Summary
The movement of substances involves processes like diffusion, osmosis, and active transport to move molecules across cell membranes. These processes are essential for maintaining cellular function and homeostasis.
- Diffusion — Net movement of molecules from a region of higher concentration to a region of lower concentration down the concentration gradient. Example: Oxygen diffusing into cells.
- Osmosis — Net movement of water molecules across a partially permeable membrane from a region of higher water potential to a region of lower water potential. Example: Water entering plant cells making them turgid.
- Active Transport — Movement of molecules or ions through transport proteins against their concentration gradient using energy from ATP. Example: Sodium-potassium pump in nerve cells.
Exam Tips
Key Definitions to Remember
- Diffusion: Movement of particles from high to low concentration.
- Osmosis: Movement of water across a membrane from high to low water potential.
- Active Transport: Movement of substances against a concentration gradient using energy.
Common Confusions
- Diffusion and osmosis both involve passive movement, but osmosis specifically refers to water.
- Active transport requires energy, unlike diffusion and osmosis.
Typical Exam Questions
- What happens to an animal cell in a hypotonic solution? It swells and may burst due to water entering by osmosis.
- How does temperature affect diffusion? Higher temperatures increase the rate of diffusion.
- Why is active transport necessary in cells? To move substances against their concentration gradient.
What Examiners Usually Test
- Understanding of how concentration gradients affect diffusion and osmosis.
- Differences between passive and active transport.
- Effects of osmosis on plant and animal cells.