MadSci Network: Cell Biology |
Lucy, Plants appear green because many of their cells contain chloroplasts which contain the green pigments, chlorophyll a and chlorophyll b. Surprisingly, the outer layer of cells covering the plant, the epidermis, is devoid of chloroplasts and is colorless or transparent. The only epidermal cells containing chloroplasts are the guard cells of the stomatal apparatus. The cells that give a plant its green appearance are chloroplast containing parenchyma cells. Leaves have two types of parenchyma cells called palisade and spongy parenchyma cells. Below ground organs of plants, such as roots and underground stems, are normally not green because their plastids contain starch which is not green. Chlorophyll develops in response to light. A good experiment to show this is to plant some pea, bean or corn seeds in a pot and then place the pot in the dark for a week or more. Plant another pot of seeds and leave it in the light. Compare the plants in the two pots and see if there is a color difference.
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