5.1.5 Plant and Animal Response Flashcards
(145 cards)
1
Q
what are ways that plants can sense changes in environment, and adapt to them
A
- can sense the direction of light (and grow towards in to maximise light absorption for photosynthesis)
- can sense gravity, so their roots and shoots grow in the right direction
- climbing plants can sense touch, so they can find things to climb and reach sunlight
2
Q
what do plants need to respond to, in order to increase chances of survival
A
- herbivory
- abiotic stress
3
Q
what is herbivory
A
being eaten by plants
- plants are more likely to survive if they can respond to this
4
Q
what toxic chemicals can plants produce, in response to being eaten
A
- ALKALOIDS: chemicals with bitter taste, noxious smells or poisonous characteristics
- so able to deter or kill herbivores
- e.g. tobaccos plants produce alkaloid nicotine in response to tissue damage, and nicotine is highly poisonous to many insects
- TANNINS: taste bitter, and in some herbivores (e.g. cattle and sheep), can bind to proteins in the gut, making the plant hard to digest
- both deter animals from eating the plant
5
Q
what are pheromones
A
signalling chemicals that produce a response in other organisms
6
Q
what pheromones do plants release in response to herbivory
A
- some release ALARM PHEROMONES in the air, in response to herbivore grazing, which causes nearby plants to detect these chemicals to start making chemical defences such as tannins
- corn plants after being eaten by caterpillars, produce pheromones which attract parasitic wasps, which then lay their eggs in the caterpillars, which eventually kills them
7
Q
what is a physical response of a plant to being touched
A
- the plants fold up
- e.g. if a single leaflet of plant Mimosa pudica is touched, the signal spreads through the whole leaf
- this causes it to quickly fold up
- helps protect it against herbivory
- as knocks off any small insects feeding on the plant
- scares off animals trying to eat it
8
Q
what is abiotic stress to plants
A
- anything living that is natural but non-living
- e.g. drought
- e.g. extreme cold
9
Q
how do some plants respond to extreme cold
A
- produce their own form of antifreeze
- e.g. carrots
- produce antifreeze proteins at low temperature
- the proteins bind to ice crystals and lower the temperature water freezes at
- stops more ice crystals from growing
10
Q
what is a tropism
A
the response of a plant to a directional stimulus (stimulus coming from a particular direction), by regulating their growth
11
Q
what is positive tropism
A
growth towards the stimulus
12
Q
what is negative tropism
A
growth away from the stimulus
13
Q
what is phototropism
A
the growth of a plant in response to light
- shoots are positively phototropic and grow towards the light
- roots are negatively phototropic, and grow away from the light
14
Q
what is geotropism
A
the growth of a plant in response to gravity
- shoots are negatively geotropic and grow upwards
- roots are positively geotropic and grwo downwards
15
Q
what is hydrotropism
A
plant growth in response to water
- roots are positively hydrotropic
16
Q
what is thermotropism
A
plant growth in response to temperature
17
Q
what is thigmotropism
A
plant growth in response to contact with an object
18
Q
what brings about some of the responses to stimuli of plants
A
growth hormones (also called growth substances)
- chemicals that speed up or slow down plant growth
19
Q
where are growth hormones produced
A
in the growing regions of the plant
- shoot tips
- leaves
but they move to where they are needed in other parts of the plant
20
Q
what does growth hormone gibberellin do
A
stimulates:
- seed germination
- stem elongation
- side shoot formation
- flowering
21
Q
what do growth hormones auxins stimulate in a plant
A
- growth of shoots by stem elongation
- where the cell walls become loose and stretchy
- so the cells get longer
22
Q
what can a high concentration of auxins cause
A
inhibition of growth in the roots
23
Q
where are auxins produced
A
the tips of shoots of flowering plants
24
Q
what is an example of an auxin, and what does it do
A
- indoleacetic acid
- IAA
- works by stimulating cell elongation
25
how does IAA move around the plant
- via diffusion and active transport over short distances
- via phloem over long distances
26
why does IAA move around a plant
- to control tropisms
- but its movement means different parts of the plant have different amounts of IAA
- and an uneven distribution of IAA means that there is uneven growth of the plant
27
how does IAA respond to phototropism
- IAA moves to the more shaded parts of shoots and roots
