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Biology > Communication And Homeostasis > Flashcards

Communication And Homeostasis Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is homeostasis

A

The maintenance of the body’s internal conditions when the external environment is changing

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2
Q

Why is homeostasis important

A

Maintenance of optimal conditions for enzyme action and cell function

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3
Q

What factors does homeostasis control

A

Conc of glucose in blood
Conc of respiratory gases
Blood water potential
Waste products (o2 , urea)
Blood pH
Body temperature

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4
Q

What two systems are involved in homeostasis

A

Endocrine system

Nervous system

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5
Q

What does the nervous system consist of

A

Central nervous system (CNS)

Periphery nervous system (PNS)

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6
Q

What does the CNS consist of

A

Brain

Spinal cord

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7
Q

What does the periphery nervous system consist of

A

All the nerves in the body

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8
Q

What is a hormone

A

A hormone is a chemical substance produced by an endocrine gland and carried by the blood

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9
Q

What is a gland

A

A gland is a group of cells which produces and releases one or more substances

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10
Q

Why does the blood glucose level need to be controlled

A

Because it affects the water potential if the blood and availability of respiratory substrates for cells

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11
Q

What is negative feedback

A

A feedback loop which helps to return the change back to the original levels

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12
Q

Positive feedback

A

When a stimulus produced a response which causes the factor to deviate from its normal range

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13
Q

What is an endotherm

A

An organism which have physiological mechanisms to control body temp

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14
Q

What is an exotherm

A

An organism which relies on behavioural characteristics to control body temp

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15
Q

What is the endotherm response to a low body temperature

A

Vasoconstriction - muscles of arteriole walls contract, so arterioles near skin constrict and allow less blood to flow near skin capillaries and direction of blood flow is directed to deeper vessels to reduce the heat lost to environment

Increased metabolic rate - most metabolic actions are exothermic so provide warmth to body. In cold environments the hormone thyroxine increases basal metabolic rate increasing heat production in body

Shivering

Erection of hairs - erector muscles in skin contract causing hairs to rise and heat to be trapped between air over skins surface

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16
Q

Why can ectotherms survive with less food

A

Because less energy and nutrients is wasted in heat regulation and so more nutrients and energy is used for growth and repair

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17
Q

Why do aquatic ectotherms have a more stable body temperature

A

Because the water has a high specific heat capacity which means it’s temperature remains relatively stable

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18
Q

What is a neurone

A

A specialised cell which carries electrical impulses around the body

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19
Q

What features are found in a neurone?

A

Long fibre called an axon

Cell body which contains a nucleus and other cell structures

The end of an axon called an axon terminal which has many nerve endings

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20
Q

What do the nerve endings at the axon terminal allow neurones to do

A

Connect to other neurones which receive impulses from axon terminal which forms a network for easy communication

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21
Q

What insulates neurones

A

Myelin sheath

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22
Q

What is a myelin sheath made of

A

Schwann cells

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23
Q

What are the gaps between myelinated parts of the neurone called

A

Nodes of ranvier

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24
Q

Why are neurones with myelin sheath faster at transporting impulses than non myelinated neurones

A

Myelinated neurones cause the impulses to jump from one node to the next so less time is wasted transferring the impulse from one neurone to the next as it doesn’t have to pass down the whole axon

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25
Q

Why does the non myelinated neurone take longer to transport impulses

A

Because the impulse has to carry down the whole axon

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26
Q

What does the sensory neurone do

A

Carries impulses from receptors to CNS

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27
Q

What do relay neurones do

A

Connect sensory and motor neurones in the CNS

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28
Q

What do motor neurones do

A

Carry impulses from CNS to effectors

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29
Q

What are the features of a motor neurone

A

Motor neurones have:
a large cell body at one end which lies within spinal cord or brain

A nucleus always in the cell body

Many branched dendrites which provide a large surface area for the axon terminals and other neurones

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30
Q

What are the features of a relay neurone

A

Short but branched axons and dendrites

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31
Q

What are the features of a sensory neurone

A

A cell body branching off in the middle of the cell

A single long dendron which carries impulses to the cell body

And a single long axon which carries impulses away from cell body

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32
Q

What are transducers

A

Something which converts energy from one form to another in an electrical impulse

