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Biology > Chapter 16 - Plant and animal responses > Flashcards

Chapter 16 - Plant and animal responses Flashcards

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1
Q

3 chemical defences plants use for the threat of herbivores

A

Tannins
Alkaloids
Pheromones

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2
Q

Tannins

A
  • water-soluble carbon compounds in flavonoids
  • stored in the vacuoles
  • toxic chemicals are produced during tannins breakdown in insect gut
  • bitter taste
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3
Q

Alkaloids

A
  • derived from amino acids
  • feeding deterrent to animals - taste bitter
  • located in growing tips and flowers, and peripheral cell layers of stems and roots
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4
Q

Pheromones

A
  • chemicals which are released by one individual and which can affect the behaviour or physiology of another in same species
  • directly toxic to herbivorous insects/trigger other chemical defences in some plants
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5
Q

Tropism

A
  • directional growth responses of plants
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6
Q

Phototropism (Abiotic)

A
  • shoots grow towards light, which enables them to photosynthesise
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7
Q

Geotropism (Abiotic)

A
  • roots grow towards the pull of gravity (+ve)
  • anchors them in the soil and helps them to take up water, which is needed for support, as a raw material for photosynthesis and to help cool the plant
  • there will also be minerals, such as nitrate in the water, needed for the synthesis of amino acids
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8
Q

Chemotropism (Abiotic or Biotic)

A
  • on a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertilisation can take place
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9
Q

Hydrotropism (Abiotic)

A
  • root tips typically grow towards damper areas of soil increasing their access to water.
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10
Q

Thigmotropism (Abiotic or Biotic)

A
  • shoots of climbing plants, such as ivy, wind around other plants or solid structures to gain support
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11
Q

Positive tropic response

A
  • if a plant responds towards a stimulus
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12
Q

Negative tropic response

A
  • if a plant responds away from a stimulus
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13
Q

Nastic responses

A
  • non-directional responses to external stimuli
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14
Q

Thigmonasty example

A
  • sensitive plant, mimosa pudica, responds to touch with a folding of the leaves
  • caused by rapid water uptake -> vol increase + rapid loss of water from adjacent cells
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15
Q

Plant hormones

A
  • chemical messengers that can be transported away from their site of
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16
Q

Abiotic

A
  • non-living components of the environment
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17
Q

Biotic

A
  • living components of the environment
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18
Q

4 examples of plant responses

A
  • tropisms
  • responses to touch
  • responses to herbivory
  • responses to abiotic stress
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19
Q

Nastic movements

A
  • non-directional responses
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20
Q

Cause of nastic movement

A
  • bioelectrical signals
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21
Q

Nastic movement origin

A
  • adaptation to protect the leaflets from herbivorous insects/reduce transpiration when the leaves no longer photosynthesise
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22
Q

Herbivory

A
  • consumption of plants by herbivores
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23
Q

Abiotic stress for plants

A
  • freezing
  • drought
  • increased soil water salinity
  • heavy metals
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24
Q

Plant response to drought

A
  • close stomata (reduce water loss through transpiration)/ drop leaves
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25
Q

Plants response to temperatures below freezing

A
  • produce antifreeze chemical in cells, that decrease ice crystal formation that destroy plant cells
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26
Q

Darwin’s Experiment

A
  • removing the tip of a coleoptile stopped phototropic response to a unidirectional light source from occurring
  • to ensure it is not due to wounding, covered the tip with an opaque cover to block light which also stopped phototropic response occurring
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27
Q

Boysen-Jensen’s Experiment

A
  • if the cut tip was replaced back on top of the coleoptile + gelatin block inserted as a barrier in between, phototropic response restored
  • stimulus for growth was a hormone which can travel through gelatin block
  • inserted a mica barrier (impermeable to chemicals) halfway through coleoptile just below tip
  • mica barrier was inserted into the lit side, phototropic response occurred
  • mica barrier was inserted into the shaded side, phototropic response didn’t occur
  • confirms that stimulus for growth was a chemical + showed it was produced at tip, before travelling down coleoptile on the shaded side
  • stimulus acted by causing growth on the shaded side (rather than inhibiting growth on the lit side)
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28
Q

