Chapter 5.1- Communication And Homeostasis

Question 1

What living conditions do all living things need to maintain?

Answer 1

• a suitable pH
• suitable temperature
• an aqueous environment that keeps the substrates and products in solution
• freedom from toxins and excess inhibitors

Question 2

What is a stimulus?

Answer 2

Environmental change which brings about a response in an organism

Question 3

What is a response?

Answer 3

The way in which an organism changes it behaviour or physiology

Question 4

What are the features of a good communication system?

Answer 4

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

Question 5

What is meant by cell signalling?

Answer 5

The way in which cells communicate with each other

Question 6

What are the two major systems of communication that work by cell signalling?

Answer 6

• neuronal system: a interconnected network of neurones that signal to each other across a synapse junctions. The neurones can conduct a single very quickly and enable rapid responses to stimuli that may be changing quickly
• hormonal system: a system that uses the blood to transport its signals. Cells in the endocrine organ release the signal (a hormone) directly into the blood. The hormone is transported throughout the body, but only recognised by specific target cells. The hormonal system enable longer-term responses to be co-ordinated.

Question 7

What is homeostasis?

Answer 7

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

Question 8

What are the different aspects that are maintained by homeostasis?

Answer 8

• body temperature
• blood glucose concentration
• blood salt concentration
• water potential of the blood
• blood pressure
• carbon dioxide concentration

Question 9

What is the standard response pathway for homeostasis?

Answer 9

stimulus–receptor—communication pathway (cell signalling)—effector—response

Question 10

What are sensory receptors?

Answer 10

cells/sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials

Question 11

What are effector cells and give some examples?

Answer 11

• a cell, tissue or organ that brings about a response

- e.g. liver cells or muscle cells

Question 12

What is negative feedback?

Answer 12

the mechanism that reverses a change, bringing the system back to the optimum

Question 13

What are the stages in temperature control via negative feedback?

Answer 13

1. Rise in core temperature
2. Thermoregulatory centre in the hypothalamus detects change
3. Nervous and hormonal systems carry signals to skin, liver and muscles
4. Less heat generated and more lost
5. temperature falls

Question 14

What is positive feedback?

Answer 14

the mechanism that increases a change, taking the system further away from the optimum

Question 15

What is the basic mechanism for positive feedback?

Answer 15

1. optimum condition
2. change away from optimum
3. receptor detects change (INPUT)
4. communication system informs effector (OUTPUT)
5. effector reacts to increase change

Question 16

What are exergonic reactions and how are they an example of positive feedback?

Answer 16

• exergonic reactions are reactions that release heat
• below a certain core body temperature enzymes become less active and this means that exergonic reactions that release heat are slower and release less heat

Question 17

Whats an example of positive feedback being beneficial?

Answer 17

• an example is at the end of pregnancy to bring about the dilation of the cervix.
• as the cervix begins to stretch this causes the posterior pituitary gland to secrete the hormone oxytocin.
• oxytocin increases the uterine contractions which stretch the cervix more, which causes secretion of more oxytocin
• once the cervix is fully dilated, the baby can be born. The birth ends the production of oxytocin

Question 18

What is a ectotherm?

Answer 18

an organism that relies on external sources of heat to maintain body temperature, as well as some behavioural adaptations

Question 19

What are some behavioural responses that ectotherms carry out when they are too cold?

Answer 19

• move into a sunny area
• lie on a warm surface
• expose a large surface area to the sun

Question 20

What are some behavioural responses that ectotherms carry out when they are too hot?

Answer 20

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

Question 21

What behavioural adaptations do snakes have that allow them to regulate its body temperature(ectotherms)?

Answer 21

• basks in the sun
• In the UK, adders can often be found lying on an exposed path beside vegetation
• this allows snakes to absorb heat directly from the sun

Question 22

What behavioural adaptations do locusts have that allow them to regulate their body temperature (ectotherms)?

Answer 22

• in the morning, they sit side-on to the sun exposing a large surface area, but at midday they face the sun head-on exposing a smaller surface area. They may also climb to the top of a plant at midday to get away from the soil surface
• they can increase their rate of breathing and the depth of breathing movements when they are hot

Question 23

What behavioural adaptations do lizards have that allow them to regulate their body temperature (ectotherm)?

