Substance move by Diffusion, Osmosis and Active Transport- Life processes need gases and other dissolves substances before they can happen. For example, photosynthesis needs carbon dioxide and water to get into the plant cells.Waste substances also need to move out of cells so that the organism can get rid of them. These substance move where they need to be by diffusion, osmosis or active transport.
Difussion - the net movement of particles from an area of high concentration to an area of low concentration. e.g perfume spreading through a room.
Osmosis - the net movement of water molecules from a high water concentration to a low water concentration.
Active transport - the movement of particles against the concentration gradient i.e from a low concentration to a high concentration. This uses a lot of energy!
Exchange surfaces are adapted to maximise effectiveness:
- They are thin, so substances only have a short distance to diffuse
- They have a large surface area so lots of a substance can diffuse at once.
- Exchange surfaces in animals have lots of blood vessels, to get stuff in and out the blood quickly.
- Gase exchange surfaces in animals (e.g alveoli) are often ventilated too - air moves in and out.
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