5.1.1

• homeostasis

  the maintenance of a constant internal environment via physiological control systems that coordinate the activity of different organs
• factors that affect cell activity

  temperature

  water levels

  glucose levels
• how does temperature affect cell activity

  low - slow metabolic rate due to less kinetic energy and collisions

  high - proteins denature , cell membrane is damaged
• how does water levels affect cell activity

  low - water moves out of cell into tissue fluid slowing metabolic reactions

  high - water moves into cell from tissue fluid causing swelling / bursting
• how does glucose levels affect cell activity

  low - slow respiration rate , less energy for reaction

  high - water moves out of cell into tissue fluid
• what does homeostasis occur in response to?


  External and internal changes outside of a certain threshold
• negative feedback loop


  when a deviation from a set limit is detected in the body by a receptor , mechanisms are put in place to restore the conditions back to their set limit
• fast cell communication occurs via

  the nervous system
• slow cell communication occurs via

  the endocrine system
• what does homeostasis control?


  body temperature , blood pH , blood glucose , blood water potential
• positive feedback loop


  When a deviation from the set limits triggers a response to increase the deviation further
• example of positive feedback loop


  dilation of cervix and contractions of uterus during birth
• what do metabolic reactions keep alive


  all cells
• ectotherms


  cannot regulate their internal temperature through metabolic reactions so change their behaviour instead
• how do ectotherms that live in water regulate their body temperature


  their body has the same temperature as the water and due to waters high specific heat capacity the temperature remains constant
• how do ectotherms that live on land regulate their body temperature


  sit in direct sunlight and hot rocks to absorb the suns heat
• endotherms


  Regulate their internal temperature using a nervous response. Body heat is generated via metabolic reactions
• signalling between distant cells , a nervous response

  Peripheral temperature receptors on the skin detect an external change

  The sensory neurones sense this change and relay neurones carry this impulse to the hypothalamus

  The hypothalamus coordinates a response to maintain internal conditions

  Relay neurones carry this impulse to motor neurones and effectors that carry out the response
• what do endotherms do when they are too hot

  sweat

  vasodilation

  arrector pili relax lowering fur / hair
• what do endotherms do when they are too cold

  shivering

  vasoconstriction

  arrector pili contract raising hair / fur
• what else do endotherms do when they are the wrong temperature?

  modify their behaviour

  in / out of sun

  more / less clothes
• why is it more difficult for insects to maintain their body temperature than humans?

  Insects are smaller and have a large surface area to volume ratio

  Insects have greater rate of heat loss

  Mammals and birds have more effective / thicker insulation
• ways thermoregulation in endotherms differs?

  different internal body temperature

  amount of behavioural vs physiological responses used

  range that internal body temperature may be

  amount of hair for insulation
• positive feedback in hypothermia


  Lower temperature reduces kinetic energy of molecules

  Enzyme activity reduced

  Respiration rate / metabolism rate reduced

  Less internal heat generated

  So that body temperature drops further
• receptors in the hypothalamus detect what?


  core body temperature and blood temperature