Which of the above statements is/are correct? (a) (i) and (ii) are correct 41 Following statement is/are the most appropriate distinction of prokaryotic cells to distinguish them from eukaryotic (b) (ii) and (iii) are correct cells : (c) (iii) is correct (i) Lack of DNA and nuclei. (d) (i), (ii), (iii) are correct. (ii) Lack of ribosomes. 38. In mitosis the daughter cells resemble each other and (iii) Having dispersed DNA without a nuclear membrane also the parent cell. In meiosis they differ not only from and lack of membrane bound organelles like parent cell in having half the number of chromosome; mitochondria. but also differ among themselves qualitatively in genetic Which of the above statement is/are correct? constitution due to : (a) (i) and (ii) are is correct (i) Independent assortment and segregation only. (b) (ii) and (iii) are correct (ii) Crossing over, independent assortment and segregation. (c) (iii) is correct (iii) Segregation and crossing over only. (d) (i) and (iii) are correct. (iv) Independent assortment and crossing over only. Which of the above statements is/are correct? 42. In mRNA, AUG is the initiation codon and there are three termination codons, therefore polypeptide cannot (a) (i) and (ii) are correct be synthesized beyond any of these triplets to the end of (b) (ii) is correct mRNA can be translated completely ? (c) (i) and (iii) are correct (i) AUG CGC GGG UUU UAA CCC (d) (i), (iii), and (iv) are correct. (ii) AUG CCC AAA UAG CGA UUU 39. A DNA molecule in E. coli is heavy (labelled with N15) (iii) CCC GAC UCG AUG GUG GGG and it is allowed to replicate in a medium containing (iv) AUG CGC AAA AUG CCU GCU N14 ; after one generation of replication the two daughter Which of the above statement's is/are correct? molecules : (i) Will differ in density from one another, but will (a) (i) and (ii) are correct resemble the parent molecule. (b) (ii) and (iii) are correct (ii) Will have the same density as that of parent DNA. (c) (iv) and (ii) are correct (iii) Will differ in densely from one another and also from (d) (iv) is correct. that of parent DNA. 43. Assuming that 50 heavy (i.e., containing N15) DNA (iv) Will be similar in density, but will differ from that of molecules are allowed to replicate twice in a medium parent DNA. containing N14, we would expect: Which of the above statements is/are correct? (i) 100 half heavy and half light and 100 light DNA. (a) (i) and (ii) are correct (ii) 100 heavy and 110 light DNA. (b) (ii) and (iii) are correct (iii) 50 heavy and 150 light DNA. Cell Biology 23
Which of the above statement's is/are correct? Which of the above statement is/are correct? (a) (i) is correct (a) (i) and (ii) are correct (b) (i) and (iii) are correct (b) (ii) and (iii) are correct (c) (ii) and (iii) are correct (c) (iii) and (iv) are correct (d) (i) and (iii) are correct. (d) (ii) and (iv) are correct. 44. The nuclease enzymes cause fragmentation of DNA at sites 47. The eukaryotic mRNA are associated with proteins to form not protected by proteins. When pure DNA was digested RNP complexes. Some of the complexes may remain in with a nuclease, the DNA fragments of all sizes were the cytoplasm for a long time before being genetically obtained, but when chromatin was similarly digested, DNA expressed. Such complexes are known as: fragments of sizes, that were multiples of a smallest unit (i) Ribosomes (ii) Polyribosomes size were obtained. This suggested that in the chromatin, (iii) Informosomes. the histones proteins are associated with DNA all along Which of the above statement's is/are correct? its length (a) (i) and (ii) are is correct (i) In a random manner. (b) (i) and (iii) are correct (ii) In the form of core particles distributed with a regular (c) (iii) is correct periodicity. (d) (i), (ii), and (iii) are correct. (iii) In the form of tetramers. 48. For the structure of nucleic acid, which of the following Which of the above statement is/are correct? statement is correct ? (a) (i) and (ii) are correct (i) DNA can be single stranded in some viruses. (b) (ii) is correct (ii) RNA can be double stranded occasionally. (c) (ii) and (iii) are correct (iii) There are as many as 12 bases per turn in Z-DNA. (d) (i), (ii) and (iii) are correct. (iv) The length of one helix is 45 A B DNA and 34 A in Z-DNA. 45. The poisons like a cyanide inhibits Na + ef ux and K + in ux during cellular transport. This inhibitory effect is Which of the above statements is/are correct? reversed by an injection of ATP. This demonstrates that : (a) (i) and (ii) are is correct (i) Na +-K + exchange pump operates in the cell. (b) (i) and (iv) are correct (ii) Energy for Na +-K + exchange pump comes from ATP. (c) (ii) and (iv) are correct (iii) ATP is the carrier protein in the transport system. (d) (iii) and (iv) are correct. Which of the above statement's is/are correct? 49. For the meiosis. Which of the following statements is (a) (i) and (ii) are correct correct ? (i) The rst division is equational and second division is (b) (ii) is correct reductional. (c) (ii) and (iii) are correct (ii) The rst division is reductional and second division (d) (i), (ii) and (iii) are correct. is equational. 46. Cultivated tobacco (Nicotiana tabacum) has 2n = 48 (iii) Both divisions are reductional. Chromosomes and is amphidiploid. Nicotiana sylvestris, Which of the above statements is/are correct? which is one of the progenitors of N. tabacum has 2n = 24 (a) (ii) is correct chromosomes and is diploid. It has contributed one genome (b) (i) and (ii) are correct to N. tabacum. When these two species are hybridized the (c) (ii) and (iii) are correct critical chromosomal associations at meiosis in the hybrid will be : (d) (i), (ii), and (iii) are correct. (i) 24 bivalents. 50. In an experiment regarding DNA replication Meselson (ii) 12 univalents +12 bivalents. and Stahl allowed E. coli cells to grow on N 15 culture (iii) 12 bivalents. for about 14 cell generations, so that all nitrogen (N14) in the DNA is replaced by N15 . They found that the two (iv) 12 bivalents +12 univalents. strand of DNA would separate from one another, maintain 24 Botany
