What is homeostasis?
The maintenance of a stable internal environment within restricted limits in organisms, despite changes in external conditions.
Why is homeostasis vital for organism survival?
- It keeps the internal environment constant for metabolic reactions
- Ensures cells function properly and avoid damage
- Helps organisms respond and adapt to external changes
What are the roles of receptors, coordinators, and effectors in homeostasis?
Receptors: detect changes in the internal and external environment.
Coordinators: process this information and send instructions.
Effectors: carry out the response to restore optimum conditions.
What is negative feedback?
Negative feedback detects changes from the optimum and activates responses that reverse the change, restoring optimal conditions.
How is blood glucose regulated by negative feedback?
Insulin lowers blood glucose when it’s too high; glucagon raises it when it’s too low.
Why is maintaining temperature and pH important in the body?
Changes can impair enzymes action
Extreme levels can denature enzymes
What is positive feedback?
Positive feedback amplifies change rather than reversing them.
A deviation from the optimum causes changes that result in a greater deviation from the optimum point.
Name two biological examples of positive feedback.
Blood clotting - clotting factors activate further clotting
Labour - Oxytocin stimulates more contractions
What is cell signalling and how does it occur?
Cell signalling is how cells communicate, often via hormones travelling in the bloodstream to target cells with specific receptors.
Define thermoregulation.
The maintenance of a relatively constant core body temperature (to ensure optimal enzyme activity).
What is the main difference between ectotherms and endotherms?
Ectotherms rely on environmental heat (e.g. reptiles, fish).
Endotherms generate heat internally via metabolism (e.g. mammals, birds).
What are key characteristics of ectotherms?
- Temperature controlled by behavioural changes (e.g. basking in sun or seeking shelter).
- Body temperature varies with the environment.
- Low metabolic heat production.
- Activity depends on external temperature (warmer environmental temperatures = increased activity)
What are key characteristics of endotherms?
- Regulate temperature internally and behaviourally.
- Relatively stable body temperature.
- High metabolic rate.
- Active in a range of environments.
How do mammals reduce high body temperature?
- Increased sweating - sweat glands produce more sweat, evaporation removes heat.
- Hair flattening - erector pili muscles relax, reduces insulation.
- Vasodilation - arterioles near skin dilate, increasing blood flow to surface and radiates heat from skin.
How do mammals increase low body temperature?
- Shivering - skeletal muscles contract, increased respiration and generate heat
*Reduce sweating
- Erecting hair - erector pili muscles contract, raising hairs and increase insulation
- Vasoconstriction - arterioles near skin constrict, reducing blood flow to surface
- Releasing adrenaline and thyroxine - hormones that speed up cellular metabolism, more heat.
What role does the hypothalamus play in thermoregulation?
It detects body temperature via peripheral receptors in skin, then signals effectors (muscles, sweat glands) to respond and restore temperature balance.