- so in SHOOTS: the cells ELONGATE and bend towards the light
- and in ROOTS: the growth is INHIBITED and the roots bend away from the light
- means there is uneven growth
28
how does IAA respond to geotropism
- IAA moves to the underside of the shoots and roots due to gravity
- so in SHOOTS: the cells ELONGATE and the shoot grows upwards
- and in ROOTS: the growth here is INHIBITED, so the root grows downwards
29
PRACTICAL: how would you carry out an investigation into phototropism
- via showing how plant shoots respond to light:
1) take 9 wheat shoots, all planted in individual pots, but same type of soil and roughly equal in height
2) cover the tips of the 3 shoots with a foil cap, leave 3 without foil and wrap the base of the final 3 with foil, so only the tip is exposed
3) set up the shoots in front of a light source and leave for 2 days
- need to make sure all shoots are same distance away from the light source, and experience same intensity of light, and all other variables (temperature, exposure to moisture) should be controlled
4) at end of experiment, should get results
- you can record the amount of growth (in mm) and direction of growth to give you quantitative results
30
PRACTICAL: what should be the results of your phototropism investigation
- the shoots with exposed tips: grown towards the light source (as positive tropism)
- this includes completely exposed and the one with the covered base, and it should still grow towards the light
- covering the tip with foil cao would've prevented growth towards the light
- AS it is the tip (where the IAA is produced) that is most sensitive to light
- so if covered, the shoot should just grow straight up
31
PRACTICAL: how could you perform a practical investigation into geotropism
1) line 3 petri dishes with moist (not soaking) cotton wool
2) should use the same volume of water and the same amount of cotton wool in each dish
3) space out 10 cress seeds on the surface of the wool in each dish, then push each one into the wool
4) tape a lid on each dish and wrap in foil (prevents light reaching the wool and affecting your results)
5) store you dishes somewhere with a warmish, pretty constant temperature, e.g. a cupboard
6) prop one dish up, at a 90°, label it and mark which way is up. place another dish on a slope at 45° angle and the third on a flat, horizontal surface
7) make sure you label the dishes carefully, so you know which way is up when you unwrap the dishes at the end of the experiment
8) leave seeds for 4 days
9) observe the seeds' shoot and root growth
- to get quantitative results, measure the amount of growth of the roots and shoots, as well as the angle of growth
32
PRACTICAL: what should be your results of the geotropism practical
- whatever the angle the dishes were places, the shoots have grown away from gravity (negative geotropism) and the roots have grown towards gravity (positive geotropism)
33
what is an apical bud
the shoot tip at the top of a flowering plant
34
what is apical dominance
auxins stimulate the growth of the apical bud and inhibit the growth of the side shoots from lateral buds
- means that the apical bud is dominant over the lateral buds
35
what does apical dominance prevent
prevents side shoots from growing
36
why is apical dominance good
- saves energy
- and prevents side shoots from the same plant competing with the shoot tip for light
- as energy isn't being used up to grow side shoots, apical dominance allows a plant in an area where there are loads of plants to grow tall very fast
- grows past the smaller plants, and can reach the sunlight
37
what happens if you remove the apical bud from a plant and leave it like this
- the plant won't produce auxins
- so side shoots will start growing
- via cell division and cell elongation
38
what happens if you remove the apical bud from a plant and replace it with a source of auxin
e.g. agar block containing auxin
- the side shoot development will still be inhibited
- SHOWS THAT apical dominance is controlled by auxin
39
why may side shoots still grow towards the bottom of a plant
- auxins become less concentrated as they move away from the apical bud to the rest of the plant
- so if a plant grows very tall
- the bottom of the plant has a low auxin concentration
- so side shoots will start to grow near the bottom
40
PRACTICAL: how could you investigate the roles of auxins in apical dominance
1) plant 30 plants, e.g. pea plants, that are similar age, height and weight in pots
2) count and record the number of side shoots growing from the main stem of each plant
3) for 10 plants, remove the tip of the shoots and apply a paste containing auxins to the top of the stem
