Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

2. Cell Chemistry & Cell Components

Active Transport

Anatomy & Physiology

2. Cell Chemistry & Cell Components

Active Transport

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Multiple Choice

Consider the transport of protons and sucrose into a plant cell by the sucrose-proton cotransport protein. Plant cells continuously produce a proton gradient by using the energy of ATP hydrolysis to pump protons out of the cell. Why, in the absence of sucrose, do protons not move back into the cell through the sucrose-proton cotransport protein?

Protons cannot move through membrane transport proteins.

Protons are freely permeable through the phospholipid bilayer, so no transport protein is needed for protons.

In the absence of sucrose, the ATP-powered proton pump does not function, so there is no proton gradient.

Protons, unlike other substances, do not diffuse down their electrochemical gradient.

The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time.

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Verified step by step guidance

Understand the concept of cotransport: Cotransport proteins, like the sucrose-proton cotransport protein, facilitate the simultaneous movement of two substances across a membrane. In this case, protons and sucrose are transported together.

Recognize the role of the proton gradient: Plant cells use ATP to pump protons out of the cell, creating a proton gradient. This gradient is a form of stored energy that can be used to drive the transport of other molecules, such as sucrose, into the cell.

Identify the dependency of cotransport: The sucrose-proton cotransport protein requires the presence of both protons and sucrose to function. The movement of protons through this protein is coupled with the movement of sucrose.

Analyze the absence of sucrose: Without sucrose, the cotransport protein cannot facilitate the movement of protons back into the cell, even though a proton gradient exists. The protein's function is dependent on the simultaneous transport of both molecules.

Conclude the mechanism: The correct explanation is that the movement of protons through the cotransport protein cannot occur unless sucrose is also present to be transported. This ensures that the energy from the proton gradient is used efficiently to import sucrose into the cell.