Answer 23

-use burrows or crevices between rocks. They will hide in the burrow during the hottest part of the day and the coolest part of the night

Question 24

What behavioural adaptations do horned lizards have which allow them to regulate their body temperature (ectotherm)?

Answer 24

• can change its shape by expanding or contracting its ribcage
• expanding its ribcage increases the surface area exposed to the sun, so more heat can be absorbed

Question 25

What are the advantages of ectothermy?

Answer 25

-they rely on external sources of heat to keep warm. They do not use up energy to keep warm. Therefore: =less of their food is used in respiration =more of the energy and nutrients gained from food can be converted to growth =they need to find less food =they can survive for long-periods without food

Question 26

What are some of the disadvantages of ectothermy?

Answer 26

-less active in cooler temperatures; this means that : =they are at risk from predators while they are cold and unable to escape =cannot take advantage of food that is available while they are cold

Question 27

What is an endotherm?

Answer 27

an organism that uses heat from metabolic reactions to maintain body temperature

Question 28

How does the skin regulate temperature in endotherms when its too hot?

Answer 28

Too HOT: - sweat bands secrete fluid onto the skin surfaces this evaporates is uses heat from the blood as the latent heat of vaporisation - haris and feathers lie flat to reduce insulation and allow greater heat loss - vasodilation of arterioles and precapillary sphincters directs blood to the skin surface so more heat can be radiated away from the body

Question 29

How does the skin regulate temperature in endotherms when its too cold?

Answer 29

Too COLD: - less sweat is secreted, so less evaporation means less heat is lost - hairs and feathers stand erect to trap hair, which insulates the body - vasoconstriction of arterioles and precapillary sphincters leading to the skin surface. Blood is diverted away from the surface of the skin and less heat is lost

Question 30

How does the gaseous exchange system regulate temperature in endotherms when its too hot?

Answer 30

Too HOT: -some animals pant, increasing evaporation of water from the surface of the lungs and airways. Evaporation uses heat from the blood as the latent heat of vaporisation

Question 31

How does the gaseous exchange system regulate temperature in endotherms when its too cold?

Answer 31

less panting, so less heat is lost

Question 32

How does the liver regulate temperature in endotherms when its too hot?

Answer 32

Too HOT: | -less respiration takes place, so less heat is released

Question 33

How does the liver regulate temperature in endotherms when its too cold?

Answer 33

Too COLD: | -increased respiration in the liver cells means that more energy from food is converted to heat

Question 34

How do the skeletal muscles regulate temperature in endotherms when its too hot?

Answer 34

Too HOT: | -fewer contractions mean that less heat is released

Question 35

How do the skeletal muscles regulate temperature in endotherms when its too cold?

Answer 35

Too COLD: | -spontaneous muscle contractions (shivering) release heat

Question 36

How do blood vessels regulate temperature in endotherms when its too hot?

Answer 36

Too HOT: | -dilation to direct blood to the extremities so that more heat can be lost

Question 37

How do blood vessels regulate temperature in endotherms when its too cold?

Answer 37

Too COLD: -constriction to limit blood flow to the extremities, so that blood is not cooled too much-this can lead to frostbite in extreme conditions

Question 38

What are some behavioural mechanisms that endotherms use to increase their body temperature when they are too cold?

Answer 38

- lie in the sun - orientate body towards suns to increase surface area exposed - move about to generate heat in the muscles or, in extreme conditions, roll into a ball shape to reduce the surface area and heat loss

Question 39

What are some behavioural mechanisms that endotherms use to decrease their body temperate when they are too hot?

Answer 39

- hide away from the sun in the shade or burrow - orientate body to reduce surface area exposed to sun - remain inactive and spread limbs out to enable greater heat loss - wet skin to use evaporation to help cool the body. Cats lick themselves and elephants spray water over their bodies

Question 40

What are the advantages of endothermy?

Answer 40

- maintain a fairly constant body temperature whatever the temperature externally - remain active when external temperatures are low, which means that they can take advantage of prey that may be available or escape from potential predators - inhabit colder parts of the planet

Question 41

What are the disadvantages of endothermy?

Answer 41

- significant amount of energy intake is to maintain body temperature - need more food - use for growth a lower proportion of energy and nutrients gained from food - may overheat in hot weather