3) for other 10, remove tip of the shoot and apply a paste without auxins to the top of the stem
4) leave the final 10 plants as they are: untreated controls [they are needed for comparison so you know the effect you see is likely to be due to the hormone, and not any other factor]
5) let each group grow for 6 days
- keep all plants in the same conditions: light intensity, water [makes sure that any variables that may affect your results are controlled, making the experiment valid]
6) after 6 days, count the number of side shoots growing from the main stem of each of your plants
7) should get results, where without any auxin, the most amount of more side shoots have grown
= show that auxins inhibit the growth of side shoots, and they are involved in apical dominance
41
where are gibberellins produced
in young leaves and seeds
42
what do gibberellins produce again
seed germination, stem elongation, side shoot formation, flowering
43
how do gibberellins stimulate the stems of plants to grow
- via stimulating stem elongation
- this helps plants to grow very tall
- e.g. if a dwarf variety of a plant is treated with gibberellin, it will grow to the same height as the tall variety
- UNLIKE auxins, gibberellins don't inhibit plant growth in any way
44
how do gibberellins stimulate seed germination
- trigger the breakdown if starch into glucose in the seed
- the plant embryo in the seeds can then use the glucose to being respiring
- can release energy as it needs to grow
- gibberellins and seed germination can be inhibited and prevented by hormone abscisic acid
45
how have scientists been able to prove the role of gibberellins in seed germination
- have produced genetically altered seeds
- that are unable to produce gibberellins
- these seeds are unable to germinate
- unless given gibberellins
46
PRACTICAL: how could you investigate the role of gibberellins in stem elongation
1) plant 40 plants, e.g. dwarf pea plants, that are similar age, height and mass in pots
2) leave 20 plants to grow as they are, watering them all in the same way and keeping them all in same conditions [your controls]
3) leave the other 20 in the same conditions, but water them with a dilute 100 mg dm-3 solution of gibberellins
4) let the plants grow for 28 days and measure the lengths of all the stems once each week
5) results would show that stems grow more when watered with the dilute solution of gibberellin
6) suggesting gibberellin stimulates stem elongation
- can also calculate the rate of growth of plants too
47
how can gibberellins and auxins be synergistic
they work together to have a really big effect, e.g. working together to help a plant grow very tall
48
how can gibberellins and auxins be antagonistic
they oppose each others actions, e.g. gibberellins stimulating the growth of side shoots, but auxins inhibiting this
49
what are deciduous plants
plants that lose their leaves in winter
- technical term for leaf loss = abscission
50
why do deciduous plants lose their leaves in the winter
- help to conserve water (which is lost from leaves) during cold parts of the year
- as here, it may be difficult to absorb water
from the soil (may be frozen)
- and there is less light for photosynthesis
51
when is leaf loss triggered
by the shortening day length in the autumn
52
which two hormones control leaf loss
auxins and ethene
53
how do auxins inhibit leaf loss
AUXINS INHIBIT leaf loss:
- auxins are produced by young leaves
- as the leaf gets older, less auxin is produced
- leading to leaf loss
54
how does ethene stimulate leaf loss
- ethene is produced by aging leaves
- as leaves get older, a layer of cells (called the abscission layer) develops at the bottom of the leaf stalk (where the leaf meets the stem)
- the abscission layer separates the leaf from the rest of the plant
- ethene stimulates the cells in the abscission layer to expand, breaking their cell walls
- causes the leaf to fall off
55
how are ethene and auxins related
they are antagonistic to each other
56
why do plants need to close their stomata
in order to reduce water loss through respiration
57
what do plants use to close their stomata
guard cells
- found either side of the stomatal pore
58
how do guard cells open and close the stomata
- when the guard cells are full of water
- they are plump and turgid, so the pore is open
- when the guard cells lose water, they become flaccid, making the pore close
59
which hormone triggers stomatal closure
abscisic acid ABA
60
how does ABA trigger stomatal closure
- ABA binds to receptors on the guard wall membranes
- this causes specific ion channels to open
