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Read the following passage - AQA - A-Level Biology - Question 10 - 2020 - Paper 2
Question 10
Read the following passage. North American black bears can hibernate for up to 7 months without food or water. The bears survive using the fat stores in their bodi... show full transcript
Worked Solution & Example Answer:Read the following passage - AQA - A-Level Biology - Question 10 - 2020 - Paper 2
Step 1
Suggest and explain how black bears can hibernate for up to 7 months without food or water (lines 1–2).
Answer
Black bears can hibernate for extended periods due to the accumulation of fat stores during the summer months. These fat reserves provide the necessary energy and essential nutrients while the bears are inactive. During hibernation, their metabolic rate significantly decreases, reducing the energy demand, which enables them to sustain themselves on these stored fats without requiring additional food or water.
Step 2
Use your knowledge of the nervous control of heart rate to describe how these are linked (lines 3–5).
Answer
During hibernation, black bears exhibit a lower heart rate and metabolic rate, regulated primarily by the autonomic nervous system. Chemoreceptors detect the reduced levels of oxygen and increased carbon dioxide in the blood, signaling the body to decrease heart rate through sympathetic pathways. This reduction in heart rate results in lower oxygen demand and energy expenditure, which is beneficial in a hibernation state.
Step 3
Suggest and explain how uncoupling proteins help maintain a constant body temperature during hibernation (lines 6–7).
Answer
Uncoupling proteins play a critical role in thermoregulation during hibernation by allowing protons to pass through the mitochondrial membrane. This process dissipates the electrochemical gradient typically used for ATP production, instead releasing energy as heat. This mechanism helps maintain a stable body temperature in the bear's body despite the reduced metabolic activities associated with hibernation.
Step 4
Suggest and explain how climatic change has reduced the survival rate of snowshoe hares in mountain habitats (lines 11–13).
Answer
Climatic change has altered the snow cover and seasonal temperature patterns in mountain habitats. As snowshoe hares rely on snow cover for camouflage during winter, reduced snow leads to increased visibility to predators. This heightened predation risk diminishes their chances of survival, thereby affecting their population adversely.
Step 5
Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats (line 15).
Answer
When snowshoe hares molt at different times, it enhances their chances of survival by ensuring that not all individuals are exposed to predation risks simultaneously. This staggered molting means that some hares will always have suitable camouflage, reducing the likelihood of entire populations being targeted by predators at once. Moreover, genetic diversity within the population increased, providing resilience against environmental changes.