• Living things have an internal environment

    • the environment changing puts stress on the organism
    • organisms need to maintain specific conditions
    • a stimulus invokes a response
  • Internal Environments:

    • If an organism is multicellular many cells are not exposed externally
    • protected by skin/bark and bathed in tissue fluid
    • Waste products diffuse from cells
      • Accumulation of waste is a stimulus
      • Cells need to respond
      • Waste needs to be removed
      • Wast enters the blood and is carried away
      • Blood concentrations must be closely monitored
  • A good communication system needs:

    • To cover the whole body
    • To allow cells to communicate
    • To allow specific communication
    • To allow rapid communication
    • To enable short and long term responses

Negative feedback

  • A change to an internal environment is detected
  • Change is signalled to other cells
  • A response is invoked to reverse the change

Negative feedback requires:

  • receptors
  • communications system
  • effector cells
  • conditions fluctuate around a set point

Positive feedback

  • Less common

  • Increases the original change

  • Useful sometimes

  • Oxytocin increases uterus contractions

Temperature Control

  • Animals that use their surroundings to warm their bodies
Less energy requiredRequires ideal environment
Less food neededRequires basking
No thermoregulatory functions neededMay not be capable of activity over winter
Can go longer without food
More energy used for growth

Temperature regulation in ectotherms:

  • Exposed body to the sun
    • increases temperature
  • Increase breathing movements
    • reduces temperature
  • Orientate body away from sun
    • reduces temperature
  • Hide in burrow
    • reduce temperature
  • Orientate to sun
    • increases temperature
  • Alter body shape
    • increases temperature
  • Change heart rate
    • Increase or decrease