bio paper 2

• Homeostasis


  An organism's ability to regulate/control its internal conditions so crucial reactions (including those involving enzymes) can happen at the best rates
• Things that need to be regulated

  • Blood glucose concentration
  • Internal temperature
  • Water levels
• Sensory neurones


  Carry information as electrical impulses from receptors
• Relay neurones


  Carry electrical impulses from sensory neurones to motor neurones
• Motor neurones


  Carry instructions (electrical impulses) from the CNS to effectors
• Effectors


  Muscles and glands which respond to nervous impulses
• Synapse


  The connection between neurones where the nerve signal is transferred by chemicals which diffuse across the gap
• Thermoregulation


  1. Brain detects temperature

  2. Sends nervous and hormonal signals

  3. To effectors

  4. Sweat glands produce water which evaporates

  5. Blood vessels dilate/constrict
• Endocrine system


  System of glands that secrete hormones, to send signals to effectors transported via blood (slower than the nervous system)
• Pituitary gland


  Master gland that sends signals to other glands
• Pancreas


  Secretes insulin and glucagon to control blood sugar
• High blood glucose levels

  Pancreas secretes insulin, causes glucose to move from bloodstream to be used for respiration, excess glucose converted into glycogen as an energy store
• Type 1 diabetes


  Pancreas cannot produce (enough) insulin, injections needed
• Low blood glucose levels

  Pancreas secretes glucagon, causes liver to convert glycogen back into glucose, this is an example of negative feedback
• Type 2 diabetes


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

  1. Water is lost through exhalation, sweating, and urinating

  2. Excess water is removed from the body by kidneys to the bladder

  3. Water is mixed with urea to make urine

  4. Urea contains ammonia (NH3) from amino acids obtained from excess proteins broken down in the liver

  5. Kidneys also filter out glucose and useful minerals and ions for the body to use
• Too much water


  • Water moves in by osmosis, cell becomes turgid and could burst
  • Too little water, water moves out by osmosis, cell becomes flaccid
• ADH (antidiuretic hormone)


  From pituitary gland, causes tubules in kidneys to reabsorb more water into the bloodstream
• Water levels too high

  1. Less ADH is made

  2. More water is sent to the bladder to be excreted as urine
• This is an example of negative feedback, where the response to a change makes the conditions return to normal
• Positive feedback would be a chain reaction
• Kidneys not working properly

  1. Dialysis is needed, blood is filtered by a machine

  2. If not done, ammonia/urea build up will be poisonous
• Menstrual cycle


  1. Females born with eggs which start to mature at puberty

  2. FSH (Follicle Stimulating Hormone) from pituitary gland causes eggs to mature and ovaries to produce oestrogen

  3. Oestrogen causes uterus lining to thicken, stops FSH so no more eggs mature until next cycle

  4. LH (Luteinising Hormone) causes egg to be released which starts to travel towards the uterus

  5. Progesterone secreted by ovaries maintains the uterus lining
• Contraception


  1. FSH-inhibiting pills, no eggs mature

  2. Progesterone injections/implant to stop eggs being released

  3. Condom/diaphragm stops sperm entering vagina

  4. IUD (Copper coil) stops egg embedding in lining

  5. Clamping oviduct or vasectomy (cutting sperm tubes)
• Fertility treatments


  • FSH/LH injections-simple
  • IVF- (in-vitro fertilisation)-hard/expensive
• IVF process


  1. Eggs collected after inducing release

  2. Eggs fertilised in a lab

  3. Embryos inserted back into woman's uterus
• Success rate of fertility treatments is very low
• Fertility treatments can potentially cause multiple embryos to develop
• Adrenaline


  • Released by the adrenal glands (attached to the top of the kidneys)
  • Increases blood flow and breathing rate to prepare the body for fight or flight
• Thyroxine


  • Secreted by the thyroid gland
  • Controls the body's metabolic rate
• Regulation of thyroxine production

  1. Hypothalamus releases TRH

  2. Pituitary gland releases TSH

  3. Thyroid gland releases more thyroxine
• Regulation of thyroxine production is an example of negative feedback
• Gibberellins


  Plant hormone that induces germination, promotes flowering, and increases fruit size
• Ethene


  Plant hormone that causes ripening, e.g. bananas release it
• Auxins


  • Plant hormone that causes shoot bending towards light (phototropism) and root growth downwards (geotropism)
  • Can be used as weed killers, rooting powders, and to promote growth in tissue cultures
• Meiosis


  1. Chromosomes in diploid cell (2n) pair up and genes are swapped

  2. Cell divides to produce two diploid cells

  3. Those cells divide again to produce four haploid cells (gametes)
• Meiosis produces genetically different cells compared to mitosis which produces identical cells
• Sexual reproduction


  • Involves gametes (pollen and egg) from two parents
  • Offspring can become better adapted to the environment
• Asexual reproduction


  • Occurs by mitosis, producing genetically identical offspring (clones)
  • Only one organism is needed to reproduce
• Some organisms like malaria parasites and fungi can reproduce both sexually and asexually