Chapter 15 Homeostasis

Question 1

Define homeostasis

Answer 1

Maintaining a stable equilibrium of the conditions within the body

Question 2

Why is it important for homeostasis to be maintained?

Answer 2

Enzymes only function within narrow pH ranges, certain temperatures
Large fluctuations would denature enzymes and disrupt function
Vital life processes would not be able to be carried out, cell, tissue and organ death

Question 3

How are changes detected by the body?

Answer 3

Sensory receptors detect changes in the internal and external environment
These are transmitted to the brain via nerve impulses, which responds by sending impulses to effectors

Question 4

What is negative feedback?

Answer 4

A system where upon a change being detected, the body will respond by initiating mechanisms to restore conditions to how they were before
Often, some of the hormones that stimulate others inhibit the ones that they have been stimulated by

Question 5

What is positive feedback?

Answer 5

If a change is detected, the body responds by enhancing the change
e.g cervix during childbirth, trigger oxytocin which stimulates the uterus to contract, head further on cervix
Depolarisation, opening of voltage gated sodium channels upon threshold

Question 6

What is thermoregulation?

Answer 6

Maintaining a constant core body temperature to maintain optimum enzyme activity

Question 7

What factors may cause temperature changes? Physics

Answer 7

Convection (gases and density) and conduction (particles)
Radiation- transmission of em waves to and from air/water/ground
Latent heat of vaporisation (sweat)

Question 8

What are ectotherms?

Answer 8

Organisms whose core temperature is dependent on their environment, they cannot control their body temperature using metabolism
e.g fish, reptiles

Question 9

What can an ectotherm do to keep warm? (same but opposite to keep cool)

Answer 9

Move into sunny areas, increase SA to expose to the sun
Move to warm ground- conduction
Movement- respiration, exothermic
Increase metabolism
Colours- light colours to minimise absorption

Question 10

Why do fish not need to really worry about core temp?

Answer 10

Water has a high SHC and high latent heat of vaporisation
Unlikely to have large changes in temperature

Question 11

Compare the energy demands of ectotherms and endotherms?

Answer 11

Endotherms need more energy, more food, than ectotherms as endotherms use their metabolism to warm up

Question 12

What are endotherms?

Answer 12

Organisms that rely on metabolism to heat up
They have higher metabolic rates and can live in a wider range of conditions

Question 13

Where are the thermoreceptors in endotherms and what do they do?

Answer 13

Skin- detect external changes
Hypothalamus- detect changes in core temperature, blood temperature]
combination used for heating to occur

Question 14

What are the main mechanisms for endotherms to cool down? state.

Answer 14

Vasodilation
Sweating
Erector pili muscles relax

Question 15

What is vasodilation and how does it work?

Answer 15

Arteriovenous shunt vessels constrict, connect arterioles and venules
Arterioles near the surface of the skin dilate
Forces blood through the capillary networks near the surface of the skin, so more heat loss by radiation

Question 16

How do sweating and hairs on the skin help with heat loss? Link to animals

Answer 16

As sweat evaporates from the skin, heat is lost, cools blood flow below (panting in animals)
Erector pili muscles relax, avoids insulating layer of air, and higher SA:v to maximise cool, pale fur to reflect radiation

Question 17

What is vasoconstriction and how does it work?

Answer 17

Arteriovenous shunt vessels dilate
Arterioles near the surface of the skin constrict, reducing blood flow to the capillary networks at the surface of the skin, less heat loss by radiation

Question 18

How does shivering increase body temperature?

Answer 18

Shivering is rapid, involuntary contracting of muscles
Heat from exothermic metabolic reactions heat up the body

Question 19

How do polar bears survive the cold?

Answer 19

Small ears, low SA so less heat loss by radiation
Fur, hair hollow so can permanently trap a a layer of air as insulation

Question 20

When are the heat loss and heat gain centre activated? What does it do?

Answer 20

Heat loss centre- when blood temp too high
Heat gain centre- when blood temp too low
Send impulses to autonomic neurones

Question 21

Why do insects find it more difficult to thermoregulate compared to mammals?

Answer 21

Insects have a larger surface area to volume ratio
This increases the rate of heat loss
They possess fewer thermoregulatory mechanisms such as production of sweat and vasoconstriction

Question 22

What are behavioural responses to change in temperature? What are they more common in?

Answer 22

Anything linked with behaviour
e.g moving to colder surfaces, huddling together…
More common in ectotherms but in both

Question 23

What are physiological responses to changes in temperature? What are they more common in?

Answer 23

Relating to changes in biological processes
e.g vasoconstriction, sweating, contraction of erector muscle, but also colours of skin so absorption of light

More common in endotherms but can be in both

Question 24

How do you compare endotherms and ectotherms?

Answer 24

Talk about amount of physiological vs behavioural mechanisms
And whether metabolism is used, metabolic demands…