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Read the following passage - AQA - A-Level Biology - Question 10 - 2023 - Paper 2
Question 10
Read the following passage. ATP is essential for muscle contraction. The concentration of ATP in skeletal muscle is approximately 5 x 10^-3 mmol g^-1. During maximu... show full transcript
Worked Solution & Example Answer:Read the following passage - AQA - A-Level Biology - Question 10 - 2023 - Paper 2
Step 1
ATP is essential for muscle contraction (line 1). Describe the roles of ATP in muscle contraction.
Answer
ATP plays a crucial role in muscle contraction by enabling the following processes:
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Breaking actomyosin bridges: ATP is required to detach the myosin head from the actin filament after contraction, allowing the cycle of muscle contraction to continue.
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Movement of Myosin Heads: The hydrolysis of ATP provides the energy to pivot the myosin heads, which in turn moves the actin filaments inward, resulting in muscle shortening.
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Active Transport: ATP is necessary for the active transport of calcium ions back into the sarcoplasmic reticulum, which helps reset the muscle fibers for the next contraction.
Step 2
Calculate how long maximum exercise would last if ATP was not resynthesised (lines 3–4).
Answer
If ATP in skeletal muscle is used at a rate of 3.7 mmol kg^-1 s^-1, and the concentration of ATP in skeletal muscle is approximately 5 x 10^-3 mmol g^-1, we can calculate the duration of maximum exercise as follows:
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Convert the ATP concentration to kg:
- For 1 kg of muscle: 5 x 10^-3 mmol = 0.005 mmol
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Calculate the time until ATP depletion:
- Time = Total ATP available / Rate of ATP use
- Total ATP available = 0.005 mmol
- Rate of ATP use = 3.7 mmol/s
- Time = 0.005 mmol / (3.7 mmol/s) = 0.00135 seconds or approximately 1.35 seconds.
Step 3
Describe and explain how taking creatine supplements (lines 5–6) and 'carbohydrate loading' (lines 6–7) can improve performance of different types of muscle fibres during different types of exercise.
Answer
Taking creatine supplements can enhance muscle performance by increasing the availability of phosphocreatine, which can quickly regenerate ATP during high-intensity, short-duration activities. This is particularly beneficial for fast-twitch muscle fibers, which are predominantly used during intense exercise, improving overall output and reducing fatigue.
Carbohydrate loading improves endurance performance by increasing glycogen stores in muscles. During long-duration, lower-intensity activities, such as marathon running, the body relies primarily on glycogen for energy. Enhanced glycogen storage ensures sustained energy release, delaying fatigue and improving performance in slow-twitch muscle fibers.
Step 4
Suggest and explain how GLUT4 and CD36 transport proteins (lines 10–11) are beneficial during exercise.
Answer
GLUT4 transport proteins facilitate the uptake of glucose into muscle cells, which is crucial during exercise when energy demands increase. This process is stimulated by insulin and exercise-induced increases in calcium ions, ensuring that muscles have adequate glucose supply for ATP production.
CD36 transport proteins assist in the uptake of fatty acids into mitochondria, allowing for enhanced fatty acid oxidation, particularly during prolonged aerobic exercise. This adaptation helps to spare glycogen and maintain energy production, contributing to improved endurance.
Step 5
An increase in muscle activity causes an increase in heart rate (lines 12–14). Describe and explain how.
Answer
An increase in muscle activity raises the level of carbon dioxide produced, detected by chemoreceptors in the body. This detection sends more impulses to the cardiac center in the brain, which in turn stimulates the heart to beat faster and stronger. Increased heart rate enhances blood flow to active muscles, ensuring sufficient oxygen and nutrient delivery as well as removal of metabolic waste products like carbon dioxide, thereby supporting sustained physical activity.