their identity and each will synthesize its complementary (i) 175 × 10 cells (ii) 5 × 10 cells strand. The mode of replication described above can be : (iii) 32 × 10 cells (iv) 35 × 10 cells (i) Conservative (ii) Semi-conservative Which of the above statement's is/are correct? (iii) Dispersive (a) (i) and (ii) are correct Which of the above statement's is/are correct? (b) (ii) is correct (a) (i) and (ii) are correct (c) (iii) is correct (b) (ii) is correct (d) (i), (ii), and (iii) are correct. (c) (i) and (iii) are correct 55. The electron-microscope differs from the ordinary light (d) (i), (ii), and (iii) are correct. microscope in having high resolving power due to the 51. The signi cance of meiosis lies in : use of : (i) Reduction of the diploid number of chromosomes to (i) Fast electrons which have a shorter wavelength than that haploid. of the ordinary light rays as the source of illumination. (ii) Maintaining constancy in the number of diploid (ii) Electrons which have a longer wavelength than the Chromosomes during sexual reproduction. ordinary light as the source of illumination. (iii) Production of genetic variability in the population of (iii) UV-rays is the source of illumination. a species. (iv) Gamma-rays as the source of illumination. Which of the above statements is/are correct? Which of the above statements is/are correct? (a) (i) and (ii) are correct (a) (i) only (b) (ii) and (iii) are correct (b) (i) and (ii) are correct (c) (i) and (iii) are correct (c) (ii), and (iii) are correct. (d) (i), (ii), and (iii) are correct. (d) (i), (ii), (iii) and (iv) are correct. 52. If you provide with root tips of onion in your class and 56. Pure fraction of cellular components can be obtained by asked to count the chromosomes. Which of the following the isolation of individual organelle from cell homogenates stages can you most conveniently look into? is achieved through : (i) Anaphase (ii) Prophase (i) Spectrophotometry. (iii) Metaphase (ii) Differential centrifugation. Which of the above statements is/are correct? (iii) X-ray diffraction. (a) (i) and (ii) are correct Which of the above statements is/are correct? (b) (ii) and (iii) are correct (a) (i) and (ii) are correct (c) (iii) is correct (b) (ii) is correct (d) (i), (ii), and (iii) are correct. (c) (i) and (iii) are correct 53. The enzyme hexokinase which catalyses glucose to (d) (i), (ii), and (iii) are correct. glucose-6-phosphate in glycolysis is inhibited by glucose- 57. In recent years, considerable attention is being given to 6-phosphate. This is an example of: DNA protein interaction, because expression of genes is (i) Competitive inhibition. regulated through binding of speci c proteins on regulatory (ii) Non-competitive inhibition. DNA sequence. The pattern of protein binding DNA can (iii) Feedback allosteric inhibition. be studied by : Which of the above statements is/are correct? (i) Ultracentrifugation. (a) (i) and (ii) are correct (ii) X-ray crystallography. (b) (i) and (iii) are correct (iii) Light microscope. (c) (iii) is correct Which of the above statement's is/are correct? (d) (i), (ii), and (iii) are correct. (a) (i) and (ii) are correct 54. A bacterium divides after every 35 minutes. If a culture (b) (ii) is correct containing 10 cells per ml. is grown for 175 minutes, what (c) (ii) and (iii) are correct will be the cell concentration per m. after 175 minutes ? (d) (i), (ii), and (iii) are correct. Cell Biology 25
58. Consider the following statements : Which of the above statements is/are correct? (i) In Plant cells, cytokinesis starts with the formation of (a) (i) and (ii) are is correct the phragmoplast. (b) (ii) and (iii) are correct (ii) Phragmoplast comprises of Interzonal Microtubules (c) (iii) is correct and Golgi vesicles. (d) (i), (ii), and (iii) are correct. (iii) Primary cell-wall is produced by microtubules. Which of the above statement's /are correct? 62. Match List I with List II and select the correct answer using the codes given below the lists: (a) (i) and (iii) (b) (i) and (ii) List I List II (c) (ii) and (iii) (d) (i), (ii), and (iii) A. Movement of gene 1. Mutation on the same 59. The rapid and irreversible cell-elongation occurs commonly chromosome in plants, but not in animals. This difference is due to the: B. Muton 2. Y-chromosome (i) Presence of chloroplasts and mitochondria. C. Holandric gene 3. Cistron (ii) Absence of centrioles and Golgi bodies. (iii) Absence of endoplasmic reticulum and presence of D. Unit of function 4. Inversion large vacuoles. A B C D (iv) Presence of large vacuoles and cell-walls. (a) 1 2 3 4 Which of the above statement's is/are correct? (b) 4 1 2 3 (a) (i) and (ii) are correct (c) 3 4 1 2 (b) (ii) and (iii) are correct (d) 2 3 4 1 (c) (i), (ii), (iii) and (iv) are correct 63. Match List I with List II and select the correct answer (d) (iv) is correct. using the codes given below the lists: 60. The plant cell-wall in a cross-section appears to be made List I List II up of many layers due to the : A. Purkinje 1. DNA (i) Presence of large amount of cellulose in the wall. B. Waldeyer 2. Mitochondria (ii) Presence of lignin which prevents the folding of C. Benda 3. Chromosome cellulose micro brils. D. Watson and Crick 4. Protoplasm (iii) Presence of different composition and structure of the A B C D lamellae, which are added continuously as the wall grows. (a) 1 2 3 4 (iv) Orientation of micro brils in the different lamellae of (b) 4 1 2 3 the wall that results in differences in the refraction of (c) 3 4 1 2 light, so that layers of the wall are emphasized. (d) 4 3 2 1 Which of the above statement's is/are correct? 