Revision from Year 8

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Respiration, digestion and rocks
Respiration
Respiration is a chemical reaction that happens in all living cells. It is the way that energy is released from glucose, for our cells to use to keep us functioning. Remember that respiration is not the same as breathing (which is properly called ventilation). The glucose and oxygen react together in the cells to produce carbon dioxide and water. The reaction is called aerobic respiration because oxygen from the air is needed for it to work.

Digestion
The glucose and oxygen react together in the cells to produce carbon dioxide and water. The reaction is called aerobic respiration because oxygen from the air is needed for it to work. Enzymes are not living things. They are just special proteins that can break large molecules into small molecules. Different types of enzymes can break down different nutrients: •carbohydrase or amylase enzymes break down starch into sugar •protease enzymes break down proteins into amino acids

lipase enzymes break down fats into fatty acids and glycerol.

The saliva in your mouth contains amylase, which is another starch digesting enzyme. If you chew a piece of bread for long enough, the starch it contains is digested to sugar, and it begins to taste sweet. Protease enzymes break down proteins into amino acids. Digestion of proteins in the stomach is helped by stomach acid, which is strong hydrochloric acid. This also kills harmful micro-organisms that may be in the food. Lipase enzymes break down fat into fatty acids and glycerol. Digestion of fat in the small intestine is helped by bile, made in the liver. Bile breaks the fat into small droplets that are easier for the lipase enzymes to work on. Minerals, vitamins and water are already small enough to be absorbed by the body without being broken down, so they are not digested. Digestive enzymes cannot break down fibre, which is why it cannot be absorbed by the body. Rocks

Rocks are made of grains that fit together. Each...
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