5.1.2 homeostasis

Question 1

effector

Answer 1

cell, tissue or organ that brings about a response

Question 2

homeostasis

Answer 2

maintaining a constant internal environment despite changes in external/internal factors

Question 3

negative feedback

Answer 3

mechanism which reverses change, bringing system back to optimum

Question 4

positive feedback

Answer 4

mechanism which increases change, taking system further away from optimum

Question 5

sensory receptors

Answer 5

cells/sensory nerve endings which respond to stimulus in internal/external environment of an organism & can create action potentials

Question 6

examples of things maintained by homeostasis

Answer 6

• body temp
• blood glucose conc
• blood salt conc
• water potential of blood
• blood pressure
• carbon dioxide conc

Question 7

standard response pathway

Answer 7

1. stimulus
2. receptor
3. communication pathway (cell signalling)
4. effector
5. response

Question 8

name the specialised structures required for response pathway to work

Answer 8

• sensory receptors
• communication system
• effector

Question 9

describe sensory receptors

Answer 9

• may be on surface of body eg. temp receptors on skin
• monitor changes in external environment
• may be internal = monitor conditions inside of body eg. temp receptors in brain
• if a receptor detects a change, it will be stimulated to send message to effector

Question 10

describe communication systems

Answer 10

eg. neuronal/hormonal systems
- acts via signalling between cells
- used to transmit message from receptor cells to effector cells via coordination centre (usually in brain)
- messages from receptor to coordination centre = input
- message sent to effectors = output

Question 11

describe effectors

Answer 11

eg. liver cells, muscle cells
- bring about response

Question 12

describe ‘feedback’

Answer 12

• when effectors respond to output from coordination centre, elicits a response changing internal conditions
• changes detected by receptors
• effects response pathway
  = input changes

Question 13

describe the steps of negative feedback

Answer 13

1. conditions change = receptor detects stimulus & sends input to coordination centre
2. coordination centre sends output to effectors & they respond to initial change in conditions = system moves closer to optimum & stimulus reduced
3. receptors detect reduction in stimulus & reduce input to coordination centre
4. output from coordination centre to effectors thus, reduced = effectors reduce activity
5. as system gets closer to optimum, response is reduced

Question 14

3 processes required for negative feedback to work

Answer 14

• change in internal environment detected
• change must be signalled to other cells
• must be effective response to reverse change in conditions

Question 15

example of positive feedback - below core body temp

Answer 15

• below certain core body temp, enzymes become less active & exogenic reactions (which release heat) are slower/release less
• allows body to cool further
• slows enzyme-controlled reactions even more

Question 16

example of positive feedback being beneficial

Answer 16

• at the end of pregnancy to bring about dilation of cervix
• as cervix begins to stretch, causes posterior pituitary gland to secrete oxytocin
• oxytocin increases uterine contractions = stretch cervix = secretion of more oxytocin