64. Match List I with List II and select the correct answer (a) (i) and (ii) are correct using the codes given below the lists: (b) (ii) and (iii) are correct List I List II (c) (i), (ii), (iii) and (iv) correct A. Chloroplast 1. Flagella (d) (iv) is correct. B. 9 + 2 pattern 2. Mitochondria of 61. Mitotic cell-cycle is divided typically into four phases : organisation G1, S, G2 and M. Considering a mitotic cycle time of 18 C. Chlorophyll 3. Photosynthetic pigments hrs; the distribution of period of time (in hrs.) for each of D. Power house of cell 4. Plastids these phases will be : A B C D Gl S G2 M (a) 4 1 3 2 (i) 1 3 5 9 (b) 2 3 1 4 (ii) 9 1 3 5 (c) 3 1 4 2 (iii) 9 5 3 1 (d) 4 3 1 2 (iv) 3 9 1 26 Botany
65. Match List I with List II and select the correct answer A B C D using the codes given below the lists: (a) 1 2 3 4 List I List II (c) 2 3 1 4 A. Ribosomes 1. Palade particles (c) 3 1 4 2 B. Vacuole 2. Tonoplast (d) 4 1 3 2 C. Osmoregulation 3. Contractile vacuole 69. Match List I with List II and select the correct answer D. Powerhouse of cell 4. Mitochondria using the codes given below the lists: A B C D List I List II (a) 1 2 3 4 A. DNA 1. Janus Green 'B' (b) 2 3 1 4 B. Mitochondria 2. Fuelgen Stain (c) 3 1 4 2 C. Nuclei 3. Hematoxylins (d) 4 1 3 2 D. Chromosome 4. Acetocarmine 66. Match List I with List II and select the correct answer A B C D using the codes given below the lists: (a) 2 1 3 4 List I List II (c) 2 3 1 4 A. Carcinogen 1. Cancerous tumour (c) 3 1 4 2 B. Anaphase-I 2. Disjunction (d) 4 1 3 2 C. Meiosis 3. Synapsis 70. Match List I with List II and select the correct answer D. Zygotene 4. Plectonemic coiling using the codes given below the list : A B C D List I List II (a) 1 2 4 3 A. Lipid storage 1. Nucleolus (b) 2 3 1 4 B. Glycolate metabolism 2. Sphaerosome (c) 3 1 4 2 C. Transport of 3. Peroxisomes (d) 4 1 3 2 macromolecules 67. Match List I with List II and select the correct answer D. RNA Synthesis 4. Plasmodesmata using the codes given below the lists: A B C D List I List II (a) 2 4 3 1 A. Toluidine blue 1. Fats (c) 1 2 4 3 B. Safranin 2. Lignin (c) 2 3 4 1 C. Cotton blue 3. RNA (d) 1 3 2 4 D. Osmium tetroxide 4. Fungal hyphae 71. Match List I with List II and select the correct answer A B C D using the codes given below the lists: (a) 1 2 4 3 List I List II (c) 3 2 4 1 A. Muller and Stadler 1. DNA structure (c) 3 4 2 1 B. Beadle and Tatum 2. Semiconservative (d) 1 4 2 3 replication of DNA 68. Match List I with List II and select the correct answer C. Watson and Crick 3. One-gene one enzyme using the codes given below the lists: theory List I List II D. Meselson and Stahl 4. Induction of mutation A. Phragmoplasts 1. Cell plate A B C D B. Colchicine 2. Polyploidy (a) 2 4 3 1 C. Prokaryotic 3. Replication fork (b) 1 2 4 3 chromosomes (c) 4 3 1 2 D. Meiosis 4. Bouquet stage (d) 1 3 2 4 Cell Biology 27
72. Death or mental retardation takes place if accumulation (a) Adenine (b) Guanine happens in (c) Uracil (d) Thymine (a) somatic cells (b) brain cells 84 . Which of the following statements is FALSE regarding (c) meristemetic cells (d) sensory cells SDS-polyacrylamide gel electrophoresis ? 73. In a normal human being number of chromosomes is (a) Proteins are separated by molecular weight (a) 23 (b) 46 (b) SDS is a detergent which gives charge to protein (c) 53 (d) 26 (c) Large proteins move more slowly through the gel 74. Pigments containing bodies which are bounded by (d) SDS is used to maintain the three dimensional structure membrane are called of protein. (a) plastids (b) chlorophyll 85 . Most of the unique physical properties of water can be (c) chloroplast (d) hemoglobin explained by ? 75. In word Lysosoma, 'lyso' means splitting and 'soma' means (a) polar nature of molecules. (a) cell (b) body (b) Its low surface tension. (c) tissue (d) organic (c) Its ability to easily dissolve non-polar substances. 76. Phagocytosed food is digested with help of enzymes which (d) Its low pH. are present in 86. Which of the following involves in the binding of a (a) ribosome (b) lysosomes molecule to other site than active site of the enzyme? (c) mitochondria (d) Golgi complex (a) Non-competitive inhibition 77. The movement of dissolved particles against the (b) Allosteric inhibition concentration gradient is called : (c) Competitive inhibition (a) Active transport (b) Endocytosis (d) All of the above (c) Exocytosis (d) Osmosis 87 Which of the following best describes the function of 78 . Which of the following is semipermeable cell membrane? oncogenes ? (a) Nucleus (b) cell wall (a) They may result in cancer (c) Lysosome (d) Plasma membrane (b) They kill cancerous cells 79 . The net movement of solute down the concentration gradient (c) They function in the normal regulation of the cell- with help of proteins in membrane is called cycle. (a) Facilitated diffusion (b) Osmosis (d) They produce newly sythesized DNA for errors. (c) Endocytosis (d) Active transport 88 . Which of the following is found only in eukaryotic cells? 