16.1 Principles of homeostasis

Question 1

What is homeostasis

Answer 1

The maintenance of an internal environment within restricted limits of an organism

Question 2

Why is homeostasis important

Answer 2

1. Maintain a constant pH - proteins are sensitive to pH changes and serious fluctuations away from the optimum can have adverse effects
2. Maintain water potential - cells can burst and die
3. Geographical advantages - Organisms with the ability to maintain a constant environment are more independent of changes in the external environment.

Question 3

What are the stages of controlling a self-regulating system

Answer 3

The optimum point, the point at which the system operates best. This is monitored by a Receptor, which detects any deviation from the optimum point and informs the Coordinator, which coordinates information from receptors and sends instructions to an appropriate Effector, often a muscle or gland, which brings about the changes needed to return the system to the optimum point. This return creates a feedback mechanism.

Question 4

What is negative feedback

Answer 4

Where a change triggers a response which reduces the effect of a change

Question 5

What is positive feedback

Answer 5

Where a change from an optimum causes changes that result in an even greater deviation from the normal

Question 6

What is an endotherm

Answer 6

An organism that derives most of their heat from metabolic activities that take place inside the body (inside heat)

Question 7

What is an ectotherm

Answer 7

An organism that derives most of their heat from outside sources, namely the environment. (outside heat)

Question 8

What is the overarching principle of ectotherms regulating heat

Answer 8

They control their body temperature by adapting their behaviour to changes in the external temperature

Question 9

How do ectotherms regulate temperature

Answer 9

1. Exposing themselves to the Sun
2. Taking shelter to hide from the sun
3. Gaining warmth from the ground

Question 10

How do endotherms regulate heat in a cold environment

Answer 10

1. Vasoconstriction - the diameter of arterioles near the surface is made smaller.
2. Shivering - The muscle undergo involuntary rhythmic contractions that produce metabolic heat
3. Raising of hair - traps a layer of still air which is a good insulator
4. Increased metabolic rate
5. Decrease in sweating, less heat evaporated
6. Behavioural mechanisms, e.g. sheltering from the wind

Question 11

How do endotherms regulate heat in a hot environment

Answer 11

1. Vasodilation - the diameter of the arterioles near the surface of the skin become larger. This allows warm blood to pass close to the skin and heat is radiated out
2. Increased sweating - evaporate water from the skin surfaces requires heat energy
3. Lowering of body hair - reduces the thickness of the insulating layer and allows more heat to be released
4. Behavioural mechanisms - avoid the heat of the day by sheltering in burrows