Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

37. Plant Sensation and Response

Phototropism

General Biology

37. Plant Sensation and Response

Phototropism

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1:54 minutes

Problem 3

Textbook Question

Auxin causes a shoot to bend toward the light by
a. Causing cells to shrink on the dark side of the shoot
b. Stimulating growth on the dark side of the shoot
c. Causing cells to shrink on the lighted side of the shoot
d. Stimulating growth on the lighted side of the shoot

Verified step by step guidance

Understand the role of auxin: Auxin is a plant hormone that regulates growth by promoting cell elongation. It is distributed unevenly in response to light, which is key to phototropism (growth toward light).

Recall the mechanism of phototropism: When light shines on one side of a shoot, auxin redistributes to the shaded (dark) side of the shoot. This uneven distribution is crucial for the bending process.

Analyze the effect of auxin on cells: Auxin stimulates cell elongation by loosening the cell wall, allowing cells to expand. This effect occurs more prominently on the side of the shoot where auxin concentration is higher.

Determine which side grows more: Since auxin accumulates on the dark side of the shoot, the cells on the dark side elongate more than those on the lighted side. This differential growth causes the shoot to bend toward the light.

Match the correct option: Based on the above understanding, the correct answer is the option that describes auxin stimulating growth on the dark side of the shoot.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phototropism

Phototropism is the growth response of a plant toward light. This phenomenon occurs because plant hormones, particularly auxins, redistribute unevenly in response to light, leading to differential growth rates on the sides of the plant. As a result, the plant bends toward the light source, optimizing its ability to capture sunlight for photosynthesis.

Auxin

Auxin is a plant hormone that plays a crucial role in regulating growth and development. It promotes cell elongation, particularly on the side of the plant that is away from light, causing the plant to bend toward the light source. This hormone is essential for various growth processes, including phototropism and gravitropism.

Cell Elongation

Cell elongation refers to the process by which plant cells increase in length, contributing to overall plant growth. Auxin stimulates this elongation by promoting the loosening of cell walls, allowing cells to expand. In the context of phototropism, greater elongation occurs on the shaded side of the plant, resulting in bending toward the light.

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Related Practice

Textbook Question

A barley mutant lacking a gibberellic acid receptor would

a. Fail to make GA.

b. Catalyze starch more quickly.

c. Fail to make α-amylase.

d. Fail to take up water.

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Textbook Question

Auxin enhances cell elongation in all of these ways except:

a. Increased uptake of solutes

b. Gene activation

c. Acid-induced denaturation of cell wall proteins

d. Cell wall loosening

975

views

Textbook Question

Which of the following statements about phytochrome is not correct?

a. It is photoreversible.

b. Its function was understood long before the protein itself was isolated.

c. The Pfr form activates the responses to red light.

d. It is involved in guard-cell opening.

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Textbook Question

Charles and Francis Darwin discovered that

a. Auxin is responsible for phototropic curvature

b. Red light is most effective in shoot phototropism

c. Light destroys auxin

d. Light is perceived by the tips of coleoptiles

How may a plant respond to severe heat stress?

a. By reorienting leaves to increase evaporative cooling

b. By creating air tubes for ventilation

c. By producing heat-shock proteins, which may protect the plant's proteins from denaturing

d. By increasing the proportion of unsaturated fatty acids in cell membranes, reducing their fluidity

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Textbook Question

The signaling molecule for flowering might be released earlier than usual in a long-day plant exposed to flashes of:

a. Far-red light during the night

b. Red light during the night

c. Red light followed by far-red light during the night.

d. Far-red light during the day

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Textbook Question

If a long-day plant has a critical night length of 9 hours, which 24-hour cycle would prevent flowering?

a. 16 hours light/8 hours dark

b. 14 hours light/10 hours dark

c. 4 hours light/8 hours dark/4 hours light/8 hours dark

d. 8 hours light/8 hours dark/light flash/8 hours dark

951

views

Textbook Question

Phytochromes can be considered 'shade detectors,' while phototropins such as PHOT1 can be considered 'sunlight detectors.' Explain why these characterizations are valid.

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Auxin causes a shoot to bend toward the light by a. Causing cells to shrink on the dark side of the shootb. Stimulating growth on the dark side of the shootc. Causing cells to shrink on the lighted side of the shootd. Stimulating growth on the lighted side of the shoot

Key Concepts

Phototropism

Auxin

Cell Elongation

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Auxin causes a shoot to bend toward the light by
a. Causing cells to shrink on the dark side of the shoot
b. Stimulating growth on the dark side of the shoot
c. Causing cells to shrink on the lighted side of the shoot
d. Stimulating growth on the lighted side of the shoot