Plants

 Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars from carbon dioxide and water, using the green pigment chlorophyll. Exceptions are parasitic plants that have lost the genes for chlorophyll and photosynthesis, and obtain their energy from other plants or fungi.

There are about 382,000 accepted species of plants,[15] of which the great majority, some 283,000, produce seeds.[16] The table below shows some species count estimates of different green plant (Viridiplantae) divisions. About 85–90% of all plants are flowering plants. Several projects are currently attempting to collect records on all plant species in online databases, e.g. the World Flora Online.

Plants range in scale from single-celled organisms such as desmids (from 10 micrometres across) and picozoa (less than 3 micrometres across),[18][19] to the largest trees (megaflora) such as the conifer Sequoia sempervirens (up to 380 feet (120 m) tall ) and the angiosperm Eucalyptus regnans (up to 325 feet (99 m) tall ).

Plant cell structure 

Plant cells have distinctive features that other eukaryotic cells (such as those of animals) lack. These include the large water-filled central vacuole, chloroplasts, and the strong flexible cell wall, which is outside the cell membrane. Chloroplasts are derived from what was once a symbiosis of a non-photosynthetic cell and photosynthetic cyanobacteria. The cell wall, made mostly of cellulose, allows plant cells to swell up with water without bursting. The vacuole allows the cell to change in size while the amount of cytoplasm stays the same.

Plant structure 

Anatomy of a seed plant. 1. Shoot system. 2. Root system. 3. Hypocotyl. 4. Terminal bud. 5. Leaf blade. 6. Internode. 7. Axillary bud. 8. Petiole. 9. Stem. 10. Node. 11. Tap root. 12. Root hairs. 13. Root tip. 14. Root cap

Most plants are multicellular. Plant cells differentiate into multiple cell types, forming tissues such as the vascular tissue with specialized xylem and phloem of leaf veins and stems, and organs with different physiological functions such as roots to absorb water and minerals, stems for support and to transport water and synthesized molecules, leaves for photosynthesis, and flowers for reproduction.

Importance of plants 

Food

Human cultivation of plants is the core of agriculture, which in turn has played a key role in the history of world civilizations.[100] Humans depend on plants for food, either directly or as feed in animal husbandry. Agriculture includes agronomy for arable crops, horticulture for vegetables and fruit, and forestry for timber.[101][102] About 7,000 species of plant have been used for food, though most of today's food is derived from only 30 species. The major staples include cereals such as rice and wheat, starchy roots and tubers such as cassava and potato, and legumes such as peas and beans. Vegetable oils such as olive oil and palm oil provide lipids, while fruit and vegetables contribute vitamins and minerals to the diet.[103] Coffee, tea, and chocolate are major crops whose caffeine-containing products serve as mild stimulants.[104] The study of plant uses by people is called economic botany or ethnobotany.

Medicines 

Medicinal plants are a primary source of organic compounds, both for their medicinal and physiological effects, and for the industrial synthesis of a vast array of organic chemicals.[106] Many hundreds of medicines, as well as narcotics, are derived from plants, both traditional medicines used in herbalism[107][108] and chemical substances purified from plants or first identified in them, sometimes by ethnobotanical search, and then synthesised for use in modern medicine. Modern medicines derived from plants include aspirin, taxol, morphine, quinine, reserpine, colchicine, digitalis and vincristine. Plants used in herbalism include ginkgo, echinacea, feverfew, and Saint John's wort. The pharmacopoeia of Dioscorides, De materia medica, describing some 600 medicinal plants, was written between 50 and 70 CE and remained in use in Europe and the Middle East until around 1600 CE; it was the precursor of all modern pharmacopoeias.

Plants are distributed almost worldwide. While they inhabit several biomes which can be divided into a multitude of ecoregions,[79] only the hardy plants of the Antarctic flora, consisting of algae, mosses, liverworts, lichens, and just two flowering plants, have adapted to the prevailing conditions on that southern continent.

Plants are often the dominant physical and structural component of the habitats where they occur. Many of the Earth's biomes are named for the type of vegetation because plants are the dominant organisms in those biomes, such as grassland, savanna, and tropical rainforest.[81]

Structural resources and fibres from plants are used to construct dwellings and to manufacture clothing. Wood is used for buildings, boats, and furniture, and for smaller items such as musical instruments and sports equipment. Wood is pulped to make paper and cardboard.[118] Cloth is often made from cotton, flax, ramie or synthetic fibres such as rayon, derived from plant cellulose. Thread used to sew cloth likewise comes in large part from cotton.

Ornamental plants 

Thousands of plant species are cultivated for their beauty and to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and reduce soil erosion. Plants are the basis of a multibillion-dollar per year tourism industry, which includes travel to historic gardens, national parks, rainforests, forests with colourful autumn leaves, and festivals such as Japan's[120] and America's cherry blossom festivals.

Plants may be grown indoors as houseplants, or in specialized buildings such as greenhouses. Plants such as Venus flytrap, sensitive plant and resurrection plant are sold as novelties. Art forms specializing in the arrangement of cut or living plant include bonsai, ikebana, and the arrangement of cut or dried flowers. Ornamental plants have sometimes changed the course of history, as in tulipomani

Further reading 

Evans, L.T. (1998). Feeding the Ten Billion – Plants and Population Growth. Cambridge University Press.ISBN 0-521-64685-5.

Kenrick, Paul; Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D.C.: Smithsonian Institution Press. ISBN 1-56098-730-8.

Raven, Peter H.; Evert, Ray F.; Eichhorn, Susan E. (2005). Biology of Plants (7th ed.). New York: W.H. Freeman and Company. ISBN 0-7167-1007-2.

Taylor, Thomas N.; Taylor, Edith L. (1993). The Biology and Evolution of Fossil Plants. Englewood Cliffs, New Jersey: Prentice Hall. ISBN 0-13-651589-4.