2.77b

2.77 Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis

• The negative feedback loop is a method of control and maintaining constant conditions.
• In the case of humans this is the idea of our fixed point is of a body temperature around 37/38 degrees centigrade.
• The receptor of humans is known as the Hypothalamus which responds to a stimulus (temperature)
• If the body temperature needs to be increased or decreased this is brought about by the effector e.g skin.
• The response would either be an inc or dec in body temp. which would in turn feedback to the receptor.
• A new output would be produced 
• A major component to the maintenance of body temperature in the skin are the sweat glands.
• Also the capillary network which allows blood to move closer or further away from the surface of the skin.
• If the body temperature stimulates responses in the skin which brings about the cooling of the skin, e.g. sweating and blood flow to the surface of the skin increases, blood vessels dilate which increases the change of heat to the outside of the body (cooling of the blood).
• In a cold environment the example would be shivering or the rise of hairs

2.77a

2.77 Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis

• Homeo refers to something being the same and stasis refers to something being of fixed point or a set of conditions
• Homeostasis is the idea that conditions are kept the same or constant
• Thermic refers to temperature
• Homeothermic is the idea of maintaining the same temperature
• Mammals are homeothermic organisms that carry out a process caused thermoregulation
• Thermoregulation is an example of homeostasis
• Other organisms vary with environmental temperatures
• The reason why mammals wish to maintain a constant body temperature is because they wish to maintain body temperatures at optimum temperature which results in high rates of reaction

2.76

2.76 Understand that organisms are able to respond to changes in their environment.

• S for MRS GREN stands for sensitivity
• Types of changes in the environment include light, temperature, pressure and chemical
• Organisms are required to have receptors in order to detect changes in environment
• And in order to respond to changes in environment organisms must have effectors
• Its the response that ensures organisms are able to survive the changes of environment