- which allows calcium ions to enter the cytosol from the vacuole
- this increased concentration of Ca+ ions in the vacuole causes other ion channels to open, allowing ions, like K+, to leave the guard cells
- this raises the water potential of the cells
- water then leaves the guard cells via osmosis
- guard cell becomes flaccid and the stomata closes
61
how is ethene used commercially
used via the fruit industry to control how different fruits develop:
- ethene stimulates enzymes that break down cell walls, break down chlorophyll and convert starch into sugars
- this makes fruit soft, ripe and ready to eat
- so e.g. bananas are harvested before they are ripe, as less likely to get damaged this way
- then exposed to ethene on arrival
- so they all ripen at the same time
- on shelves and in peoples homes
62
how are auxins used commercially
- as SELECTIVE WEEDKILLERS (HERBICIDES):
- auxins make weeds produce long stems instead of lots of leaves
- this makes the weeds grow too fast
- so they can't get enough water/nutrients
- so they die
- AS ROOTING HORMONES (in ROOTING POWDER):
- auxins make a cutting (part of a plant) grow roots
- this cutting can then be planted and grown into a new plant
- many cuttings can be taken from just one original plant
- treated with rooting hormones
- so lots of the same plant can be grown quickly and cheaply from just one plant
63
why do animals respond to changes in their environment, and give examples
- respond to external environment: avoid places that are too hot or cold
- respond to internal environment: control blood glucose concentration
- to increase their chances of survival
64
what is a stimuli, and what are the chain of events it causes
- a change in the internal or external environment
- receptor detects stimuli
- effectors bring about a response to stimuli
- receptors will communicate with effectors via the nervous system or the hormonal system
- sometimes both
65
what are the 2 main structures of the nervous system
central nervous system CNS
peripheral nervous system
66
what is your central nervous system
your brain and spinal chord
67
what is your peripheral nervous system
made up of the neurones that connect the CNS to the rest of the body
68
what are the two different function systems of the peripheral nervous system
somatic nervous system and autonomic nervous system
69
what is the somatic nervous system
controls your conscious activities, e.g. running or playing a video game
70
what is your autonomic nervous system
controls your unconscious activities, e.g. digestion
71
what are the 2 divisions of the autonomic nervous system
sympathetic and parasympathetic
72
what is your sympathetic nervous system
gets the body ready for action
- the fight or flight system
- releases neurotransmitter noradrenaline
73
what is your parasympathetic nervous system
calms the body down
- rest and digest system
- neurones release neurotransmitter acetylcholine
74
what is the location and function of the hypothalamus
- just beneath the middle part of your brain
1) automatically maintains body temperature to a normal level
2) produces hormones that control the pituitary gland
75
what is the location and function of your cerebrum
- largest part of your brain
- divided into two parts called the cerebral hemispheres
- has a thin outer layer called the cerebral cortex, which is highly folded
1) involved in vision, hearing, learning and thinking
76
what is the location and function of your pituitary gland
- found beneath the hypothalamus
- controlled by the hypothalamus
1) releases hormones and stimulates other glands, e.g. the adrenal gland, to release their hormones
77
what is the location and function of the medulla oblongata
- at the base of your brain, at the top of the spinal chord
1) automatically controls breathing and heart rate
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what is the location and function of the cerebellum
- underneath the cerebrum
- also has a folded cortex
1) important in muscle coordination, posture and coordination of balance
79
what is a reflex
where the body responds to a stimulus without making a conscious decision to respond
- as the pathway of communication doesn't involve conscious parts of your brain
80
why are reflexes so fast, and why is this good
- you don't have to spend time deciding how to respond
- so information travels very fast from receptors to effectors
- so help an organisms avoid damage to the body
- as so fast
81
what are 2 types of reflexes
- blinking reflex
- knee-jerk reflex
82
when does a blinking reflex occur
- when your body detects something that could damage your eye
