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AQA A level biology <33 > Topic 6- Responding to changes in environment > Flashcards

Topic 6- Responding to changes in environment Flashcards

1
Q

what is a stimulus?

A

change in the internal or external environment of an organism

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2
Q

what is a receptor?

A

detects the stimulus to coordinate a response

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3
Q

what is taxis?

A

directional response to a stimulus
positive- towards
negative- away

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4
Q

what is kinesis?

A

non- directional response to stimulus

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5
Q

central nervous system

A

made of brain and spinal cord

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6
Q

peripheral nervous system

A

pairs of nerves originating from the brain or spinal cord

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7
Q

sensory neurones

A

carry nerve impulses from receptors to CNS

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8
Q

motor neurones

A

carry nerve impulses away from the CNS to receptors

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9
Q

voluntary nervous system

A

carries nerve impulses to body muscles and is under conscious control

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10
Q

autonomic nervous system

A

carries nerve impulses to glands, smooth muscle and cardiac muscle and is carried out subconsciously

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11
Q

simple reflex arc

A

stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response

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12
Q

importance of reflex arcs

A

1) involuntary meaning brain is left to carry out more complex responses
2) protect body from harm
3) fast due to very few synapses

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13
Q

pacinian corpuscle

A

detects mechanical pressure (mechanoreceptor)
at resting potential when sodium ion channels are too narrow for Na+ to pass through
when pressure is applied, the layers are distorted and stretch-mediated sodium ion channels open
influx of Na+ depolarises the membrane producing a generator potential therefore producing an action potential

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14
Q

where are rod and cone cells found?

A

fovea (cone)
retina (rod)

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15
Q

rod cells

A

~ higher density
~ cannot distinguish between different wavelengths meaning colour can’t be seen
~ multiple rod cells attached to one bipolar neurone leading to retinal convergence
~ higher chance of threshold being reached
~ help us to see when light is low
~ contain rhodopsin
~ low visual acuity

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16
Q

cone cells

A

~ three types each responding to different wavelengths meaning we can see in colour
~ lower density
~ each cone cell attached to a bipolar neurone leading to high visual acuity
~ contain pigment iodopsin
~ can only respond to high light intensity

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17
Q

sympathetic nervous system

A

stimulates effectors
fight or flight response

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18
Q

parasympathetic nervous system

A

inhibits effectors
conserving nearby and replenishing the body’s reserves

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19
Q

why is the heart myogenic?

A

contraction initiated from inside rather than by nervous impulses

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20
Q

sequence of steps that control heart rate

A

1) wave of electrical excitation spreads from SAN across atria causing them to contract
2) atrioventricular septum prevents wave crossing into ventricles
3) wave of excitation enters AVN
4) AVN conveys wave between ventricles through purkyne tissue which makes up the bundle of His
5) wave conducted down to base of ventricles where it’s released from the purkyne tissue causing ventricles to contract

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21
Q

what part of the brain controls changes to heart rate?

A

medulla oblongata
centre that increases heart rate- linked to SAN by sympathetic nervous system
centre that decreases heart rate- linked to SAN by parasympathetic nervous system

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22
Q

chemoreceptors

A

found in aorta and carotid artery
detect changes in blood pH

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23
Q

process of blood pH control

A

1) carbon dioxide conc. increases meaning blood pH decreases
2) detected by chemoreceptors which increases impulses to the centre in the medulla oblongata which increases heart rate
3) increases frequency of impulses via sympathetic nervous system to the SAN which will increase heart rate
4) increased blood flow removes more carbon dioxide so blood pH rises to normal

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24
Q

baroreceptors

A

detect blood pressure
in aorta and carotid arteries

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25
Q

process when blood pressure is high

A

barocreceptors send more impulses to centre of medulla oblongata that decrease heart rate
sends impulses via parasympathetic nervous system to SAN decreasing the heart beats

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26
Q

two types of coordination in animals

A

nervous system- transported by neurones, fast, short-lived
hormonal system- transported by blood, slow, long-lasting

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27
Q

myelinated neurones

A
  • cell body
  • dendrons —> dendrites
  • axon
  • myelin sheath made of schwann cells
  • nodes of ranvier
  • impulses move by saltatory conduction making them faster than non-myelinated neurones
28
Q

resting potential

A

charge inside axon is at -70mV (polarised)
3Na+ actively transported out of axon
2K+ actively transported into axon
Na+ channel closed

29
Q

action potential

A

stimulus of sufficient size causes threshold level (-55mV) to be reached
Na+ channels open causing an influx of Na+ (depolarisation)
once potential difference of around +40mV has been reached, Na+ channels close

30
Q

repolarisation

A

K+ channels open

31
Q

hyperpolarisation

A

temporary overshoot of electrical gradient meaning inside is more negative then normal
K+ channels close

32
Q

factors affecting speed of conduction

A

myelin sheath
diameter of axon
temperature

33
Q

all-or-nothing principle

A

any stimulus, of any strength, that is at threshold level will create an action potential of the same size

