Homeostasis

Question 1

Define “homeostasis”

Answer 1

Maintenance of internal stable environment in an organism within narrow limits even as external conditions fluctuate

Question 2

What are the principles of homeostasis? 2

Answer 2

• Kept within dynamic equilibrium fluctuating at normal level
• Each condition controlled has norm/set point optimum for this condition

Question 3

What is homeostasis vital for? 2

Answer 3

• Cell normal function to stop cellular damage

- Important in exercise for increased respiration, glucose use and body temperature

Question 4

How is negative feedback carried out?

Answer 4

• Receptors used to detect deviations from the norm in response to a stimulus
• Connected to control centre
• Emits signals
• Turns effectors on/off to bring conditions back to the norm

Question 5

Give the 2 types of signals emitted by control centres

Answer 5

• Nerve impulses

- Hormones

Question 6

Give the 2 types of effector

Answer 6

• Muscles

- Glands

Question 7

What are the two types of feedback?

Answer 7

• Negative feedback

- Positive feedback

Question 8

Define negative feedback

Answer 8

Deviation from the norm results in a change in the opposite direction back to the norm

Question 9

What is the limit of negative feedback?

Answer 9

• Only works in certain limits

- If the change is too big, effectors may not be able to counteract it

Question 10

Describe negative feedback in glycolysis 7

Answer 10

• When level of ATP rises
• Inhibits enzyme catalysing early step in metabolic pathway
• ATP binds to enzyme
• Changes shape of enzyme and active site
• Enzyme substrate complex can’t form
• Enzyme activity inhibited
• Stops further glycolysis

Question 11

Describe negative feedback in a species 2

Answer 11

• Environment supports a particular size population for a species as a norm
• If population increases competition or predation causes population size to fall back to norm

Question 12

What is positive feedback? 2

Answer 12

• Output from control centre causes effectors to amplify a change
• Moves condition further from norm set point

Question 13

When is positive feedback used? 2

Answer 13

• To rapidly activate something

- When homeostatic system breaks down e.g hypothermia

Question 14

Is positive feedback a part of homeostasis and why/why not?

Answer 14

No - doesn’t keep internal environment stable

Question 15

Explain blood clotting as an example of positive feedback 6

Answer 15

• Blood vessel damage
• Platelets become activated and release chemicals
• Attracts more platelets to be activated
• These release more chemicals
• Until a blood clot is formed
• Process ends with negative feedback as body detects blood clot

Question 16

Why is a high temperature bad for the body? 5

Answer 16

• Enzyme molecules vibrate too much
• Breaks hydrogen bonds holding them in 3D shape
• Active site shape is changed and no longer works as catalyst
• Enzymes are denatured
• Metabolic reactions less efficient

Question 17

Why is a low temperature bad for the body?

Answer 17

Reactions would occur too slowly for body to remain active

Question 18

How does homeostasis control body temperature? 6

Answer 18

• Thermoreceptors detect changes in blood temperature [skin/in hypothalamus itself]
• Send impulses along sensory neurones to hypothalamus
• Sends impulses along motor neurones to effectors
• Respond to restore body temperature back to normal
• If too warm: initiates heat loss responses and inhbits heat gain responses
• If too cold: the opposite

Question 19

Give 5 heat loss responses

Answer 19

• Hairs lie flat
• Vasodilation
• Sweat glands stimulated to secrete sweat
• Liver reduces metabolic rate
• Skeletal muscles relax: no shivering
• Evaporation from moist lung surfaces

Question 20

How do hairs lie flat and how does this increase heat loss? 5

Answer 20

• Erector pili muscles relax
• Hairs lie flat
• Less heat is trapped
• Skin is insulated less
• Heat lost more easily

Question 21

How does vasodilation occur and how does this cause heat loss? 5

Answer 21

• Shunt vessel constricts
• Muscles in arteriole walls relax
• Blood flows through them making them dilate
• More blood flows through capillaries in surface layer of dermis
• More heat energy lost through skin via radiation

Question 22

How do sweat glands being stimulated to secret sweat allow for heat loss?

Answer 22

• Released on skin via sweat duct
• Evaporates, taking heat energy from skin
• Skin cools

Question 23

Give 6 heat gain responses

Answer 23

• Sweat glands inhibited
• Vasocontriction
• Hairs stand up
• Liver increases metabolic rate
• Hormones released increasing metabolic rate
• Skeletal muscles contract: shivering

Question 24

How does the inhibition of sweat glands ensure heat is gained?

Answer 24

Heat lost via evaporation reduced

Question 25

How does vasoconstriction occur and why does this lead to heat gain? 5

Answer 25

- Muscles in arterioles constrict - Reduces blood supply to surface capillaries - Blood diverted through shunt vessels - they dilate as more blood flows through them - Blood flows further from skin surface as less blood flows through capillaries in surface layers of dermis - Reduces heat loss from skin via radiation

Question 26

How do hairs stand up and why does this increase heat gain? 5

Answer 26

- Erector pili muscles contract - Hairs stand up - More air is trapped - Skin is more insulated - Heat lost less easily

Question 27

What hormones produced increase metabolic rate?

Answer 27

- Adrenaline | - Thyoxine

Question 28

Why does increasing metabolic rate increase heat gain?

Answer 28

More metabolic reactions leads to more heat energy