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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
A student looked at the results and concluded that a decrease in pH does cause a decrease in the force of muscle contraction.
Answer
To evaluate the student's conclusion, we need to analyze the data presented in Figure 3. The graph shows muscle contraction force for both mouse and rabbit muscle fibres at different temperatures (12°C, 22°C, and 32°C).
For mouse muscle fibres (control A), there is a noticeable increase in contraction force as temperature rises, reaching above 100% at 32°C. However, for mouse muscle fibres at 0.5 pH units below typical pH (condition B), the contraction force is consistently lower than that of control A across all temperatures.
Similarly, for rabbit muscle fibres (control C) and at the lower pH (condition D), this trend is also observed. Therefore, the data does support the conclusion that a decrease in pH leads to a reduction in muscle contraction force, as evidenced by the comparative results of conditions B and D against their respective controls.
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
A decrease in calcium ion concentration in muscle tissues significantly impacts muscle contraction. Calcium ions play a critical role in initiating contraction by binding to troponin. When calcium binds to troponin, it causes a conformational change that moves tropomyosin away from the actin binding sites, exposing them for myosin to attach and form cross-bridges.
If the concentration of calcium ions decreases, fewer calcium ions are available to bind to troponin. This results in troponin not moving tropomyosin away from the binding sites, limiting the ability of myosin heads to interact with actin. Consequently, fewer actin-myosin bridges are formed, leading to a reduced force of muscle contraction.
Step 3
Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.
Answer
During prolonged exercise, when oxygen levels are insufficient for aerobic respiration, pyruvate produced from glycolysis is converted to lactate. This conversion regenerates NAD+, an essential coenzyme for glycolysis to continue. Without NAD+, glycolysis would cease, halting ATP production.
By converting pyruvate to lactate, cells can maintain a continuous supply of NAD+, enabling them to keep producing ATP through anaerobic processes, which is crucial for muscle activity during strenuous exercise.