Paal Experiment

A
  • Paal cut off the tip of a coleoptile + replaced it off-centre in the dark
  • side of the coleoptile that tip was placed on grew more than other side, causing coleoptile to curve
  • in the light, the phototropic response was caused by a hormone diffusing through the plant tissue + stimulating the growth of tissue
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29
Q

Went’s Experiment

A
  • placed the cut tip of a coleoptile on a gelatin block, allowing the hormones from the tip to diffuse into the block
  • block was then placed on the coleoptile, off-centre + in dark
  • Paal’s experiment: side of the coleoptile that the block was placed on grew more than the other side, causing coleoptile to curve
  • greater the conc of hormone present in the block, the more the coleoptile curved
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30
Q

Controlling growth by elongation

A
  • auxin is synthesised in the growing tips of roots + shoots
  • auxin coordinates phototropism in plants by controlling growth by elongation
  • auxin molecules are synthesised in the meristem + pass down the stem to stimulate elongation growth
  • auxin molecules activate proteins in the cell wall known as expansins, which loosen the bonds between cellulose microfibrils, making cell walls more flexible
  • cell can then elongate
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31
Q

Phototropic mechanism

A
  • Phototropism affects shoots + top of stems
  • conc. of auxin determines the rate of cell elongation
  • if conc. of auxin is not uniform on either side of a root/shoot, then uneven growth can occur
  • in shoots, higher conc of auxin results in greater rate of cell elongation
    - auxin moves from illuminated side of a shoot to shaded
    - higher conc of auxin on shaded side = faster rate of cell elongation
    - shoot bends toward light
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32
Q

Geotropism in plant shoots + roots

A
  • when shoots grow away from gravity = -ve geotropism
  • gravity modifies auxin distribution, so that it accumulates on lower side of shoot
  • auxin increases rate of growth in shoots, causing shoot to grow upwards
  • roots grow towards gravity = +ve geotropism
  • in roots, higher conc. of IAA results in a lower rate auxin cell elongation
  • the auxin that accumulates at the lower side of the root inhibits cell elongation
  • slower rate growth on lower side
  • root bend downwards
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33
Q

Investigating the effect of IAA on root growth (apparatus)

A

Apparatus:
Seedlings
Cutting tile
Scalpel
Light source
Lightproof container
Blocks of agar
Marker/pen
Test tubes
Water

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34
Q

Investigating the effect of IAA on root growth (method)

A
  1. Use scalpel to cut a 1cm section from the root tip of each seedling
  2. Mark the root tips at 2mm marks
  3. Divide the root tips into 3 groups + place them in test tubes of water (water helps to keep plant tissue alive)
  4. Group A receives treatment 1: remove the ends of root tips using scalpel, transfer root cuttings with the end removed to an agar block, a uniform light source is present
  5. Group B receives treatment 2: transfer intact root tips to an agar block, light-proof container is placed over the seedlings to prevent light from entering
  6. Group C receives treatment 3: transfer intact root tips to an agar block, apply a directional light source to 1 side of root tips
  7. Leave all roots in their treatment conditions for 3 hours
  8. Use the 2mm marker lines to determine if growth has occurred
  9. Note if growth has been even on both sides
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35
Q

Results of IAA experiment

A

Group A: (tips removed) the roots grow evenly on both sides
- IAA is synthesised in root tips so removing them = no IAA is produced
- no inhibition of cell elongation

Group B: (no light)
- slightly less growth than group A but evenly on both sides
- equal conc. of IAA on both sides of root tip
- inhibition of cell elongation = equal on both sides of root tip
- root don’t grow due to IAA

Group C: (directional light)
- cells on illuminated side of root grow longer
- greater conc of IAA on shaded -> greater inhibition of cell elongation on shaded-> faster rate growth -> roots bend away from light

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36
Q

Limitations of experiment

A
  • same species of plant is being used = plants are still diff (certain genotypes may be more prone to bending/ slightly different sensitivities to IAA)
  • marks may be smudged
  • evenness of growth hard to determine
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37
Q

What do deciduous plants lose?

