5.1.1 - Homeostasis

Question 1

What is homeostasis?

Answer 1

The maintenance of a dynamic equilibrium of conditions in the body

Question 2

What do most of the feedback systems in the body involve?

Answer 2

Negative feedback

Question 3

What happens in a negative feedback system?

Answer 3

A small change in one direction is detected by sensory receptors, and as a result, effectors work to reverse the change and restore conditions to their base level

Question 4

What happens in a positive feedback system?

Answer 4

A change in the internal environment is detected by sensory receptors, and effectors are stimulated to reinforce the change and increase the response

Question 5

Give an example of a positive feedback system

Answer 5

When a blood vessel is damaged, platelets stick to the damaged region and they release factor that initiate clotting and attract more platelets. These platelets also add to the positive feedback cycle and it continues until a clot is formed

Question 6

Describe the positive feedback during childbirth

Answer 6

The head of the baby presses against the cervix, stimulating oxytocin production. Oxytocin stimulates the uterus to contract, pushing the head of the baby even harder against the cervix, releasing more oxytocin

Question 7

What is thermoregulation?

Answer 7

The maintenance of a constant core body temperature

Question 8

What physical processes cause changes in temperature?

Answer 8

Exothermic chemical reactions
Latent heat of evaporation
Radiation
Convection
Conduction

Question 9

What is radiation?

Answer 9

The transmission of EM waves to and from the air, water, or ground

Question 10

What is convection?

Answer 10

The heating and cooling by currents of air or water, warm air or water rises and cooler air or water sinks, setting up convection currents around an organism

Question 11

What is conduction?

Answer 11

Heating as a result of the collision of molecules.

Question 12

What are ectotherms?

Answer 12

Animals that use their surroundings to warm their body, and so their core body temperature is heavily dependent on their environment

Question 13

What are endotherms?

Answer 13

Animals that rely on their metabolic processes to warm up and usually maintain a very stable core body temperature regardless of environmental temperature

Question 14

Give examples of behavioural responses of ectotherms to increase temperature

Answer 14

• Basking in the sun when cold, and orientate their bodies so the max SA is exposed to the sun
• Pressing their bodies against warm ground to heat up by conduction
• Exothermic metabolic reactions

Question 15

Give examples of behavioural responses of ectotherms to decrease temperature

Answer 15

• Seek shade
• Press their bodies against cool earth or stones
• Orientate bodies so minimum SA is exposed to sun
• Minimise movements

Question 16

Give examples of physiological responses to warming

Answer 16

Dark colours absorb more radiation than light, and lizards living in colder climates tend to be darker coloured

Question 17

How do endotherms detect temperature changes?

Answer 17

Peripheral temperature receptors in the skin detect changes in surface temperature. Temperature receptors in the hypothalamus detect the temperature of the blood deep in the body. The combination gives great sensitivity and allows it to respond to changes, but also preempt possible problems

Question 18

Describe how endotherms may cool down

Answer 18

Vasodilation, increased sweating, and reducing the insulating effect of hair or feathers

Question 19

Describe how vasodilation cools the body down

Answer 19

The arterioles near the surface of the skin dilate when the temperature rises. The vessels connecting the arterioles and the venules constrict, so blood is forced through the capillary networks close to the surface. The skin flushes, and cools due to increased radiation

Question 20

How does sweating cool the body down?

Answer 20

As sweat evaporates from the surface of the skin, heat is lost, cooling the blood below the surface

Question 21

How does reducing the insulating effect of hair cool the body down?

Answer 21

The erector pili muscles in the skin relax, so the hair of feathers lie flat, avoiding the trapping of an insulating layer of air. It has little impact in humans

Question 22

Describe how endotherms increase their body temperature

Answer 22

Vasoconstriction, decreased sweating, and raising the body hair or feathers

Question 23

How does vasoconstriction heat the body up?

Answer 23

The arterioles near the surface of the skin constrict. The arteriovenous shunt vessels dilate, so very little blood flows through the capillary networks close to the surface of the skin. This prevents radiation

Question 24

How does decreased sweating heat the body up?

Answer 24

When core temperature is lower, the rate of sweating decreases. This reduces cooling by the evaporation of water from the surface of the skin

Question 25

How does raising the body hair or feathers heat the body up?

Answer 25

As the body temperature falls, the erector pili muscles in the skin contract, pulling the hair or feathers of the animal erect. This traps an insulating layer of air and so reduces cooling through the skin.

Question 26

How does shivering heat the body up?

Answer 26

Shivering is rapid, involuntary contraction and relaxation of the large voluntary muscles in the body. The metabolic heat from the exothermic reactions warm up the body instead of moving it