Jim Bidlack - BIO 5354/4354 PLANT ANATOMY Lecture 9 - Cell Structure, Cell Wall, & Epidermis I. Why are plants (and other organisms) divided into cells? A. Some organisms are composed of only one cell 1. Examples: Euglena (a protistan - one cell) Siphonales (a protistan [algae]) B. Why then, cells? 1. Provide strength and rigidity 2. Control of osmotic relations 3. Division of labor 4. Damage can be localized C. Generalized tissue system 1. Symplast - all living cells (plasmodesmata are symplastic) 2. Apoplast - all dead cells (intercellular spaces and cell walls are apoplastic) II. Cell wall structure A. Primary wall is deposited as the cell enlarges B. Primary wall constituents (a composite structure) 1. Cellulose 2. Hemicellulose (xylose) 3. Pectic substances (polyuronides - rhanmogalacturan) 4. Proteins C. Living connections - plasmodesmata - go through the primary wall D. Secondary wall is deposited by some cells AFTER cell enlargement E. Secondary wall constituents (typical fleshy growth)
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secondary wall, cell wall structure, primary wall, D. Secondary wall, B. Primary wall