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Aerotropism
Aerotropism or oxytropism is the growth of an organism either toward or away from a source of air/oxygen. Evidence of this behavior has been recorded in plants, bacteria, and fungi. History In 1882 Engelmann demonstrated oxygen-sensing orientation in oxytactic microorganisms relative to an oxygen gradient. The orientation of plant roots toward air was reported by Molisch in 1884 and in 1906 Pfeffer proposed that oxygen was the chemical cue that caused the plant root to change direction, as opposed to other gases that are present in air. Aerotropism versus oxytropism In a 1908 Botanical Gazette article, the author mentions an article by W. Polowzow where it is proposed that the term aerotropism be concerned with the sensitivities of organisms to air and that the term aeroidotropism be related to organism sensitivities to pure gases. The author posits that there is no need for the differentiation. Several scientists in papers cited for this article use the term “oxytropism†... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phototropism
In biology, phototropism is the growth of an organism in response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light contain a hormone called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the furthest side from the light. Phototropism is one of the many plant tropisms, or movements, which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism. Negative phototropism is not to be confused with skototropism, which is defined as the growth towards darkness, whereas negative phototropism can refer to either the growth away from a light source or towards the darkness. Most plant shoots exhibit positive phototropism, and rearrange their chloroplasts in the leaves to maximize photosynthetic energy and promote growth.G ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravitropism
Gravitropism (also known as geotropism) is a coordinated process of differential growth by a plant in response to gravity pulling on it. It also occurs in fungi. Gravity can be either "artificial gravity" or natural gravity. It is a general feature of all higher and many lower plants as well as other organisms. Charles Darwin was one of the first to scientifically document that roots show ''positive gravitropism'' and stems show ''negative gravitropism''. That is, roots grow in the direction of gravitational pull (i.e., downward) and stems grow in the opposite direction (i.e., upwards). This behavior can be easily demonstrated with any potted plant. When laid onto its side, the growing parts of the stem begin to display negative gravitropism, growing (biologists say, turning; see tropism) upwards. Herbaceous (non-woody) stems are capable of a degree of actual bending, but most of the redirected movement occurs as a consequence of root or stem growth outside. The mechanism is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