80 . Which of the following modi es and packs the protein for (a) mRNA (b) snRNA secretion ? (c) rRNA (d) tRNA (a) Endoplasmic reticulum (b) Lysosome 89 . When water evaporates which of the following bonds are (c) Golgi apparatus (d) Nucleus broken down? 81 . If the free energy change of a reaction is greater than zero, (a) Polar covalent bond (b) Nonpolar covalent bond then the reaction : (c) Ionic bonds (d) Hydrogen bonds (a) Is spontaneous (b) Is nonspontaneous 90 . The non-disjunction, in meiosis may result in an extra copy (c) Is at equilibrium (d) Is endothermic of a chromosome in a sperm cell. During which phase the 82 . Which is NOT a characteristic of proteins : above phenomenon may occurs? (a) Contain nitrogenous base (a) Prophase I, Prophase II (b) Peptide bonds (b) Metaphase I, Anaphase II (c) Can function as enzyme (c) Anaphase I, Anaphase II (d) Important in cell signalling. (d) Anaphase I, Telophase II. 83 . Which of the following nitrogenous base is NOT found 91 Which of the following is true regarding the phage lambda, in DNA ? a virus which infects bacteria ? 28 Botany
(a) In the lytic cycle, the bacterial host replicates viral (c) Molecules cross the cell-membrane. DNA, passing it on to daughter cells during binary (d) Energy is required. ssion. 99 . DNA synthesis requires a primer which consists of: (b) In the lysogenic cycle, the bacterial host replicates viral (a) Primase (b) DNA DNA, passing it on to daughter cells during binary (c) RNA (d) An Okazaki fragments ssion. (c) In the lytic cycle, viral DNA is integrated into the 100 . The endergonic chemical reaction host genome. (a) Cannot occur within a cell (d) In the lysogenic cycle, the host bacterial cell bursts, (b) Can occur within a cell at very high temperatures releasing phases. (c) Can occur because enzymes lower the energy of activation. 92 . In the Krebs cycle, the electrons are moved from NADH to : (d) Can be coupled to a more favourable reaction.
(a) FADH 2 (b) Pyruvate 101. The earliest forms of life were? (c) Ethanol (d) Oxygen (a) Unicellular autotrophs 93 . Which of the following cells have cilia ? (b) Multicellular autotrophs (a) Cells lining the human respiratory tract (c) Unicellular heterotrophs (b) Euglena (d) Multicellular heterotrophs (c) Cells lining the human urinary tract 102. Unlike animal cells the cytokinesis in plant cells involves (d) Human sperms cells the formation of a : (a) Cleavage furrow (b) Cell-plate 94. Which of the following contains thymine ? (a) DNA (b) rRNA (c) Nuclear envelope (d) Mitotic spindle (c) rRNA (d) mRNA 103. The binding of a molecule other than the substrate to the active site of an enzyme is involved in : 95 . Which of the following constitutes the secondary level of (a) Non-competitive.inhibition protein structure ? (a) Disulphide bonds cystine molecules between of (b) Feedback inhibition polypeptide chain (c) Irreversible inhibition (b) Linear sequence of amino acids joined by peptide (d) Increasing the energy of activation bonds 104. Which of the following is not found in the cellmembrane? (c) Beta pleated sheet (a) Nucleic acid (b) Carbohydrate (d) Alpha cells (c) Protein (d) Phospholipid 96 . Which cellular organelle functions in ribosome synthesis? 105. The Cells regulate membrane uidity by varying the amount (a) The endoplasmic reticulum of which of the following substance in the cell-membrane? (b) The nucleolus (a) Carbohydrate (b) Phospholipid (c) The nucleus (c) Protein (d) Cholesterol (d) The Golgi bodies 106. Which of the following sequences represents a possible 97 . Which of the following statements is true regarding cellular pathway in the production of a secretary protein ? respiration ? (a) Rough ER → Secretory vesicle → Ribosomes → (a) The end product of Glycolysis is acetyl coenzymeA, Golgi apparatus. which enters the Krebs cycle. (b) Ribosomes → Rough ER → Golgi apparatus → (b) The majority of ATP production results from glycolysis. Secretary vesicle (c) Pyruvate is converted to lactate. (c) Secretary vesicle → Golgi apparatus → Ribosomes → Rough ER. (d) NADH and FADH2 function as electron-carriers. (d) Rough ER → Ribosomes → Secretory vesicles →Golgi 98 . In active transport, unlike facilitated diffusion? apparatus. (a) Molecules are moved with their concentration gradient 107. Which of the following are the characteristic of both animal (b) Membrane proteins are not involved. and plant cells ? Cell Biology 29
(a) Nuclear membrane, Golgi apparatus, mitochondria 117. The ectoderm gives rise to : (b) Centrioles, Ribosomes, Nucleolus (a) Nails, blood vessels and epidermis (c) DNA, RNA, Chloroplast (b) Adrenal cortex and epidermis (d) Plasma membrane, central vacuole, ER. (c) Neurons and epidermis 108. Both eukaryotic and prokaryotic cells contains? (d) Kidneys, blood vessels, and heart. (a) Nucleus 118. The process of mitosis and meiosis can be best studied (b) Endoplasmic reticulum under: (c) DNA (a) Electron-microscope (d) Mitochondria (b) Light microscope 109. Which of the following correctly represents DNA (c) Phase-contrast microscope organization, from least organized to highly organized ? (d) Scanning-electron microscope. (a) DNA → nucleosomes → 30 nm ped domain → 119. The resolving power of light microscope is : chromosome. (a) 2 microns (b) 0.2 microns (b) DNA → nucleosomes —> chromosomes → 30 nm. (c) 20 microns (d) 0.02 microns (c) DNA → 30 nm → nucleosome → chromosome. 