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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Digestion
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.
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