Study Notes
The movement of substances into and out of cells involves processes like diffusion, osmosis, and active transport. These processes are essential for obtaining nutrients, removing waste, and maintaining cell functions.
- Diffusion — the net movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient. Example: Oxygen moving from alveolar air spaces into blood in capillaries.
- Osmosis — the diffusion of water molecules through a partially permeable membrane from a region of high water potential to low water potential. Example: Water moving into plant root cells from the soil.
- Active Transport — the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration. Example: Uptake of ions from soil water by root hair cells in plants.
Exam Tips
Key Definitions to Remember
- Diffusion: Movement of molecules from high to low concentration.
- Osmosis: Movement of water through a partially permeable membrane from high to low water potential.
- Active Transport: Movement of particles against a concentration gradient using energy.
Common Confusions
- Diffusion and osmosis both involve movement down a gradient, but osmosis specifically refers to water.
- Active transport requires energy, unlike diffusion and osmosis.
Typical Exam Questions
- What is diffusion? Movement of molecules from high to low concentration.
- How does osmosis differ from diffusion? Osmosis is the movement of water through a partially permeable membrane.
- Why is active transport important in cells? It allows cells to uptake substances against a concentration gradient using energy.
What Examiners Usually Test
- Understanding of concentration gradients and their effects on diffusion and osmosis.
- Ability to explain the role of the cell membrane in substance movement.
- Examples of diffusion, osmosis, and active transport in living organisms.