OCR A2 Biology F214: Communication & Homeostatis



  • All living organisms must detect and respond to changes in their environment in order to survive, e.g. fight/flight response.
  • Multicellular organisms organise and communicate the response to change using the nervous and endocrine systems.

Cell Signalling

  • Is...the communication between cells that allows effective coordination of a response.
  • Cell signals may be electrical- by means of neurones, which is faster and short-term, or chemical- by means of hormones, which is slower and long-term.


  • Is...the maintenance of a constant internal environment within an organism despite external changes. Organisms can only function if internal conditions such as temperature, pH, water potential and blood glucose levels are kept within a narrow range.
  • NEGATIVE FEEDBACK is a process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained. 
  • Any deviation from the norm results in a response being taken that restores the norm.


  • Stimulus = any change in the environment that causes a response. Receptor = a cell that detects the stimulus. Coordinator = the organ that controls the actions taken for a response. Effector = brings about a response (muscle/gland). Response = a change in behaviour or physiology




Excellent notes thanks