A
  • their leaves in very hot and dry environmental conditions, in order to reduce water loss
  • during winter when absorption of water is difficult due to frozen soils, it also sheds leaves
  • also due to photosynthesis being limited by low temperatures and reduced light
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38
Q

What are hormones produced in response to ?

A
  • shortening day length
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39
Q

abscission layer

A
  • develops at the base of the leaf stalk
  • layer of parenchyma cells with thin walls, making them weak + easy to break
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40
Q

Ethene use in abscission layer

A
  • stimulate the breakdown of cell walls in this abscission layer, causing the leaf to drop off
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41
Q

Leaf loss

auxin

A
  • inhibit leaf loss + produced in young leaves, making leaves insensitive to ethene
  • conc of auxin decreases as they age until leaf loss occurs
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42
Q

Abcisic acid

A
  • inhibits seed germination + growth
  • stimulates stomatal closure when the plant is stressed by low water availability
  • inhibits bud growth (↑ auxin = ↑ abscisic acid so when tip is removed, abscisic acid fall + bud grows)
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43
Q

Ethene

A
  • promotes fruit ripening
  • promotes abscission in deidicious trees
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44
Q

Giberellins

Fruit production

A
  • delay senescence in citrus fruit, extending the the fruit left unpicked
  • acting with cytokinins can make apples elongate to improve their shape
    -grape stalks elongate, they are less compacted + gapes get bigger
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45
Q

Gibberellins

A
  • promote seed germination + growth of stems
  • responsible for control of stem elongation (increase in internodal length)
  • flowering in long-day plants
  • cellular , transcription / translation
  • prevents leaf abscission
  • aids stomatal opening
  • promotes fruit development
  • promotes , activity of amylase / hydrolysis of starch
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46
Q

How Light Causes Redistribution Of Auxin

A
  • 2 enzymes (phototropin 1 + phototropin 2) activity is promoted by blue light
  • blue light = main component of white light that causes phototropic response
  • lots of phototropin 1 activity on light side, but less on dark side
  • this causes redistribution of auxins through effect on PIN protein
  • they control the efflux of auxin from each cell
  • PIN proteins activity is controlled by PINOID
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47
Q

Mechanism of Auxin’s effect

A
  • auxin ↟ stretchiness of cell wall by promoting active transport of H+ by ATPase enzyme into cell wall
  • low pH provides opt. conditions for expansins
  • enzymes break bonds within cellulose, so walls become less rigid + can expand as water enter
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48
Q

Auxins

A
  • plant hormones responsible for regulating plant growth
  • promote cell elongation
  • inhibit growth of side-shoots
  • inhibit leaf abscission (leaf fall)
  • causes the cells to elongate on one side so the stem bends
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49
Q

Commercial use of Auxins

A
  • taking cuttings (dipping end of cutting in rooting powder which cont. auxins + talcum powder before planting = encourages root growth)
  • seedless fruit (treating unpollinated flowers with it promotes growth of seedless fruit as it promotes ovule growth, which triggers automatic production of auxin)
  • herbicides (to kill weeds - bc they are manmade, plants find them hard to break down + can act within plant for longer. promote shoot growth that stem can’t support itself)
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50
Q

Brewing

A
  • to make beer = need malt
    how to make the malt:
  • barley seeds germinate + the aleurone layer of seed produces amylase enzymes ( stored starch -> maltose)
  • giberellins switch on genes for amylase production + speeds up the process
  • malt is produced by drying and grinding up the seed
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51
Q

Cytokinins

A
  • promote cell division
  • delay leaf senescence (so used to prevent yellowing of lettuce leaves)
  • overcome apical dominance
  • promote cell expansion
  • promote bud growth - override the apical dominance effect (↑ levels of auxin make shoot apex sink for cytokinins produced in roots + when apex is removed, it spreads evenly)
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52
Q

