Homeostasis

• Define Homeostasis:

  The maintenance of a stable internal environment despite changes in external and internal factors
• Define Stimulus:

  A change in the environment that brings about a response
• Define Negative feedback.

  The mechanism that reverses a change to bring the system back to its optimum
• In multicellular organisms, the change necessary for survival is controlled by....

  • the nervous system
  • the endocrine system
• Define Cell Signalling:

  The communication between cells via electrical signals
• State the two major systems of communication that work by cell signalling:

  • neuronal
  • hormonal
• State the differences between the endocrine system and the nervous system:

  
  

  The Endocrine System:

  • releases hormones
  • transports in the bloodstream
  • recognised by specific target cells on organs
  • triggers a slower response
  • long term

  
  

  The Nervous System
• What factors effect enzyme activity in the body?

  • pH
  • Temperature
  • Presence of an aqueous environment
  • Presence of toxins or inhibitors
• Exergonic:

  A reaction that releases energy
• Name a hormone that is involved in a positive feedback reaction:

  Oxytocin
• What does oxytocin do in a positive feeback mechanism:

  increases the uterine contractions which stretch the cervix more

  • dilates the cervix
• If the body temperature drops by 10 ℃, the rate of enzyme-controlled reactions fall by half
• Endotherms are organisms that uses heat from its metabolic reactions to maintain body temperature
• Ectotherms are organisms that rely on external sources of heat to maintain body temperature.