Coordination and Respone in Plants
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10 Terms
Q: What is a tropism?
A: A growth response of a plant in which the direction of growth is determined by the direction of a stimulus (e.g., light or gravity).
Q: What is phototropism?
A: Growth response to light. Shoots are positively phototropic (grow towards light). Roots are negatively phototropic (grow away from light).
Q: What is geotropism (gravitropism)?
A: Growth response to gravity. Roots are positively geotropic (grow downwards, towards gravity). Shoots are negatively geotropic (grow upwards, away from gravity).
Q: What hormone controls tropisms in plants?
A: Auxin, a plant growth hormone that controls the direction of growth in response to light and gravity.
Q: Where is auxin produced and how does it move?
A: Produced in the shoot tip and root tip. It moves by diffusion and active transport to other parts of the plant, often accumulating on the shaded or lower side.
Q: How does auxin cause phototropism in shoots?
Light causes auxin to move to the shaded side of the shoot.
Cells on the shaded side elongate more, so the shoot bends towards the light.
This increases light absorption for photosynthesis.
Q: How does auxin affect roots in geotropism?
In roots, auxin inhibits cell elongation.
When auxin accumulates on the lower side due to gravity, the upper cells grow faster, so the root bends downwards.
Q: How does auxin cause geotropism in shoots?
In shoots, auxin stimulates cell elongation.When the shoot is placed horizontally, auxin gathers on the lower side, causing faster growth there — so the shoot bends upwards.
Q: Why are plant growth responses important?
A: They help plants maximize survival — for example: Shoots grow towards light for photosynthesis. Roots grow downwards to anchor and absorb water/minerals
Q: What practical experiment can demonstrate phototropism?
A: Growing seedlings in one-sided light:
Control group with uniform light grows straight./ Experimental group bends towards the light source, showing positive phototropism.