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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 bodie... 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.
Answer
Black bears utilize their fat stores effectively during hibernation, which allows them to survive prolonged periods without food or water. The fat acts as a source of energy, reducing the need for external food intake. Moreover, during this state, their metabolic rate decreases by 75%, minimizing energy expenditure. By conserving energy and relying on stored fat, black bears are able to sustain themselves throughout the hibernation period.
Step 2
Use your knowledge of the nervous control of heart rate to describe how these are linked.
Answer
During hibernation, the autonomic nervous system significantly reduces the heart rate of black bears. Detected by chemoreceptors, low levels of oxygen and changes in carbon dioxide trigger a response that decreases metabolic demand. This process is mediated by the parasympathetic branch, which releases acetylcholine to slow the heart rate. Consequently, the lower metabolic state correlates with a decrease in heart rate, allowing bears to conserve energy efficiently during hibernation.
Step 3
Suggest and explain how 'uncoupling proteins' help to maintain a constant body temperature during hibernation.
Answer
Uncoupling proteins allow protons to pass through the mitochondrial membrane, dissipating energy as heat rather than converting it to ATP. This process provides a method of thermogenesis during hibernation, helping to maintain a constant body temperature even when metabolic processes slow down. Consequently, the presence of uncoupling proteins helps prevent the body from becoming too cold, ensuring the bear can survive in its hibernation state.
Step 4
Suggest and explain how climatic change has reduced the survival rate of snowshoe hares in mountain habitats.
Answer
Climatic change has led to earlier melting of snow, which disrupts the natural camouflage of snowshoe hares. As the hares transition to their brown fur too early, they may become more visible to predators against the snowy backdrop, increasing their chances of predation. This loss of camouflage, combined with reduced food availability, negatively impacts their survival rate in harsh mountain habitats.
Step 5
Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats.
Answer
By having snowshoe hares moult at different times, it creates a staggered adaptation to seasonal changes. This variation allows some hares to blend in effectively with their environment regardless of the changes in snow cover, thus reducing the risk of predation across the population. Additionally, varying moulting times may also enhance genetic diversity within the population, potentially allowing for better survival rates under fluctuating environmental conditions.