Aerobic and Anaerobic Respiration

Question 1

Cellular Respiration

Answer 1

• One of the most important metabolic processes in any cell.
• Organic molecules (food) are broken down in the cells to release energy for the cell’s activities.
• Cellular respiration can release energy from glucose (main one), amino acids, fatty acids and glycerol.

Question 2

Cellular Respiration Equation

Answer 2

Glucose + Oxygen  Carbon Dioxide + Water + Energy

• Cellular respiration is a multistep process that releases energy from glucose.

Question 3

Energy from Cellular Respiration

Answer 3

• During the breakdown of glucose, about 60% of the available energy is released as heat. Cells cannot utilise heat energy, but it is important in keeping body temperature constant.
• The remaining 40% is used to form a compound called adenosine triphosphate (ATP).
• ATP is composed of adenosine and three phosphate groups

Question 4

Energy from Cellular Respiration

Answer 4

• ATP is formed when an inorganic phosphate group is joined to a molecule of adenosine diphosphate (ADP).
• The phosphate groups in ATP are joined by high energy chemical bonds.
• ATP can be used to transfer energy between cellular respiration and processes in the cell requiring energy. ATP stores energy; the energy is released when ATP breaks down to ADP.

Question 5

Glycolysis

Answer 5

• The first phase in the breakdown of glucose does not require oxygen.
• A glucose molecule is broken down, in a series of 10 steps, to two molecules of pyruvate (pyruvic acid)

Question 6

Anaerobic Respiration

Answer 6

• If no oxygen is available, the pyruvate produced in glycolysis is then converted to lactic acid by fermentation.
• The production of lactic acid from glucose is called anaerobic respiration.
• The fermentation stage of anaerobic respiration does not produce any additional ATP; however, the glycolysis of one molecule of glucose releases enough energy to convert two molecules of ADP to ATP.

Question 7

Anaerobic Respiration

Answer 7

• The enzymes required for anaerobic respiration are available in the cytosol of the cell; therefore glycolysis and the conversion of pyruvate to lactic acid occurs in the cytosol.
• Anaerobic respiration is very important during vigorous physical activity. Lactic acid can cause muscle pain and the body incurs an oxygen debt which has to be repaid after exercise.
• Anaerobic respiration uses glucose to produce lactic acid and two ATP molecules in the absence of oxygen.

Question 8

Aerobic Respiration

Answer 8

• The complete breakdown of glucose to carbon dioxide and water requires oxygen. The pyruvate produced from glycolysis is completely broken down to carbon dioxide and water.
• Occurs in the mitochondria of the cell.
• To complete the breakdown of glucose, the two pyruvate molecules produced in glycolysis must enter a mitochondrion, where enzymes are available to allow the next series of reactions to occur.

Question 9

Aerobic Respiration

Answer 9

Step 1-
For the pyruvate to enter the next pathway it is first converted to acetyl coenzyme A (acetyl CoA). To do this, a carbon dioxide molecule is removed from the pyruvate and the remaining two-carbon structure joins to coenzyme A. No ATP is produced in this process.

Step 2-
The acetyl CoA then enters the citric acid cycle, also known as the Krebs cycle. Here the carbon atoms in the acetyl CoA are released in carbon dioxide. For every acetyl CoA that enters the citric acid cycle, one molecule of ATP is also produced. This means that two ATP molecules are produced per glucose molecule.

Question 10

Aerobi Respiration

Answer 10

Step 3- The final stage of cellular respiration is the electron transport system; the only stage that uses oxygen. Here electrons are passed between molecules, finally resulting in oxygen molecules forming water. There is some debate regarding the exact number of ATP molecules that are produced during this process. Estimates range between 26 and 34 molecules.

Thus, aerobic respiration of one molecule of glucose has the potential to generate up to 38 molecules of ATP.
2 from glycolysis, 2 from the citric acid cycle and up to 34 from the electron transport mechanism.

Question 11

Aerobic Respiration Summary

Answer 11

• Aerobic respiration uses oxygen to convert glucose into carbon dioxide and water, producing up to 38 molecules of ATP per glucose molecule.
• ATP is able to transfer energy from cellular respiration to other chemical reactions that require energy e.g. active transport

Question 12

Energy used by the cell

Answer 12

Cells need the energy that is temporarily stored in the ATP molecules for a variety of purposes.

1. Building complex molecules
2. Cell division and growth
3. Movement of cell organelles
4. Movement of the whole cell
5. Maintaining cell organisation
6. Active transport
7. Transmission of nerve impulse