Water stress causation

A
  • high temperature + reduced water supplies
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53
Q

Closure of a stoma in response to abscisic acid (ABA)

A
  • guard cells have ABA receptors on their cell surface membranes
  • ABA binds with the receptors, inhibiting proton pumps + stopping active transport H+ out of guard cells
  • ABA causes Ca2+ ions to move into cytoplasm of guard cells through cell surface membrane
  • Ca2+ act as 2nd messengers:
    cause channel proteins to open that allow -vely charged ions to leave guard cells
  • stimulates opening of further channel proteins that allow K+ to leave guard cell
  • stimulates closing of channel proteins that allow K+ to enter guard cell -> increases H20 potential -> water leaves guard cells + guard cells become flaccid
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54
Q

When seed is shed from parent

A
  • state of dormacy -> allows seed to survive harsh conditions until conditions are right for successful germination
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55
Q

Seed Components

A
  • embryo= will grow into new plant when seed germinates
  • endosperm = starch-cont. energy store surrounding embryo
  • aleurone layer= protein-rich layer on outer edge of endosperm
56
Q

Seed germination

A
  • seed starts to absorb water
  • stimulates embryo to produce gibberellins
  • gibberellin diffuse into aleurone layer + stimulate the cells to synthesise amylase
  • amylase hydrolyses starch molecules in endosperm, producing soluble maltose
  • convert maltose to glucose + transport to embryo
  • glucose can be respired by embryo, breaking dormancy + provide energy needed to grow
57
Q

Amylase synthesis by gibberellin

A
  • regulating genes inv. in synthesis of amylase, causing an increase in transcription of mRNA coding for amylase
58
Q

Abscisic acid

A
  • maintaining dormancy by inhibiting amylase production
59
Q

Determinants of germination

A

balance of abscisic acid + gibberellins present in seed

60
Q

Apical dominance

A
  • auxins that are produced at growing tip at apex of a plant stem causes stem to grow upwards + stops lateral buds from growing
61
Q

When is there no longer apical dominance?

A

if growing tip at apex of plant is removed (grazing), lateral buds grow from top of plant, as source of auxins has been removed

62
Q

What happens with time after no apical dominance?

A
  • lateral shoots that grow from these lateral buds do curl up towards the light -> plant continues to grow in an upwards direction
63
Q

What happens experimentally?

A
  • apical bud of the 1st test plant is removed
  • allows lateral buds to grow
  • a 2nd test plant is decapitated but this time the cut tip is replaced with an agar block cont. auxin
  • restores the inhibition of lateral bud growth + no lateral buds grow
64
Q

Experimental evidence for the role of gibberellin in stem elongation

A
  • Gibberellins are a group of hormones that help plants grow by stimulating cell division and elongation in the stem
  • Dwarf plant varieties have very low levels of gibberellins: due to a mutation in a gene involved in the synthesis of gibberellins
  • Treating these dwarf varieties with gibberellins results in them growing to the same height as normal varieties
  • Gibberellin applied to shorter plants to stimulate growth
65
Q

Experimental evidence for the role of gibberellin in seed germination

A
  • Seeds of mutant varieties of the Arabidopsis plant that do not produce gibberellins can be induced to germinate if gibberellins are applied
  • Seeds of certain lettuce varieties that require light in order to germinate can be made to germinate in the dark if gibberellins are applied
66
Q

3 ways hormones can be used to benefit commercial plant growing

A
  • selective weed killers
  • rooting powders
  • control ripening
67
Q

Selective weed killers

A
  • Auxins are growth-promoting however in high conc. they can cause such rapid growth that plant tissues (e.g. the roots) become distorted and damaged, allowing pathogens to enter the plant
  • synthetic auxins can be used + are applied to plants in much higher conc. than the natural hormones in plants
  • effective against weeds that occur in fields of cereal crops or grass lawns, as grasses are less sensitive to selective weed killers than weeds + so survive
68
Q

