Introduction to Plants Plants are multicellular eukaryotic organisms with the ability to produce their own food by the process of photosynthesis. (They are autotrophs.) Algae have historically been included with the plants, but they are now classified with the protists. The modern definition of plants includes organisms that live primarily on land (and sometimes in water), excluding algae that live primarily in water. Another distinguishing characteristic of plants is their type of chlorophyll. Chlorophyll is used to absorb energy from the sun during the process of photosynthesis. Plants have chlorophyll a and chlorophyll b , while many species of algae do not have chlorophyll b . Green algae have both types of chlorophyll, but they are single-celled forms. Many evolutionary biologists believe that the green algae gave rise to the land plants. Plants occur in two major groups: the nonvascular plants and the vascular plants.
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