Pearson Edexcel International A Level Biology: Skeletal Muscle, Cardiac Control and Adrenaline (YBI11) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover statements 7.9 to 7.15 of the Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology specification (YBI11), Issue 2, including Core Practical 17. Topic 7 is International A2 (IA2). There are no tiers. Study first with the study guide and the revision notes. Find weak spots with the free diagnostics. See also the course hub and the printable checklist.

Questions

1. A footballer straightens her knee to kick a ball. The quadriceps is the extensor and the hamstring is the flexor.

(a) Explain how these two muscles work as an antagonistic pair during this movement. [2] (b) State one difference in function between a tendon and a ligament. [2]

2. Describe the features of a mammalian skeletal muscle fibre that distinguish it from a typical animal cell. [4]

3. An electron micrograph of a myofibril has a magnification of ×40 000. A relaxed sarcomere measures 100 mm on the image. After contraction, the same sarcomere measures 72 mm. The A band is 1.5 µm in both states.

(a) Calculate the actual length of the sarcomere when relaxed and when contracted. [2] (b) Calculate the percentage decrease in sarcomere length. [1] (c) Calculate the total length of the I band in the contracted sarcomere. [1] (d) Explain why the A band does not change length during contraction. [2]

4. Describe how the arrival of an action potential at a skeletal muscle fibre leads to shortening of the sarcomeres. [6]

5. The table shows data supplied for two types of muscle fibre from the same muscle.

Property	Fibre type A	Fibre type B
Mitochondria (% of fibre volume)	2.5	7.0
Myoglobin (mg per g of tissue)	1.0	5.5
Lactate dehydrogenase activity (arbitrary units)	180	60
Time to fatigue when stimulated continuously (s)	40	900

(a) Identify which type is slow twitch. Use two pieces of evidence from the data. [3] (b) Calculate how many times greater the myoglobin content of type B is than type A. [1] (c) Suggest why type A fibres suit a short sprint. [1]

6. (a) Explain what is meant by the term myogenic. [1] (b) Explain why the atrioventricular node (AVN) delays the wave of excitation. [2] (c) State the role of the Purkyne fibres. [1]

7. An ECG trace was recorded at a paper speed of 25 mm per second. Five consecutive R-to-R intervals together measure 70 mm.

(a) Calculate the heart rate in beats per minute. [3] (b) Name the condition shown by your answer to (a). [1] (c) A second trace shows irregular R-to-R spacing and no clear P waves. Name the abnormal rhythm this suggests. [1]

8. A trained athlete has a resting heart rate of 58 beats per minute and a resting stroke volume of 95 cm³. At maximum exercise the heart rate is 185 beats per minute and the stroke volume is 150 cm³.

(a) Calculate the resting cardiac output in dm³ per minute. [2] (b) Calculate the cardiac output at maximum exercise in dm³ per minute. [1] (c) Calculate the percentage increase in cardiac output. [2] (d) An untrained person reaches a heart rate of 190 and a stroke volume of 100 cm³. State which factor accounts for the athlete’s higher maximum cardiac output. [1]

9. Explain how the heart rate is increased during exercise and then returned to normal afterwards. [6]

10. (a) State where adrenaline is released and how it reaches its target cells. [2] (b) Explain how adrenaline helps the body respond to danger. [3]

11. A student analysed spirometer traces. At rest, there were 5 breaths in 20 s, the tidal volume was 0.50 dm³ and the baseline fell by 0.45 dm³ in 90 s. During exercise, there were 8 breaths in 15 s, the tidal volume was 1.6 dm³ and the baseline fell by 3.9 dm³ in 3 min.

(a) Calculate the resting breathing rate. [1] (b) Calculate the resting respiratory minute ventilation. [1] (c) Calculate the breathing rate and minute ventilation during exercise. [2] (d) Calculate the oxygen consumption at rest and during exercise, in dm³ per minute. [2] (e) Explain why the baseline of the trace falls. [2]

Answers

1. (a) The quadriceps contracts and pulls on the lower leg to straighten the knee [1]; the hamstring relaxes (and is stretched), as muscles can only pull [1] [2] (b) A tendon joins muscle to bone and transmits the pull of the muscle [1]; a ligament joins bone to bone and stabilises the joint [1] [2] Examiner insight: Naming which muscle contracts and which relaxes is what the explanation needs; “they work together” does not say that.

2. Any four from: it is multinucleate (many nuclei in one cell) [1]; it is very long, with a sarcolemma that folds inwards as T tubules [1]; it has a sarcoplasmic reticulum storing calcium ions [1]; it contains myofibrils made of repeating sarcomeres, giving striations (and many mitochondria between them) [1] [4] Examiner insight: A “distinguish” question rewards features that differ from an ordinary cell; naming the organelles every cell has gains nothing.

3. (a) Relaxed: 100 ÷ 40 000 = 0.0025 mm = 2.5 µm [1]; contracted: 72 ÷ 40 000 = 0.0018 mm = 1.8 µm [1] [2] (b) (2.5 − 1.8) ÷ 2.5 × 100 = 28% [1] (c) 1.8 − 1.5 = 0.3 µm [1] (d) The thick (myosin) filaments, which make up the A band, do not shorten [1]; the thin filaments slide between them, so only the I band and H zone shorten [1] [2] Examiner insight: Show the conversion from mm to µm; it makes the working easy to follow, and a slip in powers of ten is easy to spot if each line is written out.

