5.1 - Communication and Homeostatis

Question 1

Explain why multicellular organisms require communication systems

Answer 1

Organisms need to respond to internal/external changes for survival
- Occurs through the nervous system and hormones in animals
- Occurs through hormones in plants

• Different cells rely on others for materials and removal of waste
• Different organs work together to ensure homeostasis
  e.g. brain and skin in temperature control
• Cells communicate through cell signalling

Question 2

List changes to the internal environment that would require a response

Answer 2

• Blood glucose concentration
• Internal temperature
• Water potential
• Cell pH

Question 3

List changes to the external environment that would require a response

Answer 3

• Humidity
• External temperature
• Light intensity
• Sudden sounds

Question 4

Describe how cells are able to communicate with one another

Answer 4

• Cell releases a chemical
• Which has an effect on target cell

Question 5

Outline cell signalling between adjacent cells in animals

Answer 5

Chemicals diffuse from one cell to another
- e.g. neurotransmitters across a synapse

Question 6

Outline cell signalling between distant cells in animals

Answer 6

Hormones carried by blood to target organ(s)
- e.g. ADH secreted by pituitary gland, acts on kidney cells

Question 7

What do plant cells use for communication?

Answer 7

Plant hormones
e.g. auxins

Question 8

Define homeostatis

Answer 8

Maintaining stable internal environment
- Even though environment is changing
- Using negative feedback mechanisms
- Involves hormonal or nervous control

Question 9

Give examples of homeostasis

Answer 9

• Thermoregulation (controlling body temperature)
• Blood pH
• Blood glucose
• Osmoregulation (water levels)

Question 10

Define receptor

Answer 10

Detects changes in internal and external environment of an organism

Question 11

Define effector

Answer 11

Muscles or glands that bring about a change in response to a stimulus

Question 12

Define positive feedback

Answer 12

• Change in internal environment detected by receptors
• Effectors stimulated to reinforce and amplify response
• End products stimulate effectors to increases response
• e.g. blood clotting cascade

Question 13

Define negative feedback

Answer 13

• Small change in one direction detected by sensory receptors
• Effectors work to reverse the change and restore conditions
• Conditions restored to base level
• Involved in homeostasis
• e.g. control of blood glucose concentration by insulin and glucagon

Question 14

Define thermoregulation

Answer 14

Maintenance of a constant core body temperature

Question 15

Why is thermoregulation important?

Answer 15

Maintains optimum temperature for enzyme activity

Question 16

Define endotherm

Answer 16

• Organisms that rely on metabolic processes to warm up
• Maintain stable core body temperature in any environment
• e.g. mammals, birds

Question 17

Define ectotherm

Answer 17

Organisms that use heat from surroundings to warm their bodies
- Core body temperature very dependent on environment
- e.g. insects, reptiles

Question 18

Where does most of the heat that ectotherms use to increase body temperature come from?

Answer 18

The Sun

Question 19

Outline how ectotherms increase their body temperature

Answer 19

Behavioural responses
- Bask in the Sun
- Orientate bodies so maximum surface area exposed to Sun
- Press body against warm ground - conduction
- Contract muscles and vibrate to increase exothermic cellular activity

Physiological responses
- Dark coloured skin absorbs more radiation
- Increase heart rate

Question 20

Outline how ectotherms increase their body temperature

Answer 20

Behavioural responses
- Bask in the Sun
- Orientate bodies so maximum surface area exposed to Sun
- Press body against warm ground - conduction
- Contract muscles and vibrate to increase exothermic cellular activity

Physiological responses
- Dark coloured skin absorbs more radiation
- Increase heart rate

Question 21

Outline how ectotherms decrease their body temperature

Answer 21

Behavioural responses
- Shelter in shade
- Dig burrows
- Press body against cool earth or stone
- Submerge in water or mud
- Minimise body surface area
- Minimise movement to reduce exothermic cellular activity

Physiological responses
- Light coloured skin absorbs less radiation
- Decrease heart rate

Question 22

How do endotherms detect temperature change

Answer 22

Peripheral thermoreceptors in skin
- Detect changes in surface temperature
- Likely to be caused by change in environmental temperature

Thermoreceptors in hypothalamus
- Detect temperature change of blood

Question 23

State where the core body temperature is monitored

Answer 23

Thermoregulatory centre in hypothalamus

Question 24

Outline the behavioural responses of endotherms to temperature change

Answer 24

• Basking in the Sun
• Digging burrows
• Wallowing in water or mud
• Hibernation
• Wearing clothes (humans)

Question 25

Outline the physiological responses of endotherms to decrease their core temperature

Answer 25

- Vasodilation of skin arterioles cools body - Blood carried close to surface so loses more heat to surroundings through radiation - Sweat glands produce more sweat, as the evaporation of sweat removes heat from body - Erector pili muscles in skin relax - hair / feathers lie flat so less air trapped. This reduces the insulating effect of air

Question 26

Outline the physiological responses of endotherms to increase their core temperature

Answer 26

- Vasoconstriction of skin arterioles retains body heat - Little blood carried through surface capillaries so heat loss by radiation reduced - Sweat glands produce less sweat - Less heat lost through evaporation - Erector pili muscles in skin contract. Hair / feathers raised so more air trapped, which increases the insulating effect of air - Shivering generates heat through increased exothermic metabolic reactions - Caused by increase in adrenaline or thyroxine hormones

Question 27

Describe how body temperature is maintained in humans

Answer 27

Homeostatic process - Body temperature maintained close to 37°C - Heat distributed around body by blood - Peripheral thermoreceptors in skin detect environmental temperature change - Thermoreceptors in hypothalamus monitor temperature of blood - Vasodilation of skin arterioles cools body - Blood carried close to surface so loses more heat to surroundings - Vasoconstriction of skin arterioles retains body heat - Blood carried away from surface so retains heat - Sweat glands produce sweat to cool the body when overheated - Evaporation of sweat removes heat - Shivering generates heat - Hair erection retains heat

Question 28

Describe and explain the anatomical adaptations of endotherms living in hot climates

Answer 28

Large surface area : volume ratio - Maximises cooling - More capillaries close to skin surface - e.g. large ears Pale fur/feathers Reflect radiation

Question 29

Describe and explain the anatomical adaptations of endotherms living in cold climates

Answer 29

Small surface area : volume ratio - Reduces cooling - e.g. small ears Insulating fat layers - e.g. blubber in whales

Question 30

Outline the physiological responses of endotherms to decrease their core temperature

Answer 30

- Vasodilation of skin arterioles cools body - Blood carried close to surface so loses more heat to surroundings through radiation - Sweat glands produce more sweat, as the evaporation of sweat removes heat from body - Erector pili muscles in skin relax - hair / feathers lie flat so less air trapped. This reduces the insulating effect of air