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Biology A-Level > Topic 6 - Internal and External Changes > Flashcards

Topic 6 - Internal and External Changes Flashcards

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1
Q

define a stimulus

A

a change in an organisms internal or external envrionment

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2
Q

why is it important that organisms can respond to stimuli

A

organisms increase their chance of survival by responoding to stimuli

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3
Q

what is IAA’s effect on shoot tissue

A

it stimulates cell division and elongation

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4
Q

what tropisms does IAA cause in shoot tissue

A

a positive phototropic response (phototropism) and negative gravitropic response (geotropism)

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5
Q

what tropisms does IAA cause in root tissue

A

it causes a positive gravitropic response and a negative phototropic response

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6
Q

what is IAA’s effect on root tissue

A

it inhibits cell devision and elongation

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7
Q

define a hormone

A

a chemical messener produced by a gland that travels in the bloodstream which affects a target organ

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8
Q

why is auxin a plant growth factor

A
  • it is produced by a collection of undifferentiated cells called a meristem (not a gland)
  • it diffuses through plant tissue (not transported in the blood)
  • it affects many cells/tissues including the cells that produces it
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8
Q

what is auxin

A

a group of plant growth factors

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9
Q

what auxin do we need to know about

A

IAA

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10
Q

what is a tropisim

A

growth of a plant in response to directional stimulus

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11
Q

what does positive tropism mean

A

growth of a plant towards a stimulus

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12
Q

what does negative tropism mean

A

growth of a plant away from stimulus

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13
Q

what does a clinostat enable

A

for there to be an equal gravitational force on plants when growing

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14
Q

state 3 things that have an impact on growth response

A
  • growth factor
  • concentration of the growth factor
  • tissue responding to the growth factor
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15
Q

what type of concentration of IAA do weed killers have

A

very strong

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16
Q

explain gravitropism in flowering plants

A
  • cells in trip of shoot/root produce IAA
  • IAA diffuses down shoot/root intially evenly
  • IAA moves to lower side of shoot/root so concentration increase
  • cell elongation in shoots is stimulated whereas in roots it inhibits cell elongation
  • shoots bend away from gravity whereas roots bend towards gravity
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17
Q

explain phototropism in flowering plants

A
  • cells in tip of shoot/root produce IAA
  • IAA diffuses down shoot/root evenly initially
  • IAA moves to shaded side of shoot/root so concentration increases
  • in shoots, this stimulates cell elongation whereas in roots, this inhibits cell elongation
  • shoots bend towards light whereas roots bend away from light
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18
Q

how can organisms increase their chance of survivial

A

they can respond to changes in their environment

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19
Q

what is the sympathetic nervous system responsible for

A

it is responsible for the fight or flight response

20
Q

what is the parasympathetic nervous system response

A

the rest and relax actions - e.g. digestion

21
Q

what is the autonomic nervous system responsible for

A

for involutary actions e.g. heart beat, pupil dilation

22
Q

what is the somatic nervous system responsible for

A

responsible for voluntary movements e.g. muscle movements

23
Q

what does the central nervous system control

A

the brain and spinal cord

24
Q

what does the peripheral nervous system control

A

the cranial and spinal nerves

25
Q

what is the central nervous system responsible for

A

sensory activities, storing memories and emotions

26
Q

what does the peripheral nervous system do

A

it brings messages to and from the CNS to the rest of the body

27
Q

describe the structure of a motor neurone

A

should have mentioned:
- nucleus
- cytoplasm (in cell body)
- dendron branched into dendrites
- axon (also cytoplasm)
- myelin sheath
- schwann cell (make up the myelin sheath)
- node of ranvier (gap btwn the schwann cells)

28
Q

describe the structure of a sensory neurone

A
  • axon
  • dendrites
  • dendron
  • cell body (partway along the axon, adjacent)
29
Q

describe the structure of an intermediate/relay neurone

A
  • axon
  • dendrites
  • dendron
  • cell body is part of the axon and not parallel to it
30
Q

define nerve impulse

A

a self propagating wave of electrical disturbance that travels along the surface of the axon membrane

31
Q

describe resting potential

A

the axon cytoplasm is less positively charged compared to the surrounding tissue fluid

32
Q

explain how a resting potential is established across the axon membrane in a neurone

A
  • Na\k pump actively transports (using ATP) Na out of the axon and K into the axon
  • this causes an electrochemical gradient = higher K conc inside and higher Na conc outside
  • differential membrane permeability = more permeable to K - move by FD. less permeable to Na
33
Q

what does self propagating mean

A

the previous section causes the next section to become depolarised

34
Q

what does electrical disturbance mean

A

unequal distribution of positive ions NaK

35
Q

what does surface of an axon mean

A

only impacts the surface of the phospholipid bilayer = diameter of the neurone can affect the speed of an action potential

36
Q

describe action potential

A

when the axon cytoplasm becomes more positively charged than the surrounding tissue fluid

37
Q

how many sodium and potassium ions are pumped out each time

A

3 sodium out for 2 potassium in

Na-OUT and K-in

38
Q

how is the unequal distribution of Na and K in the cytoplasm and tissue fluid maintained (how is a resting potential maintained)

A
  • the phospholipid bilayer of the axon is impermeable to Na and K
  • intrinsic proteins are found in the phospholipid bilayer: Na voltage gated channels are closed. K voltage gated channels are some are alwaysopen and some are closed when it is resting potential
  • a sodium otassium pump actively transports Na and K across the axon membrane: 3 Na out, 2 K in
39
Q

what is the approx value of the resting potential

A

-65 mV (milli volts)

40
Q

what is the peak value of the action potential

A

+40 mV

41
Q

can you draw/label a graph showing action potential

A

labelled:
- voltage gated Na channels open
- Na channels open
- hyperpolarisation
- resting potential
- stimulus
- depolarisation
- repolarisation
- voltage gated Kchannel open,Na channel closed
- voltage gated K+ channel close

42
Q

define action potential

A

when a stimulus detected by a receptor and the energy causes a temporary reversal of the charges on the axon membrane

43
Q

what is the membrane like during action potential

A

depolarised

44
Q

why does depolarisation occur

A

due to the voltage gated channels

45
Q

what is the difference between resting and action potential

A

resting - more +ve outside
action - move +ve inside

46
Q

describe action potential

A

at resting potential:
- some K+ gated channels are open
- all Na+ gated channels are closed
the energy of the stimulus causes some of the Na+ gated channels to open
- Na+ diffuses into the axon along the electrochemical gradient
- this causes a reversal in potential difference across the membrane
Na+ diffuses into the axon
- axon cytoplasm becomes more positive = more Na+ gated channels open
- amplifies the influx of Na+
when the action potential reaches +40mV the Na+ gated channels close
- additonal K+ gated channels open
K+ gated channels are open = electrochemical gradient is reversed
- K+ diffuses out of the axonn = repolarisation of the axon
hyperpolarisation (axon cytoplasm is more negative than usual)
- K+ gated channels close
- NaK pump resores to 65 mV
- axon is replenished

47
Q
A

Biology A-Level (11 decks)

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