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Bop8e Chapter03 REVISED W16 Part 1 Ray F. Evert • Susan E. Eichhorn Raven Biology of Plants Eighth Edition CHAPTER 3 The Plant Cell and the Cell Cycle © 2013 W. H. Freeman and Company Powerhouse of the Plant Cell • The chloroplast is the site where light energy is used to produce the organic molecules required by the plant cell • In this image, the flattened and stacked membranes of the grana can be seen inside the chloroplast • Chlorophyll and other pigments embedded in the chloroplast membranes capture the sun's energy, the first step in the process essential to life—photosynthesis Hooke's Microscope • The English microscopist Robert Hooke first used the term "cell" to refer to the small chambers he saw in magnified slices of cork • (a) One of Hooke's microscopes, made for him around 1670 • Light from an oil lamp (far left) was directed to the specimen through a water-filled glass globe that acted as a condenser • The specimen was mounted on a pin, just below the tip of the microscope • The microscope was focused by moving it up and down using a screw held to the stand by a clamp • (b) This drawing of two slices of cork appeared in Hooke's book, Micrographia, published in 1665 Chapter Overview • Prokaryotes and Eukaryotes • The Plant Cell: An Overview • Nucleus • Chloroplasts and Other Plastids • Mitochondria • Peroxisomes • Vacuoles • Endoplasmic Reticulum • Golgi Apparatus • Cytoskeleton • Flagella and Cilia • Cell Wall • The Cell Cycle • Interphase • Mitosis and Cytokinesis Main Points of this Chapter • The cell is the fundamental unit of life • Cells are of two fundamentally different types: prokaryotic and eukaryotic • Plant cells typically consist of a cell wall and a protoplast • The nucleus is surrounded by a nuclear envelope and contains nucleoplasm, chromatin, and one or more nucleoli • Ribosomes are the sites of protein synthesis • There are three main types of plastids: chloroplasts, chromoplasts, and leucoplasts • Mitochondria are the sites of respiration • Plastids and mitochondria share certain features with prokaryotic cells • Peroxisomes are surrounded by a single membrane Main Points of this Chapter, continued • Vacuoles perform a variety of functions • The endoplasmic reticulum is an extensive three-dimensional system of membranes with a variety of roles • The Golgi apparatus is a highly polarized membrane system involved in secretion • The cytoskeleton is composed of microtubules and actin filaments • The cell wall is the major distinguishing feature of the plant cell • Dividing eukaryotic cells pass through a regular sequence of events known as the cell cycle • During prophase, the duplicated chromosomes shorten and thicken • Metaphase, anaphase, and telophase followed by cytokinesis result in two daughter cells Prokaryotes and Eukaryotes Prokaryote (Escherichia coli) Prokaryote • Electron micrograph of cells of Escherichia coli, a bacterium that is a common, usually harmless inhabitant of the human digestive tract • However, some E. coli strains, which generally are acquired by ingestion of contaminated food or water, produce toxins that cause massive secretion of fluids into the intestine, resulting in vomiting and diarrhea • This heterotrophic (nonphotosynthetic) prokaryote is the most thoroughly studied of all living organisms Prokaryote, continued • Each rod-shaped cell has a cell wall, a plasma membrane, and cytoplasm • The genetic material (DNA) is found in the less granular area in the center of each cell • This region, known as the nucleoid, is not surrounded by a membrane • (In prokaryotes, nucleoid contains most or all of the cell's genetic material) • The densely granular appearance of the cytoplasm is largely due to the presence of numerous ribosomes, which are involved with protein synthesis • The two cells in the center have just divided but have not yet separated completely Photosynthetic Eukaryote Plasma Membrane Photosynthetic Eukaryote • Electron micrograph of a cell from the leaf of a maize (Zea mays) plant • The granular material within the nucleus is chromatin • It contains DNA associated with histone proteins • The nucleolus is the region within the nucleus where the RNA components of ribosomes are synthesized • Note the many mitochondria and chloroplasts, all bounded by membranes • (Mitochondria – sites of respiration involving conversion of energy-rich molecules to do cellular work and release of waste products; chloroplasts – sites of photosynthesis) • The vacuole, which is a fluid-filled region enclosed by a membrane, and the cell wall are characteristic of plant cells Plasma Membrane (Eukaryote) • Under high magnification, cellular membranes often have a three-layered (dark-light-dark) appearance, as seen here (following slide) • This is a plasma membrane on either side of the common