Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

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

Topic 6 - Internal and External Changes Flashcards

1
Q

define a stimulus

A

a change in an organisms internal or external envrionment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

why is it important that organisms can respond to stimuli

A

organisms increase their chance of survival by responoding to stimuli

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is IAA’s effect on shoot tissue

A

it stimulates cell division and elongation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what tropisms does IAA cause in shoot tissue

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what tropisms does IAA cause in root tissue

A

it causes a positive gravitropic response and a negative phototropic response

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is IAA’s effect on root tissue

A

it inhibits cell devision and elongation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

define a hormone

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is auxin

A

a group of plant growth factors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what auxin do we need to know about

A

IAA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is a tropisim

A

growth of a plant in response to directional stimulus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what does positive tropism mean

A

growth of a plant towards a stimulus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what does negative tropism mean

A

growth of a plant away from stimulus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what does a clinostat enable

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what type of concentration of IAA do weed killers have

A

very strong

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how can organisms increase their chance of survivial

A

they can respond to changes in their environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is the sympathetic nervous system responsible for

A

it is responsible for the fight or flight response

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is the parasympathetic nervous system response

A

the rest and relax actions - e.g. digestion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is the autonomic nervous system responsible for

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is the somatic nervous system responsible for

A

responsible for voluntary movements e.g. muscle movements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what does the central nervous system control

A

the brain and spinal cord

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what does the peripheral nervous system control

A

the cranial and spinal nerves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what is the central nervous system responsible for

A

sensory activities, storing memories and emotions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what does the peripheral nervous system do

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

describe the structure of a sensory neurone

A
  • axon
  • dendrites
  • dendron
  • cell body (partway along the axon, adjacent)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

define nerve impulse

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

describe resting potential

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

what does self propagating mean

A

the previous section causes the next section to become depolarised

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

what does electrical disturbance mean

A

unequal distribution of positive ions NaK

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

describe action potential

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

describe the all or nothing principle

A
  • for an action potential to be produced, depolarisation must exceed the threshold potential
  • action potentials produced are always the same magnitude/size at the same potential
48
Q

what is the effect of bigger stimuli on the action potentials

A

they increase the frequency of action potentials

49
Q

What happens according to the all or nothing principle when depolarisation is below the threshold

A

NOTHING

no action potential which means that there is no impulse generated

any stimulus whatever the strength below the threshold value will fail to generate an action potential

50
Q

what happens according to the all or nothing action potential when depolarisation is above the threshold level

A

ALL

action potential generated so the nerve impulse will travel

the action potential are the same size at the same potential and always peak at the same maximum voltage

the strength of a stimulus does not affect the size of action potential

51
Q

how can an organism perceive the size of a stimulus if all action potentials are the same size

A

number of impulses passing in given time (frequency) - larger stimulus = more impulses generated in a given time

different neurons with different threshold values - brain interprets number/types off neurons that pass impulses as a result of a given stimulus = determines the size

52
Q

why is the all or nothing principle important

A

ensure animals only respond to large enough stimuli rather than responding to every slight change in the environment which would overwhelm them

53
Q

describe the nature of the refractory period

A

the time taken to restore the acon to resting potential when no further action potential can be generated as the Na+ channels are closed and will not open

54
Q

explain the importance of the refractory period

A

ensure discrete impulses are produced - action potentials don’t overlap
limits the frequency of impulse transmission at a certain intensity - prevents over reaction to stimulus
- higher intensity stimulus cuases a higher frequency of action potentials only up to a certain intensity
ensures action potentials travel in one direction

55
Q

define nerve impulse

A

the transmission of an action potential along an axon

56
Q

describe the speed an action potential moves

A

0.5 m/s - 120 m/s

57
Q

suggest how damage to the myelin sheath can lead to slow responses and/or jerky movements

A

less saltatory conduction = depolarisation occurs along the whole length of the axon, so nerve impulses take longer to reach neuromascular junction/delay in muscle contraction

ions/depolarisation may pass/leak to other neurones = wrong muscle fibres contract

58
Q

describe how the passage of an action potential along non-myelinated axons result in nerve impulse

A

action potential passes as a wave of depolarisation
influx of Na+ in one region increases permeability of adjoining region to Na+ by causing voltage-gated Na+ channels to open so adjoining region depolarises

59
Q

describe how the passage of an action potential and myelinated axons results in nerve impulses

A

myelination provides electrical insulation
depolarisation of axon at nodes of Ranvier only
results in saltatory conduction [local currents circuits]
so there is no need for depolarisation along the whole length of axon

60
Q

describe the function of the myelin sheath and how it affects the speed of an action potential

A
  • insulates the axon preventing an action potential from forming in parts of the axon covered in schwann cells
  • results in saltatory conduction where the action potential jumps from one node of ranvier to the next
61
Q

what is the affect of saltatory conduction in myelinated vs non myelinated neurones

A

triples the speed in myelinated neurones

62
Q

state 3 factors that affect the speed of an action potential

A

myelin sheath
diameter of the axon
temperature

63
Q

describe how the diameter of the axon affectts the speed of an action potential

A

greater the diameter of an axon, the faster the speed of conductance due to:
- greater diamater = smaller SA:V = smaller leakage and membrane potential is easier to maintina
- greater diameter = large SA = larger area for attachment of voltage-gated channels = faster diffusion = faster switch in potentiall difference

