Structures and Functions in Living Organisms · 7 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 14% of your exam marks.
Nervous system structure, reflex arcs, and hormones are all commonly examined.
The two systems differ in speed, signal type, target, and duration of effect.
| Feature | Nervous system | Endocrine (hormonal) system |
|---|---|---|
| Signal type | Electrical impulses along neurones | Chemical signals (hormones) carried in the blood |
| Pathway | Through nerves (bundles of neurones) | Through the bloodstream |
| Speed | Very fast (impulses up to 100 m/s) | Slower (seconds to hours) |
| Target | Specific cells at the end of the neurone | Many cells, but only those that have the matching receptors respond |
| Duration of response | Short (the response stops the moment the signal stops) | Long (the response lasts until the hormone is broken down) |
| Example | The pain-withdrawal reflex | Insulin lowering blood glucose; adrenaline raising heart rate |
The nervous system is the right tool for jobs that need an immediate response: pulling away from a sharp object, flinching from a loud noise, balancing on a moving bus. The endocrine system is the right tool for longer-lasting changes that affect lots of cells at once: growing taller, going through puberty, regulating blood sugar between meals.