Thermoregulation

Question 1

What is the purpose of homeostatic mechanisms?

Answer 1

To help organisms keep their internal body conditions within restricted limits

Question 2

What is a key factor that needs to be controlled?

Answer 2

Temperature

Question 3

Why should temperature be controlled?

Answer 3

A stable core temperature is vital for enzyme activity

Question 4

What is the result of lower temperatures?

Answer 4

Lower temperatures reduce the kinetic energy available for molecules and slow down chemical reactions

Question 5

What is the effect of higher temperatures?

Answer 5

Higher temperatures speed up reactions up to a point, above which the rate of reaction drops sharply as the enzyme begins to denature

Question 6

What is thermoregulation?

Answer 6

The control of internal body temperature

Question 7

What are the two groups involved in thermoregulatory mechanisms?

Answer 7

Endotherms and ectotherms

Question 8

What are endotherms

Answer 8

Animals that possess physiological mechanisms for the maintenance of internal body temperature

Question 9

What are ectotherms

Answer 9

Animals that rely on behavioural mechanisms to ensure to maintain internal body temperature, e.g. by moving in and out of the sun or huddling together

Question 10

Give an example of endotherms

Answer 10

Mammals and birds

Question 11

Give an example of ectotherms

Answer 11

Reptiles and amphibians

Question 12

What are the endothermic responses to high body temperature

Answer 12

• Vasodilation
• Sweating
• Flattening of hairs

Question 13

How does vasodilation occur

Answer 13

During vasodilation the muscles in the walls of arterioles relax, causing dilation and allowing more blood to flow into skin capillaries - causing heat to be lost by radiation

Question 14

Describe the mechanism of sweating

Answer 14

Sweat is secreted by sweat glands in the skin, which cools the skin by evaporation (heat energy from the body is used to convert liquid into water vapour)

Question 15

When is sweating less effective?

Answer 15

In humid environments as there is a reduced water vapour concentration gradient between the skin and air when humidity is high

Question 16

Describe the mechanism of hairs flattening

Answer 16

The hair erector muscles in the skin relax, causing hairs to lie flat.
This stops them forming an insulating layer of air and instead allows air to circulate over skin, removing heat as it is lost by radiation

Question 17

Give the endothermic responses to low body temperature

Answer 17

• Vasoconstriction
• Increased metabolic rate
• Shivering
• Erection of hairs

Question 18

Describe the mechanism of vasoconstriction

Answer 18

• During vasoconstriction the muscles in arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through skin capillaries.
  Therefore heat loss by radiation is reduced

Question 19

Describe the mechanism of increased metabolic rate

Answer 19

• Most of the metabolic reactions in the body are exothermic and this provided warmth to the body
• In cold environments, the hormone thyroxine increases the basal metabolic rate, increasing heat production in the body -> thyroxine is released by the thyroid gland

Question 20

Describe the mechanism of shivering

Answer 20

Muscles contract and relax repeatedly in quick succession
The metabolic reactions required to power this muscle contraction releases heat energy to warm the blood and raise the core body temperature

Question 21

Describe the mechanism of erection of hairs

Answer 21

The hair erector muscles in the skin contract, causing hairs to stand on end. This traps an insulating layer of air over the skins surface, reducing heat loss by radiation

Question 22

How do ectotherms warm up?

Answer 22

• Seek out the sun or warmer surfaces and ‘bask’ in these locations as they warm until their body temperature has been increased sufficiently
• Huddle together to retain heat that may have been gained from the sun earlier in the day

Question 23

How do ectotherms cool down?

Answer 23

• Seek shade
• Move their bodies into water

Question 24

Why do ectotherms use behavioural mechanisms?

Answer 24

As they do not have the ability to respond to fluctuating environmental changes via internal temperature regulation mechanisms

Question 25

How is the behaviour of ectotherms restricted?

Answer 25

By environmental temperatures, meaning they can’t easily colonise habitats that are hot or cold

Question 26

What type of environments can ectotherms survive in?

Answer 26

They can survive in environments where food is limited as they save a lot of energy by not regulating their body temperature internally - therefore nutritional requirements may be much lower

Question 27

Why do aquatic ectotherms have little difficulty maintaining a stable internal body temperature

Answer 27

Due to the high specific heat capacity of water - meaning water temperatures are significantly less variable than those on land