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NAME OF THE TEACHER: SR. RENCY GEORGE SUBJECT: BIOLOGY TOPIC: CHAPTER -1 CLASS: IX MOBILE NO:9340839715 Chapter-1 The Fundamental Unit Of Life

Objectives Students should be able to explain and apply theory Students should be able to describe the major components of a cell, including the , , nucleus, , etc.. Students should appreciate the differences between a plant and animal cell. Students should have a basic understanding of chromosomes, and cell division.

Learning Outcomes – Students will be able to:- Explain the role that each part of the membrane plays in performing its function.

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RESOURCES:

i.Text books ii.Learning Materials iii.Lab manual iv.E-Resources,video ,L.C.D etc… Introduction Every organism in this universe are made of tiny basic structural units called cells. Cells were discovered by Robert Hooke in 1665. Cells are the building blocks of an element that cannot be seen with naked eyes but can be seen under a microscope. Every living-element is made up of numerous tiny cells. There are some single celled organisms as well that live on their own. Organisms can be classified into unicellular and multicellular organisms depending upon the number of cells present in their body.

All living organisms in this universe are made up of cells.

They either exist as a single cell or as a combination of multiple cells. Discoveries about Cells – The Fundamental Unit of Life

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Discovered By Period of time What they discovered?

Robert Hooke 1665 noticed the presence of cells in a cork slice

Leeuwenhoek 1674 found the presence of living cells in the pond water

Robert Brown 1831 recognized the existence of a nucleus in the cell

Purkinje 1839 invented the term ‘Protoplasm’ which is the liquid present in a cell

Schleiden and Schwann 1838, 1839 presented the cell theory that all organisms are actually made up of cells

Virchow 1855 suggested that all cells come from cells that already exist in nature The Cell Theory

1. A cell is the structural and functional unit of all living organisms.

2. All the living organisms are made up of cells.

3. Cells are formed from pre-existing cells.

• Unicellular Organisms – The organisms that consist of a single cell such as Amoeba. • Multicellular Organisms – The organisms which contain various cells that perform different functions in the organism such as plants fungi and animals How can multicellular organisms originate from a single cell?

A cell has the capability to divide itself into cells of its own type. Therefore, more cells can generate from an already existing cell. The Shape of the Cell

• The shape of the cell may vary depending upon the type of function they perform in an organism.

• Cells are capable of changing their shape. For example, the white blood cells and amoeba can change shapes on their own.

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Figure 1 - Cells can have different Shaped and Sizes How can cells perform distinct functions in organisms? Cells are capable of performing multiple functions in an organism. A cell contains specific components which are called . Each in the cell can perform different functions such as making new cells or clearing the waste of the cell. Thus, organelles allow a cell to perform several kinds of activities in an organism. The Organization of a Cell

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Figure 2 – The Structure of Cells in Plants and Animals

A cell contains three features –

• The Plasma Membrane

• Nucleus

• Cytoplasm Plasma Membrane

• It is just like an envelope that covers the whole cell. Therefore, a cell gets separated from the external environment because it has a plasma membrane.

• The plasma membrane has the capability to decide which materials should enter or leave the cell and which should not. That is why it is also called as a ‘Selectively Permeable Membrane’. The of Plasma Membrane

• The Fluid Mosaic model explains the structure of the plasma membrane. According to it, the plasma membrane comprises of 3 components - , and Carbohydrates. These components can flow freely and fluidly inside the plasma membrane.

• There are two types of lipids (fats) in the plasma membrane –

o Phospholipid – It is a made up of glycerol, two fatty acids, and phosphate. It creates a semi-permeable membrane which allows flow of only certain materials inside/ outside the cell o Cholesterol - It is a lipid which provides fluidity to the surface of plasma membrane.

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• The proteins act as receptors of the cell and help in transportation across the cell membrane. The carbohydrates attach themselves with the lipids and proteins and are found on extracellular side of the membrane.

Figure 3 -Structure of the Plasma Membrane How can substances move in and out of a cell? Gaseous Exchange between the Cell and its External Environment –

• Movement of Oxygen and Carbon dioxide to and from the cell is carried out by means of diffusion.

