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Lecture 12

BISC 101 Lecture 12: BISC 101 - midterm 2 review- Environment Interactions

Biological Sciences
Course Code
BISC 101
Tony Williams

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BISC 101 - midterm 2 review: Environment Interactions
1. What are the steps in information process?
- 1. Receptor cell perceives external stimulus & transduces info→ external signal
- 2. A hormone (cell-cell signal) released by receptor cell travels throughout body
- 3. Responder cells receive hormonal signal, transduce it→ external signal changes
2. What are hormones?
- Plant growth regulators
3. What is positive phototropism? How is it caused?
- Plant growth toward light
- Caused by differential growth cells, opposite sides of coleoptile
- Cells on dark side elongate faster than light
4. What is a coleoptile?
- Grass seedling
5. What is the experimental evidence that supports the hormone hypo for
- W permeable barrier shoot bends
- Suggests hormone diffuses from tip down to shoot
- Shoot bends away from hormone
6. What is the first plant hormone discovered?
- auxin
7. How do photoreceptors allow plants to detect presence direction, intensity &
wavelength of light?
- Phototropic response = occurs with blue light
- b/c mediated by light photoreceptors phototropin
- Sensitive to blue light
8. What are 2 photoreceptors that mediate light response?
- 1. Phototropins - blue
- Proteins encoded by PHOT1/PHOT2 genes
- Involved phototropic response/light dependent opening/closing stomata
- Cytochromes involved in timing of flowering
- 2. Phytochrome photoreceptors
- Absorbs red/far red light
- Shows photoreversibility, switching b/w 2 diff conformations
- Involved seed germination/ shade avoidance/ flowering
9. Explain photoreversibility
- Molecular switching mechanism
- Red light (660 nm) increased germination (drives photosynthesis)
- Far red light (730 nm) decreased germination (indicates shade)
10. Explain how auxin works in the elongation of plants?
- Auxin binds auxin receptors (TIR1, ABP1) signal transduction
- 1. Increased # proton pumps (H+-ATPases) in plasma membrane
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