Rooting powders

A
  • At low doses, auxins can be used to stimulate cuttings to grow new roots
  • auxins are sold commercially in the form of rooting powders
  • lower end of the cutting is dipped in the powder before being planted in compost + roots begin to grow shortly afterwards
    This technique is often used by florists (commercial flower-sellers)
69
Q

The control of ripening

A
  • ethene can be used to stimulate fruit to ripen
  • used for fruits that are soft when ripe eg. bananas + can be damaged in transport
  • fruits can be harvested when unripe, transported + then ripened artificially using ethene
70
Q

What are the other uses of auxins + gibberellins?

A
  • make unpollinated flowers develop fruit
  • often used in the production of seedless fruits (parthenocarpic fruits)
  • auxins can be used to stop trees from dropping their fruit before it has been harvested
71
Q

What are the 2 systems in the human nervous system ?

A
  • CNS (brain + spinal cord)
  • PNS (all the nerves - peripheral)
72
Q

What are the 2 parts functionally, the nervous system can be divided into?

A
  • the somatic nervous system
  • autonomic nervous system
73
Q

What is the somatic nervous system required for?

A
  • voluntary control of body movements
74
Q

What 3 types of nerves does the somatic nervous system consist of?

A
  • sensory nerves = these consist of sensory neurones + carry impulses from sense organs to the CNS
  • motor nerves = consist of motor neurones + carry impulses from CNS to muscles + glands
  • spinal nerves = found in spinal cord, these are mixed nerves that consist of both sensory + motor neurones
75
Q

What is autonomic nervous system?

A
  • self-controlling system that is required for involuntary actions + functions. such as heart rate, regulation of blood vessel diameter
76
Q

What 2 parts are autonomic nervous system divided into?

A
  • sympathetic nervous system (controls flight-or-flight)
  • parasympathetic nervous system (controls rest+digest system)
77
Q

What does the sympathetic nervous system control?

A
  • release of adrenaline
  • released during fight-or-flight response
  • heart rate increases -> rapid increase in blood supply to respiring muscles -> muscles will have more 02 + glucose for respiration
  • enables high-intensity activities like running away from a predator to be an immediate response
78
Q

Cerebrum

A
  • largest part of the brain in humans
  • carries out: vision, hearing, speech, thinking, memory
  • consists of 5 lobes
  • divided into 2 halves (cerebral hemispheres)
  • hemispheres are joined together by a band of nerve fibres, known as the corpus callosum
  • right hemisphere controls the left side of the body and the left one controls the right side
  • thin outer layer known as the cerebral cortex or ‘grey matter’
  • cerebral cortex consists of the cell bodies of neurones
  • highly folded, (increases its SA + allows it to contain a greater number of neurones)
  • more neurones -> more connections between neurones can be made -> greater the ability of the brain to carry out more complex behaviours
  • beneath cerebral cortex/ grey matter layer = white matter cons. of myelinated axons of neurones
79
Q

Hypothalamus

A
  • middle of the lower part of the brain
  • above the pituitary gland
  • monitors blood as it is flowing through it + in response, releases hormones (involved in homeostasis) itself or stimulates the pituitary gland to release certain hormones
80
Q

What are the 4 main functions of hypothalamus?

A
  • Regulating body temperature by monitoring blood temp + initiating a homeostatic response if this temperature gets too high or too low
  • Osmoregulation - by monitoring how concentrated the blood is + if it gets too concentrated, stimulating the posterior pituitary gland to release anti-diuretic hormone (ADH), which causes increased water retention in the kidneys. The hypothalamus also generates a feeling of thirst -> increase water intake
  • Regulating digestive activity - controls the secretion of enzymes in the gut and peristalsis.
    The hypothalamus generates a feeling of hunger -> increase our food intake if blood nutrient concentrations get too low
  • Controlling endocrine functions -> hypothalamus releases chemicals that cause pituitary gland to release certain hormones that control a variety of processes (e.g. metabolism, growth and development, puberty sexual functions, sleep, mood
81
Q

The pituitary gland

A
  • bottom of the brain, below the hypothalamus
  • produces range of hormones -> directly influence + regulate processes in the body but some stimulate the release of further hormones from specific, remote locations in the body
  • divided into two sections: the anterior pituitary + posterior pituitary
82
Q

What does the anterior pituitary do?

