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Scientists investigated the effect of a decrease in pH on muscle contraction - AQA - A-Level Biology - Question 4 - 2019 - Paper 1
Question 4
Scientists investigated the effect of a decrease in pH on muscle contraction. The scientists did the investigation with four different preparations of isolated muscl... show full transcript
Worked Solution & Example Answer:Scientists investigated the effect of a decrease in pH on muscle contraction - AQA - A-Level Biology - Question 4 - 2019 - Paper 1
Step 1
Use Figure 3 to evaluate this conclusion.
Answer
The student's conclusion about a decrease in pH causing a decrease in muscle contraction strength can be assessed by examining Figure 3. In the figure, it is evident that muscle fibers B (at 0.5 pH units below typical pH) show a reduction in force of muscle contraction compared to the control (A). This trend is consistent across the temperature measurements provided (12°C, 22°C, and 32°C), where the force recorded for B is consistently below that of the control, indicating that lower pH levels correlate with reduced muscle contraction. However, without additional statistical analysis to confirm significance, the conclusion should be treated cautiously, as other factors may influence these results.
Step 2
Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction.
Answer
Calcium ions play a crucial role in muscle contraction by facilitating the interaction between actin and myosin filaments. When calcium levels decrease, fewer calcium ions are available to bind to troponin, leading to less movement of tropomyosin away from the binding sites on actin. Consequently, fewer actin-myosin cross-bridges can form, resulting in weaker muscle contractions. Moreover, without sufficient calcium, the activation of myosin ATPase (which energizes the myosin heads) is impaired, further diminishing contraction strength.
Step 3
Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.
Answer
In anaerobic conditions, cells convert pyruvate to lactate to regenerate NAD+. This regeneration is essential because NAD+ is a coenzyme needed for glycolysis, the pathway through which glucose is broken down to produce ATP. By converting pyruvate to lactate, the process maintains the supply of NAD+, allowing glycolysis to continue and, consequently, enabling the sustained production of ATP even in the absence of oxygen.