Edexcel A-Level Biology: Control Systems
6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
When an action potential arrives at the end of a presynaptic neurone, it cannot pass directly across the gap to the next neurone. Instead, transmission across a cholinergic synapse depends on a sequence of events involving a chemical messenger.
Describe and explain how an impulse is transmitted across a cholinergic synapse, from the arrival of the action potential at the presynaptic membrane to the initiation of an action potential in the postsynaptic neurone.
(6 marks)
In a glucose tolerance test, a person drinks a measured glucose solution after fasting, and their blood glucose concentration is recorded over the next two hours. The table shows the results for Person A (no diabetes) and Person B (recently diagnosed with type 2 diabetes).
| Time after drink / min | Blood glucose of Person A / mmol dm⁻³ | Blood glucose of Person B / mmol dm⁻³ |
|---|---|---|
| 0 | 4.5 | 7.0 |
| 30 | 7.8 | 11.6 |
| 60 | 6.6 | 13.4 |
| 90 | 5.2 | 12.8 |
| 120 | 4.6 | 11.9 |
(a) For Person A, calculate the percentage decrease in blood glucose concentration between 30 minutes and 120 minutes. Show your working. (2 marks)
(b) Using the data, explain how the response of Person A shows that their blood glucose concentration is being controlled by negative feedback, and suggest one reason why Person B's response is different. (4 marks)
A physiologist measured how long an action potential took to travel along a fixed length of two different axons from the same animal: one myelinated and one non-myelinated. Each axon was stimulated at one end and the signal detected 0.30 m further along. The mean conduction times are shown below.
| Axon | Distance / m | Mean conduction time / ms |
|---|---|---|
| Myelinated | 0.30 | 5.0 |
| Non-myelinated | 0.30 | 25.0 |
(a) Calculate the conduction speed of the myelinated axon in m s⁻¹. Show your working. (2 marks)
(Note: 1 ms = 0.001 s.)
(b) The non-myelinated axon conducts the impulse far more slowly. Explain why myelination increases the speed of conduction along an axon. (3 marks)
A grower wants tomato seedlings to grow tall and straight rather than bending sideways. The seedlings are grown in a greenhouse where natural daylight reaches them only from one side through a large window.
A researcher suggests fitting a second bank of lamps on the opposite wall so that the seedlings receive even light intensity from both sides.
Suggest and explain, using your knowledge of the plant hormone auxin (IAA), why providing even light from both sides should make the seedlings grow straight upwards rather than bending. (5 marks)
A long-distance swimmer prepares to cross a cold open-water channel. Before entering the water their skin looks flushed and pink, but after a few minutes in the cold water their exposed skin becomes noticeably pale, even though their core body temperature stays close to 37 °C.
Explain how the response of the blood vessels in the skin keeps the swimmer's core temperature stable in the cold water, and why this makes the skin look pale. (4 marks)
When a person touches a sharp pin, they pull their hand away rapidly before they are aware of any pain. This rapid, automatic response is a spinal reflex brought about by a reflex arc.
Describe the pathway taken by the nerve impulse in this reflex arc, naming the three types of neurone involved in the correct order. (3 marks)