A

produces and releases certain hormones

83
Q

What does the posterior pituitary do?

A

stores and releases hormones produced by the hypothalamus
(e.g. ADH and oxytocin)

84
Q

Cerebellum

A
  • lies below the cerebrum
  • controls motor coordination incl balance includes balance which is highly complex + requires coordination between multiple parts
  • Functions only subconsciously (involuntary actions)
85
Q

medulla oblongata

A
  • base of the brain, where it joins the spinal cord
  • contains 3 ‘centres’ that control different functions:
    -> cardiac centre - controls heart rate
    > vasomotor centre - controls blood pressure by controlling the contraction of smooth muscles in arteriole walls
    -> respiratory centre - controls breathing rate (contains an inspiratory centre and an expiratory centre)
86
Q

What are reflex actions?

A
  • involuntary responses to certain stimuli
  • very fast and usually have a protective purpose or survival value eg. blinking, swallowing
87
Q

What are the sequence of components in a reflex action?

A

Stimulus → Receptor → Coordinator → Effector → Response

88
Q

What is the knee-jerk reflex used for?

A

used by doctors to assess whether the nervous system of a patient is working properly or not

89
Q

What is the knee-jerk flex?

A

doctor uses a small specialised hammer to hit a ligament between the knee cap and the tibia, the leg of the patient will involuntarily straighten in a small kicking motion

90
Q

What does the knee-jerk reflex consist of? (sequence)

A

———————– the mechanism:

  • when hit, patella tendon causes muscles in thigh to stretch
  • stretch receptors called muscle spindles are triggered
  • send impulse down sensory neurone
  • acetyl choline diffuses across synapse
  • action potential sent along motor neurone
  • effector muscle in thigh contracts
  • kick
91
Q

What happens in the nervous pathway of the knee-jerk reflex?

A
  • Stimulus - stretching of the quadriceps muscle caused by pressure on the ligament (this pressure is created by the hammer)
  • receptor - stretch receptors (of quadricep muscles) send impulses down a sensory neurone, which connects directly (via a synapse) with a motor neurone in the spinal cord.
  • Coordinator - spinal cord
  • No relay neurone in the knee-jerk reflex
  • motor neurone carries the impulses to the effector (the quadriceps muscle), which contracts causing the leg to straighten which is the response
92
Q

Why are reflex actions fast and automatic?

A
  • Nerve impulses are delayed by synapses
    If these impulses are transmitted via the brain (as occurs in voluntary actions) they have to travel across many synapses
  • for reflex action, the signal only has to cross a single synapse, allowing for a very rapid response
  • connections from the spinal cord to the brain will still allow information about the stimulus to be sent to the brain but by the time it receives and processes this information, the response will have already occurred
93
Q

What is the blinking reflex?

A
  • a reflex response caused by something travelling towards the eye at high speed, something contacting the cornea, or by drying of the cornea
  • nervous pathway of this reflex action does go via the brain but not via any decision-making areas and the number of synapses is still minimal
94
Q

What happens in the nervous pathway of the blinking reflex?

A
  • Irritation or drying of the cornea sends impulses down the sensory nerve to the medulla of the brain, where it connects with other neurones to transmit the signal to the effector muscles
  • Relay neurones are involved in the transmission of impulses to the effectors in the lower eyelid
  • Effectors for the blinking reflex include the superior levator palpebrae muscle, which lowers the upper eyelid, and the orbicularis oculi muscle, which pulls the eyelids inwards and helps to close them

———————— mechanism:

  • pressure on cornea
  • action potential along sensory neurone from cornea to pons
  • acetylcholine diffuses across synapse
  • action potential along relay neurone
  • acetylcholine diffuses across synapse
  • action potential along motor neurone to effector
  • muscle contracrs
  • BLINK
95
Q

When may an animal produce a ‘fight-or-flight’ response?

