1. In anaerobic respiration, what is the advantage of animal cells converting pyruvate into lactic acid, and plant and fungi cells converting pyruvate into ethanol and carbon dioxide ?
Answer
In order to oxidize NADH and regenerate NAD+, so that it can be reused in glycolysis and allow the process to continue.
2. Coenzyme A is involved in the link reaction in aerobic respiration. What is coenzyme A's specific role in aerobic respiration ?
Answer
To combine with acetate in the link reaction, so that it can react with a four-carbon molecule in the Krebs cycle.
3. How is pyruvate transported into the mitochondria ?
Answer
Active transport.
4. A student set up the respirometer shown in the figure below to investigate respiration in living seeds. Explain the purpose of tube A.
Answer
The purpose of tube A is to balance the pressure.
5. The student allowed the seeds to respire for several hours. After this time he was able to see a movement in the fluid in the U-tube manometer. Describe and explain how the fluid moved.
Answer
The fluid on the right side of the tube had risen, while the fluid on the left side had fallen. The seeds were respiring and consuming oxygen, while carbon dioxide was being produced. The carbon dioxide was absorbed by the soda lime, resulting in a lower gas volume in the tube. The drop in pressure and gas volume in the right-hand container caused the fluid in the U-tube to rise.
6. Explain the reason for carrying out this investigation in a water bath.
Answer
Temperature affects the enzymes used in respiration therefore affects rate of respiration. Water bath allows temperature to remain constant so there is only one variable.
7. A student was investigating respiration in germinating seeds. She divided germinating seeds evenly into two groups. She boiled one of the two groups and then sterilised both groups by washing them in disinfectant. She set up the equipment as shown in the figure below. Cotton wool plugs were used to keep the thermometer in place and ensure that the flasks were not sealed. Explain the reason why the student boiled the seeds in flask B.
Answer
The student boiled the seeds in flask B to act as a control for comparison with the living seeds. This shows that any temperature change is due to respiration by the living seeds.
8. Explain the reason why the student sterilised the seeds in both flasks.
Answer
The student sterilised the seeds in both flasks to kill any bacteria that might be present on the seeds, as the bacteria could also respire and contribute to the temperature change.
9. Explain why it was important to use cotton wool to keep the thermometer in place.
Answer
Cotton wool allows oxygen to enter the container, so the seeds can respire aerobically.
10. The student recorded the temperature every day for 6 days. The results can be found in the table below. Describe and explain the results.
Answer
The temperature of germinating seeds increases over time because the seeds are respiring. In contrast, dead (boiled) seeds do not respire, so there is no temperature change.