B5- homeostasis and response

• What is homeostasis?

  Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
• Why is homeostasis important for cellular function?

  It maintains optimum conditions for enzyme and cellular function.
• What are examples of conditions maintained by homeostasis in the body?


  • Blood glucose concentration
  • Body temperature
  • Water levels
• What two types of responses are used in body control systems?

  Nervous and chemical responses are used.
• What are the three components of all control systems?

  • Receptors
  • Coordination centres
  • Effectors
• What is the function of a receptor in a control system?

  Receptors detect changes in the environment (stimuli).
• What is the function of a coordination centre?

  Coordination centres obtain and process information from receptors.
• What is the function of an effector?

  Effectors bring about responses to stimuli.
• What is the primary function of the nervous system?

  The nervous system allows the body to react to its surroundings and coordinate an appropriate response.
• How does a stimulus lead to a response in the body?

  A stimulus is converted into an electrical impulse by the receptors.
• What happens after the electrical impulse passes along sensory neurones?

  The electrical impulse passes to the central nervous system (CNS).
• What role does the CNS play in response coordination?

  The CNS coordinates an appropriate response and sends an electrical impulse along motor neurones to the effector.
• What is the sequence of events that describes how the nervous system works?

  Stimulus → receptor → coordinator → effector → response.
• What is a reflex action?

  A reflex action is an automatic and rapid response which does not involve any conscious input from the brain.
• Why are reflex actions important?

  Reflex actions aid survival by preventing harm to the body.
• Describe how a reflex action occurs via a reflex arc.

  • The stimulus is detected by a receptor.
  • An electrical impulse passes along a sensory neurone to the spinal cord (CNS).
  • At a synapse, a chemical diffuses and stimulates a new impulse in the relay neurone.
  • The same process occurs at a synapse between the relay neurone and the motor neurone.
  • At the effector, an appropriate response is carried out.
• What is the difference between a reflex pathway and a conscious pathway?

  In a reflex pathway, the coordination centre is a relay neurone in the spinal cord, while in a conscious pathway, it is in the conscious part of the brain.
• What is the function of the cerebral cortex?

  The cerebral cortex controls consciousness, intelligence, memory, and language.
• What is the function of the cerebellum?

  The cerebellum controls muscular coordination.
• What is the function of the medulla?

  The medulla controls unconscious activities such as breathing and heart rate.
• What stimuli are the receptors of the eye sensitive to?

  Receptors of the eye are sensitive to light intensity and colour.
• What are the two main functions of structures found within the eye?

  • Focusing on near or distant objects (accommodation).
  • Adapting to dim light.
• Describe the structure and function of the retina.

  The retina is a light-sensitive layer found at the back of the eye that sends impulses to the brain when stimulated by light.
• Describe the structure and function of the optic nerve.

  The optic nerve connects the eye and the brain, carrying impulses to the brain for image visualization.
• Describe the structure and function of the sclera.

  The sclera is the tough outer layer of the eye that protects its internal structures.
• Describe the structure and function of the cornea.

  The cornea is the curved transparent layer at the front of the eye that lets light in and focuses it onto the retina.
• Describe the structure and function of the iris.

  The iris is a muscle that controls the size of the pupil by contracting or relaxing, allowing the eye to adjust to different lighting conditions.
• Describe the structure and function of the ciliary muscles and suspensory ligaments.

  • The ciliary muscles and suspensory ligaments hold the lens in place.
  • They control the shape of the lens for focusing.
• Describe how the iris alters the size of the pupil in both bright and dim light.

  • Bright light: circular muscles contract, radial muscles relax - pupil smaller.
  • Dim light: circular muscles relax, radial muscles contract - pupil larger.
• What is accommodation in the context of vision?

  Accommodation is the alteration of the lens’ shape to focus on near or distant objects.
• What do the ciliary muscles and suspensory ligaments do in the eye?

  They hold the lens in place and control its shape.
• How does the iris alter the size of the pupil in bright and dim light?

  • Bright light: circular muscles contract, radial muscles relax, pupil smaller.
  • Dim light: circular muscles relax, radial muscles contract, pupil larger.
• What is accommodation in the context of the eye?

  It is the alteration of the lens’ shape to focus on near or distant objects.
• How does the eye focus on a nearby object?

  • Ciliary muscles contract.
  • Suspensory ligaments loosen.
  • Lens becomes thicker and more curved.
• How does the eye focus on a far away object?

  • Ciliary muscles relax.
  • Suspensory ligaments tighten.
  • Lens becomes thinner.
• What is myopia?

  Myopia is short-sightedness caused by the lens being too curved.
• How can myopia be treated?


  Myopia can be treated using glasses with a concave lens.
• What is hyperopia?

  Hyperopia is long-sightedness caused by the lens being too flat.
• How can hyperopia be treated?

  Hyperopia can be treated using glasses with a convex lens.
• What are the two types of contact lenses?

  • Hard: rigid material, long-lasting, must be kept sterile.
  • Soft: flexible material, shorter lifespan, more comfortable.