IGCSE Revision- Biology
Chapter 3- Movement into and out of cells
3.1 Diffusion
- The more kinetic energy particles have, the faster they move
DIFFUSION DOWN A CONCENTRATION GRADIENT
- Diffusion: The net movement of particles from a region of their higher
concentration to a region of their lower concentration, as a result of their random
movement
- Net movement: Overall or average movement
- Concentration gradient: An imaginary ‘slope’ from a high concentration to a low
concentration
DIFFUSION IN LIVING ORGANISMS
- Diffusion is important in gas exchange for respiration in animals and plants. Cell
membranes are freely permeable to oxygen and carbon dioxide, so these gases
easily diffuse into and out of cells
- Solute: substance that has dissolved in a liquid which is called a solvent
3.2 Osmosis
- Compound: A substance formed by the chemical combination of two or more
elements in fixed proportions
- Water can make up about 80% of an organism’s body
- Partially permeable membrane: A membrane that lets some particles move
through it, but prevents others from passing through
- Osmosis: The diffusion of water molecules through a partially permeable
membrane
WATER POTENTIAL
- High water potential: A dilute solution
- Low water potential: A concentrated solution
- Water potential gradient: A difference in water potential between two areas
OSMOSIS AND ANIMAL CELLS
- If an animal cell is placed in a concentrated solution, water leaves the cell by
osmosis and the cell shrinks
OSMOSIS AND PLANT CELLS
- The plant cell doesn’t burst like an animal cell because it has a strong cell wall
- Turgid: A description of a plant cell that is tight and firm
- Turgor pressure: The pressure of the water pushing outwards on a plant cell wall
- Flaccid: A description of a plant cell that if soft
- Plasmolysed: A description of a cell in which the cell membrane tears away from
the cell wall
Chapter 3- Movement into and out of cells
3.1 Diffusion
- The more kinetic energy particles have, the faster they move
DIFFUSION DOWN A CONCENTRATION GRADIENT
- Diffusion: The net movement of particles from a region of their higher
concentration to a region of their lower concentration, as a result of their random
movement
- Net movement: Overall or average movement
- Concentration gradient: An imaginary ‘slope’ from a high concentration to a low
concentration
DIFFUSION IN LIVING ORGANISMS
- Diffusion is important in gas exchange for respiration in animals and plants. Cell
membranes are freely permeable to oxygen and carbon dioxide, so these gases
easily diffuse into and out of cells
- Solute: substance that has dissolved in a liquid which is called a solvent
3.2 Osmosis
- Compound: A substance formed by the chemical combination of two or more
elements in fixed proportions
- Water can make up about 80% of an organism’s body
- Partially permeable membrane: A membrane that lets some particles move
through it, but prevents others from passing through
- Osmosis: The diffusion of water molecules through a partially permeable
membrane
WATER POTENTIAL
- High water potential: A dilute solution
- Low water potential: A concentrated solution
- Water potential gradient: A difference in water potential between two areas
OSMOSIS AND ANIMAL CELLS
- If an animal cell is placed in a concentrated solution, water leaves the cell by
osmosis and the cell shrinks
OSMOSIS AND PLANT CELLS
- The plant cell doesn’t burst like an animal cell because it has a strong cell wall
- Turgid: A description of a plant cell that is tight and firm
- Turgor pressure: The pressure of the water pushing outwards on a plant cell wall
- Flaccid: A description of a plant cell that if soft
- Plasmolysed: A description of a cell in which the cell membrane tears away from
the cell wall
