F214 - Communication

• Cell signalling - communication between cells using nerves or hormones

• Homeostasis - the maintenance of the internal environment in a constant state despite external changes

• Stimulus - any change in the internal or external environment

• Response - a change in behaviour or physiology as a result of a change in the environment

Homeostasis

• Temperature - low temperatures slow down metabolic reactions and high temperatures denature enzymes.

• Amount of water - A lack of water in the tissue fluid causes water to move out of the cell by osmosis, which causes metabolic reactions to slow down, too much water causes water to move into the tissue fluid causing the cell to swell or even burst.

• Concentration of glucose - glucose is needed by cells for respiration, so a lack of it causes respiration to slow down. Too much can cause water to move out of cells by osmosis.

Maintaining a constant environment involves a mechanism called negative feedback. A negative feedback system requires a…