5.1 Communication and Homeostasis

Question 1

Define homeostasis

Answer 1

maintaining a constant internal environment despite changes in internal and external factors.

Question 2

What is the process?

Answer 2

stimulus -> receptor -> communication pathway -> effector -> response

Question 3

Where can sensory receptors be?

Answer 3

• on body surface e.g. temp receptors on skin that monitor changes in external environment
• internal to monitor conditions inside body e.g. temp receptors in brain

Question 4

what is the job of the communication system?

Answer 4

transmits a message from receptor cells to effectors via coord centre (usually brain)

Question 5

What do the effector cells do?

Answer 5

• muscle/gland
• bring about a response

Question 6

What is negative feedback?

Answer 6

• mechanism that reverses the change to bring the body back to optimum/within a narrow range
• as system gets closer to optimum, response is reduced
• conditions will never remain perfectly constant

Question 7

What is positive feedback?

Answer 7

• mechanism that increases a change, taking the body further from the optimum/out of the range

Question 8

What are some examples of positive feedback?

Answer 8

• neurones
• body temp too low = decreases enzyme activity = slower EXERGONIC reactions = less heat released = decreases activity more = downwards spiral
• cervix stretches = oxytocin released = inc contractions = stretches cervix more

Question 9

What is a stimulus?

Answer 9

change in internal or external environment

Question 10

What is a response?

Answer 10

a way in which the organism changes its behaviour or physiology

Question 11

What are examples of conditions all living things need to maintain?

Answer 11

• suitable temperature
• suitable pH
• aqueous environment
• freedom from toxins

Question 12

The activities of cells alter their own. ——– The accumulation of excess ——- or —— in this internal environment must act as a ——– to cause removal of these.

Answer 12

environment
wastes
toxins
stimulus

Question 13

What is the composition of tissue blood maintained by?

Answer 13

the blood

Question 14

Why is a multicellular organism more efficient? What is needed to ensure different parts of the body work effectively?

Answer 14

• cells are differentiated
• its cells are specialised to perform particular functions, then forming tissues and organs.
• communication system

Question 15

What makes a good communication system?

Answer 15

• cover the whole body
• enable cells to communicate with each other
• enable specific communication
  enable rapid communication
• enable short and long term responses

Question 16

What is cell-cell signalling? What are the two major systems that work by it?

Answer 16

communication between cells

neuronal: uses neurones. can conduct a signal very quickly and enable rapid responses to stimuli that may be changing quickly

hormonal: uses blood to transport. hormone transported throughout body and recognised by target cells. enables longer term responses.

Question 17

What is an ectotherm?

Answer 17

• rely on external sources of heat and their body temperature fluctuates with the external temperatures

Question 18

What are some behavioural responses for if its too cold?

Answer 18

• move into sunny area
  lie on warm surface
  expose larger SA to sun

Question 19

What are some behavioural responses for if its too hot?

Answer 19

• move out of sun
• move underground
• reduce body surface exposed to sun

Question 20

What does a snake do?

Answer 20

basks in sun to directly absorb heat

Question 21

What does a locust do?

Answer 21

• sit side on to sun exposing large SA in morning, and at midday they face sun head-on ( less heat)
• also may climb to top of plant to gain less heat from soil
• increases breathing rate as water evaporates from trachea

Question 22

What does a lizard do?

Answer 22

• burrows/crevices due to more stable temp. Colder during hottest part of day and vice versa

Question 23

What are the advantages and disadvantages of ecothermy?

Answer 23

less food in respiration
more energy in food used for growth
need less food

less active in cooler temps, at risk of predators and unable to take advantage of food

Question 23

What does a horned lizard do?

Answer 23

• can change shape by expanding or contracting its ribcage to inc SA exposed to sun

Question 24

What is an endotherm?

Answer 24

• generate heat from metabolism and are largely independent of external temperatures

Question 25

What are some responses when an endotherm is too cold?

Answer 25

• sweat glands secrete less fluid so less heat is lost
• hairs and feathers stand erect to trap air
• vasoconstriction of arterioles (pre-capillary sphincters close)
• increases respiration
  less panting
• spontaneous muscle contractions
• limit of blood flow to extremeties

Question 26

What are some responses when an endotherm is too hot?

Answer 26

• more sweat secreted
• direct blood to extremeties
• fewer contractions
  less respiration
  panting
  vasodilation of arterioles (pre-capillary sphincters open)
  -hairs lie flat

Question 27

Suggest the consequences of an increase in thermogenic set point

Answer 27

• fever
• raised temp helps to kill pathogens
• causes an increase in antibody production
• can result in organ damage or failure

Question 29

It is more difficult for moths and bumblebees to maintain their body temperature than for mammals and birds to maintain their body temperature. Explain why

Answer 29

They have a larger SA:V ratio, so a greater rate of heat loss