Question
A respirometer is used to measure the oxygen consumption of germinating seeds. The distance that the oil drop moves is measured at 15-minute intervals.
What is the function of chemical X?
A. Absorbs carbon dioxide so the oxygen released by the seeds can be measured
B. Absorbs carbon dioxide so the oxygen absorbed by the seeds can be measured
C. Absorbs oxygen so the carbon dioxide released by the seeds can be measured
D. Absorbs oxygen so the carbon dioxide absorbed by the seeds can be measured
▶️Answer/Explanation
Answer: B. Absorbs carbon dioxide so the oxygen absorbed by the seeds can be measured
Explanation:
This setup is a respirometer, used to measure respiration (specifically oxygen consumption) in germinating seeds.
- During respiration, seeds absorb oxygen and release carbon dioxide.
- If CO₂ accumulates, it would counteract the volume change caused by O₂ absorption, making measurements inaccurate.
- Chemical X (often sodium hydroxide or potassium hydroxide) is used to absorb the carbon dioxide.
- This ensures that the only gas change observed is the decrease in oxygen, allowing accurate measurement of oxygen consumption (shown by movement of the oil drop toward the seeds).
Options Evaluation:
A. Incorrect – Seeds do not release oxygen during respiration; they absorb it.
B. Correct – X absorbs CO₂, so the O₂ absorbed by the seeds can be measured properly.
C. Incorrect – X absorbs CO₂, not oxygen.
D. Incorrect – CO₂ is released by seeds, not absorbed.
Question
Which compound is a waste product of anaerobic respiration in humans?
A. Carbon dioxide
B. Ethanol
C. Lactate
D. Pyruvate
▶️Answer/Explanation
Answer: C. Lactate
Explanation:
In anaerobic respiration (respiration without oxygen) in humans, the body breaks down glucose to release some energy, but instead of producing carbon dioxide and water like in aerobic respiration, it produces lactate as a waste product.
This happens especially during intense exercise when the muscles run low on oxygen.
Glucose → Pyruvate → Lactate
(Pyruvate is converted into lactate when oxygen is not available.)
Options Evaluation:
A. Incorrect – Carbon dioxide is a waste product of aerobic respiration, not anaerobic in humans.
B. Incorrect – Ethanol is a waste product of anaerobic respiration in yeast, not humans.
C. Correct – Lactate is the correct waste product formed in human anaerobic respiration.
D. Incorrect – Pyruvate is an intermediate, not a final waste product. In anaerobic respiration, it is converted into lactate.
Question
Yeast cells, Saccharomyces cerevisiae, were incubated with and without glucose at three different temperatures for a period of four minutes, during which the rate of CO2 production was measured with a CO2 sensor.
What conclusion can be drawn from the results of this experiment?
A. Yeast uses lipids rather than glucose in respiration at low temperatures.
B. Addition of glucose has a greater impact on rates of cell respiration at lower temperatures.
C. Rates of cell respiration increase with temperature.
D. More glucose is produced at higher temperatures.
▶️Answer/Explanation
Answer: C. Glucose increases the rate of respiration
Explanation:
This experiment measures carbon dioxide production, a waste product of respiration. Here’s how to interpret the data:
- At all temperatures, the rate of CO₂ production is higher with glucose than without it.
- At 50°C, the rate of CO₂ production spikes sharply when glucose is present.
This indicates that glucose is being used in respiration, leading to more CO₂ production — especially at a higher temperature, where enzyme activity is increased (up to the point before denaturation).
The presence of glucose means more substrate is available for respiration, which directly increases the rate of CO₂ production.
Options Evaluation:
A. Incorrect – Enzymes can denature at high temperatures, but this would reduce the rate, not increase it. Here, the rate is higher with glucose.
B. Incorrect – Oxygen availability is not shown to change and doesn’t explain the difference with and without glucose.
C. Correct – Glucose provides the substrate for respiration, so its presence increases CO₂ production.
D. Incorrect – CO₂ is a product of respiration, not photosynthesis. This experiment does not involve photosynthesis.