34
Q

refractory period

A

Na+ channels are closed for a period of time
ensures action potentials go in one direction
produces discrete impulses
limits number of action potentials

35
Q

synapse structure

A

presynaptic and postsynaptic neurones
synaptic cleft
synaptic vesicles
neurotransmitters
Na+ channels
Ca2+ channels

36
Q

unidirectionality of synapses

A

synapses can only pass information in one direction- from presynaptic to postsynaptic neurone

37
Q

spatial summation

A

many presynaptic neurones release enough neurotransmitters to exceed threshold level in the postsynaptic neurone

38
Q

temporal summation

A

single presynaptic neurone releases neurotransmitter many times over a very short period.

39
Q

inhibitory synapses

A

postsynaptic neurone hyperpolarised due to Cl- moving in and K+ moving out

40
Q

cholinergic synapses

A

1) action potential arrives at presynaptic neurone
2) Ca2+ channels open causing an influx (depolarisation)
3) synaptic vesicles move towards membrane and fuse
4) acetylcholine diffuses down conc. gradient in synaptic cleft and binds to receptors on Na+ channels
5) Na+ channels open causing an influx
6) if threshold is reached an action potential is generated
7) acetylcholinesterase hydrolyses acetylcholine into choline and acetyl which diffuses back across
7) prevents action potentials from being continuously generated
8) ATP recombines the 2 products into acetylcholine for future use

41
Q

neuromuscular junction

A

works in a similar way to cholinergic synapses except there’s no postsynaptic neurone, just muscles fibres
only excitatory
action potential ends here

42
Q

What are the 3 changes in the environment that plants respond to?

A

light (phototropism)
gravity (gravitropism)
water (hydrotropism)

43
Q

plant growth factors

A

hormone-like substances released in a response to external stimuli

44
Q

What does IAA stand for?

A

indoleacetic acid

45
Q

what is IAA?

A

type of auxin
found in the top of shoots (apex)
controls plant elongation

46
Q

what type of phototropism is found in plants?

A

positive phototropism (grows towards light)

47
Q

what type of phototropism is found in roots

A

negative phototropism

48
Q

positive phototropism in shoots

A

1) Cells in the tip produce IAA
2) IAA is initially transported evenly throughout the shoot
3) light causes IAA to move from the light side to shaded side
4) greater concentration of IAA on shaded side
5) IAA stimulates cell elongation
6) shoot grows towards the light

49
Q

negative phototropism in roots

A

1) IAA moves away from light side to shaded side
2) IAA inhibits cell elongation
3) Roots grow away from the light

50
Q

what type of gravitropism is found in shoots?

A

negative gravitropism

51
Q

what type of gravitropism is found in roots?

A

positive gravitropism

52
Q

negative gravitropism in shoots

A

1) IAA accumulates on lower side of the shoot
2) stimulates cell elongation
3) shoot grows away from gravity

53
Q

positive gravitropism in roots

A

1) IAA accumulates on lower side
2) inhibits cell elongation
3) Root grows towards gravity

54
Q

acid growth hypothesis

A

active transport of hydrogen ions from cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cell to elongate by expansion.

55
Q

how do neuromuscular junctions work?

A

same process as cholinergic synapses up to the depolarisation of the sarcolemma
~ depolarisation travels down tubules leading to release of calcium ions from stores in sarcoplasmic reticulum
~ acetylcholine broken down

56
Q

what are the 3 types of muscles?

A

cardiac
smooth
skeletal

57
Q

smooth muscle

A

found in lining of internal organs
involuntary
non-striated
spindle shape and only have one nucleus

58
Q

cardiac muscle

A

in heart
involuntary
specialised striated
single nucleus per fibre
branching

59
Q

skeletal muscle

A

attached to skeleton
voluntary
contacts in one direction
run parallel
multinucleated

60
Q

what are myofibrils?

A

tiny muscle fibre that makes up an individual muscle

61
Q

describe the structure of muscle fibres

A

t-tubules
sarcolemma (cell membrane)
mitochondria (ATP for contraction)
sarcoplasm
myofibrils
sarcoplasmic reticulum

62
Q

what are sacromeres?

A

repeating units of myofibrils

63
Q

hierarchy of muscle organisation

A

muscles
muscle fibres
myofibrils
protein fibres

64
Q

what are the two types of muscle fibre?

A

myosin
actin

65
Q

slow twitch fibres

A

contact more slowly
less powerful contractions over a longer period of time
adapted to endurance work
aerobic respiration
darker in colour due to the rich blood supply and large store of myoglobin

66
Q

fast twitch fibres

A

contact more rapidly
more powerful contractions over a short period of time
adapted to intense exercise
anaerobic respiration
high concentration of glycogen
store of phosphocreatine which can rapidly generate ATP form ADP

AQA A level biology <33 (12 decks)

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