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Farming cattle for humans to eat is less efficient than farming crops because of energy transfer - AQA - A-Level Biology - Question 4 - 2022 - Paper 1
Question 4
Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Nitrogen-fixing bacteria such as *Azotobacter chroococcum* use the... show full transcript
Worked Solution & Example Answer:Farming cattle for humans to eat is less efficient than farming crops because of energy transfer - AQA - A-Level Biology - Question 4 - 2022 - Paper 1
Step 1
Farming cattle for humans to eat is less efficient than farming crops because of energy transfer.
Answer
The primary reason farming cattle is less efficient than farming crops involves energy transfer. When humans consume cattle, only 10% of the energy stored in the food they eat is converted to body mass. This inefficiency occurs because energy is lost at each trophic level, primarily through metabolic processes, heat loss, and overall maintenance of the animal. In contrast, consuming plants allows for more energy to be harnessed directly from the primary producers.
Step 2
Step 3
A student concluded that this investigation showed that ammonia inhibits nitrogenase activity in nitrogen-fixing bacteria. Use all the information to evaluate the student's conclusion.
Answer
The student's conclusion is supported by the data, as it shows a clear correlation between increasing ammonium chloride concentration and the decrease in nitrogenase activity. As the concentration of ammonium chloride rose, the nitrogenase activity fell significantly, reaching zero at higher concentrations. This aligns with the understanding that ammonia can inhibit nitrogenase, thus confirming the student's evaluation. However, additional experiments would be necessary to fully establish causation, as this data alone does not eliminate other factors that may affect enzyme activity.
Step 4
Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. Explain how nitrogen-fixing bacteria may benefit from ammonia inhibiting nitrogenase activity.
Answer
When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria can conserve resources. By avoiding the high energy expenditure associated with nitrogen reduction, these bacteria can redirect energy to essential cellular functions, enhancing survival and reproductive success. Additionally, when ammonia is present in sufficient quantities, nitrogen-fixing bacteria may benefit by utilizing this readily available nitrogen source for growth, rather than relying on the energy-intensive process of nitrogen fixation.
Step 5
During the 48 hours, the coloured liquid moved to the left. Explain why.
Answer
The movement of the colored liquid to the left indicates that carbon dioxide was produced as a byproduct of respiration. This process consumes oxygen and releases carbon dioxide, causing a decrease in pressure within the apparatus. As the pressure drops, the liquid moves toward the area of lower pressure, demonstrating that respiration is taking place.
Step 6
Step 7
The student used the same apparatus to determine the volume of carbon dioxide the seeds produced during 48 hours. Give the change the student would need to make to the contents of the apparatus and describe how he could calculate the volume of carbon dioxide produced.
Answer
The student would need to remove the potassium hydroxide, which absorbs carbon dioxide, from the apparatus. By doing this, all carbon dioxide produced would remain in the solution. The student could then measure the change in liquid level or volume in the apparatus to calculate the volume of carbon dioxide produced during the experiment.
Step 8
Calculate the oxygen uptake in cm³ g⁻¹ hour⁻¹.
Answer
The total oxygen uptake over 48 hours is 6.2 × 10⁻³ cm³ for 40 g of seeds. To find the rate per gram per hour:
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Calculate the uptake per gram:
rac{6.2 imes 10^{-3} ext{ cm}^3}{40 ext{ g}} = 1.55 imes 10^{-4} ext{ cm}^3 ext{ g}^{-1}
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Calculate the uptake per hour:
rac{1.55 imes 10^{-4} ext{ cm}^3 ext{ g}^{-1}}{48 ext{ hours}} = 3.23 imes 10^{-6} ext{ cm}^3 ext{ g}^{-1} ext{ hour}^{-1}
The oxygen uptake is approximately 3.23 × 10⁻⁶ cm³ g⁻¹ hour⁻¹.