- you automatically blink
- so you quickly close your eyelid to protect your eye
- then open it again
- e.g. if eyelid is touched
83
how does the blinking nerve reflex occur, if something touched your eye
- the sensory nerve endings in your cornea (front part of your eye) are stimulated by touch
- the nerve impulse is sent along the sensory neurone to a relay neurone in the CNS
- the impulse is then passed from the relay neurone to motor neurones
- the motor neurones send impulses to the effectors
- the orbicularis oculi muscles that move your eyelids
- these muscles contract
- cause your eyelid to close quickly
- to prevent your eyelid from being damaged
84
when does a knee-jerk reflex occur, and why
- it works to quickly straighten your leg if the body detects your quadriceps is suddenly stretched
- helps to maintain posture and balance
- e.g. if your knees buckle after landing from a jump, the reflex causes your quadriceps to contract to keep you upright
85
how does the knee-jerk reflex take place
- stretch receptors in the quadriceps muscles detect the muscle is being stretched
- a nerve impulse is passed along the sensory neurone, which communicated directly with a motor neurone in the spinal chord (no relay neurone involved)
- the motor neurone carries to nerve impulse to the effector (quadricep muscle) causing it to contract, so the lower leg moves forward quickly
86
what happens when an organism is threatened
- it responds by preparing the body for action, e.g. fighting or running away
- called the "fight or flight" response
- nerve impulses from the sensory neurones arrive at the hypothalamus, activating both the hormonal system and the sympathetic nervous system
87
how is the hormonal system activated during fight or flight
- the pituitary gland releases a hormone called ACTH
- this causes the cortex of the adrenal glands to release steroidal hormones
88
how is the sympathetic nervous system activated during fight or flight
- triggers the release of adrenaline from the medulla region of the adrenal gland
89
what are the effects of adrenaline and the sympathetic nervous system on fight or flight
- heart rate is increased: so blood is pumped around the body faster
- muscles around the bronchioles relax: so breathing is deeper
- glycogen is converted to glucose (glycogenolysis): so more glucose is available for muscles to respire
- muscles in the arterioles supplying the skin and the gut constrict, and muscles supplying the heart, lungs and skeletal muscles dilate: so that blood is diverted to the latter
- erector pili muscles in the skin contract: makes the hair stand on end so the animal looks bigger
90
what systems does control of heart rate involve
nervous AND hormonal systems
91
how is heart rate controlled
- the sinoatrial node SAN generates electrical impulses that cause the cardiac muscles to contract
- the rate at which the SAN fires, and therefore the heart rate, is unconsciously controlled
- by part of the brain, called the medulla
92
why do organisms need to alter their heart rate
- to respond to internal stimuli
- e.g. to prevent fainting due to low blood pressure or make sure the heart rate is high enough to supply the body with enough oxygen
93
what 2 receptors detect stimuli to do with heart rate
pressure receptors and chemical receptors
94
what are the cardiac pressure receptors
- called baroreceptors
- in the aorta and the vena cava
- they're stimulated by high and low blood pressure
95
what are the cardiac chemical receptors
- called chemoreceptors
- in the aorta, carotid artery (major artery in the neck), and in the medulla
- they monitor the oxygen level in the blood
- also monitor CO2 and pH, which are both indicators of O2 levels
96
what happens once receptors detect a stimuli to do with the heart
- electrical impulses are sent to the medulla along the sensory neurones
- the medulla processes the information and sends impulses to the SAN along motor neurones
97
what happens during high blood pressure
- baroreceptors detect high blood pressure
- impulses are sent to the medulla, which sends impulses along the vagus nerve, which secretes acetylcholine, which binds to receptors in the SAN
- the effector is the cardiac muscles
- which respond by slowing down the heart rate, so blood pressure reduces down to normal
98
what happens during low blood pressure
- baroreceptors detect low blood pressure
- impulses are sent to the medulla, which sends impulses along the accelerator nerve, which secretes noradrenaline, which binds to receptors on the SAN
- the effector is the cardiac muscle
- which responds by speeding up the heart rate to increase blood pressure back to normal
