Plant cells: Typical of eukaryotes Cell wall Protoplast Ergastic substances Cell wall: Mostly cellulose, a polymer of glucose Strong but flexible Stains blue-green in prepared slides Secondary wall interior to the primary wall and both exterior to the plasma membrane Other constituents include hemicelluloses, pectins and glycoproteins Lignin in certain walls; nonflexible and strong Waxes (hydrophobic) Suberin (bark) Cutin (epidermis) Stain red in prepared slides Layers of cell wall: Middle lamella Primary cell wall Produced first Plastic Primary pit fields permit cytoplasmic connections (plasmodesmata) between cells Secondary cell wall: Laid down after primary wall and is therefore inside the primary wall (closest to the membrane) Generally lignified and rigid Laid down in chunks Openings (pits) around the plasmodesmata more obvious than openings in primary wall Simple pits in angiosperms (flowering plants) and bordered pits in gymnosperms (conifers). Questions: What is the difference between pits and primary pit fields? What are plasmodesmata? What is the difference between plastids and mitochondria? Protoplast: Plasma Membrane Nucleus Plastids Mitochondria Microbodies Ribosomes ER and Golgi bodies Vacuole Cytoskeleton Plastids: Bound by two membranes, the inner one organized into a system of vesicles Chloroplasts have photosynthetic pigments on internal membrane Leucoplasts have no color; may synthesize various substances ? same structure as plastids Chromoplasts have nongreen fat-soluble pigments (orange and yellow usually) on the internal membrane. Amyloplasts contain starch synthesized in the plastid (storage for plants) Plastid development begins with immature chloroplasts (proplastids) that take on distinguishing characteristics with age. Plastids resemble bacteria Bacterial DNA sequences Protein synthesis similar to bacteria DNA of plant chloroplasts is frequently used in phylogenetic studies. Mitochondria: Same as in animal cells Two unit membranes Inner one organized into folds (cristae) with enzymes involved in respiration Like plastids, probably arose by endosymbiosis. Microbodies: Organelles bound by a single unit membrane Contain enzymes responsible for various metabolic processes Peroxisomes responsible for photorespiration Vacuole: Large, central water-filled organelle bound by a single membrane (tonoplast) Regulates internal pressure Sometimes filled with ergastic substances (products from metabolism) Oil bodies ? storage for energy Ribosomes: Particles composed of proteins and RNA; sites of protein synthesis Polysomes (cluster of ribosomes) observed in sites of active synthesis Endoplasmic Reticulum: Internal membrane system Sometimes with ribosomes (rough ER) or without ribosomes (smooth ER) Packages a substances within Golgi bodies Golgi apparatus: All dictymoes Cytoskeleton: Microtubles: thin protein tubes made of tubulin; hollow Made of a dimer of alpha and beta tubulin Microfilaments: small fibers made of actin; solid Two strands twisted together Ergastic substances: Nonliving materials Storage (starch) Defensive (tannins ? gives the bitter after taste) Crystals (stores oxalic acid)
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