What are stem cells used for, and how does the nervous system carry information?
Stem cells in animals and plants and their uses, the structure of the nervous system, the reflex arc, and the structure and function of neurones.
A focused answer to Edexcel GCSE Combined Science Topic 2 (CB2), covering stem cells in animals and plants and their uses, the structure of the nervous system, the reflex arc, and the structure and function of sensory, relay and motor neurones.
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What this dot point is asking
Edexcel wants you to describe what stem cells are and give their uses in animals and plants, describe the structure of the nervous system, explain how a reflex arc produces a fast automatic response, and describe the structure and function of sensory, relay and motor neurones.
Stem cells
Stem cells could be used to replace damaged cells and treat conditions such as type 1 diabetes (replacing insulin-producing cells) or paralysis (replacing nerve cells). In plants, meristem stem cells are used to produce clones quickly, for example to grow large numbers of identical, disease-resistant crops. Medical uses raise issues: embryonic sources are controversial, and transplanted cells could be rejected or carry infection.
The nervous system
The nervous system lets organisms react to their surroundings and coordinate behaviour. It uses fast electrical impulses carried by neurones (nerve cells). The central nervous system (CNS) is the brain and spinal cord; it coordinates a response. Information travels: stimulus, receptor, sensory neurone, CNS, motor neurone, effector, response.
The reflex arc
In a reflex arc:
- A receptor detects a stimulus (for example heat or pressure).
- A sensory neurone carries the impulse to the CNS (often the spinal cord).
- A relay neurone in the CNS passes the impulse on.
- A motor neurone carries the impulse to an effector.
- The effector (a muscle or gland) produces the response.
Between neurones there are tiny gaps called synapses. The impulse causes a chemical (a neurotransmitter) to be released, which diffuses across the gap and triggers an impulse in the next neurone.
The three types of neurone
- Sensory neurone: carries impulses from receptors to the CNS. It has a long dendron.
- Relay neurone: found in the CNS, it connects sensory and motor neurones. It is short.
- Motor neurone: carries impulses from the CNS to effectors. It has a long axon and branched endings.
Neurones are adapted with a myelin sheath (a fatty insulating layer that speeds up the impulse) and a long shape so impulses travel a long way in one cell.
Try this
Q1. Name the two parts of the central nervous system. [1 mark]
- Cue. The brain and the spinal cord.
Q2. State one use of stem cells in medicine and one risk. [2 marks]
- Cue. Use: treating diabetes or paralysis (replacing damaged cells). Risk: rejection, infection, or ethical objections to embryonic sources.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20184 marksDescribe the path taken by a nervous impulse in a reflex arc when a person touches a hot object and pulls their hand away.Show worked answer →
A 4-mark describe question rewards the components in the correct order.
A receptor in the skin detects the heat (the stimulus) and sends an impulse along a sensory neurone to the spinal cord (1 mark). In the spinal cord (the central nervous system), the impulse passes to a relay neurone (1 mark), then to a motor neurone (1 mark). The motor neurone carries the impulse to the effector, a muscle in the arm, which contracts to pull the hand away (1 mark).
Markers reward the order receptor, sensory neurone, relay neurone, motor neurone, effector, and the idea that the reflex is automatic and fast.
Edexcel 20223 marksExplain two ways the structure of a motor neurone is adapted to carry electrical impulses quickly to a muscle.Show worked answer →
A 3-mark explain question linking structure to function.
A motor neurone is long, so it can carry the impulse a large distance (for example from the spinal cord to a muscle) in one cell (1 mark). It has a myelin sheath, a fatty layer that insulates the axon and speeds up the impulse (1 mark). It also has branched endings (dendrites and axon terminals) that connect to other neurones or the muscle so the impulse can be passed on (1 mark).
Markers reward two clear structure-to-function links, such as length for distance and myelin for speed.
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Sources & how we know this
- Edexcel GCSE (9-1) Combined Science (1SC0) specification — Pearson (2016)