One plant is any organism in the kingdom Plantae. Kingdoms main divisions, in which scientists classify all living things on Earth. Other kingdoms: Monera (single-celled organisms without nuclei), Protista (single-celled organisms with a nucleus) fungi, and Animalia (animals). The scientific study of plants is called botany.
The general definition of the plant is any organism that contains chlorophyll (green pigment contained in specialized cells called chloroplasts) and can produce its own food. Another feature of plants is that their rigid cell walls consist mainly of cellulose, a complex carbohydrate which is insoluble (it can not be dissolved) in water.
Due to the large number of plants that exist, cellulose is the most abundant organic compound on Earth. Biologists have identified about 500 species of plants, although there are many undiscovered species, especially in tropical forests.
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