120. In DNA, the amount of thymine is equal to : (d) Nucleosome → DNA —> 30 nm → chromosome. (a) The amount of uracil 110. How do the membranes of eukaryotic cells differ? (b) The amount of adenine (a) Certain membranes consists of a single layer of (c) The amount of cytosine phospholipids. (d) The amount of guanine (b) In some cells the hydrophobic tails of the phospholipids face the cytoplasm. 121. The normal human eyes cannot resolve the distance: (a) Smaller than 1000 microns (c) Different proteins are found in different cell membranes. (b) Smaller than 100 microns (d) Some membranes do not contain phospholipids. (c) Larger than 100 microns 111. The level of depolarization, which must be reached before (d) Larger than 1000 microns an action potential is triggered, is called the : (a) Threshold potential (b) Membrane potential 122. The structure of biological macromolecules are studied (c) Water potential (d) Graded potential with the help of : (a) Electron microscope 112. A cell can only arise from a preexisting cell is the astatement (b) Scanning-electron microscope of: (a) Cell theory (b) Cell lineage theory (c) X-ray microscope (c) Law of heredity (d) None of the above. (d) Phase-contrast microscope. 113. The Living specimens can be observed by : 123. Which of the following is not an organic substance? (a) Light microscope (a) Water (b) Glucose (b) Electron-microscope (c) Phospholipid (d) DNA (c) Phase-contrast microscope 124. Which one is not an example of "cell" ? (d) All of the above. (a) Sperm of frog (b) An egg of hen 114. The cell-plate formation is involved in : (c) A virus (d) All of the above (a) Viral replication (b) Bacterial replication 125. The smallest organelle of a cell is : (c) Bacterial conjugation (d) Plant cell mitosis (a) Nucleus (b) Mitochondria 115. The smallest cell is : (c) Ribosome (d) Lysosome (a) Bacteria (b) Virus 126. Which of the following statement is true regarding (c) PPLO (d) Protozoa membranes ? 116. The term protoplasm was given by : (a) Membranes consists only of phospholipids. (a) Mendel (b) Purkinje (b) Phospholipids within the membrane are randomly (c) Leeuwenhoek (d) None. arranged. 30 Botany
(c) Membranes consists only of protein. 138. The centriole/centrosome takes part in: (d) Different membranes have different proteins embedded (a) Nucleus formation (b) Start of cell division within them. (c) Cell plate formation (d) Spindle formation 127. Which one of the following is found in a cell in highest 139. The middle lamella is chemically made up of: number ? (a) Plasmalemma (b) Protein (a) Nucleus (b) Ribosome (c) Pectin (d) Hemicellulose (c) Mitochondria (d) Chloroplast 140. The Protoplasmic connections between two adjacent cells are called : 128. Which is element found in maximum number cell? (a) Plasmalemma (b) Plasma membrane (a) Hydrogen (b) Carbon (c) Plasmodesmata (d) Plasma-cord (c) Oxygen (d) Nitrogen 141. After meiosis, the number of chromosomes in a sperm 129. The chief metallic ion found in ribosome is: cell is 6. What is the somatic chromosome number of the +2 + (a) Ca (b) K organisms ? (c) Mg +2 (d) Na + (a) 3 (b) 6 130. Which compound is next to water in amount in a cell? (c) 9 (d) 12 (a) Protein (b) Fat 142. The lignin may be found in the cell-wall of : (c) Carbohydrates (d) Vitamins (a) Algae (b) Fungi 131. Which element occupies the highest position in the dry (c) Bryophyta (d) Pteridophyta weight of a cell ? 143. The needle like crystals of calcium oxalate found in the (a) Hydrogen (b) Carbon cell of Pistia are called : (c) Oxygen (d) All of the above (a) Cystolith (b) Autolith (c) Raphides (d) Inulin 132. In the cell-cycle, DNA replicate on occurs during which phase ? 144. In adipose cells, ER is a complex consist of (a) Prophase (b) Metaphase (a) Tubules and vesicles (b) Cistemae, tubules, vesicles (c) Anaphase (d) Interphase (c) Tubules and cistemae 133. Which orle occupies the highest position in a cell by (d) vesicles weight ? (a) Oxygen (b) Hydrogen 145. The prokaryotes are found in which kingdom ? (a) Monera (b) Protista (c) Carbon (d) Nitrogen (c) Fungi (d) Plantae 134. To separate ribosomes from the other important organelles 146. The arrangement of microtubules in eukaryotic agella is of cell, which of the following apparatus is used ? referred to as (a) Electron-microscope (a) undulating (b) basal (b) UV-microscope (c) 9 + 2 (d) ciliary (c) Ultra-centrifuge 147. Which of the following is not a characteristic of (d) Scanning-Electron microscope prokaryotes? 135. The cholesterol is found in the cell-membranes of: (a) DNA (b) cell membrane (a) E. Coli (b) Yeast (c) cell wall (d) endoplasmic reticulum (c) Com (d) Fish 148. The term "nuclear envelope" is more correct than the term 136. Which organic compound is most abundant in a cell? "nuclear membrane" because (a) the enclosure has pores which membranes do not (a) Water (b) Carbohydrates (b) the enclosure is made up of two membranes (c) Proteins (d) Fats (c) the chemical composition is inconsistent with cellular 137. Which of the following is the "living limit" of cell? membranes (a) The cell-wall (b) The extraneous coats (d) None of the above. The two terms are perfect synonyms. (c) The plasma membrane (d) The cytoplasm. Cell Biology 31
149. Oxidative metabolism is carried out ____ of mitochondria . 150. Ribosomes are made up of ____ subunits. (a) in the intermembrane space (a) 0 (They are whole.) (b) 2 (b) on the surface of the inner membrane (c) 3 (d) 4 (c) in the inside of the outer membrane (d) in the matrix ANSWERS