99
what happens during high blood O2 levels (or low CO2 or high pH)
- chemoreceptors detect chemical changes in the blood
- impulses are sent to the medulla, which sends the impulses along the vagus nerve, which secretes acetylcholine, which binds to receptors on the SAN
- the effector is the cardiac muscle
- and the response is the heart rate decreasing to return O2, CO2 and pH levels back to normal
100
what happens during low O2 (or high CO2, or low pH)
- the chemoreceptors detect chemical changes in the blood
- the impulses are sent to the medulla, which sends impulses along the accelerator nerve, which secretes noradrenaline, which binds to receptors on the SAN
- the effector is the cardiac muscle
- which responds by increasing the heart rate, returning O2, CO2 and pH levels to normal
101
how does your hormonal system assist in controlling heart rate
- releases adrenaline, e.g. during a fight or flight response
- adrenaline binds to specific receptors in the heart
- which causes the cardiac muscle to contract more frequently and with more force
- so heart rate increases
- and the heart pumps more blood
102
PRACTICAL: how would you measure your own heart rate
- find your pulse on your wrist by placing your index and middle finger where the base of your thumb meets your forearm
- count the number of beats in 15 seconds
- then multiply by 4 to get the number of beats per minute
103
PRACTICAL: how would you investigate the effect of exercise on heart rate
1) measure heart rate at rest and record it on a table
2) do some gentle exercise, e.g. stepping on and off a step for 5 minutes
3) immediately afterwards, measure your heart rate again
4) return to a resting position
5) measure your heart rate every minute until it returns to the starting rate
6) record how long it takes to return to normal
- could also use an electrical heart rate monitor instead, which contain sensors to measure your heart rate
104
what is a statistical test you could use for calculating the effect of exercise on a group of people with, or without endurance training
a student's t-Test
105
what does the CNS do
- brain and spinal chord
- receives sensory information and decides what kind of response is needed
106
what does the CNS do if it needs to respond with a movement
- CNS sends signals along neurones to tell skeletal muscles to contract
107
what is skeletal muscle
- also called striated, striped or voluntary muscle
- type of muscle you use to move
- e.g. biceps and triceps to move lower arm
108
what is skeletal muscle made up of
large bundles of long cells, called muscle fibres
109
what is the structure of a muscle fibre
- the cell membrane of muscle fibre cells is called sarcolemma
- bits of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm (muscle cells cytoplasm)
- makes folds called transverse T tubules
- network of internal membranes called sarcoplasmic reticulum run through the sarcoplasm
- have lots of mitochondria to provide ATP needed for muscle contraction
- multinucleate (contain many nuclei)
- have lots of long, cylindrical organelles called microfibrils, made of proteins and highly specialised for contraction
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what is the function of the transverse T tubules
help spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
111
what is the function of the sarcoplasmic reticulum
stores and releases calcium ions that are needed for muscle contraction
112
what do myofibrils contain
bundles of thick and thin myofilaments that move past each other to make muscles contract
113
what are thick and thin filaments made out of
thick = myosin
thin = actin
114
what would you be able to see of a myofibril under a microscope
- a pattern of alternating dark and light bands
- DARK: contain thick myosin filaments, and some overlapping thin actin filaments (the A band)
- LIGHT: only thin actin filaments, called the I band
115
what are microfibrils made of
many short units called sarcomeres
116
what is the Z-line
the end of each sarcomere
117
what is the M-line
the middle of each sarcomere
(M is Middle of the Myosin filaments)
118
what is the H zone
around the M-line
only contains myosin filaments, non overlapping
119
what is the structure of a sarcomere
- Z line at each end
- M line in the middle
- I band next to the Z line, contains non-overlapping thin actin filaments
- H zone around the M line, containing only thick myosin filaments, not overlapping
- A band containing all of myosin filaments, including overlapping A too
120
what theory explains how muscles contract
the sliding filament theory
121
