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

Tropisms and Hormones

General Biology

37. Plant Sensation and Response

Tropisms and Hormones

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1:26 minutes

Problem 2

Textbook Question

During winter or periods of drought, which one of the following plant hormones inhibits growth and seed germination?
a. Ethylene
b. Abscisic acid
c. Gibberellin
d. Auxin

Verified step by step guidance

Understand the role of plant hormones: Each plant hormone has specific functions. Ethylene is involved in fruit ripening and stress responses, gibberellin promotes growth and seed germination, auxin regulates cell elongation and growth, and abscisic acid is known for its role in inhibiting growth and promoting dormancy during unfavorable conditions.

Focus on the environmental context: The problem mentions winter or drought, which are stressful conditions for plants. During such times, plants often enter a state of dormancy to conserve energy and resources.

Identify the hormone associated with dormancy: Abscisic acid (ABA) is the hormone responsible for inducing dormancy, inhibiting growth, and preventing seed germination under stressful conditions like drought or cold temperatures.

Compare the options: Ethylene, gibberellin, and auxin are not primarily associated with dormancy or growth inhibition during stress. Abscisic acid is the correct hormone for this function.

Conclude the reasoning: Based on the functions of the hormones and the environmental context provided, abscisic acid is the hormone that inhibits growth and seed germination during winter or drought.

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Key Concepts

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

Plant Hormones

Plant hormones, or phytohormones, are chemical messengers that regulate various physiological processes in plants, including growth, development, and responses to environmental stimuli. They play crucial roles in processes such as seed germination, flowering, and fruit ripening, influencing how plants adapt to their surroundings.

Abscisic Acid (ABA)

Abscisic acid is a plant hormone primarily involved in stress responses, particularly during drought or unfavorable conditions. It inhibits growth and promotes seed dormancy, helping plants conserve resources and survive periods of environmental stress by preventing germination until conditions improve.

Seed Germination

Seed germination is the process by which a seed develops into a new plant, requiring specific environmental conditions such as moisture, temperature, and light. Hormones like gibberellins promote germination, while abscisic acid acts as an inhibitor, ensuring that seeds do not germinate prematurely during adverse conditions.

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The hormone that helps plants respond to drought is:

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b. Abscisic acid

c. Cytokinin

d. Ethylene

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Test your knowledge of the five major classes of plant hormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene) by matching one hormone to each lettered box. (Note that some hormones will match up to more than one box.)

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Which of the following statements about hormones is correct?

a. They tend to be large molecules.

b. They exert their effects only on the same cells that produce them.

c. They can exert strong effects only when they are present in high concentrations.

d. They trigger a response by binding to target-cell receptors.

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Textbook Question

In autumn, the amount of _________ increases and the amount of _________ decreases in fruits and leaf stalks, causing a plant to drop fruit and leaves.

a. Ethylene … auxin

b. Gibberellin … abscisic acid

c. Cytokinin … abscisic acid

d. Auxin … ethylene

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Textbook Question

What evidence suggests that ABA from roots can signal guard cells to close?

a. If roots are given sufficient water, guard cells close anyway.

b. If roots are dry, guard cells begin to close—even though leaves may not be experiencing water stress.

c. Applying ABA to guard cells directly causes them to close.

d. If roots are dry, the ABA concentration in leaf cells drops dramatically.