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Biology A Level > Communication and Homeostasis > Flashcards

Communication and Homeostasis Flashcards

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1
Q

What set of conditions does an organism need to maintain within their cells to survive?

A
  • Suitable temperature
  • Suitable pH
  • Aqueous environment that keeps substrates and products in solution
  • Freedom from toxins and excess inhibitors
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2
Q

Why are most cells not exposed to the external environment?

A

They are protected by epithelial tissue and organs such as skin or bark

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3
Q

What is a tissue?

A

A group of specialised cells working together to carry out a specific function

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4
Q

What is an organ?

A

A group of specialised tissues working together to carry out a specific function

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5
Q

What are the two main systems of communication that communicate by cell signalling?

A
  • Neuronal system

- Hormonal system

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6
Q

What conditions does homeostasis maintain?

A
  • Body temperature
  • Blood glucose concentration
  • Blood salt concentration
  • Water potential of the blood
  • Blood pressure
  • CO2 concentration in the blood
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7
Q

What is the standard response pathway to a change in stimulus?

A

Stimulus → receptor → communication pathway/output → effector → response

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8
Q

Give an example of a change in stimulus

A

Change in body temperature

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9
Q

Give an example of a sensory receptor

A

Thermoreceptor, this detects a change in temperaure and sends a signal to an effector

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10
Q

Give an example of an effector

A

Muscle cells, these cells will bring about a response if they have received a signal from receptor cells

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11
Q

Describe the body’s response to a fall in core body temperature

A
  • Thermoreceptors in hypothalamus detect that core body temperature has fallen below the optimum temperature
  • Nervous and hormonal systems carry signals to skin, liver and muscles
  • Vasoconstriction, piloerection, shivering and increased respiration of the liver all occur
  • This causes more heat to be generated and less heat to be lost, therefore returning temperature back to its optimum
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12
Q

What are the 4 responses to a decrease in body temperature?

A
  • Vasoconstriction
  • Piloerection
  • Shivering
  • Increased metabolism in liver
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13
Q

What are the 4 responses to an increase in body temperature?

A
  • Vasodilation
  • Pilorelaxation
  • Sweating
  • Decrease in metabolism in the liver
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14
Q

What is positive feedback?

A

A change occurs to take conditions away from the optimum temperature, receptors detect the change and the communication system informs the effectors, the effector reacts to take the conditions further away from the optimum

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15
Q

How would an ectotherm respond to a decrease in body temperature?

A
  • Move into a sunny area
  • Lie on a warm surface
  • Expose a larger surface to the sun
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16
Q

How do ectotherms respond to an increase in body temperature?

A
  • Move out of the sun
  • Move underground
  • Reduce the surface are they’re exposing to the sun
17
Q

What would a snake do to increase its body temperature?

A

Bask in the sun, this enables them to absorb heat directly from the sun

18
Q

What would a locust do to regulate its body temperature?

A
  • In the morning sit side on to the sun to expose a larger surface area to the sun while the sun is cooler, midday sit face on to the sun to reduce surface area exposed when the sun is at its hottest. They may also climb to the top of a plant at midday to get away from the soil surface which is hot as it radiates heat
  • Locusts may also increase breathing rate and the depth of breathing movements when it’s hot so that more water evaporates from the tracheal system, this cools the Locust’s body due to energy being used from the locust’s body due to water’s high specific latent heat
19
Q

How do Lizards regulate their body temperature?

A

Lizards tend to hide in burrows or crevices at the hottest and coolest parts of the day, this is because the burrow has a more stable temperature than the air meaning that in the hottest part of the day the lizards keep cool when it’s hot and keep warm when it’s cold

20
Q

What do horned lizards do to regulate their body temperature?

A

Horned lizards can expand their ribcage, this increases the surface area of their body that is exposed to the sun and therefore they can absorb more heat

21
Q

What are the responses of the skin of an endotherm to an increase in body temperature?

A
  • Sweat glands secrete fluid onto skin surface, as this evaporates it uses heat from the blood due to the high specific latent heat of water
  • Hairs and feathers lie flat to reduce insulation and allow greater heat loss
  • Vasodilation of arterioles and precapillary sphincters directs blood to the skins surface, increasing heat loss by radiation
22
Q

What is the gaseous exchange system of an endotherm’s response to an increase in body temperature?

