Green leaves and yellow flowers of adaffodil plantA picture of a Grassy grass plant
Plants are one of six big groups (kingdoms) of living things. They areautotrophiceukaryotes, this means they have complexcells, and make their own food. Usually, they cannot move (not countinggrowth). Plants need sunlight, soil and water whereas seeds need warmth.
Most plants grow in the ground, withstems in the air androots below the surface. Some float on water. The root part absorbs water and somenutrients the plant needs to live and grow. These climb the stem and reach the leaves. The evaporation of water from pores in theleaves pulls water through the plant. This is calledtranspiration.
A plant needssunlight,carbon dioxide, minerals from the soil andwater to make food byphotosynthesis. A green substance in plants calledchlorophyll traps theenergy from the Sun needed to make food. Chlorophyll is mostly found in leaves, insideplastids, which are inside theleafcells. The leaf can be thought of as a food factory. Leaves of plants vary in shape and size, but they are always the plant organ best suited to capture solar energy. Once the food is made in the leaf, it is transported to the other parts of the plant such as stems and roots.[6][7]
The word "plant" can also mean the action of putting something in the ground. For example,farmers plantseeds in the field.
Theroots of plants perform two main functions. First, they anchor the plant to the ground. Second, they absorbwater and variousnutrients dissolved in water from thesoil. Plants use the water to make food. The water also provides the plant with support. Plants that lack water become very limp and their stems cannot support theirleaves. Plants which specialise indesert areas are calledxerophytes or phreatophytes, depending on the type of root growth.
Water is transported from the roots to the rest of the plant through special vessels in the plant. When the water reaches the leaves, some of itevaporates into the air. Many plants need the help offungi to make their roots work properly. This plant/fungisymbiosis is calledmycorrhiza.Rhizobiabacteria in root nodules help some plants getnitrogen.[10]
Reproductive parts of Easter Lily (Lilium longiflorum). 1.Stigma, 2.Style, 3.Stamens, 4.Filament, 5.Petal
Flowers are the reproductive organ only offlowering plants (Angiosperms). The petals of a flower are often brightly colored and scented to attractinsects and other pollinators. Thestamen is the male part of the plant. It is composed of thefilament (a stalk) that holds theanther, which produces the pollen.Pollen is needed for plants to produce seeds. Thecarpel is the female part of the flower. The top part of the carpel contains thestigma. Thestyle is the neck of the carpel. Theovary is the swollen area at the bottom of the carpel. The ovary produces the seeds. Thesepal is a leaf that protects a flower as a bud.
How pollen moves from one flower to another flower is calledpollination. This transfer can happen in different ways. Insects such asbees are attracted to bright, scented flowers. When bees go into the flower to gathernectar, the spiky pollen sticks to their back legs. The sticky stigma on another flower catches the pollen when the bee lands or flies nearby it.
Some flowers use the wind to carry pollen. Their dangling stamens produce lots of pollen that is light enough to be carried by the wind. Their flowers are usually small and not highly coloured. The stigmas of these flowers are feathery and hang outside the flower to catch the pollen as it falls.[11]
A plant produces manyspores orseeds. Lower plants such asmoss andferns produce spores. Theseed plants are theGymnosperms and Angiosperms. If all the seeds fell to the ground beside the plant, the area might become overcrowded. There might not be enough water and minerals for all the seeds. Seeds usually have some way to get to new places. Some seeds can be dispersed by the wind or by water. Seeds inside juicy fruits are dispersed after being eaten. Sometimes, seeds stick to animals and are dispersed that way.[12]
If by plants we include all types of algae, then the earliest knownred algae lived 1.6 billion years ago. Fossils of them were recently found in India.[20]
Acritarchs (a group of organic-walled microfossils) may be reproductivecysts of green algae. If so, they are present in theNeoproterozoicera, 1000 mya.[22]
Otherwise, there is a large increase inplanktonic algae around 540 mya in theCambrian period.[22]
By theSilurian, fossils of whole plants are preserved, including thelycophyteBaragwanathia. From theDevonian, detailed fossils ofrhyniophytes have been found. Early fossils of these ancient plants show the individual cells within the plant tissue. The Devonian period also saw the evolution of the first tree in the fossil record,Wattieza. This fern-like tree had a trunk with fronds, and producedspores.
Thecoal measures are a major source ofPalaeozoic plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect;coal itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the Fossil Forest at Victoria Park inGlasgow the stumps ofLepidodendron trees are found in their original growth positions.
↑Lewis, L.A.; McCourt, R.M. (2004). "Green algae and the origin of land plants".American Journal of Botany.91 (10):1535–1556.doi:10.3732/ajb.91.10.1535.PMID21652308.
↑Asimov, Isaac 1968.Photosynthesis. Basic Books, New York, London.ISBN0-465-05703-9.
↑Intermediate Learn Science, grades 5-6, by Mike Evans and Linda Ellis
↑Smith A.L. 1997.Oxford dictionary of biochemistry and molecular biology. Oxford University Press. p508ISBN0-19-854768-4. "Photosynthesis -- the synthesis by organisms of organic chemical compounds, esp. carbohydrates, from carbon dioxide using energy obtained from light rather than the oxidation of chemical compounds".
↑Rabinowitch E. and Govindjee 1969.Photosynthesis. Wiley, London.ISBN0-471-70424-5
↑Mauseth, James D. 2003.Botany: an introduction to plant biology. Jones & Bartlett, Boston.
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