C1.2.6 Variables affecting the rate of cell respiration Notes

1. Temperature

1. Cell respiration relies on enzymes, which work best at optimal temperatures.
2. Higher temperatures increase enzyme activity, speeding up respiration.
3. However, if the temperature exceeds the optimum temperature, enzymes can denature and stop working.

2. Type of Respiratory Substrate

1. Different substrates (e.g., glucose, lipids) yield varying amounts of energy.
2. Carbohydrates are often used first because they are easy to break down.
3. Lipids provide more energy per gram but are metabolized more slowly.

3. Oxygen Availability

1. Oxygen is the final electron acceptor in the electron transport chain of aerobic respiration.
2. Limited oxygen forces cells to switch to anaerobic respiration, which is less efficient and produces much less ATP.
3. Animal cells produce lactate under low oxygen, while yeast produces ethanol and carbon dioxide.

4. Substrate Concentration

1. Higher concentrations of glucose or other substrates can increase the rate of respiration, up to a point.
2. Once enzymes are saturated, adding more substrate won’t increase the rate further.

5. pH Levels

1. Enzymes involved in respiration have an optimal pH range.
2. Deviations from this range can slow down or halt the process.

Measuring the Rate of Cell Respiration

1. Oxygen Uptake

1. Respirometers measure oxygen consumption, which reflects the rate of aerobic respiration.
2. A typical respirometer setup includes:
   1. A sealed chamber with the organism or tissue.
   2. An alkali (e.g., potassium hydroxide) to absorb carbon dioxide.
   3. A capillary tube with fluid to measure changes in air volume, indicating oxygen uptake.

2. Carbon Dioxide Production

1. During aerobic respiration, glucose is oxidized into carbon dioxide and water.
2. The amount of carbon dioxide produced can be measured with a gas sensor or by using a color indicator in a closed system.

3. Substrate Consumption

1. By measuring the decrease in glucose or other substrates over time, you can infer the rate of respiration.
2. Here, other variables like temperature and pressure must always be controlled to ensure accurate results.

Designing Experiments to Investigate Variables

1. Respirometers are versatile tools for exploring how different factors affect respiration. Here are some experimental ideas:
   1. Temperature: Compare respiration rates at different temperatures using a water bath to maintain constant conditions.
   2. Substrate Type: Investigate whether yeast respires faster with glucose or sucrose.
   3. Oxygen Availability: Measure respiration rates in aerobic versus anaerobic conditions.

Calculating the Rate of Cell Respiration

1. To calculate the rate of cell respiration from experimental data, you need to:
   1. Determine the amount of oxygen consumed or CO₂ produced.
   2. Divide the change in oxygen or CO₂ concentration by the time to calculate the rate.