biology paper 2

• homeostasis-regulations of conditions in your body to maintain a stable environment
• negative feedback-when the level of something gets too high or too low negative feedback brings it back to normal
• CNS-brain and spinal cord
• sensory neurones-neurons that carry information as electrical impulses from the receptors to the CNS
• motor neurones-neurones that carry electrical impulses from the CNS to effectors
• effectors-all your muscles and glands that respond to nervous impulses
• receptors-cell that detects stimuli
• connection between two neurones is called a synapse
• nerve signal is transferred by chemicals that diffuse across the gap
• reflexes are rapid automatic unconscious responses to a stimuli
• reflex arc

  stimuluses detected by receptors

  impulses are sent across a sensory neurone to the CNS

  when impulses reach a synapse between the sensory neurone and a relay neurone they trigger chemicals to be releases and these cause the impulses to be sent across a relay neurone

  same thing happens across a motor neurone

  impulses travel along motor neurone to the effector

  muscle contracts
• cerebral cortex- outer layer of brain, responsible for conscious thought and memory
• medulla- the part of the brain that controls the heart rate and breathing rate
• cerebellum-responsible for muscle coordination and balance
• methods to study the brain-look at people with brain damage,electrically stimulate brain,MRI
• CORNEA- transparent layer of the eye that refracts light and focuses it on the retina
• iris- controls the size of the pupil, which controls the amount of light entering the eye
• lens- refracts light, focuses it on the retina
• optic nerve- carries impulses from the retina to the brain
• in a very bright light-circular muscles contract and radial muscles relax which makes the pupil smaller
• focusing on a near object-ciliary muscles contract and suspensory ligaments slacken so the lens becomes more curved
• when your too hot

  hairs lie flat

  sweat is produced

  blood vessels dilate
• when your too cold

  hairs stand up

  no sweat

  vasoconstriction

  shiver
• hormones are chemical molecules released in the blood
• pituitary gland- releases hormones that control other glands
• thyroid- produces thyroxine, regulates metabolism, and controls body temperature
• adrenal gland- produces adrenaline and cortisol
• pancreas- produces insulin and glucagon, regulates blood glucose
• type one diabetes- pancreas produces little or no insulin
• type two diabetes- insulin resistance, pancreas can't produce enough insulin
• substances removed from the body in urine include

  urea

  ions

  water
• FSH-causes an egg to mature
• oestrogen- female sex hormone produced by ovaries, stimulates the development of the uterus
• LH-stimulates release of an egg
• auxin is a plant hormone that controls growth near the tips of shoots and roots
• shoots grow towards light
• more auxin is produced on the lower side when a shoot is growing sideways
• auxins have many uses

  killing weeds

  growing from cuttings with rooting powder

  growing cells in tissue culture
• gibberellin

  stimulates seed germination ,stem growth and flowering
• ethene stimulates ripening of fruit