Question 1
Paper 1A style
Which process in the human digestive system is under involuntary control by the enteric nervous system?
- Initiation of swallowing
- Chewing of food
- Peristalsis in the small intestine
- Egestion of faeces
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Answer: C [1]
Question 2
Paper 2A style
A person touches a sharp pin and pulls their hand away before feeling pain. Describe the pathway of the pain reflex arc that produces this response.
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- free nerve ending (of a sensory neuron) in the hand acts as the pain receptor [1]
- sensory neuron carries impulse to the spinal cord / CNS [1]
- synapse with (a single) interneuron in the grey matter (of the spinal cord) [1]
- interneuron synapses with / passes impulse to motor neuron [1]
- motor neuron carries impulse to skeletal muscle / effector [1]
- muscle contracts, pulling the hand away [1]
- [max 4]
Question 3
Paper 1B style
A student's heart rate, ventilation rate and blood pH were measured at rest, after 5 minutes of vigorous exercise and after 5 minutes of recovery. The data are for practice. (a) Calculate the percentage increase in heart rate from rest to exercise. [1] (b) Explain the change in blood pH during exercise. [2] (c) Explain how the change in blood pH causes the change in ventilation rate. [2]
| Condition | Heart rate / beats min⁻¹ | Ventilation rate / breaths min⁻¹ | Blood pH |
|---|---|---|---|
| At rest | 70 | 14 | 7.40 |
| After 5 min exercise | 140 | 30 | 7.33 |
| After 5 min recovery | 85 | 16 | 7.38 |
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- (a) (140 − 70) ÷ 70 × 100 = 100% [1]
- (b) increased (aerobic) respiration in muscles produces more CO₂ [1]
- (b) CO₂ dissolves / forms carbonic acid, which releases H⁺ ions, lowering pH [1]
- (b) Accept lactic acid from anaerobic respiration lowers pH [1]
- (c) chemoreceptors in the brainstem / medulla / carotid / aortic bodies detect the fall in pH [1]
- (c) medulla sends (more) nerve impulses to the diaphragm and intercostal muscles [1]
- (c) muscles contract more frequently, increasing ventilation rate, removing CO₂ (negative feedback) [1]
- [max 5]
Question 4
Paper 2A style
Outline how the effects of epinephrine (adrenaline) facilitate intense muscle contraction.
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- epinephrine is secreted by the adrenal glands [1]
- heart rate / stroke volume increases, so more blood reaches muscles [1]
- arterioles to skeletal muscles dilate / blood diverted from gut and skin [1]
- airways widen / ventilation rate increases, so more oxygen is supplied [1]
- glycogen in liver broken down to glucose, raising blood glucose for respiration [1]
- more oxygen and glucose for (aerobic) respiration / ATP for contraction [1]
- [max 3]
Question 5
Paper 2B style
Explain how heart rate is controlled by feedback following sensory input from baroreceptors and chemoreceptors.
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- baroreceptors monitor blood pressure [1]
- baroreceptors located in the walls of the aorta / aortic arch and carotid arteries [1]
- chemoreceptors monitor blood pH / concentration of CO₂ / O₂ [1]
- chemoreceptors located in aortic bodies / carotid bodies / brainstem [1]
- receptors send nerve impulses (along sensory neurons) to the medulla [1]
- medulla coordinates the response [1]
- impulses along sympathetic nerve increase heart rate [1]
- and increase stroke volume / force of contraction [1]
- impulses along vagus / parasympathetic nerve decrease heart rate [1]
- nerves act on the sinoatrial node / pacemaker [1]
- eg fall in pH / rise in CO₂ in exercise causes heart rate to increase [1]
- rise in blood pressure causes heart rate to decrease [1]
- negative feedback returns the variable to its normal level / set point [1]
- [max 6]