1. (d) 2. (c) 3. (b) 4. (a) 5. (d) 6. (a) 7. (d) 8. (a) 9. (d) 10. (d) 11. (d) 12. (c) 13. (d) 14 (c) 15. (d) 16. (c) 17. (b) 18. (d) 19. (d) 20. (d) 21. (c) 22. (c) 23. (d) 24. (c) 25. (d) 26. (d) 27. (d) 28. (c) 29. (a) 30. (c) 31. (d) 32. (a) 33. (a) 34 (b) 35. (c) 36. (c) 37. (c) 38. (b) 39. (d) 40. (c) 41. (c) 42. (a) 43. (a) 44. (b) 45. (b) 46. (d) 47. (c) 48. (a) 49. (a) 50. (b) 51. (d) 52. (c) 53. (c) 54. (c) 55. (a) 56. (b) 57. (b) 58. (b) 59. (d) 60. (d) 61. (c) 62. (b) 63. (d) 64. (c) 65. (a) 66. (a) 67. (b) 68. (a) 69. (a) 70. (c) 71. (c) 72. (b) 73. (b) 74. (a) 75. (b) 76. (b) 77. (d) 78. (d) 79. (a) 80. (c) 81. (b) 82. (a) 83. (c) 84. (d) 85. (a) 86. (b) 87. (a) 88. (b) 89. (d) 90. (c) 91. (b) 92. (a) 93. (a) 94. (a) 95. (c) 96. (b) 97. (d) 98. (d) 99. (c) 100. (d) 101. (c) 102. (b) 103. (c) 104. (a) 105. (d) 106. (b) 107. (a) 108. (c) 109. (a) 110. (c) 111. (a) 112. (a) 113. (c) 114. (d) 115. (c) 116. (b) 117. (c) 118. (c) 119. (b) 120. (b) 121. (b) 122. (c) 123. (c) 124. (c) 125. (c) 126. (d) 127. (b) 128. (a) 129. (c) 130. (a) 131. (c) 132. (d) 133. (a) 134. (c) 135. (d) 136. (c) 137. (c) 138. (d) 139. (c) 140. (c) 141. (d) 142. (d) 143. (c) 144. (a) 145. (a) 146. (c) 147. (d) 148. (b) 148. (b) 150. (b)
ASSERTION AND REASONS
Instruction for Questions : 3. Assertion : Study of internal structure is called anatomy. Reason : Anatomy is useful for phylogenetic study. In each of the following questions, a statement of Assertion A) is given followed by a corresponding statement of Reason 4. Assertion : First Nobel Laureate in biology was Emil Von Behring. (R) just below it. Of the statements, mark the correct answer : Reason : He got rst Nobel Prize for the discovery of (a) If both assertion and reason are true and reason is the serum therapy for diphtheria. correct explanation of assertion 5. Assertion : Resolving power is the ability to distinguish (b) If both assertion and reason are true but reason in the between two close points. correct explanation of assertion Reason : Microscope reduces resolving power. (c) If assertion is true but reason is false 6. Assertion : Microsomal fraction includes microsome, (d) If both assertion and reason are false endoplasmic reticulum, Golgi bodies, microbodies etc. (e) If assertion is false but reason is true. Reason : It separates out at 100000 × g for 60 minutes. 1. Assertion : Term biology was coined by Lamarck and 7. Assertion : Ribosomes came to our knowledge after the Traviranus (1802). discovery of electron microscope. Reason : Biology is the science dealing with the study of Reason : Electron microscope has lowest magni cation different aspects of living beings. and resolving power. 2. Assertion : Aristotle is called Father of Zoology as well 8. Assertion : Transmission Electron Microscope (TEM) as Botany. provides two dimensional images. Reason : Louis Pasteur is considered as Father of Reason : Scanning Electron Microscope (SEM) provides Microbiology. three dimensional images. 32 Botany
9. Assertion : Certain dyes can be used even in case of 19. Assertion : Two amino acids are interlinked by peptide living material. bonds to form dipeptide. Reason : They are called vital stains. Reason : Oligopeptide have upto 25 amino acids. 10. Assertion : Autoradiography involves radioactive isotopes 20. Assertion : Chemosynthesis is an autotrophic nutrition. 14 32 35 like C , P , S etc. Reason : Chemosynthesis contains chlorophyll pigments. 3 Reason : H (in thymidine) was employed by Taylor (1958) 21. Assertion : Water shows hydrolytic splitting. for studying chromosome replication. Reason : Water has high thermal conductivity. 11. Assertion : A potted plant placed in a window shows 22. Assertion : Basic fuchsin is speci c for DNA. bending of stem towards light. Reason : Acetocarmine is used for the staining of nucleus Reason : This is an example of Teleology. 23. Assertion : Resolving power is the ability to distinguish 12. Assertion : Chance unexpected and intuitive discoveries between two close points. are called serendipity. Reason : Microscope reduces resolving power. Reason : Pasteur point out chance favours the trained mind. 24. Assertion : Ribsomes came to our knowledge after the discover of electron microscope. 13. Assertion : Living beings are an open system. Reason : An open system receives continuous in ow of Reason : Electron microscope has a high magni cation energy directly or indirectly. and resolving power. 14. Assertion : In plants, carbohydrates are mostly translocated 25. Assertion : The science of classifying organisms is called as sucrose. taxonomy. Reason : In plants, excess of sugar is stored as starch. Reason : Systematics and taxonomy have same meaning. 15. Assertion : Life was originated in water. 26. Assertion : Hypothesis is an educated guess. Reason : Water remains liquid between 4°C – 90°C. Reason : It is based on observation of experiments. 16. Assertion : Respiration is an example of catabolism. 27. Assertion : Short term adaptation have little role in evolution. Reason : Catabolism is a destructive metabolism. Reason : They are acquired. 17. Assertion: Selaginella bryopteris is called resurrection plant. 28. Assertion : Living systems have a high degree of tendency for undergoing entropy. Reason : Resurrection plants dry up during drought and turn green with moisture or rain. Reason : Living systems are unable to overcome entropy. 18. Assertion: DNA is the store house of all hereditary 29. Assertion : DNA serves as hereditary material. informations in eukaryotes. Reason : DNA functions as blue-print for building and Reason: DNA is capable of replication. running cellular machinery.
