Biology Paper 2 - Homeostasis and Response

• Homeostasis


  The regulation of the internal conditions of the body
• Automatic Control System


  1. Stimulus

  2. Receptors

  3. Co-ordination centre

  4. Effector

  5. Response
• Stimulus


  The change in the body's environment (internal conditions)
• Receptors


  Pick up the change in the body and pass the information to a coordination centre
• Coordination centre


  Includes the brain, spinal cord and pancreas
• Effector


  Usually a muscle or gland, that brings about the response that counteracts the change
• Nervous System


  1. Stimulus detected by receptor

  2. Electrical impulse sent through sensory neuron

  3. Reaches synapse, electrical transmitters sent to relay neuron

  4. Information sent through motor neuron

  5. Effector (muscle contracts or gland secretes) brings about response
• Central Nervous System


  Comprising the brain and spinal cord, serves as the primary coordination centre of the nervous system
• Required Practical 7: Reaction Time


  Measures how quickly a person can react to a stimulus

  IV: The person

  DV: Reaction time

  CV: Conditions in the room, such as distance between thumb and 1st finger
• We can also measure the effect of certain chemicals on reaction time (e.g., caffeine). However, we must ensure there are no health risks.
• Cerebral Cortex


  The highly folded outer part of the brain that controls language, memory and consciousness
• Medulla


  Controls heart rate and breathing rate
• Cerebellum


  Controls our balance and coordination
• MRI scans can be used to investigate the brain. However, the brain is very difficult to access because the skull protects it and has an extremely complex structure.
• Cornea


  Their job is to start focusing on the light rays
• Iris


  The coloured part of the eye
• Optic nerve


  Sends electrical impulses to the brain from the eye
• Sclera


  The tough outer part of the eye
• Retina


  The back of the eye, where light is focused. It contains receptor cells to light
• Pupil reflex in the eye

  1. Muscles contract in dark room, pupil becomes bigger

  2. Pupil gets smaller in bright room, allowing less light to enter
• Myopia


  Short-sightedness and a concave lens are required to fix this
• Hyperopia


  Long-sightedness and a convex lens is needed to fix this
• Accommodation


  The ability to change the shape of a lens to focus on near and distant objects
• Ciliary muscles


  Connected to the lens by fibres called suspensory ligaments, which loosen to thicken the lens. Alternatively, the suspensory ligaments stretch the lens thin when the ciliary muscles relax.
• Thermoregulatory centre


  The brain, which contains receptors sensitive to the temperature of the blood
• Skin temperature receptors


  Send electrical impulses down sensory neurons to the brain
• Thermoregulation when body temperature is too high

  Sweat glands released on skin's surface, evaporation cools body
• Thermoregulation when body temperature is too low

  Vasoconstriction occurs, capillaries become narrower, less blood flow and heat loss
• Endocrine system


  Contains several glands that secrete hormones into the bloodstream
• Ovaries and testes


  Release hormones involved in puberty and reproduction
• Thyroid gland


  Produces hormones involved in growth
• Adrenal glands


  Release the hormone adrenaline
• Glucose


  Needed by every cell to release energy by respiration
• Pancreas


  Monitors the blood glucose concentration and produces insulin
• Insulin


  Triggers muscle and glucose cells to store excess glucose as glycogen
• Type 2 diabetes


  The body stops responding to insulin cells
• Control of blood glucose when it falls

  Glucagon converts glycogen back into glucose
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Ways to lose water

  Via the lungs when we exhale, sweating and via the kidneys in urine
• Kidney filtration and reabsorption

  Blood passes through capillaries, small molecules filtered out and passed through a tube, then some water and ions reabsorbed back into blood (selective reabsorption), urea, excess ions, glucose and water released as urine