A

Some animals pant to increase evaporation of water from the surface of the lungs and airways, evaporation uses heat from the blood due to the high specific latent heat of water

23
Q

What are the advantages of being an ectotherm?

A
  • Less of their food is used in respiration as they don’t use up energy to keep warm
  • More of the energy and nutrients gained from food is used for growth
  • They need to find less food
  • They can survive for longer periods without food
24
Q

What are the disadvantages of being an ectotherm?

A
  • Ectotherms don’t generate heat
  • They are less active in cooler temperatures to conserve heat energy, this means they are at risk from predators when they are cold
  • They also can’t take advantage of food that is available when it’s cold as they need to conserve heat energy
25
Q

What is the liver of an endotherm’s response to an increase in core body temperature?

A

Respiration in liver decreases so less heat is generated

26
Q

What are the skeletal muscles of an endotherm’s response to an increase in core body temperature?

A

Fewer contractions so less heat is generated from respiration

27
Q

What are the blood vessels of an endotherm’s response to an increase in core body temperature?

A

Vasodilation of arterioles and precapillary sphincters to direct blood to the surface of the skin to increase heat loss

28
Q

What is the skin of an endotherm’s response to a decrease in core body temperature?

A
  • Less sweat is secreted to reduce heat loss
  • Hairs and feathers stand up to trap a layer of air which provides insulation for the body
  • Constriction of arterioles and precapillary sphincter muscles to direct blood flow away from the surface of the skin
29
Q

What is the gaseous exchange system of an endotherm’s response to a decrease in body temperature?

A

Less panting so less evaporation of water from the surface of the lungs and airways, this decreases the amount of heat lost as energy isn’t lost evaporating the water

30
Q

What is the liver of an endotherm’s response to a decrease in body temperature?

A

Increased respiration in liver means more energy from food is converted to heat

31
Q

What are the skeletal muscles of an endotherm’s response to a decrease in core body temperature?

A

Spontaneous muscle contractions occur (shivering) which generates heat

32
Q

What are the blood vessels of an endotherm’s response to an decrease in core body temperature?

A

Vasoconstriction of arterioles and precapillary sphincter muscles to direct blood flow away from skin’s surface reducing the amount of heat lost by radiation

33
Q

What are the main advantages of being an endotherm?

A
  • Can maintain a constant body temperature whatever the external temperature
  • Remain active even when external temperature is low, this enables them to escape from predators or take advantage of prey that are ectothermic meaning they are inactive in the cold weather, so won’t be able to escape
  • Inhibit colder parts of the planet
34
Q

What are the main disadvantages of being an endotherm?

A
  • Use a significant part of their energy from respiration to maintain body temperature in the cold
  • Need more food
  • Use less energy and nutrients from food for growth
  • May overheat in hot weather
35
Q

What is the function of thermoreceptors in the skin?

A
  • To detect changes in temperature of the external environment and feed information to the thermoregulatory centre in the hypothalamus in the brain
  • If the thermoregulatory centre receives signals from the thermoreceptors in the skin that the external environment is very cold or hot then the brain can initiate responses to the hot or cold before core body temperature falls or rises as it is much easier to maintain temperature than it is to increase or decrease temperature
36
Q

What are the features of a good communication system?

A
  • 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
37
Q

What is the neuronal system?

A

An interconnected network of neurones that signal to each other across synapse junctions. Neurones can conduct a signal very quickly and enable rapid responses

38
Q

What is the hormonal system?

A

A system that uses the blood to transport its signals, cells in an endocrine organ release the signal (a hormone) directly into the blood. The hormone is transported throughout the body but only is recognised by complementary receptors on the target molecule. The hormonal system enables longer term responses

39
Q

Describe the mechanism of homeostasis

A
  • A sensory receptor such as a thermoreceptor detects a change and sends signals to the effector
  • The communication system such as the nervous system or the hormonal system transmits a message from the receptor cells to the effector via a coordination centre which is usually in the brain, messages sent to the coordination centres are known as the input and messages sent to the effectors are known as the output
  • Effector cells such as liver cells and muscles, these cells bring about a response

Biology A Level (21 decks)

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