Part 3: Metabolism

Question 1

What does ‘metabolism’ mean?

Answer 1

The sum of all the reactions that take place in a cell or the body.

Question 2

What does ‘metabolic rate’ mean?

Answer 2

The total energy expended by an organism over a specific period of time.

Question 3

State examples of metabolic reactions. (6)

Answer 3

1. The reactions of respiration
2. The reactions of photosynthesis
3. The conversion of glucose to starch, glycogen and cellulose.
4. The formation of lipid molecules from a molecule of glycerol and three fatty acid molecules.
5. The use of glucose and nitrate ions to form amino acids that are then used to make proteins.
6. The breakdown of excess proteins in the liver to form urea for excretion in the urine by the kidneys.

Question 4

What is unusual about the liver’s blood supply? (2)

Answer 4

1. Most organs have an artery supply and a vein.
2. The liver has two artery systems bringing in the oxygen

Question 5

By looking at a liver cell under an electron microscope, how can you tell that it was very metabolically active?

Answer 5

Liver cells contain many mitochondria in order to respire (a metabolic reaction).

Question 6

Describe the functions of the liver. (5)

Answer 6

1. Detoxifying poisonous substances such as ethanol from alcoholic drinks.
2. Passing the breakdown products into the blood so they can be excreted in the urine via the kidneys.
3. Breaking down old worn out blood cells and storing the iron until it is needed to synthesise more blood cells.
4. Converts lactic acid into glucose
5. Produces bile

Question 7

Discuss if liver is an organ of respiration. (4)

Answer 7

1. Yes
2. Liver carries out many metabolic processes that require energy.
3. Therefore has to carry out aerobic respiration to provide energy for these processes.
4. For example, breaking down excess amino acids and producing bile.