These automatic control systems may involve nervous responses or chemical…

The idea

Automatic control systems keep internal conditions steady without conscious thought. They work through two complementary routes. Nervous responses use electrical impulses travelling along neurones: a receptor detects a stimulus, a coordination centre processes the information, and an effector responds. This is fast and short-lived, suiting rapid changes such as touching something hot. Chemical responses use hormones carried in the blood plasma: a gland secretes a hormone, which travels to a target organ with matching receptors and triggers a response. This is slower but longer-lasting, suiting sustained regulation such as blood glucose concentration. Both routes share the same three-part framework of receptor, coordination centre and effector, so the key skill is identifying which route a scenario describes and justifying that choice using speed, duration and transmission method.

What earns the marks

• Nervous responses involve electrical impulses travelling along neurones, whereas chemical responses involve hormones transported in the blood plasma.
• Nervous responses are generally rapid and short-lived; hormonal responses are generally slower and longer-lasting.
• A named example of a nervous response, such as the reflex withdrawal of a hand from a hot surface, contrasted with a named hormonal example, such as insulin lowering blood glucose concentration.
• Hormones act only on target organs or cells that possess complementary receptors, whereas nervous impulses travel along defined neurone pathways to specific effectors.
• A valid comparison must address both routes; describing only one route cannot earn comparison credit.

Common mistakes and how to put them right

• Saying hormones travel along nerves.

  Put it right by stating that hormones are secreted into the blood and carried in the plasma to target organs.

• Claiming nervous responses are always longer-lasting than hormonal ones.

  Put it right by stating that nervous responses are typically rapid and short-lived, while hormonal responses are slower and longer-lasting.

• Treating the two systems as completely separate with no shared components.

  Put it right by noting that both use receptors, coordination centres and effectors.

• Describing a response as chemical simply because a chemical is involved, such as a neurotransmitter.

  Put it right by classifying the response according to whether the signal travels as an electrical impulse along neurones or as a hormone in the blood.

Exam tips

• When a question asks you to compare, write paired statements about the same feature, for example speed of nervous versus speed of hormonal response.
• Name a specific example for each route, such as a reflex arc for nervous control and insulin or adrenaline for chemical control, to show secure understanding.
• Use the terms electrical impulse, neurone, hormone, blood plasma and target organ precisely; vague wording such as 'signals' loses clarity.
• If asked to identify which system is involved in a scenario, justify your choice using at least two features such as speed and duration of the response.