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Figure 3 shows pressure and blood flow during the cardiac cycle in a dog - AQA - A-Level Biology - Question 3 - 2020 - Paper 1
Question 3
Figure 3 shows pressure and blood flow during the cardiac cycle in a dog. At P on Figure 3, the pressure in the left ventricle is increasing. At this time, the rate... show full transcript
Worked Solution & Example Answer:Figure 3 shows pressure and blood flow during the cardiac cycle in a dog - AQA - A-Level Biology - Question 3 - 2020 - Paper 1
Step 1
At P on Figure 3, explain why the rate of blood flow has not yet started to increase.
Answer
At point P, the aortic (semi-lunar) valves are closed. The pressure in the aorta is higher than in the left ventricle. As a result, even though the pressure in the left ventricle is increasing, the blood cannot flow into the aorta until the pressure in the ventricle exceeds that in the aorta.
Step 2
At Q on Figure 3, explain how the pressure and rate of blood flow increase in the aorta.
Answer
At point Q, the semi-lunar valve opens due to the pressure in the left ventricle exceeding that in the aorta. This opening allows blood to flow into the aorta, causing both the pressure and the rate of blood flow to increase. This is important as it ensures adequate blood supply to the organs and systems of the body.
Step 3
Describe one way in which the student's curve would be similar to and one way it would be different from the curve shown in Figure 3.
Answer
Similarity: The pressure curve for the right ventricle would show peaks during the same time intervals as the left ventricle, reflecting the synchronized contraction of both ventricles.
Difference: The pressure in the right ventricle would be lower than that in the left ventricle at corresponding points, since the right ventricle pumps blood into the pulmonary arteries under lower pressure compared to the systemic circulation.
Step 4
Use information from Figure 3 to calculate the heart rate of this dog.
Answer
The heart rate can be calculated by dividing 60 seconds by the time period for one cardiac cycle from the graph. From the graph, if one complete cycle takes about 0.6 seconds, the heart rate is:
ext{Heart Rate} = rac{60}{0.6} = 100 ext{ beats per minute}