what happens to make a muscle contract
myosin and actin filaments slide over one another to make the sarcomeres contract
- myosin filaments DON'T CONTRACT THEMSELVES
- the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
- the sarcomeres will return to their original length as the muscle relaxes
122
what is the difference in structure of a contracted and relaxed sarcomere
- the sarcomere gets shorter as
- the I band gets shorter
- the H-zones get shorter
- BUT the A band stays the same length
123
what is the structure of a myosin and actin filament
- have globular heads, that are hinged so can move back and forth
- each myosin head has a binding site for actin and a binding site for ATP
- actin filaments have a binding site for myosin heads, called actin-myosin binding sites
- actin also contains tropomyosin and troponin, found between the filaments
- the two proteins are attached to each other, and help myofilaments move past each other
124
how is myosin and actin structured in a resting, unstimulated muscle
- the actin-myosin binding site is blocked by tropomyosin, which is held in place by troponin
- this means myofilaments cannot slide past eachother because myosin heads cannot bind to the actin-myosin binding site on the actin filaments
125
what is the first step of muscle contraction, where an action potential reaches the muscle cell
- an action potential from a motor neurone stimulates a muscle cell
- this depolarises the sarcolemma
- this spreads down the T-tubules to the sarcoplasmic reticulum, causing it to release its stored Ca2+ ions into the sarcoplasm
- the calcium ion binds to troponin, causing it to change shape
- this pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament
- this exposes the binding site, so that the myosin head can bind to it
- this bond formed between myosin head and actin filament is called an actin-myosin cross bridge
126
what is the second step of muscle contraction, once the cross bridge has been formed
- the calcium ions also activate the enzyme ATPase, which breaks down ATP (into ADP and Pi) to provide energy for muscle contraction
- this energy released from ATP moves the myosin head, which pulls the actin filament along in a rowing action
127
what is the third step of muscle contraction, once the myosin head has moved
- ATP also provides energy to break the actin-myosin cross-bridge
- means that the myosin head detaches from the actin filament after it has moved
- it then reattaches to a different binding site further along the actin filament
- a new cross-bridge is formed and the cycle is repeated (attach, move, detach, reattach somewhere)
- many cross bridges form and break very rapidly, pulling the actin filament along
- this shortens the sarcomere, causing the muscle to contract
- cycle continues as long as calcium ions are present and bound to troponin
128
what happens to the muscle once it stops being stimulated
- calcium ions leave their binding sites on troponin molecules and are moved by active transport back into the sarcoplasmic reticulum (needs ATP too)
- troponin molecules return to their original shape
- pulls the attached tropomyosin molecules with them
- they now block the actin-myosin binding sites again
- muscles are not contracted, as no myosin heads are attached to actin filaments, so no cross bridges
- the actin filaments slide back to their relaxed position, lengthening the sarcomere
129
what gets used up really fast during muscle contraction
ATP, as so much energy is needed when muscles contract
- it has to be continually regenerated for exercise to continue
130
what are the 3 ways of getting ATP for muscle contraction
1) aerobic respiration
2) anaerobic respiration
3) ATP-Creatine Phosphate (CP) System
131
how does aerobic respiration generate ATP for muscle contraction
- most ATP is generated here via oxidative phosphorylation
- in a cells mitochondria
- only works when oxygen is available
- for long periods of low-intensity exercise, e.g. jogging and walking
132
how does anaerobic respiration generate ATP for muscle contraction
- made rapidly by glycolysis
- end product is pyruvate, which is converted to lactate by lactate fermentation
- lactate can build up quickly in muscles and causes muscle fatigue (where muscles can't contract as forcefully as before)
- good for short period of hard exercise, e.g. 400 m sprint
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how is ATP generated via Creatine Phosphate
- ATP is made by phosphorylating ADP
- and the phosphate group is taken from creatine phosphate
- CP is stored inside cells and the ATP-CP system generates ATP very quickly
