a cell varies. This number depends on
the changing of environmental conditions that the plant encounters and how
the plant adjusts to these changes. The number of plastids in a cell also
depends on the type of species the plant is. Plant Cell Plastids
By: Katie Briscoe
Plastids are organelles that
only exist in plant cells and photosynthetic protists. They are found in
the cytoplasm
of the cell and have a double membrane surrounding them. The number of plastids
in a cell varies. This number depends on
the changing of environmental conditions that the plant encounters and how
the plant adjusts to these changes. The number of plastids in a cell also
depends on the type of species the plant is.
Picture of a plastid-- source: Audesirk, Teresa and Gerald; Biology Prentice Hall Inc. 1999
The primary function of plastids is to store molecules. One molecule that they store is pigment; pigments give fruits and vegetables an orange or red color when they are ripe. Plastids also store photosynthetic products for plants that continue to grow year after year. These products that are obtained during the summer, and they are stored in the plastid for the winter and spring. Plastids are also very important for the storage of starch; "most plants convert sugars made during photosynthesis into starch" (Audesirk, 103). Foods full of starch contain many plastids. Potatoes, for example, have many plastids in their cells.
Some of the many types of plastids are proplastsids, etioplasts, chromoplasts, and chloroplasts. Proplastids are very small plastids that are found in dividing cells. Their primary function is "to give rise to other types of plastids" (Sheeler, 441). Chromoplasts are another type of plastid that gives color to the petals of flowers, roots, or fruits. The function of chromoplasts is unknown; the bright colors chromoplasts produce attracts insects to various plants. Etioplasts (picture below) are typically found in the leaves of plants that are grown in the dark. Etioplasts are useful to the cell in that when they are put into light, etioplasts develop into chloroplasts. Chloroplasts are the "site" of photosynthesis.
Souce: Sheeler, Philip; Cell Biology New York; John Wiley mad Sons Inc. 1983
For more information on plastids go to: http://www.cellsalive.com/search.htm
Back to home Page: http://sun.menloschool.org/~cweaver/cells/index.html
Bibliography:
1. Audesirk, Teresa and Gerald; Biology Prentice Hall Inc. 1999
2. Sheeler, Philip; Cell Biology New York; John Wiley mad Sons Inc. 1983
3. Stern, William Louis and Oswaldo Tippo; Humanistic Botany New York; W.W. Norton and Company Inc. 1977