Summary
Movement into and out of cells involves various processes that allow substances to cross cell membranes. These processes include diffusion, osmosis, active transport, endocytosis, and exocytosis.
- 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 roots.
- Active Transport — Movement of molecules or ions through transport proteins across a cell membrane against their concentration gradient using energy from ATP. Example: Uptake of glucose in the intestines.
- Endocytosis — Bulk movement of liquids or solids into a cell by the infolding of the cell membrane to form vesicles. Example: White blood cells engulfing bacteria.
- Exocytosis — Bulk movement of substances out of a cell by the fusion of vesicles with the cell surface membrane. Example: Release of neurotransmitters from nerve cells.
Exam Tips
Key Definitions to Remember
- Diffusion: Movement of molecules 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 vs. Osmosis: Diffusion involves any molecules, while osmosis specifically involves water.
- Active Transport vs. Passive Transport: Active transport requires energy, passive does not.
Typical Exam Questions
- What is the main difference between diffusion and active transport? Diffusion is passive, while active transport requires energy.
- How does osmosis affect plant cells in a hypertonic solution? Plant cells lose water and become plasmolyzed.
- Why do animal cells burst in hypotonic solutions? They lack a cell wall to prevent overexpansion.
What Examiners Usually Test
- Understanding of concentration gradients and their effects on diffusion.
- Ability to explain the role of ATP in active transport.
- Differences in osmosis effects between plant and animal cells.