📘 GCSE Biology · Notes & worksheet
Homeostasis and Response.
Notes
Homeostasis
Keeping internal conditions (temperature, blood glucose, water content) within a narrow range for enzymes and cells to work. It uses negative feedback: a change is detected and a response reverses it.
Control system: receptor → coordination centre → effector.
The nervous system
Stimulus → receptor → sensory neurone → CNS (brain or spinal cord) → motor neurone → effector (muscle or gland) → response.
- Reflex arc: fast, automatic, involves a relay neurone in the spinal cord and does not involve the conscious brain.
- At a synapse the signal crosses the gap as a chemical (neurotransmitter), which diffuses across and binds to receptors on the next neurone.
The endocrine system
Hormones are chemicals released into the blood by glands. They act more slowly than nerves, but their effects last longer.
Blood glucose control
| Event | Response |
|---|---|
| Glucose too high (after a meal) | Pancreas releases insulin. Liver and muscles take in glucose and store it as glycogen. Blood glucose falls. |
| Glucose too low | Pancreas releases glucagon. Liver breaks glycogen down to glucose. Blood glucose rises. |
Diabetes
- Type 1: the pancreas makes little or no insulin. Treated with insulin injections and diet control.
- Type 2: body cells stop responding to insulin. Linked to obesity. Treated with diet, exercise and sometimes medication.
Water and ions: the kidneys and ADH
The brain monitors blood water content. If it is too low (for example in hot weather) the pituitary gland releases ADH, which makes the kidney tubules reabsorb more water. The urine becomes concentrated and smaller in volume. When blood water is high, less ADH is released and urine becomes dilute.
Temperature control
Too hot: vasodilation (more blood flow near the skin) and sweating. Too cold: vasoconstriction, shivering, and hairs stand on end.
Common mistakes
- Mixing up insulin and glucagon, or saying insulin "makes glucose".
- Saying vasodilation moves capillaries towards the skin. The capillaries do not move; blood flow to the skin capillaries increases.
- Writing "negative feedback" without describing what is detected and what reverses it.
Exam tips
- For every hormone question, give the gland, the target and the effect.
- Use the word "effector" when describing a reflex arc.
Worksheet
Prints the questions only, without answers. Choose “Save as PDF” in the print window to download.
Total: 28 marks.
- Put these stages of a reflex arc in order when a hand touches a hot object: motor neurone, receptor, relay neurone, effector, sensory neurone. (2)
- Explain why a reflex response is quicker than a voluntary response. (2)
- Describe how the body reduces blood glucose after a carbohydrate-rich meal. Name the organ, hormone and storage molecule. (4)
- Compare Type 1 and Type 2 diabetes. Include cause and treatment for each. (4)
- A hiker sweats heavily on a hot day and drinks little. Explain how ADH helps maintain her water balance. (4)
- Explain how negative feedback keeps blood glucose within a narrow range. (3)
- Compare the nervous system and the endocrine system in terms of speed, duration and pathway. (3)
- Explain why vasodilation helps cool the body. (2)
- A person with Type 1 diabetes eats a large sugary meal and does not take insulin. Predict and explain what happens to their blood glucose. (4)
Show mark scheme and answers (tutor copy)
Try the worksheet first, then check your work here.
- receptor → sensory neurone → relay neurone → motor neurone → effector. (B1 for correct order of the first three; B1 for the rest.)
- A reflex does not involve the conscious brain, so the impulse takes a shorter route (B1) with fewer synapses to cross (B1).
- Blood glucose rises and is detected by the pancreas (B1). The pancreas releases insulin (B1). Insulin makes liver and muscle cells take up glucose (B1) and convert it to glycogen for storage (B1).
- Type 1: pancreas does not produce enough insulin (B1). Treated with insulin injections and careful diet (B1). Type 2: body cells no longer respond to insulin (B1). Treated with a carbohydrate-controlled diet, exercise and weight loss, and sometimes medication (B1).
- Sweating reduces the water content of the blood (B1). This is detected by the brain, and the pituitary gland releases more ADH (B1). ADH makes the kidney tubules reabsorb more water into the blood (B1), so less water is lost and the urine is smaller in volume and concentrated (B1).
- When glucose is too high, insulin is released and lowers it (B1). When glucose is too low, glucagon is released and raises it (B1). The response reverses the original change, returning glucose to the normal level (B1).
- Nervous: fast response, short-lasting, electrical impulses along neurones. Endocrine: slower response, longer-lasting, chemical hormones carried in the blood. (B1 each for speed, duration, pathway)
- Blood vessels near the skin widen, so more blood flows through skin capillaries (B1). More heat is radiated from the skin to the surroundings (B1).
- Blood glucose rises very high (B1) because there is no insulin (B1), so the liver and muscles do not take up glucose and store it as glycogen (B1). Glucose may exceed the kidneys' ability to reabsorb it and appear in the urine, and the person needs insulin urgently. (B1)