B15 - Homeostasis & Thermoregulation

Question 1

Define homeostasis (2)

Answer 1

• body maintaining stable/constant internal environment.
• within narrow range/about a set point
• even though environment is changing

Question 2

Describe the role of receptors and effectors in homeostasis

Answer 2

• sensory receptors detect change in internal/external environment.
• info transmitted to brain & impulses sent along motor neurones to effectors.
  effectors restore equilibrium in body.
• stimulus continously monitored by receptors so that it fluctuates around a set value.

Question 3

Explain the role of negative feedback systems in homeostasis (1)

Answer 3

• effectors work to restore conditions to base level
• reverse initial stimulus

Question 4

Explain the role of positive feedback systems in homeostasis. (1)

Answer 4

• effectors stimulated to increase/heighten response
• enhance initial stimulus

Question 5

Give an example of positive feedback (1)

Answer 5

• blood clotting: platelets stick to damaged blood vessels and release factors to attracts more platelets.
• childbirth: baby head presses against cervix causing release of oxytocin (hormone) which causes the uterus to contract, pushing the baby head harder against the cervix. This in turn releases more oxytocin. Process continues until childbirth

Question 6

Give an example of negative feedback (1)

Answer 6

• blood sugar control with insulin and glucagon

Question 7

Describe the term ‘endotherms’.

Answer 7

• mammals & birds
• rely on own internal exothermic metabolic reactions to increase core body temperature.
• can also take warmth from environment.

Question 8

Describe the term ‘ectotherms’

Answer 8

• cannot control body temp via their own metabolism alone.
• rely on outside heat from environment to regulate core body temp.
• invertebrates, fish, reptiles etc.

Question 9

State where the core body temperature is monitored (1)

Answer 9

hypothalamus

Question 10

What are the two control centres involved in controlling core temperature? Explain their functions. (4)

Answer 10

Heat loss centre:
- activated when blood temp in hypothalamus increases.
- send impulse through autonomic (parasympathetic) motor neurones to effectors.
- lower core body temperature.

Heat gain centre:
- activated when blood temp in hypothalamus decreases.
- impulse sent through autonomic (sympathetic) motor neurones to effectors
- increase core body temp

Question 11

How is core body temperature increased in endotherms? (6)

Answer 11

Shivering:
- rapid, involuntary contracting and relaxing of large muscles.
- metabolic heat from exothermic reactions warm body up to raise core body temperature

Vasoconstriction:
- atrerioles near skin surface contract.
- AV shunt vessels dilate, so little blood flow to capillary network near skin.
- less heat loss via radiation.

raising body hair:
- erector pili muscles contract
- traps insulating layer of air
- dramatic effect in hairy endotherms but little effect in humans.

Question 12

How is core body temperature decreased in endotherms?

Answer 12

Vasodilation:
- arterioles dilate near skin surface
- AV shunt vessels constrict
- blood forced through capillary network close to skin surface
- skin flushes and cools due to increase radiation

Sweating:
- secreted by sweat glands
- sweat evaporates, causing heat loss

Reduced insulation of hair:
- erector pili muscles relax
- avoid trapping insulated air layer

• large SA:V in hot climates to maximise cooling
• behavioural adaptations in humans e.g. clothes, housing, heating

Question 13

Give examples of physiological responses of thermoregulation in ectotherms.

Answer 13

• dark colours absorb more radiation than light e.g. lizards darker in cold climates to absorb more radiation and stay warm
• alter heart rate to alter metabolic rate and help warm/cool
• can survive in difficult habitats with short food supply as need less food and energy regulating temp than endotherms do.

Question 14

Give examples of behavioural responses of thermoregulation in ectotherms (increasing and decreasing)

Answer 14

Increasing body temp:
- basking in sun to reach temperature where metabolic reactions are fast enough for them to stay active.
- orientate bodies to maximise surface area exposed to sun
- press bodies against ground to conduct heat

Decrease body temp:
- seek shade/shelter
- hide in cracks, dig burrows
- press bodies against cool surface
- orientate bodies away from sun
- minimise movement to reduce metabolic heat generated

Question 15

How to endotherms detect temperature changes? (2)

Answer 15

• Peripheral temperature receptors in skin detect change in surface temperature.
• Hypothalamus has thermoreceptors/temp receptors that monitor blood temperature.