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CHAPTER 2 : Basic components of living systems
The ultrastructure of plant cells
Cellulose cell wall
-Plant cell walls are made of cellulose, a complex carbohydrate
-Freely permeable
-Give the cell shape
-Contents of cell press against cell wall making it rigid, supporting the cell individually
and the plant as a whole
-Acts as a defense mechanism, protecting the contents of the cell against invading
pathogens
-All plants have cellulose cell walls
Plant cell organelles
-Unlike animal cells, plant cells are rigid structures
-Structures unique to plant cells include vacuoles and chloroplasts
Vacuoles
-Membrane lined sacs in cytoplasm containing cell sap
-Most plant cells have large permanent vacuoles, important in the maintenance of
turgor, so contents of cell push against wall and maintain a rigid framework for the
cell
-Membrane of a vacuole in a plant cell is called the tonoplast, selectively permeable,
some small molecules can pass through, others cannot
-If they appear in animal cells, they're small and transient (not permanent)
Chloroplasts
-Organelles responsible for photosynthesis in plant cells
-Found in cells green parts, eg

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