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OCR Biology Paper 1 > 5.1 - Communication and Homeostatis > Flashcards

5.1 - Communication and Homeostatis Flashcards

1
Q

Explain why multicellular organisms require communication systems

A

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
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2
Q

List changes to the internal environment that would require a response

A
  • Blood glucose concentration
  • Internal temperature
  • Water potential
  • Cell pH
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3
Q

List changes to the external environment that would require a response

A
  • Humidity
  • External temperature
  • Light intensity
  • Sudden sounds
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4
Q

Describe how cells are able to communicate with one another

A
  • Cell releases a chemical
  • Which has an effect on target cell
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5
Q

Outline cell signalling between adjacent cells in animals

A

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

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6
Q

Outline cell signalling between distant cells in animals

A

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

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7
Q

What do plant cells use for communication?

A

Plant hormones
e.g. auxins

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8
Q

Define homeostatis

A

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

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9
Q

Give examples of homeostasis

A
  • Thermoregulation (controlling body temperature)
  • Blood pH
  • Blood glucose
  • Osmoregulation (water levels)
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10
Q

Define receptor

A

Detects changes in internal and external environment of an organism

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11
Q

Define effector

A

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

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12
Q

Define positive feedback

A
  • 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
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13
Q

Define negative feedback

A
  • 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
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14
Q

Define thermoregulation

A

Maintenance of a constant core body temperature

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15
Q

Why is thermoregulation important?

A

Maintains optimum temperature for enzyme activity

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16
Q

Define endotherm

A
  • Organisms that rely on metabolic processes to warm up
  • Maintain stable core body temperature in any environment
  • e.g. mammals, birds
17
Q

Define ectotherm

A

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

18
Q

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

A

The Sun

19
Q

Outline how ectotherms increase their body temperature

A

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

20
Q

Outline how ectotherms increase their body temperature

A

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

21
Q

Outline how ectotherms decrease their body temperature

A

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

22
Q

How do endotherms detect temperature change

A

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

23
Q

State where the core body temperature is monitored

A

Thermoregulatory centre in hypothalamus

24
Q

Outline the behavioural responses of endotherms to temperature change

A
  • Basking in the Sun
  • Digging burrows
  • Wallowing in water or mud
  • Hibernation
  • Wearing clothes (humans)
25
Q

Outline the physiological responses of endotherms to decrease their core temperature

A
  • 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
26
Q

Outline the physiological responses of endotherms to increase their core temperature

A
  • 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
27
Q

Describe how body temperature is maintained in humans

A

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

28
Q

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

A

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

29
Q

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

A

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

30
Q

Outline the physiological responses of endotherms to decrease their core temperature

A
  • 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

OCR Biology Paper 1 (20 decks)

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