4. The action potential spreads along the sarcolemma and down the T tubules, and the sarcoplasmic reticulum releases calcium ions [1]; calcium ions bind to troponin, which changes shape, so tropomyosin moves and exposes the myosin-binding sites on actin [1]; myosin heads attach to actin as cross-bridges [1]; the heads tilt and pull the actin filaments inwards, releasing ADP and phosphate [1]; ATP binds, detaching the heads, and ATPase hydrolyses it to re-set the heads [1]; repeated cycles pull the thin filaments inwards, so the sarcomere shortens [1] [6] Examiner insight: A strong answer keeps the order of events; listing the protein names without saying what each does tends to earn little.

5. (a) Type B is slow twitch [1]; it has more mitochondria (7.0 against 2.5) so more aerobic respiration [1]; it has higher myoglobin and a much longer time to fatigue (900 s against 40 s) [1] [3] (b) 5.5 ÷ 1.0 = 5.5 times [1] (c) Type A has high lactate dehydrogenase activity, so it can produce ATP quickly by anaerobic glycolysis [1] [1] Examiner insight: Quote figures from the table with units when comparing; a bare “type B is higher” does not use the data.

6. (a) The cardiac muscle contracts and relaxes on its own, without a nerve impulse starting each beat [1] [1] (b) The delay gives the atria time to finish contracting [1]; so the ventricles fill with blood before they contract [1] [2] (c) They carry the wave of excitation up through the ventricle walls from the apex, so the ventricles contract from the bottom upwards [1] [1] Examiner insight: For (b) give a purpose as well as the fact of a delay; that is the reasoning the “explain” asks for.

7. (a) Total time = 70 ÷ 25 = 2.8 s [1]; one interval = 2.8 ÷ 5 = 0.56 s [1]; heart rate = 60 ÷ 0.56 = 107 beats per minute [1] [3] (b) Tachycardia (rate above 100) [1] (c) Atrial fibrillation [1] Examiner insight: Dividing by five intervals before converting is the step that is often missed; write the interval time on its own line.

8. (a) 58 × 95 = 5510 cm³ [1] = 5.51 dm³ per minute [1] [2] (b) 185 × 150 = 27 750 cm³ = 27.75 dm³ per minute [1] (c) (27.75 − 5.51) ÷ 5.51 × 100 [1] = 404% [1] [2] (d) Stroke volume: the athlete’s is larger, while the heart rates are similar (untrained cardiac output is 19.0 dm³ per minute) [1] Examiner insight: Convert cm³ to dm³ once and say so; mixing units between parts is a common way to lose accuracy.

9. Muscles respire faster and release more carbon dioxide, so blood pH falls [1]; chemoreceptors in the carotid arteries and aorta detect this [1]; they send impulses to the cardiovascular control centre in the medulla oblongata [1]; the accelerator pathway sends impulses along sympathetic neurones to the SAN [1]; the SAN fires faster and the heart rate rises [1]; afterwards, as pH returns to normal, impulses pass along the vagus nerve (decelerator pathway) to slow the SAN [1] [6] Examiner insight: A full answer runs stimulus, receptor, centre, effector and response in order; naming only the medulla and the SAN leaves out the middle links.

10. (a) Released from the adrenal glands (medulla) [1]; carried in the blood plasma [1] [2] (b) Increases heart rate and stroke volume, so more oxygenated blood reaches muscles [1]; liver glycogen is converted to glucose, giving more respiratory substrate [1]; arterioles to muscles dilate and those to gut and skin constrict, diverting blood to muscle [1] [3] Examiner insight: Each effect earns credit when linked to its benefit; “heart beats faster” alone is only half of the point.

11. (a) 5 ÷ 20 × 60 = 15 breaths per minute [1] (b) 0.50 × 15 = 7.5 dm³ per minute [1] (c) Rate = 8 ÷ 15 × 60 = 32 breaths per minute [1]; ventilation = 1.6 × 32 = 51.2 dm³ per minute [1] [2] (d) Rest: 0.45 ÷ 1.5 = 0.30 dm³ per minute [1]; exercise: 3.9 ÷ 3 = 1.3 dm³ per minute [1] [2] (e) Carbon dioxide breathed out is absorbed by soda lime [1]; oxygen is used by the volunteer, so the volume of gas in the circuit decreases [1] [2] Examiner insight: Convert 90 s to 1.5 min before dividing; time units must match the per-minute unit asked for.

Where marks are usually lost

• Saying muscles push, or not stating that the antagonist relaxes.
• Writing that the A band shortens in contraction.
• Skipping the source of energy: ATP detaches the myosin head and ATPase re-sets it.
• Saying calcium ions bind to actin or myosin rather than troponin.
• Saying the AVN “speeds up” the signal, or that nerves start each heartbeat.
• Not dividing by the number of intervals when finding heart rate from an ECG.
• Mixing seconds with minutes or cm³ with dm³.
• Describing the effects of adrenaline without linking them to the benefit for muscle.

Next steps

• Revise with the revision notes and the study guide.
• Visit the Edexcel A Level Biology hub and the printable checklist.
• Take the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Pearson Edexcel International Advanced Subsidiary/Advanced Level in Biology (YBI11), Specification, Issue 2, February 2021, Pearson Education Limited. Statements 7.9 to 7.15 of Topic 7, including Core Practical 17.