Plant cells are eukaryotic and have many of the structures found in animal cells.
Link to pages describing these.
Plant cells differ from animal cells in lacking:
The electron micrograph shows cells from a sunflower leaf. It was supplied through the courtesy of H. J. Arnott and Kenneth M. Smith.
Chloroplasts are the most familiar plastids. They are usually disk-shaped and about 5-8 µm in diameter and 2-4 µm thick. A typical plant cell has 20-40 of them.
Chloroplasts are green because they contain chlorophylls - the pigments that harvest the light used in photosynthesis.
Chloroplasts are probably the descendants of cyanobacteria that took up residence in the ancestor of the plants.
Plant cells that are not engaged in photosynthesis also have plastids that serve other functions, such as
- intermediate filaments
The rigid cell wall of plants is made of fibrils of cellulose embedded in a matrix of several other kinds of polymers such as pectin and lignin.
- storing starch (when they are called leucoplasts) [View]
- storing the carotenoids that give flowers and fruits their color (when they are called chromoplasts).
The linear nature of cellulose molecules and the many opportunities for side-to-side intermolecular hydrogen bonding provide just what one would want to build long, stiff fibrils.
The cell walls of parenchyma and meristems are uniform in thickness. Both pictures show primary cell walls.
Although each cell appears encased within a box, in fact primary cell walls are perforated permitting plasmodesmata to connect adjacent cells.
The cells of
have secondary deposits of lignified cellulose which provide mechanical strength to the tissue.
Vacuoles are bounded by a single membrane. Young plant cells often contain many small vacuoles, but as the cells mature, these unite to form a large central vacuole.
Vacuoles serve several functions, such as
Plant cells avoid bursting in hypotonic surroundings by their strong cell walls. These allow the build-up of turgor within the cell. Loss of turgor causes wilting.
When a freshwater (or terrestrial) plant is placed in sea water, its cells quickly lose turgor and the plant wilts.
This is because sea water is hypertonic to the cytoplasm. As water diffuses from the cytoplasm into the sea water, the cells shrink - drawing their plasma membrane away from the cell wall.
The photomicrograph shows plasmolyzed cells in the freshwater plant Elodea which has been placed in sea water. Note how the cell walls now show clearly.
5 November 2000