64
Q

describe how temperature affects the speed of an action potential

A

causes an increased rate of diffusion therefore action potentials generated more rapidly
active transport of ions by NaK pump requires ATP from respiration which requires enzymes that is affected by temperature
gated channels and NaK pump will denature = control of ion distribution is lost and impulses cannot be conducted

65
Q

state 5 ways the synapse’s structure has adapted to its function

A
  • bulbous knob giving a large surface area: for attachment of transport proteins to allow rapid facilitated diffusion + active transport
  • small diffusion distance: decreases time taken for an action potential to be created in the post-synaptic neurone
  • mitochondria: ATP to provide energy for synthesis of neurotransmitter/vesicles/proteins
  • RER: synthesis of transport proteins
  • SER: synthesis of neurotransmitter and vesicles
66
Q

explain how acetylcholine contributes to a synapse being unidirectional

A
  • acetylcholine is released from the presynaptic side
  • receptors in postsynaptic side
67
Q

why are synapses important

A
  • a single impulse can be transmitted to multiple neurones = single impulse can create multiple responses
  • multiple impulses from multiple receptors can be passed to a single neurone = single response from multiple different stimuli
68
Q

describe the transmission across a cholinergic synapse in the presynaptic neurone

A
  • depolarisation of pre-synaptic membrane causes the opening of volted-gated Ca2+ channels, diffuse into pre-synaptic knob
  • causes vesicles containing acetylcholine to move and fuse with the pre-synaptic membrane, releasing ACh into the synaptic cleft by exocytosis
69
Q

describe transmission across a cholinergetic synapse in the postsynaptic neurone

A
  • ACh diffuses across the synaptic cleft to bind to specific receptors on post-synaptic membrane causing Na+ channels to open
  • Na+ diffuse into post-synaptic knob causing depolarisation, if the threshold is met, action potential is initiated
70
Q

describe what happens to acetylcholine after synaptic transmission

A
  • hydrolysed by acetylcholinesterase
  • products are reabsorbed by presynaptic neurone
    this is to stop overstimulation, if not removed it would keep binding to receptors causing depolarisation
71
Q

describe temporal summation

A
  • one pre-synaptic neurone releases neurotransmitter many times over a short period of time
  • sufficient NT to reach threshold to trigger an action potential
72
Q

describe spatial summation

A
  • many pre-synaptic neurones share one post synaptic neurone
  • collectively release sufficient neurotransmitters to reach threshold to trigger an action potential
73
Q

describe inhibition by inhibitory synapses

A

inhibitory neurotransmitters hyperpolarise postsynaptic membrane:
Cl- channels open (diffuse in) + K+ channels open (diffuse out)
more Na+ required for depolarisation
reduces likelihood of threshold being met and action potential formation at post-synaptic membranes

74
Q

describe how muscles work

A

they work in antagonistic pairs = pull in opposite directions
- one muscle contracts, pulling on the bone
- one relaxes

75
Q

what is the advantage of muscles working in antagonistic pairs

A

the second muscle is required to reverse the movement caused by the first and it helps to maintain posture

76
Q

describe the gross structure of skeletal muscle

A

made up of many bundles of muscle fibres packaged together, they are attached to bones by tendons

77
Q

what do muscle fibres contain

A

muscle fibres are made up of long cylindrical cells containing many nuclei and myofibrils

  • sarcolemma (cell membrane)
  • sarcoplasm (cytoplasm)
  • sarcoplasmic reticulum (endoplasmic reticulum)
  • multiple nuclei
  • many myofibrils
  • many mitochondria
  • T (transverse) tubles from sarcolemma folding inward
78
Q

describe the ultrastructure of a myofibril

A

made of two types of long protein filaments arranged in parallel = myosin (thick) and actin (thin)

arranged in functional repeating units called sarcomeres = Z line, M line, H zone

79
Q

what causes the characteristic banding pattern of myofibrils

A

characteristic banding pattern due to the arrangement of myofilaments

80
Q

what is cross-striations

A

when muscle cells are composed of alternating light and dark bands

81
Q

explain the banding pattern in I bands

A

light band containing only thin actin filaments

82
Q

explain the banding pattern in A bands

A

dark bands containing thick myosin and some actin filaments

83
Q

explain the banding pattern in the H zone

A

it contains only myosin

84
Q

what does A in A band stand for

A

anisotropic

85
Q

what does I in I band stand for

A

isotropic

86
Q

why is summation by synapses important

A

low frequency of action potentials release insufficient neurotransmitter to exceed the threshold

87
Q

define excitatory synapse

A

a synapse that increases the likelihood of an action potential in the post-synaptic membrane

88
Q

explain the effect of drugs on a synapse

A
  • stimulate the nervous system leading to more action potentials = similar shape to NT, stimulates the release of more NT, inhibits the enzyme that breaks down the NT = Na+ continues to enter
  • inhibit the nervous system leading to less action potentials = inhibits the release of NT and blocks the receptors mimicking the shape of NT
89
Q

name the gap between the pre-synaptic membrane and post-synaptic membrane

A

synaptic cleft

90
Q

how does myosin and actin interact

A

the myosin head attaches to actin and bends

91
Q

suggest why ATP is needed in the presynaptic membrane

A

active transport of ions, movement of vesicles

92
Q
A

Biology A-Level (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions