Homeostasis is the maintenance of a stable internal environment within restricted limits in organisms.

This ensures that cells function normally despite external changes.

1. Maintains a constant internal environment for metabolic reactions
2. Allows cells to function normally and avoid damage
3. Helps organisms respond to and adapt to external changes

1. Receptor - detects a derivation from the optimum point (stimulus)
2. Coordinator - receives and interprets information from receptors and sends instructions to an appropriate effector
3. Effector - often a muscle or gland, brings about responses needed to return the system to the optimum point

Negative feedback is when a derivation from the optimum point leads to changes that bring the system back to the optimum point.

Positive feedback occurs when a deviation from an optimum causes changes that result in an even greater deviation from the optimum point.

1. Temperature - a derivation from the optimum point can impair the action of enzymes
2. Blood pH - a derivation from the optimum point can impair the action of enzymes
3. Water potential in blood and tissue fluid - prevents cells from shrinking or bursting due to osmosis
4. Blood glucose concentration - helps maintain water potential and provides glucose for respiration

The optimum point is the point at which the system operates best.