33
Q

What are pacinian corpuscles an example of

A

A mechanoreceptor

34
Q

Where are pacinican corpuscles found

A

In the feet, fingers, joints, tendons , ligaments

35
Q

What do pacinian corpuscles respond to changes in

A

Pressure

36
Q

Describe how a pacinian corpuscle functions

A

No pressure
Stretch mediated sodium channels are too narrow so sodium remains outside membrane. This helps maintain resting potential

Pressure applied
Layers distorted causing stretch mediated sodium channels to open. Sodium ions enter axon of sensory neurone

Generator potential established
Influx of sodium ions changes the potential of the axon which causes depolarisation of the membrane. If enough generator potential produced an action potential will be established and nerve impulse moves along axon

37
Q

What is between the layers of pascilian corpuscles

A

Positively charged Na+ ions

38
Q

What does the resting potential mean

A

The inside of the neurone is more negative than the outside

39
Q

What is the resting potential

A

-70mV

40
Q

What maintains the resting potential in neurones

A

Sodium-potassium pumps actively pump 3Na+ ions out of the neurone for every 2k+ pumped in (therefore outside more positive)

Potassium channels which makes the membrane more permeable to potassium ions than sodium ions

Anions inside the cytoplasm which are negative

41
Q

What are the stages of an action potential

A

Stimulus

Depolarisation

Depolarisation

Hyperpolarisation

Resting potential

42
Q

Describe in detail the process of generating an action potential

A

Stimulus - stimulus detected resulting in sodium channels opening. This causes some Na+ ions to diffuse into the neurone making it slightly more positive inside. This generated a small potential difference.

Depolarisation - once the potential difference created meets the threshold of about -40mV, an action potential is generated and voltage gated sodium channels open causing a huge influx of sodium ions down the electrochemical gradient into the neurone making it more positive compared to the outside. This triggers more sodium channels to open.

Once depolarisation meets a threshold of about +30mV, the sodium channels close and the voltage gated potassium channels open. This causes an influx of potassium ions out of the neurone making it more negative than the outside of the neurone. This returns the potential difference back to resting potential.

However as the voltage gated potassium channels close slowly, it results in hyperpolarisation where the potential difference becomes more negative than the resting potential. The resting potential is later restored due to the sodium-potassium pump.

43
Q

What is the refractory period

A

A period during hyperpolarisation when the sodium ion channels are closed (during depolarisation) and the potassium ion channels are closed (during hyperpolarisation) and the axon is ‘recovering and unresponsive’

44
Q

Where does the refractory period begin

A

When repolarisation starts and when resting potential is re-established

45
Q

Why is the refractory period important

A

Stops action potentials merging into one

Ensures ‘new’ action potentials generated ahead rather than behind original action potential so impulses can only travel in one direction

46
Q

What is the speed of conduction determined by

A

Myelination

Diameter of axon

Temperature

47
Q

Why do myelinated areas have a faster speed of conduction

A

Because they contain Schwann cells

This means that myelin areas cannot be depolarised and therefore action potentials cannot be generated as myelin blocks the diffusion of sodium and potassium ions

Therefore the action potential is only generated through saltatory conduction where the action potential ‘jumps’ between nodes of ranvier

48
Q

Why do thicker axons have a higher speed of conduction

A

Thicker axons have a large surface area for the diffusion of ions. This increases the rate of diffusion of sodium and potassium ions through protein channels which increases the rate of depolarisation and action potentials

Thicker axons also have greater volume of cytoplasm which reduces their electrical resistance so an action potential can push into next section faster

49
Q

How does temperature affect the rate of conductivity

A

In colder temperatures, the sodium and potassium ions have less kinetic energy which means that the rate of facilitated diffusion and therefore generation of an action potential is lower

50
Q

What is a synapse

A

A junction when two neurones meet

51
Q

What do synapses consist of

A

Presynaptic knob

Synaptic cleft

Postsynaptic membrane

52
Q

What are synapses which use acetylcholine described as being

A

Cholinergic synapses

53
Q

Describe how synapses work to transport the action potential across the gap

A

An action potential reaches the presynaptic knob. This causes the voltage gated calcium channels to open allowing calcium ions to diffuse into the presynaptic knob. This causes the synaptic vesicles to move and bind to the presynaptic membrane. Then acetylcholine is released by exocytosis. Then acetylcholine diffuses across the presynaptic cleft and binds to the receptions on the sodium ion channels on the post synaptic membrane. This causes the sodium channels to open causing an influx of sodium ions causing a generator potential. If there is enough generator potentials then an action potential is created. The acetyl cholinesterase enzyme breaks down the acetylcholine into acetic acid and choline/ recycled back to presynaptic knob

