8. Respiration

Question 1

Respiration

Definition + Types

Answer 1

Respiration is the process where glucose is broken down to release energy, in the form of ATP, in all living cells.

There are two types of respiration, aerobic respiration and anaerobic respiration.

Question 2

Aerobic Respiration

Definition + Overall Equation

Answer 2

Aerobic respiration is the breakdown of glucose in the presence of oxygen with the release of 38 ATP molecules. Carbon dioxide and water are released as waste products.

Glucose + Oxygen → Carbon Dioxide + Water + ATP
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

Question 3

Glycolysis

Where it takes place + Process

Answer 3

• Glycolysis takes place in the cytosol in the cytoplasm
• 1 glucose molecule is broken down to form 2 pyruvate molecules and 2 ATP molecules in the process

Question 4

What happens to pyruvate in the presence of oxygen?

Answer 4

In the presence of oxygen,

• 2 pyruvate molecules would enter the mitochondrion, where they are completely oxidised into carbon dioxide and water.
• Each pyruvate molecule yields 18 ATP molecules.

Question 5

Anaerobic Respiration

Definition

Answer 5

Anaerobic respiration is the breakdown of glucose in the absence of oxygen, resulting in the release of lesser energy than aerobic respiration.

Question 6

What happens to pyruvate in the absence of oxygen?

Answer 6

In the absence of oxygen,

• Pyruvate would not enter the mitochondrion
• Instead, pyruvate is converted into lactic acid (lactic acid fermentation) or ethanol and carbon dioxide (alcoholic fermentation), which are removed as metabolic waste products

Question 7

Alcoholic Fermentation

Where and when it occurs + Process + Overall Equation

Answer 7

Alcoholic fermentation

• Occurs in yeast in the absence of oxygen (used in beer brewing and bread making, where the carbon dioxide genereated allows the dough to rise).
• Pyruvate is converted into ethanol and carbon dioxide

Glucose → Ethanol + Carbon Dioxide + ATP (small amount)
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + ATP (small amount)

Question 8

Lactic Acid Fermentation

Where and when it occurs + Process + Overall Equation

Answer 8

Lactic acid fermentation

• Occurs in fungi and bacteria in the absence of oxygen (used in production of cheese and yoghurt).
• Occurs in human muscle cells when there is insufficient oxygen in muscle cells during vigorous excercise, to release extra energy which supplements the energy released by aerobic respiration to allow the muscles to continue contracting.
• Pyryvate is converted into lactic acid, with no release of carbon dioxide

Glucose → Lactic Acid + ATP (small amount)
C₆H₁₂O₆ → 2C₃H₆O₃ + ATP (small amount)

Question 9

Uses of ATP in the human body

7 uses

Answer 9

1. Muscle contraction
2. Protein synthesis
3. Cell division
4. Active transport
5. Growth
6. Passage of nerve impulses
7. Maintainence of a constant body temperature

Question 10

Describe the production of lactic acid in muscles during vigorous exercise

Process

Answer 10

1. During vigorous muscular contractions, the muscle cells first respire aerobically.
2. Breathing rate increases to remove carbon dioxide and take in oxygen at a faster rate. Heart rate also increases to transport oxygen to the muscles at a faster rate. However, there is a limit to the increase in the rate of breathing and heartbeat. Therefore, there is insufficient oxygen to meet the demands of the vigorous muscular contractions.
3. In such cases, muscle cells also respire anaerobically for short durations in order to meet the energy demands of the activity.
4. The extra energy released by anaerobic respiration supplements the energy released by aerobic respiration to allow muscles to continue contracting.
5. When anaerobic respiration occurs, there is a build-up of lactic acid in muscle cells.
6. Since there is insufficient oxygen to meet the demands of the vigorous muscular contractions, the muscles are said to incur an oxygen debt.
7. Lactic acid concentrations build up slowly in the muscles and may eventually become high enough to cause fatigue and muscular pains. The body then needs to rest and recover.

Question 11

Recovery period

Process

Answer 11

1. During the period of rest, the breathing rate continues to be high for some time.
2. This is to provide the ‘extra’ oxygen to repay the oxygen debt.
3. Lactic acid is removed from the muscles and transported to the liver.
4. In the liver, some of the lactic acid is oxidised (using the oxygen that is taken in) to release energy. This energy is used to convert the remaining lactic acid back into glucose.
5. When all the lactic acid has been converted into glucose, the oxygen debt is repaid.
6. Glucose is then transported back to the muscles and the body is now ready for another exercise.

Question 12

Compare Aerobic Respiration and Anaerobic Respiration

Similarities and differences

Answer 12

Similarities:

• Both involve enzymes
• Both produce ATP molecules
• Both involve the breakdown of glucose

Differences:

• Oxygen is required for aerobic respiration whereas oxygen is not required for anaerobic respiration.
• Aerobic respiration takes place in the mitochondria whereas anaerobic respiration takes place in the cytoplasm.
• Products of aerobic respiration are carbon dioxide, water and ATP molecules whereas products of anaerobic respiration are lactic acid and ATP molecules in muscles, and ethanol, carbon dioxide and ATP molecules in yeast.