Homeostasis and response — GCSE Biology Revision
Everything you need to revise homeostasis and response for GCSE Biology: clear notes, the key facts and terms to learn, the mistakes that cost students marks, and practice questions with answers.
Revision notes
Introduction to Homeostasis
Homeostasis is the maintenance of a constant internal environment in the body, despite changes in the external surroundings. This process is crucial for optimal cell function and survival. Key factors regulated include body temperature, blood glucose levels, and water balance. Maintaining stable conditions ensures enzymes work efficiently and metabolic processes can occur effectively. Control systems involve receptors, coordination centres, and effectors working together to detect changes and bring about responses, often through negative feedback loops.
Thermoregulation: Controlling Body Temperature
Thermoregulation is the process by which the body maintains a stable core internal temperature, typically around 37°C. The thermoregulatory centre in the hypothalamus of the brain monitors blood temperature and receives impulses from temperature receptors in the skin. When too hot, blood vessels dilate (vasodilation) and sweat is produced. When too cold, blood vessels constrict (vasoconstriction), hairs stand on end, and shivering occurs. These responses ensure enzymes function optimally.
Blood Glucose Regulation
Blood glucose levels are carefully controlled to provide a constant energy supply to cells. This regulation is primarily handled by the pancreas. After a meal, blood glucose rises, stimulating the pancreas to release insulin, which causes glucose to move into cells and be stored as glycogen in the liver and muscles. If blood glucose falls too low, the pancreas releases glucagon, which triggers the liver to convert stored glycogen back into glucose and release it into the blood, raising levels.
The Endocrine System and Hormones
The endocrine system is a chemical control system that uses hormones to send messages around the body. Glands secrete hormones directly into the bloodstream, which then travel to target organs to produce a response. Unlike the faster nervous system, hormonal responses are generally slower but longer-lasting. Key endocrine glands include the pituitary, thyroid, pancreas, adrenals, and gonads. Hormones are vital for growth, metabolism, reproduction, and stress response, all contributing to homeostasis.
Key facts
- Homeostasis is vital for maintaining a stable internal environment.|Negative feedback mechanisms are key to homeostatic control.|The nervous system and endocrine system coordinate responses.|Thermoregulation keeps body temperature stable, mainly at 37°C.|Insulin and glucagon regulate blood glucose levels.|Hormones are chemical messengers secreted by glands.
Key terms
- Homeostasis::The maintenance of a constant internal environment despite changes in the external environment.|Negative Feedback::A control system that reverses any change in a condition, bringing it back to the normal level.|Receptor::A cell or organ that detects a stimulus (a change in the environment).|Effector::A muscle or gland that brings about a response to a stimulus.|Hormone::A chemical messenger produced by endocrine glands and transported in the blood to target cells.|Insulin::A hormone produced by the pancreas that lowers blood glucose levels.
Common mistakes
- Confusing negative feedback with positive feedback (e.g., believing negative feedback increases the original change).|Not knowing the specific roles of the nervous system and endocrine system (e.g., thinking hormones are fast-acting like nerves).|Mixing up the functions of insulin and glucagon (e.g., saying insulin raises blood glucose).|Forgetting that enzymes need a stable temperature and pH to function correctly, linking it back to homeostasis.|Describing vasoconstriction/vasodilation incorrectly (e.g., saying blood vessels expand to conserve heat).|Not mentioning the specific organs involved in regulation (e.g., pancreas for glucose, hypothalamus for temperature).
Exam tips
- Practice drawing and labelling diagrams of feedback loops, especially for thermoregulation and blood glucose.|Learn specific examples of receptors and effectors for each homeostatic control system.|Clearly distinguish between the roles of the nervous system and the endocrine system, and how they interact.|Use scientific terminology accurately, such as 'vasodilation', 'vasoconstriction', 'glycogen', and 'hypothalamus'.
Quick quiz
1. Which of the following is an example of homeostasis?
- A. A plant growing towards light.
- B. Maintaining a constant body temperature.
- C. A chameleon changing its skin colour.
- D. A spider spinning a web.
Show answer
B. Maintaining a constant body temperature. — Homeostasis specifically refers to the body's ability to maintain a stable internal environment, such as regulating temperature or blood glucose levels.
2. Which part of the brain is responsible for thermoregulation?
- A. Cerebrum
- B. Cerebellum
- C. Medulla
- D. Hypothalamus
Show answer
D. Hypothalamus — The hypothalamus contains the thermoregulatory centre, which monitors blood temperature and coordinates responses to maintain a stable body temperature.
3. What happens to blood vessels in the skin when the body is too hot?
- A. They constrict (vasoconstriction).
- B. They dilate (vasodilation).
- C. They remain unchanged.
- D. They stop carrying blood.
Show answer
B. They dilate (vasodilation). — Vasodilation increases blood flow near the skin surface, allowing more heat to be lost to the surroundings through radiation and convection.
4. What hormone is released by the pancreas when blood glucose levels are too high?
- A. Adrenaline
- B. Glucagon
- C. Insulin
- D. Thyroxine
Show answer
C. Insulin — Insulin is released when blood glucose is high, causing cells to take up glucose and the liver to convert it to glycogen, thereby lowering blood glucose.
5. Which of these is an effector in a homeostatic control system?
- A. A temperature receptor in the skin.
- B. The brain's thermoregulatory centre.
- C. A muscle or gland.
- D. A change in blood glucose levels.
Show answer
C. A muscle or gland. — An effector is a cell or organ (like a muscle or gland) that carries out the response to a stimulus, bringing about a change.
Exam-style questions
Describe the process of thermoregulation when a person becomes too hot. [4 marks]
Show mark scheme
- Temperature receptors detect increased body temperature.
- The thermoregulatory centre in the hypothalamus receives this information.
- The body responds by vasodilation, increasing blood flow to the skin surface.
- Sweat glands produce more sweat, which evaporates to cool the skin.
Explain how blood glucose levels are regulated in the body after a sugary meal. [4 marks]
Show mark scheme
- Blood glucose levels rise after a sugary meal.
- The pancreas detects this rise and releases insulin.
- Insulin causes liver and muscle cells to take up glucose from the blood.
- Glucose is converted into glycogen for storage in the liver and muscles, lowering blood glucose.
Compare the roles of the nervous system and the endocrine system in controlling body functions. [3 marks]
Show mark scheme
- Nervous system uses electrical impulses; endocrine system uses chemical hormones.
- Nervous responses are fast and short-lived; endocrine responses are slower and longer-lasting.
- Nervous impulses travel via nerves; hormones travel via the bloodstream to target organs.
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