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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0:23 minutes

Problem 2

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.

Verified step by step guidance

Understand the role of phytochrome: Phytochrome is a photoreceptor in plants that is sensitive to light in the red and far-red region of the electromagnetic spectrum. It plays a crucial role in regulating various plant developmental processes.

Review the concept of photoreversibility: Phytochrome exists in two interconvertible forms, Pr and Pfr. The Pr form absorbs red light and converts to Pfr, while the Pfr form absorbs far-red light and converts back to Pr. This photoreversibility is a key feature of phytochrome.

Examine the historical context: The function of phytochrome in plant development, such as seed germination and flowering, was studied and understood before the actual protein was isolated and characterized.

Analyze the role of Pfr: The Pfr form of phytochrome is the active form that triggers various physiological responses in plants, such as seed germination and flowering, in response to red light.

Consider the involvement in guard-cell opening: Phytochrome is primarily known for its role in processes like seed germination and flowering, but it is not typically associated with the opening of guard cells, which is more directly influenced by blue light receptors.

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Key Concepts

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

Phytochrome

Phytochrome is a photoreceptor in plants that detects light and is crucial for regulating various developmental processes. It exists in two forms, Pr and Pfr, which are interconvertible depending on the light conditions. This photoreversibility allows plants to respond to changes in light quality, influencing processes like seed germination and flowering.

Photoreversibility

Photoreversibility refers to the ability of phytochrome to switch between two forms, Pr and Pfr, in response to red and far-red light. This reversible transformation enables plants to sense and adapt to their light environment, playing a critical role in processes such as photoperiodism and shade avoidance.

Guard-cell Function

Guard cells are specialized cells in the epidermis of plant leaves that regulate the opening and closing of stomata, controlling gas exchange and water loss. While phytochrome influences many light-dependent processes, its direct involvement in guard-cell opening is not well-established, making this statement potentially incorrect in the context of phytochrome's known functions.