• Gaseous substances have a tendency to move to areas where their concentration is less from the areas where there is higher. This movement is defined as the process of diffusion. Diffusion can take place of solids, liquid, gases. Movement of Water between the Cell and its External Environment – It is carried out by the means of osmosis. Osmosis is a process in which water moves from the region of high concentration to one where its concentration is low through a semi permeable membrane. Therefore we can say that Osmosis is just a special case of the process of diffusion. Hypotonic Solutions

• If the concentration of water outside the cell is higher than the concentration of water inside the cell the cell gains water by the process of osmosis.

• Water can move into the cell from the cell membrane. In the case of hypotonic solutions, more amount of water enters the cells which results in swelling of the cells.

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Figure 4 - Hypotonic Solution Isotonic Solutions

• If the cells are put in an environment which has similar concentration of water as present inside. This state allows for the free movement of water across the membrane without changing concentration of solutes on either side.

• Therefore, the size of the cell does not vary in an isotonic solution because there is no net movement of water.

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Figure 5 - Isotonic Solution Hypertonic Solutions

• If the cells are kept in an environment which has lower concentration of water than what is present inside the cells then due to the process of osmosis water moves out of the cells.

• This results in a decrease in size of the cells (they shrink) as more amount of water comes out of the cell.

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Figure 6 - Hypertonic Solution What is Endocytosis? (Olympiad)

It is a process by which the plasma membrane engulfs food and other materials inside the cell.

Cell Wall

• The is a outer, hard covering of the cell which maintains the shape of the cell.

• The cell wall is generally made up of cellulose.

• What is plasmolysis? Plasmolysis is a process in which the contents of the cell that are away from the cell wall shrink or contract when a cell loses water due to Osmosis when it is kept in hypertonic solution.

• Can dead cells absorb water? No, dead cells cannot absorb water through osmosis. • How plants, fungi, and bacteria can exist in hypotonic medium? Plants, fungi, and bacteria exist in such situations because of their rigid cell membranes. Even if the cells swell up the cell membrane is able to prevent them from bursting out. The Nucleus

Nucleus is a prominent, organelle present in cell which is the controlling centre of all activities of cell.

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Figure 7 - Nucleus of a Cell The Structure of the Nucleus

• A nucleus has a nuclear membrane which covers it all around.

• There are pores present on the nuclear membrane that allow movement of substances in and out of the nucleus.

• There are chromosomes, rod-shaped structures present in the nucleus which contain genetic information.

The chromosomes contain two types of things -

1. DNA - This is responsible for organizing and constructing new cells 2. Proteins - These help in packaging and condensation of DNA. Chromatin

Chromatin is thread-like material present in a cell. The chromatin organizes itself into chromosomes whenever the cell is about to divide.

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Figure 8 – Chromosomes and Chromatin It is called as the Brain of the Nucleus. It comprises of 25% of the volume of the nucleus. It consists of proteins and ribonucleic acids (RNA). It helps in formation of which help in formation of proteins inside the cell.

Figure 9 - Nucleolus inside a Nucleus What is a ? Sometimes cells do not have a well-defined nucleus because they lack a nuclear membrane. Such a nucleus with no definite nuclear boundaries is called a Nucleoid. What are the ? Organisms whose cells do not have a definite cell membrane are called Prokaryotes. What are eukaryotes? Organisms whose cells contain a well-defined nuclear membrane are called Eukaryotes. Are there any further differences between prokaryotes and eukaryotes?

Prokaryotes Eukaryotes

There is no presence of nucleus The nucleus exists in the cells

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A single chromosome is present There are multiple chromosomes

They undergo asexual reproduction They undergo sexual as well as a sexual reproduction

They are generally unicellular organisms They are generally multicellular organisms

There are membrane bound cell organelles present inside the There are no membrane bound cell organelles cells

Example – Bacteria, Blue green algae Example – Fungi, Plants and Animals ()

Figure 10 - Eukaryotic and Prokaryotic Cells Cytoplasm

• The plasma membrane has a fluid like substance in it which is called the cytoplasm.

• The cytoplasm contains several organelles that can perform distinct functions of the cell Functions of Cytoplasm

• It supports and suspends the cell organelles and molecules.

• The cellular processes occur in cytoplasm such as formation of proteins.