- CP runs out after a few seconds, so used for short bursts of vigorous exercise, e.g. tennis serve
- is anaerobic (no oxygen) and alactic (makes no lactate)
134
what is a neuromuscular junction
a synapse between a motor neurone and a muscle cell
135
what is the neurotransmitter and receptors for a neuromuscular junction
- acetylcholine ACh
- nicotinic cholinergic receptors
136
how do neuromuscular junctions work
- the same way as synapses between neurons (release neurotransmitter, which triggers depolarisation in the postsynaptic cell)
- this depolarisation causes the muscle cell to contract, if threshold level is reached
- acetylcholinesterase (AChE) is stored in the clefts of the postsynaptic membrane, and is released to break down ACh after use
137
what is the structure of a neuromuscular junction
- motor neurone
- presynaptic membrane
- ACh in vesicles
- postsynaptic membrane (also called the motor end plate)
- nicotinic cholinergic receptors
- AChE stored in clefts
138
how can a neuromuscular junction be affected by
- a chemical, e.g. drug, can block the release of a neurotransmitter, or affect the way it binds to receptors on the post synaptic membrane
- this can prevent an action potential from being passed to the muscle, so the muscle will not contract
- can be fatal, especially if on muscles involved in breathing
- e.g. diaphragm and intercostal muscles, if they can't contract, ventilation can't take place and the organism cannot respire aerobically
139
what are the characteristics of skeletal (voluntary) muscle
- controlled consciously (you have to voluntarily decide to contract it)
- made up of many muscle fibres and have many nuclei
- the muscle fibres are many cm long
- have a striped pattern (cross-striations) under a microscope
- some contract quickly (speed and strength) but fatigue quickly too
- some contract and fatigue slowly (endurance and posture)
140
what would you see on a stained section of a skeletal muscle under a light microscope/examine a photomicrograph of one
- long muscle fibres
- cross striations (alternating darker and lighter pink strips (A and I bands)
- many nuclei in each muscle fibre, stained blue
141
what are the characteristics of smooth muscle
- also called involuntary muscle
- controlled unconsciously, without you deciding
- doesn't have striped appearance
- found in walls of hollow internal organs, e.g. gut [contract to move food along via peristalsis] and blood vessels [contract to reduce the flow of blood]
- each muscle fibre has one nucleus
- spindle shaped with pointed ends, only about 0.2mm long
- contract slowly, and don't fatigue
142
what are the characteristics of cardiac muscle
- found on the walls of your heart
- contracts on its own, is myogenic [but the rate of contraction is controlled involuntarily via the ANS]
- made of muscle fibres connected by intercalated discs, with low electrical resistance to nerve impulses can pass easily between cells
- branched, to allow nerve impulses to spread quickly through the whole muscle
- each fibre has one nucleus
- shaped like cylinders, about 0.1mm long
- some cross striations, but not as strong as skeletal
- contract rhythmically and don't fatigue
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PRACTICAL: how can electrical signals monitor muscle fatigue
- muscles contract in response to nerve impulses, which are electrical signals
- these electrical signals can be detected by electrodes placed on the skin
- they are connected to a computer to allow electrical signals to be monitored
- called electromyography, and generates and electromyogram
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PRACTICAL: how would you generate an electromyogram
1) attach two electrodes to area of muscle you want to record from, e.g. biceps in arm
2) third electrode goes on an inactive point as a control, e.g. bony wrist area
3) switch off any other electrical equipment that you do not need (generates noise that can interfere with the electrical signal from the muscle)
4) connect the electrode to an amplifier and a computer
5) keep muscles relaxed (straight line)
6) contract muscle, e.g. bend arm, and you should see spikes in the graph as motor units are activated to contract the muscle
7) if you lift a weight, amplitude of trace increases, as more electrical signals due to more motor units required to lift weight
8) if you continue holding weight, muscle fatigues, and you will see trace increase further, as your brain tries to activate more motor units to generate force needed to hold weight up
145
what is a motor unit
made up of the motor neurone and all the muscles and fibres that it connects to