ANSWERS
1. (b) 2. (d) 3. (b) 4. (a) 5. (c) 6. (a) 7. (c) 8. (b) 9. (a) 10. (b) 11. (b) 12. (b) 13. (a) 14 (b) 15. (b) 16. (a) 17. (a) 18. (a) 19. (b) 20. (c) 21. (b) 22. (a) 23. (c) 24. (a) 25. (c) 26. (c) 27. (a) 28. (c) 29. (a)
HINTS 1. Biology is the branch of science dealing with the study of different aspects of living beings. The term Biology was coined by Lamarck and Traviranus in 1802. 2. Theophrastus, a pupil of Aristotle is known as Father of Botany. Aristotle is called Father of Zoology as well as Biology and Louis Pasteur is considered to be Father of Microbiology. 3. Anatomy is the study of internal structures which can be observed with unaided eye after dissection. It is used in phylogenetic similarity (Homology) and dissimilarity (Analogy). Cell Biology 33
4. First Nobel Laureate in biology was Emil von Behring who got this prize for discovery of serum therapy for diphtheria. 5. Resolving power is the ability to distinguish two closely placed objects. As distinct resolving power of naked eye is 100 μm, compound microscope is 0.25 – 0.3 μm and that of electron microscope is 10 Å. Microscope increases resolving power. 6. Microsomal fraction separates out at 100000 μg for 60 minutes. The fraction includes microsomes, endoplasmic reticulum, Golgi bodies, Microbodies etc. Microsomes are broken parts of E.R. 7. Ribosomes are very minute, sub microscopic cell organelles which came to our knowledge after the discovery of electron microscope. Electron microscope has a high magni cation and resolving power. 8. Electron microscope have very high resolving power. It uses a beam of electrons for illumination of object and image formation and electromagnetic lenses (i.e., condenser, objective and projector). There are two types of electron microscope : (i) Transmission Electron Microscope (TEM) : It is used to study internal structure of the specimen and gives two dimensional view (2D). TEM is the most commonly used electron microscope, resolution power of which is 10 Å and magni cation power is 1–2 lac times. (ii) Scanning Electron Microscope (SEM) : SEM is especially useful for examining the surface of a specimen. It gives three dimensional (3D) surface view of objects. The resolution power of a SEM is about 50 Å and its magni cation power is usually around 20,000 times. 9. Vital staining involves the staining of structures in living cells, either in the body (in vivo) or in vitro. Janus green B, neutral red and methylene blue are widely used as vital stain. Janus green B is used for mitochondria, neutral red for plant vacuoles and methylene blue is used for staining the dividing cells. 10. Autoradiography is used to study the synthesis of molecules and to trace the metabolic pathway or events in the cell. It involves the incorporation of radioactive substance into the molecules and the detection of their presence by photographic technique. The most useful radioactive isotopes employed in auto radiography are b-emitters like H 3, C 14 , P 32 , C a45 , I 131 , F e59 and S 35 . Autoradiography was also utilized by J.H. Taylor and his co-workers for the study of duplicating chromosomes in the root tip cells of Vicia faba. 11. Light stimulates the movement of different plant parts in speci c direction. It is called photrotropism. On keeping a potted plant near an open window of a dark room, we observe the plant bending towards the light source as a result of phototropism. Teleology involves the explanation of natural phenomena in terms of need of organisms e.g., Stem bends towards light because ‘they need light for growth. 12. Serendipity, is the act of accidental discovery such as discovery of penicillin by A. Flemming, law of gravitation by Newton etc. Louis Pasteur pointed out that “Chance favours the trained mind” i.e., only a person who is trained in scienti c method is more likely to make a chance discovery. 13. The system which exchanges energy and matter with the environment is called open system. The system which does not gain or lose energy or mass from the environment is called a closed system. Living beings are an open system because biological system can not live without input of energy. They must also receive materials from outside for growth or repair and give out waste products as well as dissipate energy. 14. Typically, about 90% of the total solute carried in the phloem is the carbohydrate sucrose, a disaccharide. This is a relatively inactive and highly soluble sugar, playing little direct role in metabolism and so making an ideal transport sugar, since, it is unlikely to be used in transit. At its destination, sucrose can be converted back to the more active monosaccharides (i.e., glucose and fructose). Due to iis high solubility, it can be present in very high concentrations. Starch is a polymer of glucose. It is major reserve food in plants. Starch has two components i.e., amylose (an unbranched polymer) and amylopectin (a branched polymer). 15. Water is the most abundant substance of living beings. Water is the only molecule that exists in liquid state over a wide range of temperature i.e., 4 – 90°C. Water has the maximum density at 4°C. It freezes at 0°C and boils at 100°C. Life was originated in water more than 3 billion years ago by aggregation and interaction of organic molecules of monosaccharides, polysaccharides, amino acids, lipids, nucleotides, polynucleotides and proteins. 16. Metabolism refers to all the chemical activities involving various energy exchange in a cell. Metabolism has two phases i.e., anabolism and catabolism. Anabolism involves a series of synthetic reactions. Growth, repair, storage and reproduction are anabolic reactions. Catabolism is a destructive metabolism. Digestion and respiration are catabolic processes in which the breakdown of bonds release energy. Mitochondria is rich in catabolic enzymes and is the chief site for cellular respiration. 34 Botany