• It allows movement of substances in the cell such as hormones.

• It dissolves cellular wastes. The Cell Organelles

• In the case of Eukaryotic organisms, the cells contain organelles that have their own membranes apart from the overall cell membrane of the cell.

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Figure 10 - Different Cell Organelles What is the significance of membrane-bound organelles in a cell? The cells perform several functions. The organelles are useful because they allow separation of different functions that are being performed by the cell.

Organelles which carry out important activities in a Cell –

1. Endoplasmic Reticulum

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4. Mitochondria

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8. Ribosomes

9. Endoplasmic Reticulum (ER)

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Figure 11 - Endoplasmic Reticulum

• The structure of the ER is quite similar to that of the plasma membrane. It is a network-like structure which consists of membrane-bound tubes and sheets.

• Two types of ER – o Rough ER o Smooth ER

• Rough ER contains ribosomes that are responsible for the manufacturing of proteins in the cells. They give a rough texture to the cell.

• The smooth ER manufactures fats or lipids in the cell which allow the functioning of the cell.

• What are the functions of lipids and proteins?

o Proteins and lipids synthesised on ER are used for making cell membrane. The process is known as Membrane Biogenesis.

o Proteins can act as an enzyme

o Both and lipids can act as hormones

• Functions of ER

o Transportation of material between different parts of the cytoplasm and also between the nucleus and cytoplasm

o Folding of proteins which are synthesised by ribosome on RER.

o Detoxifying poisons and drugs out of the cell is the function of SER. Golgi Apparatus

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Figure 12 – Golgi Apparatus • Camillo Golgi discovered the Golgi Apparatus. o It contains vesicles that are arranged parallel in stacks. These stacks are called Cisterns. These vesicles have their own membranes. These membranes are sometimes connected to those of the ER. • Functions of Golgi Apparatus

o Golgi apparatus carries materials synthesized by the ER to different parts of the cell. The material is stored and packaged in vesicles.

o Formation of complex sugar

o Formation of lysosomes. Lysosomes

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Figure 13 – Structure of

• They are single membrane vesicles which are responsible for cleaning the cell. They can digest any foreign material such as food or bacteria and even the worn out cell organelles.

• How lysosomes can digest any foreign material that enters the cell?

o Lysosomes are capable of doing so because they have digestive enzymes in them. These enzymes break the materials and digest them. These enzymes are synthesized by RER and packaged into lysosome by Golgi bodies.

• Why lysosomes are called ‘suicide bags’? o If the cell’s own material gets damaged or dead gets there are chances that lysosomes burst out, thus digesting its own cell. Mitochondria It is a double membrane organelle which has its own DNA and that is why often called ‘Semi Autonomous Organelle’

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Figure 14 – Structure of Mitochondria • The cell requires energy in order to carry out several activities. This energy is generated by mitochondria which are often called as the ‘Powerhouse’ of the Cell. Mitochondria are site of cellular respiration. They use oxygen from air to oxidise the carbohydrates and thereby release energy.

• What are energy currencies of a cell?

• The Mitochondria generates ATP (Adenosine Triphosphate) which are energy giving molecules of the cell that are often called as their ‘Energy Currency’. • The two membranes of Mitochondria

o Outer Membrane – Porous in Nature

o Inner Membrane – Deeply Folded

• The Inner Membrane of Mitochondria called as Cristae Facilitates Generation of ATP molecules as it has a larger surface area. Plastids

Just like mitochondria it is also double membraned organelle which has its own DNA and ribosome.

Plastids exist in plant cells only. Depending upon the type of function they play in the cell they can be classified as –

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Chromoplast

Coloured in nature, contain a pigment called Colourless in nature chlorophyll

Cause in plants Act as storage spaces of the cells

Contain orange and yellow pigments Contain starch, proteins and oil

Can further be divided into , and Can further be divided into or aleuroplast.

Figure 15 – Types of Plastids Classification of Plastids 1. Amyloplast

• They are found in tubers, cotyledons and endosperm in plants.

• They are used to store starch.

2. Elaioplast

• They are found in epidermal cells of the plants

• They store oil.

3. Proteinoplast

• They are found in seeds and nuts.

