Homeostasis
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
# Ectotherms
- Animals that use their surroundings to warm their bodies
| Advantages | Disadvantages |
|---|---|
| Less energy required | Requires ideal environment |
| Less food needed | Requires basking |
| No thermoregulatory functions needed | May 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