Plant biology is the science of plant life. There are over 410,000 species of land plants on earth, of which 391,000 are vascular plants, and approximately 20,000 are bryophytes, a group of three divisions of non-vascular land plants, the liverworts, hornworts and mosses.
All plants are multicellular eukaryotes, with their DNA stored in their nuclei. The characteristics of plant cells that distinguish them from animals and fungi include a primary cell wall, and membrane bound organelles known as plastids with unique photosynthetic and biosynthetic functions – including chloroplasts, in which photosynthesis occurs. Photosynthesis is the process where sunlight is used to convert water and carbon dioxide into sugars and other organic molecules, with hugely significant consequences for life as the by-product, oxygen, is required by nearly all living things on earth. Unlike animals, many plant cells do not terminally differentiate but are totipotent with the ability to give rise to a new individual plant.
Plants synthesise a number of polymers, like polysaccharides, from which plant cell walls are constructed. Many medicinal drugs, such as caffeine, morphine and nicotine come directly from plants. Sugar, starch, cotton, linen, vegetable oils, wax, and natural rubber are examples of commercially important materials made from plant tissues.