- Diffusion is an essential process that is going on inside your body constantly and keeping you alive. It is the net movement of gas or dissolved molecules.
- Your body's survival depends on oxygen and dissolved food molecules getting into your cells.
- Oxygen and dissolved food molecules must diffuse in and out of the blood by transportation around the body.
- The lungs have a large surface area. This maximises the exchange of oxygen and carbon dioxide with each breath.
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- Carbohydrates, proteins and fats are made up of large molecules that cannot be used directly by the body.
- Digestion breaks up larger molecules into smaller molecules, so they are more easily used by the body.
- Dissolved fod molecules then need to be transported from the small intestine into the bloodstream.
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Inside the small intestine
- The inner wall of the small intestine is lined with thousands of villi. Each villi has a network of capillaries to carry digested food away from the intestine.
- The concentration of dissolved food molecules is higher in the small intestine than in the blood entering the villus.
- This means that the dissolved food molecules dissolve from the small intestine into the blood, moving from higher to lower concentration.
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Adaptions of the villi
- Good blood supply: this maintains a steep concentration gradient
- Large surface area: so there is a higher chance of diffusion taking place.
- Thin cell walls: so there is less distance for the gases to travel.
- Moist linings: so the gases can dissolve easier.
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