AQA GCSE Bio homeostasis

• Part of brain responsible for making a decision

  Cerebral cortex
• How does the brain receive information about light entering the eye? [3]

  • cells in the retina sensitive to light
  • impulse travels along sensory neurone
  • along optic nerve
• Explain how a person’s eye adjusts to form a clear image of a near object [6]

  • ciliary muscles contract
  • so they have a smaller diameter
  • so suspensory ligaments slacken
  • so lens thickens
  • a thicker lens is more convergent
  • light rays are focused on retina
• Explain why a long-sighted person has difficulty seeing near objects clearly [2]

  • Eyeball is too short or lens cannot be thickened enough
  • so light focuses behind retina
• How can glasses correct long-sightedness? [3]

  • convex lens
  • light rays refracted more
  • light rays focus on retina
• Describe how a reflex action is coordinated [6]

  • receptor detects stimulus
  • receptor generates impulses
  • sensory neurone conducts impulses to spinal chord
  • impulse crosses a synapse between neurones
  • chemical diffuses through synapse
  • chemical stimulates impulse in relay neurone
  • relay neurone conduct impulse through synapse to motor neurone
  • motor neurone conducts impulse to effector
  • effector carries out response
  • muscles contract or gland secretes hormones
• How does information pass through a synapse? [2]

  • chemical released at end of one neurone
  • diffuses across synapse
  • stimulates impulse in next neurone
• Why are 10 reaction times measured for each person rather than 3 in ruler drop practical? [2]

  • to increase validity and repeatability
  • to get representative results
  • because of variation in results
• Why is ruler drop test not a reflex action?

  Involves conscious part of the brain
• What is meant by the term ‘reflex action’? [2]


  A response/reaction that is involuntary/not conscious
• What does the cerebral cortex control?

  • memory
  • learning
  • personality
  • consiousness
  • language
  • intelligence
  • voluntary movements
• What does the hypothalamus control?

  Homeostatic control
• What does the cerebellum control?

  coordination of muscular activity and balance
• What does the medulla oblongata control?

  • gut movement
  • blood pressure
  • heart rate
  • breathing rate
• What does the pituitary gland do?

  Produces and releases hormones
• What does the pons do?

  Connects cerebellum to cerebral cortex
• Control variables in ruler drop practical

  • drop ruler from same height
  • use same hand each time
  • thumb same distance from ruler at the start
  • use same weight of ruler
  • drop ruler without any force each time
  • keep arm resting on the edge of table
• What is the sclera?

  Tough outer layer of eye which protects it and holds it in place
• Function of the retina

  Made up of light-sensitive receptor cells that pick up light. Contains rod and cone cells
• What is the cornea?

  Transparent region of the sclera at the front of the eye. It refracts light as it enters the eye
• Function of iris

  Has sets of muscles that control the size of the pupil and regulate light reaching the retina
• Function of lens

  Focuses light rays on retina
• Function of the pupil

  Hole in centre of iris that allows light to pass through
• The fastest measured time of a human is about 0.1 s. Why can a person’s reaction time not be faster than this? [3]

  • It takes time for an impulse to travel across a nerve
  • the nervous system has synapses
  • it takes time for chemicals to diffuse across synapses
  • which further adds to reaction time
• Define homeostasis


  Maintenance of a constant internal environment
• Describe the main components of a control system [6]

  • consist of receptors, co-ordination centres and effectors
  • receptors detect stimuli
  • such as light/sound/temperature
  • co-ordination centre processes information
  • such as brain/spinal chord/ pancreas
  • effectors contract a muscle or a gland secrete a hormone
• Why is damage to the brain very hard to treat? [4]

  • brain is very complex - it is not known fully how it works
  • brain is very delicate
  • surgery may result in damage to another area
  • many drugs will not pass from the blood across the brain membrane