BIO PAPER 2

• Homeostasis


  An organism's ability to regulate internal conditions (eg. blood glucose concentration, internal temperature, water levels).
• Nervous system:

  Receptor detects a change due to stimulus sending electrical signal to spine through sensory and relay neurones (nerve cells). Signal travels across synapse by a neurotransmitter chemical. Once at the spine, the signal can go to the brain where you can make the conscious decision to act. This signal goes back to an effector (eg. muscle in arm) via relay and motor neurones to move.
• Reflex arc


  Signal bypasses brain, goes straight through the spine to the effector. Much faster than a conscious decision. Glands can also be effectors - they secrete chemicals.
• Reaction times practical

  • drop ruler between finger and thumb
  • measure distance fallen before caught, repeat, calculate mean
  • Independent variable = stimulant or depressant
• Cerebral cortex


  Higher functions: memory, speech, problem solving. Large, top of head.
• Cerebellum


  Motor skills: movement, balance, coordination. Back, bottom of head.
• Medulla Oblongata


  Unconscious actions: heart and breathing rate, signals to adrenal glands
• Eye focusing on farther objects

  Ciliary muscles relax, suspensory ligaments tighten, results in thin lens so light refracts only a bit and focuses light on retina.
• Eye focusing on close objects

  Ciliary muscles contract, suspensory ligaments slacken, results in thick lens so light is refracted more and light focuses on retina.
• Retina cells

  • rods only detect light intensity
  • cones sensitive to red, blue or green wavelengths of light provide colour information
  • these signals travel to the brain via the optic nerve
• Myopia is short-sightedness, hyperopia is long-sightedness. Both can be treated with glasses, contact lenses or laser eye surgery (changing the shape of cornea in surgery).
• Thermoregulation - hot

  sweat glands produce water which evaporates, taking away heat. Blood vessels also dilate (vasodilation).
• Thermoregulation- cold

  Hairs stand on end to trap air (layer of insulation). Shivering - muscles produce more heat. Blood vessels contract (vasoconstriction).
• Pituitary gland


  'master' gland, sends signals to other glands
• Thyroid

  Controls growth, metabolism and more (in throat area).
• Pancreas

  Secretes insulin (and glucagon) to control blood sugar (between kidneys)
• Adrenal glands

  Release adrenaline (above kidneys).
• Controlling blood sugar - high blood glucose levels

  • Pancreas secretes insulin
  • Causes glucose to move from bloodstream into cells to be used for respiration
  • Excess glucose converted into glycogen as energy store
• Controlling blood sugar - low blood glucose levels

  • Pancreas secretes glucagon
  • causes liver and muscles to convert glycogen back into glucose (negative feedback)
• Type 1 Diabetes

  Pancreas cannot produce (enough) insulin, injections needed.
• Type 2 Diabetes

  Cells do not absorb glucose as they should, obesity increases risk of developing.
• Controlling water + nitrogen levels

  Excess water is removed by kidneys to the bladder. There, it mixes with urea to make urine. Urea contains ammonia (NH3) from amino acids obtained from excess proteins broken down in liver.
• Too much water in body = water moves in by osmosis, cell becomes turgid and could burst.
• Too little water in body = water moves out by osmosis, cell becomes flaccid.
• Kidneys also filter out glucose and useful minerals and ions for the body to use. If kidneys do not work, dialysis is needed (blood filtered by machine). If not done, ammonia/urea build up will be poisonous.
• ADH hormone

  Produced in pituitary gland, causes kidney tubules to reabsorb more water into bloodstream. If water levels are too high, less ADH is produced, so more water is sent to bladder to leave body as urine (negative feedback).
• FSH - Follicle Stimulating Hormone

  From pituitary gland, causes an egg to mature and for ovaries to produce oestrogen. (first step in cycle)
• Oestrogen

  Causes uterus lining to thicken, inhibits FSH so no more eggs mature until next cycle. Also causes pituitary gland to secrete LH. (second in cycle)
• LH - Luteinising Hormone

  Causes egg to be released, starts to travel to uterus. (third in process)
• Progesterone

  Secreted by ovaries to maintain uterus lining. (fourth in process)
• Contraception

  • FSH inhibiting pills
  • Progesterone injection/implant (stops eggs being released)
  • IUD (copper coil) stops egg embedding in lining
• Fertility treatments

  • FSH/LH injections (simple)
  • IVF (hard and expensive)- released eggs collected to be fertilised, success rate low and can potentially cause multiple embryos
• Adrenal glands

  Release adrenaline into body, increasing blood flow and breathing rate to prepare for 'fight or flight'.
• Thyroxine

  Controls body's metabolic rate.

  Too low = hypothalamus in brain releases TRH, causing pituitary gland to release TSH which causes thyroid to release more thyroxine (negative feedback).
• Plant hormones - gibberellins

  • induce germination
  • promote flowering
  • increase fruit size
• Plant hormones - ethene

  • Causes ripening (bananas release this, have to be stored separately).
• Plant hormones - auxins


  Sunlight destroys it, causing cells on shaded side to grow quicker. Shoot bends towards sun (phototropism).

  Also gathers on bottom of roots, inhibits growth, grows downwards (geotropism).
• Geotropism practical


  seeds on damp cotton wool in petri dish stood on edge. Turn 90 degrees in a few days to observe geotropism in roots.
• Meiosis 


  The process by which gametes are made - genetically different from parent cells.
• Meiosis process

  • chromosomes in diploid cell (23 pairs) copied
  • similar chromosomes pair up and genes swapped between them
  • cell divides producing 2 diploid cells
  • divide again producing 4 haploid cells (gametes)