Anaerobic Respiration

Question 1

What carries out anaerobic respiration?

Answer 1

• Microorganisms such as yeast and bacteria
• Animal muscle tissue during extreme excercise

Question 2

In the absence of oxygen, only glycolysis will occur. Explain why.

Answer 2

No oxygen to act as the final electron acceptor in the elecron tranport chain
The link reaction and the Krebs cycle cannot occur because the reduced NAD cannot be reoxidised. Oxidative phosphorylation will not take place and so the yield of ATP molecules produced by anaerobic respiration is greatly reduced

Question 3

How many ATP molecules are produced in anaerobic respiration?

Answer 3

Gross production = 4 molecules of ATP
Net gain = 2 molecules of ATP because 2 molecules of ATP are used up to phosphorylate glucose

Question 4

How is glycolysis able to continue in the absence of oxygen in animal cells?

Answer 4

Pyruvate becomes reduced and accepts hydrogen from reduced NAD forming lactate

Question 5

How is glycolysis able to continue in the absence of oxygen in yeast and higher plants?

Answer 5

Pyruvate is decarboxylated to form ethanal (2C)
Ethanal becomes reduced and accepts the hydrogen from reduced NAD to form ethanol

Question 6

Draw out the process of anaerobic respiration in animals

Answer 6

Page 4

Question 7

Draw out the process of anaerobic respiration in yeast and higher plants (fermentation)

Answer 7

Page 5

Question 8

What is pyruvate converted to during fermentation?

Answer 8

Ethanol and carbon dioxide

Question 9

In addition to glucose, under certain circumstances, what else can be used as respiratory substrates?

Answer 9

Lipids and proteins

Question 10

What does the term respiratory substrate mean?

Answer 10

A molecule that can be oxidised through respiration to fuel the synthesis of ATP

Question 11

When will lipids be used as an energy source?

Answer 11

When carbohydrate levels are low

Question 12

What happens to the products of lipid digestion?

Answer 12

• Glycerol is phosphorylated by ATP, dehydrogenated and converted into triose phosphhate (3C). This is an intermediate of glycolysis so can then enter glycolysis
• Fatty acid chains are split into 2C acetate fragments. Each of these fragments can enter the Krebs cycle as acetyl co-enzyme A

Question 13

Why are very large numbers of ATP produced as a result of using lipids as a respiratory substrate?

Answer 13

Each fatty acid produces many 2C acetate fragments which means the Krebs cycle can go many times producing large numbers of reduced NAD and reduced FAD to fuel the ETC

Question 14

Why does the precise number of ATP molecules depend upon the length of the hydrocarbon chain of the fatty acid?

Answer 14

Each fatty acid chain will produce a different number of 2C fragments. The longer the chain, the more fragments and the more ATP produced

Question 15

When is protein used as a respiratory substrate?

Answer 15

After reserves of carbohydrates and lipids have been used up, for example when an individual is suffering starvation

Question 16

Describe how proteins are used as a respiratory substrate

Answer 16

Proteins are hydrolysed into their constituent amino acids
In the liver, the amine group is removed from amino acids (deamination). The removed amine group is converted to ammonia and then combines with CO2 to produce urea which travels in the bloodstream to the kidneys to be excreted in the urine
The rest of the amino acid (residue) forms a keto acid
- Some keto acids (eg pyruvate) are fed into glycolysis
- Some keto acids are converted into Krebs cycle intermediates so fed into the Krebs cycle