- cells are living things, they constantly have to replace substances which are used up (e.g. food and oxygen) and remove other substances which would accumulate (e.g. carbon dioxide, waste products)
- Diffusion takes place automatically without the need for energy.
- Diffusion is the spreading of the particles of gas which results in a net movement from a higher concentrated area to a lower concentrated area.
- The greater the difference in concentration, the faster the rate of diffusion
- Osmosis is the movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
- The membrane allows the water molecules through but not the solute molecules as they are too large.
- The effect of Osmosis is to gradually dilute the solution. A good example is hair root cells.
- Green plants make their food using sunlight, this is called photosynthesis.
- Four things needed are:
- light from the sun
- carbon dioxide diffused from the air
- water from the soil
- chlorophyll in the leaves
- Two things produced:
- glucose - for biomass and energy
- oxygen - released into the atmosphere as a by-product.
- Word equation for photosynthesis:
carbon dioxide + water --> glucose + oxygen
- This is the division of body cells to produce new cells. This occurs for growth and repair (also in asexual reproduction),
- Before the cell divides, a copy of each chromosome is made so the new cells has exactly the same genetic information. This means that the cells of asexually reproduced offspring contain the same genes as the parents.
- When gametes join at fertilisation, one chromosome comes from each parent and a single body cell with new pairs of chromosomes is formed.
- This then divides repeatedly by mitosis to form a new individual, giving rise to variation.