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• They store proteins. Chloroplasts

• Chloroplasts are cell organelles that conduct photosynthesis in plants.

• is derived from two Greek words Chloro and Plasts which means green and plants respectively.

• Chloroplasts contain photosynthetic pigments called ‘Chlorophyll’ along with lipids, carbohydrates, minerals, DNA, RNA, grana, thylakoids and stroma.

• The main functions of chloroplasts are:

o Conducting photosynthesis in plants.

o Protein synthesis

o Releases oxygen

o Storage of Starch

Figure 16 – Chloroplast containing thylakoids, stroma and grana Light-dependent Reactions in Photosynthesis – During photosynthesis chlorophyll absorbs the light energy which is then used to for two molecules ATP and NADPH. Thylakoids – They are pillow shaped compartments in the chloroplast. The light-dependent reactions in photosynthesis take place in the thylakoids. Stroma – It is a fluid-filled matrix in the chloroplasts. It is colorless fluid that contains all the enzymes that are needed for the light-dependent reactions in Photosynthesis.

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Grana – Stacks of thylakoids are called Grana. They are found in the stroma. They provide a large surface area so that the reactions of photosynthesis can take place. Vacuoles

Vacuoles are the places where cells can store the liquids and solids. They are present in both plants and animals but the plant vacuoles are bigger in size than the animal vacuoles.

Plant Cell Vacuoles Animal Cell Vacuoles

Plant cell vacuoles store all the material that is required for the Animal cell vacuoles contain food items in plant to stay alive such as water unicellular organisms

Animal vacuoles can also expel water and Plant vacuoles maintain the turgidity of the plant cell waste out of the cell

Plant cells generally contain a single large Animal cells contain several small vacuoles

Animal vacuoles are scattered throughout Plant vacuoles are present in the center of the cell the cell

Types of Vacuoles

• Sap Vacuoles

• Contractile Vacuoles

• Food Vacuoles

Sap Vacuoles

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Figure 17 - Sap Vacuoles These vacuoles are filled with a fluid called Vascular Sap. The fluid contains Amino Acids, Salt, Sugar, Proteins, Water, and Waste Materials. Sap vacuoles are separated from the cytoplasm by a semi-permeable membrane called Tonoplast. Their main function is to allow rapid exchange between cytoplasm and the surrounding environment. A number of sap vacuoles are found in young plant cells and animal cells. In mature plants the small sap vacuoles combine together to form a single large central vacuole.

Contractile Vacuoles

Figure 18 – Osmoregulation in Amoeba through Contractile Vacuoles They are found in protistan and algal cells in fresh water. The membrane of the contractile vacuoles is highly extensible and collapses easily. These vacuoles are responsible for osmoregulation (maintaining the water content of the cells) and excretion in the cells.

Food Vacuoles

Figure 19 – Food Vacuoles and Digestion

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They are found in the cells of protozoans and several lower animals. Food vacuoles are responsible for digestion of food in the cells as they contain food enzymes. The digested food then passes into the cytoplasm. Found in single celled organisms like Amoeba. Centrioles

• A is a small set of arranged in a specific way.

• Their main purpose is to help a cell in cell division.

• They are found near the nucleus but they can be seen only during the cell division.

• They are found in pairs and form a special substance called which appears near the nucleus.

• When the cell divides, the centrosome divides into two parts and each part moves to opposite sides of the cell.

Figure 20 - Centrioles Ribosomes

• They are cell organelles responsible for protein synthesis.

• Ribosomes can be found in both prokaryotes and eukaryotes because the synthesis of proteins is important in both of them.

• In prokaryotes, the ribosomes float freely in the cytoplasm.

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• In eukaryotes, they can be found floating in the cytoplasm or they are often attached to the endoplasmic reticulum.

• The ribosomes attached to the ER synthesize proteins that are to be exported out of the cell while the ribosomes floating inside the cell synthesize proteins that are used inside the cell. Peroxisomes

• Peroxisomes are small vesicles found in the cells.

• These enzymes are used to break the toxic materials inside the cell.

• They digest the fatty acids of the cell as well as amino acids by carrying out oxidation reactions in the cell.

• They are also responsible for digestion of alcohol in the human body. Hence, the liver contains a large number of Peroxisomes.

