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Flashcards · 5090 · Topic 3
Movement into and out of cells flashcards
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Topic 3: Movement into and out of cells
- Diffusion
- The net movement of molecules or ions from a region of their higher concentration to a region of their lower concentration (down a concentration gradient), as a result of their random movement.
- Osmosis
- The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.
- Active transport
- The movement of molecules or ions into or out of a cell through the cell membrane, from a region of their lower concentration to a region of their higher concentration (against a concentration gradient), using energy released during respiration.
- Source of energy for diffusion and osmosis
- The kinetic energy of the random movement of molecules and ions. No energy from respiration is used.
- Factors that increase the rate of diffusion
- Larger surface area, higher temperature, steeper concentration gradient, shorter distance.
- Surface area to volume ratio of a 3 cm cube
- Surface area = 6 × 3² = 54 cm²; volume = 3³ = 27 cm³; SA:V = 2 : 1. (A 1 cm cube is 6 : 1.)
- Plant cell vs animal cell placed in pure water
- Both gain water by osmosis. The plant cell becomes turgid; its cellulose wall stops it bursting. An animal cell, such as a red blood cell, has no wall, so it swells and bursts.
- Turgid, flaccid and plasmolysed
- Turgid: has taken in water; firm, membrane pressed against the wall (turgor pressure). Flaccid: has lost water and turgor pressure; soft. Plasmolysed: membrane and cytoplasm pulled away from the wall.
- A potato cylinder goes from 4.0 g to 3.4 g in a sucrose solution. % change and meaning?
- (3.4 − 4.0) ÷ 4.0 × 100 = −15%. The solution had a lower water potential than the cells, so water left by osmosis.
- Why must root hair cells take up mineral ions by active transport?
- The ion concentration in soil water is lower than in the cell, so ions must move against the concentration gradient. This needs energy from respiration, so lack of oxygen reduces ion uptake.