Homeostasis

Question 1

Define stimulus and response

Answer 1

Stimulus: change to external environment

Response: change in organism’s behaviour or physiology in response to a stimuli

Question 2

Define homeostasis

Answer 2

Maintaining a constant internal environment despite external/internal changes

Question 3

Define negative feedback

Answer 3

Reversal of a change to bring the system back to optimum

Question 4

Define positive feedback

Answer 4

Increasing a change, taking the system further away from optimum

Question 5

Outline the basic mechanism of negative feedback

Answer 5

Change away from optimum

Sensory receptor detects change (input)

Communication system informs effector (output)

Effector reacts to reverse change

Returns to optimum condition

Question 6

Outline the mechanism of temperature control by negative feedback

Answer 6

Fall in core temp below 37 degrees

Thermoregulatory centre in hypothalamus detects change

Nervous & hormonal systems carry signals to skin, liver & muscles

More heat generated

Temp rises

Vice versa

Question 7

Despite negative feedback a core body temp could be measures above or below the optimum. Why?

Answer 7

A slight overshoot during time taken for response to be initiated

Question 8

Why does body temp need to stay within a narrow range of 37 degrees

Answer 8

So enzymes and other proteins can function and aren’t altered tertiary structure

Question 9

Outline the basic mechanism of positive feedback

Answer 9

Change away from optimum condition

Receptor detects change (input)

Communication systems inform effectors (output)

Effectors react to increase change

Moves further away from optimum

Question 10

Outline the mechanism of cervix dilation during pregnancy

Answer 10

Cervix begins to stretch

Posterior pituitary gland secretes more oxytocin hormone

Once fully dilated, baby is born & oxytocin production ends

Question 11

Is neurone activity positive or negative feedback?

Answer 11

Positive - more membrane channels open to increase depolarisation

Question 12

What is an ecotherm?

Answer 12

Organism that relies on external heat sources to maintain body temp

Question 13

What is an endotherm?

Answer 13

Organism that uses heat from metabolic reactions to maintain body temp

Question 14

Advantages of ectothermy

Answer 14

Less food used for respiration- more energy can be used for growth

Can survive for longer periods w/out food so dont need to find it often

Question 15

Disadvantages of ectothermy

Answer 15

Less active in cooler temperatures - at risk of predatation and cant take advantage of available food when cold

Question 16

What do ectotherms do when they are too cold?

Answer 16

Move to sunny area
Lay on warm surface
Expose a larger surface area to sun

Question 17

What to ectotherms do when too hot

Answer 17

Reduce body surface exposed to sun

Move out of sun

Move underground

Question 18

Advantages of endothermy

Answer 18

Remain active whatever the temperature- can always take advantage of prey or escape predators

Can inhabit colder parts of planet

Question 19

Disadvantages of endothermy

Answer 19

Use lots if energy intake to maintain body temp (higher metabolic demand)

Need more food

Lower proportion of energy and nutrients used for growth

May overheat in hot weather

Question 20

Physiological response to endotherms being too hot

Answer 20

Skin: sweat glands secrete swear- uses heat from blood as latent heat of vaporisation when it evaporates

• hairs / feathers lay flat to reduce insulation
• vasolidstion of precapillary sphincters directs blood to skin surface so more eat radiated away from body

Gaseous exchange system: increased breathing rate therefore evaporation of water from surface of lungs & airways; used heat from blood as latent heat of vaporisation = PANting

Liver: metabolism slows; less respiration; less heat released from exergonic reactions

Skeletal muscles: fewer contractions; less heat released

Blood vessels: dilation to direct blood to extremities

Question 21

Physiological response to endotherms being too cold

Answer 21

Skin: less sweat secreted; less evaporation so less heat used, hairs/feathers erect to trap air (insulates), vasoconstriction of arterioles & precapillary sphincters leading to skin surface; blood diverted away from surface

Gaseous exchange system: slower breathing rate so less heat lost through evaporating water

Liver: increased metabolism therefore respiration therefore heat production

Skeletal muscles: spontaneous muscle contraction (shivering) releases heat by exergonic reactions of respiration

Blood vessels: constrict to limit blood flow to extremities; so blood isnt cooled as much

Question 22

Behavioural responses to endotherms being too hot and too cold

Answer 22

Too hot: hide from sun, reduce surface area exposed to sun, remain inactive and spread limbs out to enable greater heat loss, wet skin to use evaporation to cool the body (eg cats licking self)

Too cold: lay in sun, orientate body towards sun to increase SA exposed, be more active to generate heat, remain dry

Question 23

What do peripheral temperature receptors do?

Answer 23

Skin receptors that monitor temperature in extremities and send info to hypothalamus if it is very hot or very cold so that behavioural mechanisms are initiated - the person starts to FEEL hot/cold so will move to shade/heat source

Question 24

What does homeostasis need to maintain?

Answer 24

blood pH, core temperature, blood conc. of urea & sodium ions