Figure 21 - Peroxisomes in a cell

Question and Answers:-

1. Who discovered cells and how? Answer- Cell was discovered by an English Botanist, Robert Hooke in 1665. He used self-designed microscope to observe cells in a cork slice back then.

2. Why the cell is called the structural and functional unit of life?

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Answer- Cells are called the structural and functional unit of life because all the living organisms are made up of cells and all the functions that take place inside the organisms are performed by cells.

3. How do substances like CO2 and water move in and out of the cell? Discuss. Answer- The substances like CO2and water move in and out of a cell through the process called diffusion from the region of concentrated region to low concentrated one. When the concentration of carbon di-oxide and water is higher in external environment than that inside the cell, CO2and water moves inside the cell. When the concentration outside the cell is low but it is high inside the cell, they move outwards. 4. Why the plasma membrane is called a selectively permeable membrane? Answer- Plasma membrane called a selectively permeable membrane because it regulates the movement of substances from within to outside of the cell. This means that the plasma membrane allows the entry of some substances while preventing the movement of some other substance. 5. Can you name the two organelles we have studied that contain their own genetic material? Answer- Mitochondria and plastids their own genetic material 6. If the organization of a cell is destroyed due to some physical or chemical influence, what will happen? Answer- If the organization of a cell is destroyed due to some physical or chemical influence then cell will not be able to perform its basic functions like digestion, excretion, respiration etc. This may stop all the life activities and the life of an individual may come to an end. 7. Why are lysosomes known as suicide bags? Answer- Lysosomes are called suicide bags because in case of any disturbance of their cellular metabolism they release their own enzymes to digest their own cell. 8. Where are proteins synthesized inside the cell? Answer- The proteins are synthesized in the Ribosome

9. Make a comparison and write down ways in which plant cells are different from animal cells. Answer Animal cell Plant cell Has a cell wall. Has cell wall made up of cellulose. It does not contain chloroplast. It contains chloroplast. It has centrosome. It does not has centrosome. Vacuoles are smaller in size. Vacuoles are larger in size. Lysosomes are larger in Lysosomes are absent or very few in number. number Prominent Golgi bodies are Subunits of Golgi bodies are present.

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present. 10. How is a prokaryotic cell different from a eukaryotic cell? Answer Prokaryotic cell Eukaryotic cell Most eukaryotes are multi- Most prokaryotes are unicellular. cellular. Size of the cell - (0.5- 5 μ). Size of the cell - (50- 100 μ). It contains more than one It contains a single chromosome. chromosome. Nucleolus is absent. Nucleolus is present. Cell organelles such as Membrane-bound cell organelles mitochondria, plastids, such as plastids, mitochondria, endoplasmic reticulum, Golgi endoplasmic reticulum, Golgi apparatus, lysosomes, etc. are apparatus, etc. are absent. present. Cell division occurs through binary Cell division occurs by mitosis.

11. What would happen if the plasma membrane ruptures or breaks down? Answer- If ever the plasma membrane ruptures or breakdown then the cell will not be able to exchange material from its surroundings by diffusion. As a result of it the protoplasmic material will disappear and the cell will die.

12. What would happen to the life of a cell if there was no Golgi apparatus? Answer- Golgi apparatus performs the function of a storage modification and packaging of products. If Golgi apparatus is not there then materials synthesized by cell will not be packaged and transported.

13. Which organelle is known as the powerhouse of the cell? Why? Answer- Mitochondria are known as the powerhouse of cells because energy required for various chemical activities needed to support life is released by mitochondria in the form of ATP (Adenosine triphosphate) molecules.

14. Where do the lipids and proteins constituting the cell membrane get synthesized? Answer- Lipids are synthesized in Smooth endoplasmic reticulum and the proteins are synthesized in endoplasmic reticulum.

15. How does an Amoeba obtain its food? Answer- Amoeba obtains food using temporary finger-like extensions on the cell surface which fuse over the food particle forming a food-vacuole. Complex substances

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16. What is osmosis? Answer- Osmosis is the process in which water molecules moves from the region of high concentration to a region of low concentration through a semi permeable membrane.

Assignment

Make a 3-D model of Animal Cell and Plant Cell.

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