Human Coordination & Homeostasis

IGCSE Edexcel Biology
2.76–2.81 Nervous system, reflexes, hormones and homeostasis
Key Concepts: The nervous system uses electrical impulses via neurones for rapid, short-lived responses. The hormonal system uses chemicals carried in the blood for slower, longer-lasting responses. Homeostasis maintains a stable internal environment using negative feedback, controlling blood glucose, body temperature and water potential.

Section A — Nervous System

1. State the difference between a stimulus and a response. [2]
2. Name the three types of neurone in a reflex arc and state the role of each. [6]
NeuroneRole
3. Explain why a reflex action is faster than a voluntary action. [2]
4. Describe what happens at a synapse when a nerve impulse is transmitted from one neurone to the next. [3]

Section B — Nervous vs Hormonal Coordination

5. Complete the table comparing nervous and hormonal coordination. [6]
FeatureNervousHormonal
Speed of response
Duration of effect
Method of transmission
6. Define the term hormone and name the gland that releases each of the following. [4]
HormoneGland that releases it
Insulin
Glucagon
Adrenaline

Section C — Homeostasis: Blood Glucose

7. Define homeostasis and explain the principle of negative feedback. [3]
8. Describe how the body responds when blood glucose concentration rises after a meal. Name the hormone involved and the organ that responds. [4]
9. Describe how the body responds when blood glucose concentration falls too low. Name the hormone involved. [3]

Section D — Homeostasis: Temperature Regulation

10. State which part of the brain monitors and controls body temperature. [1]
11. Describe three ways the body responds to an increase in body temperature. [6]
12. Describe two ways the body responds when body temperature falls below normal. [4]

Total marks: 44

Mark Scheme

1. A stimulus is a change in the environment (internal or external) detected by receptors [1]; a response is the reaction of an effector (muscle or gland) to a stimulus [1] [2]
2. Sensory neurone: carries impulses from receptor to the spinal cord/relay neurone; Relay neurone (interneurone): connects sensory and motor neurones in the spinal cord/brain; Motor neurone: carries impulses from relay neurone to the effector (muscle or gland) [6 — 2 per row]
3. A reflex arc bypasses the brain [1]; the impulse travels a shorter pathway (through the spinal cord only), so the response is faster [1] [2]
4. The impulse reaches the end of the pre-synaptic neurone [1]; neurotransmitter molecules are released into the synaptic gap [1]; they diffuse across and bind to receptors on the post-synaptic neurone, triggering a new impulse [1] [3]
5. Speed: nervous = fast; hormonal = slow; Duration: nervous = short-lived; hormonal = long-lasting; Transmission: nervous = electrical impulse along neurones; hormonal = chemical carried in blood [6 — 2 per row]
6. A hormone is a chemical messenger produced by a gland and transported in the blood to a target organ [1]; Insulin: pancreas; Glucagon: pancreas; Adrenaline: adrenal glands [4 — 1 for definition + 1 per correct gland]
7. Homeostasis is the maintenance of a stable internal environment [1]; negative feedback: when a condition moves away from the set point, a corrective response is triggered [1]; the response brings the condition back to normal, which then switches off the response [1] [3]
8. Blood glucose rises; the pancreas detects this [1]; pancreas releases insulin [1]; insulin causes liver (and muscle) cells to convert glucose to glycogen (glycogenesis) [1]; blood glucose falls back to normal [1] [4]
9. Blood glucose falls; the pancreas releases glucagon [1]; glucagon causes the liver to convert glycogen back to glucose (glycogenolysis) [1]; blood glucose rises back to normal [1] [3]
10. The hypothalamus [1]
11. Any three: sweating — water evaporates from skin surface, removing heat energy [2]; vasodilation — blood vessels near the skin surface widen, more blood flows to skin, more heat lost by radiation [2]; hairs lie flat — erector muscles relax, hairs are flat, less insulating air trapped [2] [6]
12. Any two: shivering — rapid muscle contractions generate heat [2]; vasoconstriction — blood vessels near the skin surface narrow, less blood flows to skin, less heat lost [2]; hairs stand on end — erector muscles contract, hairs trap an insulating layer of air [2] [4 — 2 per response]