17. Resurrection fern is a drought resistant, evergreen, epiphytic fern which appears to be a ball of coiled, dead leaves in the dry season but revives with moisture such as Polypodium polypodioides, Selaginella lepidophylla, Selaginella bryopteris etc. S. bryopteris is sold in market under the name Sanjivani. 18. DNA is the genetic material of most organisms including many viruses. Some viruses, however, have RNA as their genetic material. DNA is the store house of all hereditary information in eukaryotes. DNA is capable of replication. DNA on replication forms DNA and on transcription forms RNA. 19. A dipeptide is formed when two amino acids are linked together by a peptide bond with the elimination of a water molecule.
The condensation reaction occurs between the NH 2 (Amino) group of one amino acid and COOH (Carboxyl) group of another amino acid. An oligosaccharide may have up to 25 amino acids and a polypeptide may have 25-50 amino acids and compounds having more than 50 amino acid residues are called proteins.
20. Autotrophs are organisms whose sole source of carbon is CO 2. Autotrophs include both photosynthetic and chemosynthetic organisms. The photosynthetic autotrophs utilize energy from sunlight while chemosynthetic autotrophs derive their energy from oxidation of inorganic materials like iron, sulphur, ammonia etc. Chemoautotrophs do not use light energy, therefore, lack chlorophyll pigments. 21. Water is required in many cases when larger molecules split up into smaller ones. The phenomenon is called hydrolytic splitting e.g., Protein into amino acids, starch into glucose. Water has high thermal conductivity, so, it helps in quick distribution of heat to all parts of the body. 22. Feulgen reaction is a speci c test for establishing the presence of DNA. Feulgen reaction was developed by R. Feulgen and H. Rossenbeck in 1924. This reaction involves a mild acid hydrolysis of DNA exposing aldehyde group and subsequent staining with ‘Schiff’s reagent’ (Leucobasic fuchsine). Schiff’s reagent is prepared by treating basic fuchsin with sulfurous acid. Acetocarmine is used for the staining of nucleus. 23. Assertion is true but reason is false. Resolving power is the ability to distinguish two close points as distinct points. Microscope increases resolving power. For example, human eye has a resolving power of 100 μm, optical microscope 0.25 μm and electron microscope 2-10 A°. 24. Both assertion and reason are true and reason is the correct explanation of assertion. With the aid of electron microscope, ribosomes and several other submicroscopic cell organells were observed. They are extremely minute in size. For example, the ribosome is a spheroidal particle of 23 nm. The resolving power of electron microscope is 2-10 Å and a magni cation of 100,000 - 300,000 can be obtained in an electron microscope. 25. Assertion is true but reason is false. Taxonomy is the science of identi cation, nomenclature and classi cation of organisms. But taxonomy and systematics are different terms. Systematics is the branch of biology that deals with diversity of organisms at very level of classi cation. 26. Assertion is true but reason is false. On the basis of post scienti c literature of preliminary experimentation, the investigator makes guesses or hypotheses. Hypothesis is not supported by any critical, accurate and repeatable experimentation or observation. 27. Both assertion and reason are true and reason is the correct explanation of assertion. Short term adaptation (like defoliation of lives in auumn) are changes develop in living organisms in response to temporary environmental changes. These changes are temporary changes. Such changes are noninheritable i.e. acquired. As in these, DNA is not changed so these play no role in evolution. On the other hand long term adaptation (like type of beak in birds, modi cation of structures in plants) involve change in DNA hence they play an important role in evolution. 28. Assertion is true but reason is false. Law of entropy states when a living or non living system is left to itself, then it tends to increase its disorder or randomness i.e. entropy. So entropy is the degree of unavailable or useless energy. Living systems carry a number of chemical reaction and physical changes. Since no energy transfer or transformation is cent percent ef cient, there is a regular loss of energy, thus bringing entropy. Living system overcome entropy by continuous input of usable or free energy. The living organism obtain this required free energy either from radiant energy by photosynthesis (e.g. plants) or from ready made food (e.g.). 29. Both assertion and reason are true and reason is the correct explanation of assertion. DNA is the genetic material in most of living organism except the plant viruses and some bacteriophages. It is the only molecule which can replicate itself or can form its own carbon copy. The phenomenon is called molecular reproduction. All the infomation required for growth, differentiation, running cellular machinery and reproduction is contained in DNA molecules. These genetic information of DNA are like the blue print. During cell division (which involve DNA replication, the daughter cell receive the same blue print or genetic material as in the parental cell).