1. Define and compare active and passive transport mechanisms.
Answer:
Definition:
- Active transport is the movement of molecules across a membrane against their concentration gradient, requiring energy (ATP).
- Passive transport is the movement of molecules down their concentration gradient without requiring energy.
Comparison:
| Feature | Active Transport | Passive Transport |
|---|---|---|
| Energy Requirement | Requires ATP | No energy required |
| Direction of Movement | Against concentration gradient | Along concentration gradient |
| Examples | Sodium-potassium pump | Diffusion, osmosis |
2. Explain the role of the sodium-potassium pump in active transport.
Answer:
The sodium-potassium pump is a membrane protein that actively transports sodium ions out of the cell and potassium ions into the cell. It maintains a high concentration of sodium outside and potassium inside, crucial for nerve impulses and muscle contractions. This pump uses ATP to change its conformation and move ions against their gradients.
3. Describe the process of diffusion as a type of passive transport.
Answer:
Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration. It occurs due to the random kinetic motion of particles. Diffusion continues until equilibrium is reached. For example, oxygen enters cells, and carbon dioxide exits cells by diffusion.
4. What is osmosis, and how does it differ from diffusion?
Answer:
Osmosis is the passive transport of water molecules across a semipermeable membrane from a region of low solute concentration to a region of high solute concentration.
Difference:
- Osmosis specifically involves water, whereas diffusion involves any substance.
- Osmosis requires a membrane, while diffusion can occur in open spaces.
5. How does facilitated diffusion differ from simple diffusion?
Answer:
- Simple diffusion allows molecules to pass directly through the lipid bilayer.
- Facilitated diffusion requires carrier or channel proteins to transport molecules, such as glucose or ions, across the membrane. Both processes are passive and do not require energy.
6. Describe the process of endocytosis as a form of active transport.
Answer:
Endocytosis is the process by which cells engulf external substances or particles. The cell membrane forms a vesicle around the material and brings it inside.
Types of Endocytosis:
- Phagocytosis: Engulfing solid particles.
- Pinocytosis: Engulfing liquids.
- Receptor-mediated endocytosis: Specific molecules are taken in after binding to receptors.
7. Explain the process of exocytosis and its importance in cells.
Answer:
Exocytosis is the active transport process where cells expel materials in vesicles. The vesicle fuses with the membrane, releasing its contents outside. It is important for removing waste, secreting hormones, and delivering proteins to the membrane.
8. What are aquaporins, and what role do they play in osmosis?
Answer:
Aquaporins are specialized membrane proteins that facilitate the rapid transport of water molecules across cell membranes. They are essential in maintaining water balance, particularly in kidneys and plant cells.
9. Describe the process of secondary active transport.
Answer:
In secondary active transport, energy is indirectly used to transport molecules. The gradient of one molecule (created by primary active transport) drives the movement of another molecule.
Example: Sodium-glucose symport, where sodium’s movement down its gradient drives glucose into the cell.
10. What happens to a cell in hypotonic, hypertonic, and isotonic solutions?
Answer:
- Hypotonic: Water enters the cell, causing it to swell and possibly burst (lysis).
- Hypertonic: Water exits the cell, leading to shrinkage (crenation in animal cells).
- Isotonic: No net water movement; the cell remains unchanged.
11. Explain the role of protein pumps in active transport.
Answer:
Protein pumps, such as the sodium-potassium pump, are integral membrane proteins that use ATP to transport molecules against their concentration gradient. They maintain essential cellular ion gradients and pH levels.
12. How do lipid bilayers influence transport across cell membranes?
Answer:
The lipid bilayer acts as a selective barrier. Nonpolar molecules diffuse easily, while polar or charged molecules require transport proteins or channels. Its fluidity and composition also affect the movement.
13. What is the difference between symport and antiport systems?
Answer:
- Symport: Two molecules move in the same direction through a protein.
- Antiport: Two molecules move in opposite directions.
Example: Sodium-calcium antiport in cardiac cells.
14. Discuss the factors affecting the rate of passive transport.
Answer:
- Concentration gradient: Larger gradients increase the rate.
- Temperature: Higher temperatures increase kinetic energy, speeding transport.
- Membrane permeability: More permeable membranes facilitate faster transport.
- Molecule size: Smaller molecules diffuse faster.
15. How does temperature influence active and passive transport?
Answer:
- Passive Transport: Increases with temperature due to higher molecular kinetic energy.
- Active Transport: Enzyme activity in active transport systems may increase with temperature up to an optimal point.
16. Compare phagocytosis and pinocytosis.
Answer:
| Feature | Phagocytosis | Pinocytosis |
|---|---|---|
| Substance type | Solid particles | Liquids |
| Vesicle size | Large | Small |
| Example | Engulfing bacteria by WBCs | Absorption of nutrients by cells |
17. What is membrane potential, and how does it relate to active transport?
Answer:
Membrane potential is the voltage difference across a cell membrane. Active transport, such as the sodium-potassium pump, creates and maintains this potential, essential for processes like nerve signaling.
18. How do ion channels facilitate passive transport?
Answer:
Ion channels are specialized proteins that allow ions to pass down their concentration gradient. They are selective, often gated, and critical for nerve impulses and muscle contractions.
19. What is bulk transport, and how is it different from molecular transport?
Answer:
Bulk transport moves large molecules or particles via vesicles (e.g., endocytosis, exocytosis). Molecular transport moves individual molecules, often through channels or carriers.
20. Explain the energy dependence of active transport with an example.
Answer:
Active transport requires energy to move substances against their gradient. For instance, the sodium-potassium pump hydrolyzes ATP to transport sodium out and potassium into the cell, maintaining ionic balance.
These questions and answers provide a comprehensive understanding of active and passive transport mechanisms.
