Unit 3- Module 8 Sensory Systems and Responses

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14 Terms

1
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Q: What is the inactive form of phytochrome, and what is it triggered by?

A: Pr (phytochrome red); triggered by red light (660 nm) which converts it to the active form Pfr.

2
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Q: How do plants use the phytochrome system?

A: To detect light quality, duration (photoperiod), and direction; helps regulate germination, flowering, and growth.

3
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Q: What is phototropism a response to?

A: Light; specifically blue light.

4
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Q: What ensures that roots grow into soil and shoots grow toward sunlight?

A: Gravitropism and phototropism, regulated by auxin (IAA) distribution.

5
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Q: Define Phototropism.

A: Growth response of a plant toward or away from light.

6
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Q: Define Thigmotropism.

A: Directional growth response to touch or physical contact (e.g., vines coiling).

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Q: Define Gravitropism.

A: Growth response to gravity; roots grow downward, shoots grow upward.

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Q: Define Thigmonastic response.

A: Rapid, non-directional movement in response to touch (e.g., Venus flytrap closing).

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Q: Define Thigmomorphogenetic response.

A: Long-term structural changes due to mechanical stress like wind or repeated touch.

10
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Q: What controls the response to gravity?

A: Statoliths—starch-filled organelles that settle with gravity and signal auxin redistribution.

11
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Q: What does a high concentration of IAA in response to gravity stimulate? Where?

A: In shoots: stimulates cell elongation on the lower side → bends upward.
In roots: inhibits elongation on the lower side → bends downward.

12
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Q: What is the first line of defense in plants?

A: Structural barriers such as the cuticle, bark, and cell walls.

13
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Q: What structures have been modified to become thorns and spines?

A: Thorns = modified stems; Spines = modified leaves.

14
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Q: What are alkaloids? What are they used for? Know some examples.

A: Nitrogen-containing compounds used in plant defense; toxic or bitter to herbivores.
Examples: morphine, caffeine, nicotine, quinine.