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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
process when blood pressure is high
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
26
two types of coordination in animals
nervous system- transported by neurones, fast, short-lived hormonal system- transported by blood, slow, long-lasting
27
myelinated neurones
- 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
resting potential
charge inside axon is at -70mV (polarised) 3Na+ actively transported out of axon 2K+ actively transported into axon Na+ channel closed
29
action potential
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
repolarisation
K+ channels open
31
hyperpolarisation
temporary overshoot of electrical gradient meaning inside is more negative then normal K+ channels close
32
factors affecting speed of conduction
myelin sheath diameter of axon temperature
33
all-or-nothing principle
any stimulus, of any strength, that is at threshold level will create an action potential of the same size
34
refractory period
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
synapse structure
presynaptic and postsynaptic neurones synaptic cleft synaptic vesicles neurotransmitters Na+ channels Ca2+ channels
36
unidirectionality of synapses
synapses can only pass information in one direction- from presynaptic to postsynaptic neurone
37
spatial summation
many presynaptic neurones release enough neurotransmitters to exceed threshold level in the postsynaptic neurone
38
temporal summation
single presynaptic neurone releases neurotransmitter many times over a very short period.
39
inhibitory synapses
postsynaptic neurone hyperpolarised due to Cl- moving in and K+ moving out
40
cholinergic synapses
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
neuromuscular junction
works in a similar way to cholinergic synapses except there’s no postsynaptic neurone, just muscles fibres only excitatory action potential ends here
42
What are the 3 changes in the environment that plants respond to?
light (phototropism) gravity (gravitropism) water (hydrotropism)
43
plant growth factors
hormone-like substances released in a response to external stimuli
44
What does IAA stand for?
indoleacetic acid
45
what is IAA?
type of auxin found in the top of shoots (apex) controls plant elongation
46
what type of phototropism is found in plants?
positive phototropism (grows towards light)
47
what type of phototropism is found in roots
negative phototropism
48
positive phototropism in shoots
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
negative phototropism in roots
1) IAA moves away from light side to shaded side 2) IAA inhibits cell elongation 3) Roots grow away from the light
50
what type of gravitropism is found in shoots?
negative gravitropism
51
what type of gravitropism is found in roots?
positive gravitropism
52
negative gravitropism in shoots
1) IAA accumulates on lower side of the shoot 2) stimulates cell elongation 3) shoot grows away from gravity
53
positive gravitropism in roots
1) IAA accumulates on lower side 2) inhibits cell elongation 3) Root grows towards gravity
54
acid growth hypothesis
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
how do neuromuscular junctions work?
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
what are the 3 types of muscles?
cardiac smooth skeletal
57
smooth muscle
found in lining of internal organs involuntary non-striated spindle shape and only have one nucleus
58
cardiac muscle
in heart involuntary specialised striated single nucleus per fibre branching
59
skeletal muscle
attached to skeleton voluntary contacts in one direction run parallel multinucleated
60
what are myofibrils?
tiny muscle fibre that makes up an individual muscle
61
describe the structure of muscle fibres
t-tubules sarcolemma (cell membrane) mitochondria (ATP for contraction) sarcoplasm myofibrils sarcoplasmic reticulum
62
what are sacromeres?
repeating units of myofibrils
63
hierarchy of muscle organisation
muscles muscle fibres myofibrils protein fibres
64
what are the two types of muscle fibre?
myosin actin
65
slow twitch fibres
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
fast twitch fibres
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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