What metabolism means, the reactions that build and break down molecules in the body, and how the liver deals with lactic acid and excess protein.
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1.What is metabolism?
The sum of all the reactions happening in a cell or in the body.
2.What provides the energy for metabolic reactions?
The energy transferred by respiration.
3.How is starch made in a plant?
Glucose molecules are joined together to form the larger insoluble molecule.
4.How is cellulose made?
From glucose, which is joined into long chains and used to strengthen plant cell walls.
5.How is glycogen made and where?
From glucose, stored in the liver and the muscles of animals.
6.How are lipids made?
From one molecule of glycerol and three molecules of fatty acids.
7.How are amino acids made in a plant?
Glucose is combined with nitrate ions taken up from the soil.
8.What are amino acids used for?
They are joined together to make proteins.
9.What breaks proteins down, and into what?
Protease enzymes break them down into amino acids.
10.Why can the body not store excess protein?
There is no storage molecule for amino acids, so any surplus has to be broken down and excreted.
11.What happens to excess amino acids?
They are broken down in the liver to produce urea, which is carried by the blood to the kidneys and excreted in urine.
12.What is deamination?
The removal of the nitrogen-containing part of an amino acid in the liver, producing ammonia which is converted to urea.
13.Why is urea produced rather than ammonia being excreted directly?
Ammonia is very toxic, so the liver converts it into the much less toxic urea.
14.Give two examples of metabolic reactions that build larger molecules.
Making starch from glucose, and making proteins from amino acids.
15.Give two examples of metabolic reactions that break molecules down.
Respiration breaking down glucose, and protease breaking down protein into amino acids.
16.Why does the liver play a central role in metabolism?
It converts lactic acid back into glucose, breaks down excess amino acids into urea, and stores glycogen.
17.What is the link between respiration and metabolism?
Respiration supplies the energy that all the other metabolic reactions need in order to happen.
18.Why do the cells of an active muscle contain many mitochondria?
Muscle contraction needs a lot of energy, which is transferred by aerobic respiration in the mitochondria.
19.What is the difference between glycogen and starch?
Both are storage carbohydrates made from glucose. Glycogen is the animal store, starch is the plant store.
20.Why must glucose be converted to an insoluble store?
Soluble glucose would affect the water balance of cells by osmosis, and would be used up or moved away.
21.Where does the nitrogen in amino acids ultimately come from?
Nitrate ions absorbed from the soil by plant roots, which then pass along the food chain.
22.Why does the body need a constant supply of energy even at rest?
Metabolic reactions such as building proteins, maintaining body temperature and keeping the heart beating continue all the time.
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