BIOLOGY PAPER 2

• What is homeostasis?


  Maintaining a stable internal environment
• What is negative feedback?


  A response to a change in the body that counteracts or opposes the initial change.
• What is positive feedback?


  Body ENHANCES original stimulus to make deviation greater
• What is the CNS?

  central nervous system; brain and spinal cord
• What are sensory neurones?


  The neurones that carry information as electrical impulses from the receptors to the CNS
• What are motor neurones?

  The neurones that carry electrical impulses from the CNS to effectors
• What are relay neurones?


  Carries messages from one part of the CNS to another. (Allow communication between sensory and motor neurones.)
• What are effectors?


  All your muscles and glands, which respond to nervous impulses
• What are receptors?


  Cells that detect stimuli
• Give an example of a receptor?

  sense receptors in the skin or retina in eye is covered in light receptor cells.
• What are synapses?


  gaps/ connections between neurones
• How do the electrical impulses travel across synapses?

  They diffuse over the gap as chemicals
• What are reflexes?


  Rapid, automatic responses to a certain stimuli that dont involve the conscious part of the brain.
• Give an example of a stimulus that causes a reflex reaction?

  Skin touches something hot and automatically pulls away from it.
• Which CNS does reflex arcs go through?

  The spinal chord.
• How is a reflex reaction different to a normal one?

  Much quicker because you dont have to think about it, does not use the conscious part of the brain, is involuntary.
• Describe the pathway of the reflex action of a hand pulling away from a hot pan from stimulus to effector?

  1) The receptor cells in the skin detect the stimulus (hot pan)

  2) The receptors send electrical impulses along the sensory neurones to a relay neurone in the CNS (spinal chord in a reflex arc).

  3) The relay neurones send the impulse to motor neurones.

  4) The electrical impulse diffuses over the synapses as chemicals.

  5) The motor neurones carry the impulse to the effectors which then carry out a response (the muscle contracts to move it away).
• Describe the required practical for investigating reaction times?

  E.g testing how caffeine effects reaction times.

  1) The person tested should sit with their arm resting on the edge of a table.

  2) Hold a ruler vertically between their thumb and forefinger and make sure the zero end of the ruler is level with their thumb and forefinger.

  3) The person being tested should try to catch the ruler as soon as it drops. They should have no indication of when it will drop.

  4) Measure the reaction time by looking at the number that their fingers are closest too on the ruler. The further down the ruler, the slower the reaction time.

  5) The person tested should then have a set volume of a caffeinated drink.

  6) Control variables include the person being tested, the height the ruler is dropped from and the hand catching the ruler.
• What does the cerebral cortex do?


  Responsible for consciousness, intelligence, memory and language
• What does the medulla do?

  It controls your unconscious activities, like breathing and your heartbeat
• What does the cerebellum do?

  Controls balance, equilibrium, and muscle coordination.
• Label the correct parts of the eye

  1) iris

  2) Cornea

  3) pupil

  4) lens

  5) ciliary muscle

  6) sclera

  7) optic nerve

  8) retina

  
• What does the iris do?

  Contains muscles that control how much light enters the pupil by changing its diameter.
• What does the cornea do?

  Refracts light into the eye
• What does the pupil do?

  -Allows the amount of light through

  -Shrinks when there is lots of light

  -Dilates when there is not much light
• What does the lens do?

  Focuses light onto retina
• What do the ciliary muscles do?

  adjust the shape of the lens to make it more or less curved
• What does the optic nerve do?

  Carries impulses from the receptors on the retina to the brain
• What does the sclera do?

  protects the eye and maintains shape.
• What is the iris reflex?

  Pupil goes smaller when there is a lot of light- the circular muscles in the iris contract and the radial muscles relax, reducing the amount of light entering the eye.

  
  

  Pupil goes bigger when there is not a lot of light-the circular muscles relax and the radial muscles contract, increasing the amount of light entering the eye.
• How does the eye focus on near objects?

  1) Ciliary muscles contract which slackens the suspensoirs ligaments

  2) The lens becomes fatter/more curved

  3) This increases the amount by which it refracts light.
• How does the eye focus on distant objects?

  1) The ciliary muscles relax, which tightens the suspensoirs ligaments.

  2) This makes the lens thinner/less curved

  3) This refracts the light by a smaller amount.
• What is myopia and how is it corrected?

  - Shortsightedness- the eyeball is too long so the image forms in front of the retina, unfocused.

  - Concave lenses curves inwards, so the light can focus on the retina.
• What is hyperopia and how is it corrected?

  - longsightedness- the eyeball is too short so the images are focused behind the retina.

  - Convex lenses curve outwards so the light can focus on the retina.
• How is body temperature regulated?

  Thermoregulatory centre in the brain which contains receptors that are sensitive to the temperature of the blood flowing through the brain. It also receives impulses from temperature receptors in the skin.
• How does the body respond when you are too hot?

  1) Temperature receptors detect that the temp is too high

  2) The thermoregulatory centre receives information from the temperature receptors and triggers the effectors automatically.

  3) The effector (sweat glands) produce sweat and this evaporates from the skin to the environment.

  4) The blood vessels dial ate so more blood flows closer to the surface so the heat energy is transferred into the environment.
• How does the body respond when you are too cold?

  1) Temperature receptors detect that temp is too low

  2) The thermoregulatory system receives information from the temp receptors and triggers the effectors automatically.

  3) The effectors carry out responses: Hair stands up to trap an insulating layer of air

  4) Blood vessels constrict so heat cannot be lost through the skin

  5) Muscles contract causing shivering which needs respiration, which transfers some energy to warm the body.
• What are hormones?


  chemical messengers secreted by the endocrine glands
• Give differences between endocrine and nervous system?

  - Endocrine is slower

  - Endocrine acts for a longer time

  - Nervous system acts in a very precise way whereas the endocrine system acts in a more general way.
• Describe the fight or flight response

  - adrenaline is released into the body produced by the adrenal gland.

  - Triggers mechanisms that prepare the body for 'fight or flight' e.g increased heart rate