54
Q

What is the enzyme which breaks down acetylcholine after it has bound to the membrane on the sodium channels on the postsynaptic membrane

A

Acetylcholinesterase

55
Q

What is acetylcholine broken down into

A

Ethanoic acid (acetic acid)

Choline

56
Q

Why does the presynaptic bulb contain lots of mitochondria and endoplasmic reticulum

A

Mitochondria - it is an active process so mitochondria involved. ATP also required to form acetylcholine after it has been returned to the presynaptic bulb in the form of acetic acid and choline

Endoplasmic reticulum - to pack the synaptic vesicles which contains the neurotransmitter

57
Q

Why is it important that the presynaptic cleft contains acetylcholinesterase

A

To ensure a constant action potential is not generated

58
Q

Why do synapses only conduct an electrical impulse one way

A

As neurotransmitters are released on one side and the other side is receptors so chemical transmission can only go in one direction

59
Q

Why are some impulses unable to trigger an action potential

A

This is because the impulse is too small so only a little acetylcholine is released. This means that only a few voltage gated sodium channels open so few sodium ions diffuse into the membrane and threshold potential is not reached

60
Q

What is summation

A

Summation is when impulses are added together to produce an action potential

61
Q

What are the advantages of summation

A

Allows for effect of stimulus to be magnified

Combination of different stimuli can trigger a response

Avoids nervous system being overwhelmed

62
Q

What is temporal summation

A

Temporal summation is when multiple impulses arrive in quick succession and added together to produce an action potential

63
Q

What is spatial summation

(Spatial = simultaneous and several synaptic knobs)

A

Spatial summation is when multiple impulses arrive simultaneously at different synaptic knobs which stimulates the same cell body which triggers an action potential

64
Q

What can happen after repeated stimulation of a neurone

A

It becomes fatigued as the vesicles run out of neurotransmitter. Therefore the synapse no longer responds to stimulus

It has become HABITUATED

65
Q

How is habituation a good thing

A

It prevents over stimulation of an effector which can cause damage

66
Q

What do IPSPs do (inhibitory post synaptic potential)

A

It decreases the effect of summation to prevent an action potential in the post synaptic neurone

67
Q

What does an EPSP do (excitatory post synaptic potential)

A

Increases the effect of summation

68
Q

What are the two layers of the adrenal glands

A

Inner part is the medulla

Outer part is the cortex

69
Q

What does the cortex release

A

The cortex releases steroid hormones
- regulates salt conc through aldosterone
- regulates metabolism of glucose, proteins and fats to release energy

70
Q

What does the medulla release

A

The medulla releases adrenaline and noradrenaline

71
Q

Describe how peptide hormones signal to other cells

A

They are not fat soluble so cannot diffuse through phospholipid bilayer

This means they have to bind to a complimentary receptor. This activates a G protein which then activates the enzyme acetyl Cyclase which catalyses the reaction of ATP —-> cAMP (second messenger). Because cAMP is the second messenger it can then go onto either having a direct effect on a target cell or can be used to trigger a cascade of other enzyme reactions

72
Q

What are the three areas in the cortex

A

Zona glumerulosa

Zona fasciculata

Zona reticuluaris

73
Q

What is the function of the Zona glomerulosa

A

Secretes mineralcorticoids such as aldosterone
It regulates salt concentration

74
Q

What is the function of the Zona fasciculata

A

Secretes glucocorticoids like cortisol which regulate starch/carbohydrate metabolism

75
Q

What is the function of the Zona reticularis

A

Secretes androgens (precursor molecules) which control sex hormones

76
Q

What are 2 things the pancreas secretes

A

Pancreatic juices to aid digestion

Hormones secreted from islets of langerhans into blood

77
Q

What do alpha cells secrete

A

Glucagon

78
Q

What do beta cells secrete

A

Insulin

79
Q

What cells do the islets of langerhan contain

A

Both beta cells and alpha cells

Biology (8 decks)

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