cell wall between two cells from an onion (Allium cepa) root tip • The numerous circular structures bordering the wall are microtubules Plasma Membrane The Plant Cell: An Overview Nucleus Nuclear Aspects as considered in Selaginella kraussiana • Selaginella kraussiana (right) • (image: Wikipedia) Nucleus • Electron micrographs of nuclei in parenchyma cells of the seedless vascular plant Selaginella kraussiana show the nuclear pores (a, see arrow in following slide) Nuclear Pores in Selaginella kraussiana (surface view), a (arrow) Note the polysomes (coils of ribosomes) on the surface of the nuclear envelope Nucleus • Electron micrographs of nuclei in parenchyma cells of the seedless vascular plant Selaginella kraussiana show the nuclear pores (b) in sectional view • The rough endoplasmic reticulum is seen paralleling the nuclear envelope in (b) • The nucleus is to the left Nuclear Pores in Selaginella Kraussiana (sectional view), b, rough endoplasmic reticulum (nucleus to the left of the arrows) Chromatin in Nicotiana tabacum Chromatin • Parenchyma cell from tobacco (Nicotiana tabacum) leaf, with its nucleus "suspended" in the middle of the cell by strands of cytoplasm (arrows) • The dense granular substance in the nucleus is chromatin, distinguishing it from the nucleoplasm • The less granular regions surrounding the nucleus are portions of a large central vacuole that merge beyond the plane of this cell section Nicotiana quadrivalvis (Indian tobacco) • Used by Native Americans from Oregon to British Columbia • (text & image: Wikipedia) Diagram of a Chloroplast- Containing Plant Cell Diagram of a Chloroplast-containing Plant Cell • Typically, the disk-shaped chloroplasts are located in the cytoplasm along the cell wall, with their broad surfaces facing the surface of the wall • Most of the volume of this cell is occupied by a vacuole (surrounded by the tonoplast), which is traversed by a few strands of cytoplasm • Tonoplast: membrane surrounding the vacuole • Cytosol, thick fluid that fills a cell • Cytoplasm: cytosol plus organelles • In this cell, the nucleus lies in the cytoplasm along the wall, although in some cells (see Figure 3—6) it might appear suspended by strands of cytoplasm in the center of the vacuole Ribosomes are formed in the cytosol and serve as the sites of protein synthesis Polysomes (or Polyribosomes), complexes of an mRNA molecule and two or more, that are formed during active translation (mRNA involved in providing information translated in ribosomes indicating amino acid sequences to synthesize proteins in ribosomes) Polysomes • Numerous polysomes (clusters of ribosomes) are seen here on the surface of rough endoplasmic reticulum • The endoplasmic reticulum is a network of membranes extending throughout the cytosol of the eukaryotic cell, dividing it into compartments and providing surfaces on which chemical reactions can take place • Cytosol: part of the cell inside of the cell membrane, excluding the organelles • Polysomes are the sites at which amino acids are assembled into proteins • This electron micrograph shows a portion of a leaf cell from the fern Regnellidium diphyllum Regnellidium diphyllum • Regnellidium is a monotypic genus of ferns of family Marsileaceae • The single living species, Regnellidium diphyllum, the two-leaf water fern, is native to southeastern Brazil and adjacent regions of Argentina • It resembles its relatives from the genus Marsilea [M. vestita, water-clover, is native to WA] • (image and text: Wikipedia) Chloroplasts and Other Plastids Chloroplasts are the sites of photosynthesis Orientation of Chloroplasts Orientation of Chloroplasts • As shown in cross sections through the leaf of Arabadopsis thaliana, chloroplasts move to maximize or minimize their absorption of light, which is entering from the top of the micrographs • (a) Under dim light, chloroplasts (dark objects along the edges of the cells) move to the cell walls parallel to the leaf surface, thus maximizing light absorption for photosynthesis • (b) In bright light, chloroplasts migrate to the cell walls perpendicular to the light surface, thus minimizing light absorption and photodamage Internal Structure of a Chloroplast Internal Structure of a Chloroplast • (a) Section of a chloroplast of a maize (Zea mays) leaf showing grana and stroma thylakoids • The word thylakoid comes from the Greek word thylakos meaning "sac" or "pouch" • Grana <grain • (b) Detail showing a granum, which is composed of stacks of disklike thylakoids • The thylakoids of the various grana are interconnected by the stroma thylakoids Chloroplast Structure • Showing: • Thylakoids (membrane-bound compartments inside chloroplasts, associated with photosynthesis) • Consist of a thylakoid membrane surrounding a thylakoid • Stroma (and, in previous
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