AQA GCSE Biology - Homeostasis and Response

Homeostasis
1. Homeostasis - Maintaining a stable internal environment
  1. The cells in your body need the right conditions to function properly.
2. The main automatic control systems: nervous and hormonal.
  1. Every automatic response system is made up of three main components: receptors, coordination centres (the brain, spinal cord & pancreas) and effectors
3. Negative feedback - counteracts changes
The Nervous System
1. The Nervous System - detects and reacts to stimuli. This helps humans to react to their surroundings and coordinate their behaviour.
2. Central Nervous System (CNS) - In vertebrates, it consists of the brain and spinal cord only. In mammals, it is connected to the body by sensory neurones and motor neurones.
3. Sensory neurone - neurones that carry information as electrical impulses from the receptors to the CNS.
4. Relay neurones - carry the electrical impulses through the CNS
5. Motor neurones - carry the electrical impulses from the CNS to effectors
6. Effectors - muscles and glands which respond to nervous impulses
7. Receptors - detects the stimuli
The Brain
1. The brain is a part of the CNS. It is responsible for complex behaviour and is made up of billions of interconnected neurones. Each region of the brain controls a different part which helps scientists to work out what each part does when studying a patient with brain damage.
2. The different regions and the functions they carry out:
3. There are many different ways scientists use to study the brain, here are three:
  1. Studying patients with brain damage: If a small part of the brain has been damaged, the effect this has on the patient can tell you what that part does.
  2. Electrically stimulating the brain: Scientists push a tiny electrode into the tissue and give it a small zap. This allows them to see what the part does from the stimulation.
  3. MRI scans - Magnetic resonance imaging scanners produce very detailed pictures of the brain's structures. They use this to see what part of the brain is active when the patient is doing things e.g. listening to music or trying to recall memory.
4. The brain is very delicate so when studying it there are many risks.
  1. It can cause physical damage to the brain.
  2. It can cause more problems for patients with brain damage.
  3. It can cause increased problems with brain function e.g. difficulties with speech.
The Eye
1. Here is a labeled picture of an eye:
  1. Sclera - the tough, supporting wall of the eye
  2. Cornea - transparent outer layer in front of the eye, refracts light into the eye
  3. Iris - muscles that control the diameter of the pupil and how much light enters the eye
  4. Lens - focuses the light onto the retina
  5. Retina - contains receptor cells sensitive to light intensity and colour
  6. Ciliary Muscles and Suspensory Ligaments - controls the shape of the lens
  7. Optic Nerve - carries impulses from the receptors on the retina to the brain
2. The Iris Reflex
  1. Bright light - a reflex forces the pupil to decrease in size. The circular muscles in the iris contract and the radial muscles relax. This reduces the amount of light that can enter the eye.
  2. Dim light - the circular muscles in the iris relax and the radial muscles contract. The pupil increases in size which allows more light to enter the eye.
3. Focusing on near and distant objects
  1. Near objects - the ciliary muscles contract which slackens the suspensory ligaments. The lens curve more which increases the amount by which it refracts light.
  2. Distant objects - the ciliary muscles relax which tightens the suspensory ligaments. The lens curve less which decreases the amount by which it refracts light.

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AQA GCSE Biology - Homeostasis and Response

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