Author: Roy Eassa
Date: 10:14:56 10/10/01
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On October 09, 2001 at 11:01:15, Joshua Lee wrote: >On October 08, 2001 at 15:34:05, Roy Eassa wrote: > >>On October 08, 2001 at 15:31:06, Joshua Lee wrote: >> >>>Can you use that in a sentence like : I went to the Store yesterday to find some >>>tropism for my Piece's but they were sold out. >> >> >>Involuntary response of an organism, or part of an organism, involving >>orientation toward (positive tropism) or away from (negative tropism) one or >>more external stimuli. >> >>The term tropism is usually applied to growth and turgor movements in plants; an >>involuntary orientation of a microorganism toward or away from an external >>stimulus is commonly called a taxic movement, or taxis-e.g., the negative >>phototaxis of certain protozoans that move away from light. Tropistic stimuli >>include light, heat, moisture, gravity, electricity, and chemical agents. Plant >>stems are positively phototropic and negatively geotropic, i.e., they grow >>toward light and against gravity; roots are the reverse, as well as positively >>hydrotropic (moisture-seeking). Tropistic growth in plants is believed to be >>triggered by the presence of plant hormones (see auxin) that promote cell >>growth. Auxin action is apparently inhibited by light; hence, if a plant is >>placed in a position of unequal lighting, the cells on the shadier side elongate >>faster than those on the illuminated side, and the plant bends toward the light. >>There is also evidence that auxins are affected by gravity, i.e., they >>accumulate in the lower portions of the plant organs. Since an overconcentration >>of these hormones inhibits growth, the cells on the underside of a root elongate >>more slowly than those on the upper side, resulting in the root's downward >>growth. Generalized plant responses to a stimulus are called nastic movements, >>or nasties. These include the opening of bud scales and of flower petals, growth >>movements that occur in response to stimuli such as light and heat without >>regard for the direction of the stimulus. Some spring flowers exhibit >>thermonasties, i.e., their flowers open in response to warmth rather than the >>amount of light. Turgor movements are effected by changes in the water content >>of cells and are often quite rapid. Examples are the "sleep movements of clover, >>the sudden drooping of the leaves of the sensitive plant (mimosa) when touched >>(thigmotropism), and the reactions of insectivorous plants to the presence of >>their prey. The exact mechanism controlling the sudden loss of water pressure in >>certain cells, producing turgor movements, is not clearly understood. > >Sounds like Conditioned Response was the first thing that poped into my mind but >it isn't exactly. > >Are you a Biology Teacher you sound really good at this, I could've used you >I'm sure i would've gotten an A. I hate to burst that nice bubble, but I just did a search on the 'net, copied what looked like a good resulting page, and pasted the text here!
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