Biology - B3 - AQA - GCSE - Movement of Molecules

Diffusion
1. The movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient. This does not require energy.
  2. Example - Carbon dioxide in the air into the leaf. Higher concentration in the air, diffusion means that the higher concentration of carbon dioxide is taken into the leaf for photosynthesis.
  3. Example - Oxygen in the air into the lungs. Higher concentration in the air (because it is transported around the body), diffusion means that the higher concentration of oxygen is taken into the lungs to be passed around the body in the bloodstream.
Active transport
1. The movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient. This requires energy.
  1. Because it is against the concentration gradient, it requires energy.
    1. A helpful way to remember this is a hill. You need to use a lot of energy when pushing against the hill to climb it.
  2. Example - mineral ions in the soil into the roots. Higher concentration in the roots, active transport means that the lower concentration in the soil can be absorbed through the roots. Mitochondria are needed to get the energy for the process.
  3. Example - Glucose in the small intestine. Higher concentration in the bloodstream/villi, active transport means that the lower concentration in the small intestine can be absorbed by the villi. Mitochondria are needed to get the energy for the process.
  4. Having a greater surface area means that there are more places for collisions to occur.
Osmosis
1. The movement of water molecules from an area of high water concentration to an area of low water concentration down a water concentration gradient. This does not require energy. Occurs across a partially permeable membrane.
  1. Because it is down the concentration gradient, it does not require energy.
    1. A helpful way to remember this is a hill. You can roll down a steep hill without using much energy.
  2. Example - water in the soil into the roots. Higher water concentration in soil (because it is immediately taken up the plant), osmosis means that the higher water concentration in the soil is absorbed through the roots. The membrane is partially permeable.
  3. Example - red blood cell in pure water. Higher water concentration in the pure water, osmosis means that the higher water concentration enters the red blood cell. Red blood cell swells and bursts. Occurs across a partially permeable membrane.
Default framework
1. The movement of [?] from an area of high/low concentration to an area of low/high concentration down/against a concentration gradient. This does (not) require energy. (Partially permeable membrane?)

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Biology - B3 - AQA - GCSE - Movement of Molecules

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