Homeostasis & response
Control systems, the nervous system and reflexes, and hormonal control including blood glucose regulation and diabetes.
Learn
Homeostasis & response, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Explain what homeostasis is and why it matters
Homeostasis keeps the internal conditions of the body steady - temperature, blood glucose, water - so cells and enzymes can work well despite changes outside. It works by control systems that detect a change with receptors and correct it with effectors (muscles or glands). Keeping conditions near an optimum is what stops small changes turning into big problems.
Describe the nervous system and the reflex arc
The nervous system carries fast electrical impulses. Receptors detect a stimulus, sensory neurones carry the signal to the central nervous system, and motor neurones carry the response out to effectors. A reflex skips conscious thought for speed - in a reflex arc a relay neurone in the spinal cord links sensory to motor, so your hand pulls off a hot plate before you feel the pain.
Compare nervous and hormonal control
Nerves send fast, short-lived electrical signals to precise targets; hormones are chemicals released by glands into the blood, giving slower, longer-lasting effects over a wider area. Adrenaline readies the body for action quickly, while growth hormones act over years. Matching speed and duration to the job is why the body keeps both systems.
Explain how blood glucose is controlled and what diabetes is
The pancreas monitors blood glucose. When it rises after a meal, insulin is released and cells take glucose in, storing the excess in the liver as glycogen. In Type 1 diabetes the pancreas stops making enough insulin, so it must be injected; Type 2 is when cells stop responding to insulin, and is often managed by diet and exercise.
Describe hormones in human reproduction
At puberty, hormones trigger the development of adult body features - testosterone in males, oestrogen in females. In the menstrual cycle several hormones interact: FSH matures an egg, oestrogen builds the womb lining, LH triggers the egg's release, and progesterone maintains the lining. Understanding this cycle explains how hormonal contraception and fertility treatments work.
Describe methods of contraception
Contraception prevents pregnancy either with hormones or by a barrier. Hormonal methods - the pill, implant or injection - stop eggs maturing or being released. Barrier methods like condoms physically stop sperm meeting an egg, and condoms also reduce the spread of infections. Each method has different reliability and side effects, which is why choice matters.
Homeostasis & response key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Homeostasis
- The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes.
- Receptor
- A cell or organ that detects a stimulus, a change in the environment.
- Effector
- A muscle or gland that carries out the response: muscles contract, glands secrete hormones.
- Reflex action
- An automatic, rapid response to a stimulus that does not involve the conscious part of the brain, protecting the body from harm.
- Synapse
- The junction between two neurones. The signal crosses it as a chemical that diffuses across the gap and triggers a new impulse.
- Hormone
- A chemical messenger produced by a gland, carried in the blood to a target organ where it produces an effect.
- Negative feedbackHigher only
- A control system that responds to a level rising or falling by triggering the opposite change, returning conditions to normal.
Practice
Try a Homeostasis & response question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
Which of these correctly orders the parts of a reflex arc?
- Effector → motor neurone → relay neurone → sensory neurone → receptor
- Receptor → motor neurone → relay neurone → sensory neurone → effector
- Receptor → sensory neurone → relay neurone → motor neurone → effector
- Receptor → relay neurone → sensory neurone → motor neurone → effector
Show the answer and the working
Answer: Receptor → sensory neurone → relay neurone → motor neurone → effector
The impulse passes from the receptor, along the sensory neurone, through a relay neurone, along the motor neurone, to the effector.
- The impulse starts at the receptor and must reach the CNS.
- The sensory neurone carries it in, the relay neurone passes it across in the CNS.
- The motor neurone then carries it out to the effector, giving receptor → sensory → relay → motor → effector.