A

high level of stress, fear or aggression induced by environmental stimuli

96
Q

How is a fight or flight response carried out?

A

stimulus -> coordinator -> effector

97
Q

what is the sympathetic nervous system responsible for?

A
  • coordinating many of the responses to danger
  • actions are supported by the effect of two hormones: adrenaline and cortisol (both secreted from the adrenal glands
98
Q

Who controls the initial part of the response and the rest?

A

The initial part of the response is controlled by the nervous system, the response is continued by the endocrine system

99
Q

What is the mechanism of the fight-or-flight response?

A
  • Sensory neurones detect environmental stimuli associated with danger and send impulses to the brain
  • amygdala (a small region of the brain located in the cerebrum) sends impulses to various other parts of the brain, including the hypothalamus
  • hypothalamus is stimulated to send impulses via the sympathetic nerves to the adrenal glands
  • causes the adrenal medulla to secrete the hormone adrenaline
  • Adrenaline stimulates target organs + tissues to increase sensory awareness, making the organism more alert + improving its ability to respond to danger
  • hypothalamus also releases a peptide hormone that stimulates the anterior pituitary gland to release ACTH (adrenocorticotropic hormone) which is transported to the adrenal glands via the bloodstream
  • causes the adrenal cortex to secrete the hormone cortisol
  • cortisol stimulates target organs and tissues to increase blood pressure, blood glucose ensuring the tissues have sufficient glucose and oxygen needed for rapid response
  • cortisol also suppresses the immune system
100
Q

What is the 2nd messenger model and adrenaline?

A
  • When adrenaline is secreted it increases the concentration of blood glucose
  • It does this by binding to different receptors on the surface of liver cells that activate the same enzyme cascade that occurs when glucagon binds to its specific receptors
  • adrenaline binds to specific receptors on the membrane of liver cells
  • causes the enzyme adenylyl cyclase to change shape and become activated
  • active adenylyl cyclase catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP)
  • cAMP binds to protein kinase A enzymes, activating them
  • Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them
  • Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
  • Active glycogen phosphorylase enzymes catalyse the breakdown of glycogen to glucose (glycogenolysis)
  • enzyme cascade described above amplifies the OG signal from adrenaline + results in the releasing of xtra glucose by liver to increase the blood glucose concentration back to a normal level
  • adrenaline also stimulates the breakdown of glycogen stores in muscle during exercise
  • glucose produced remains in the muscle cells where it is needed for respiration
101
Q

What are the 3 types of muscle found within mammals?

A
  • smooth
  • skeletal
  • cardiac
102
Q

Skeletal muscle

A
  • Striated muscle makes up the muscles in the body that are attached to the skeleton
  • made from muscle fibres
103
Q

What is a muscle fibre?

A
  • contains an organised arrangement of contractile proteins in the cytoplasm
  • is surrounded by a cell surface membrane
  • contains many nuclei – why muscle fibres are not usually referred to as cells
104
Q

What are the alternative names provided for parts of muscle fibres?

A

Cell surface membrane = sarcolemma
Cytoplasm = sarcoplasm
Endoplasmic reticulum = sarcoplasmic reticulum (SR)

105
Q

What is the structure of sarcolemma?

A

The sarcolemma folds up in on itself to form transverse tubules also known as T tubules - help to transmit electrical impulses very quickly through the whole muscle fibre
These run close to the SR

106
Q

What is the structure of sarcoplasm?

A
  • sarcoplasm contains mitochondria and myofibrils
  • mitochondria carry out aerobic respiration to generate the ATP required for muscle contraction
  • Myofibrils are bundles of actin and myosin filaments, which slide past each other during muscle contraction
107
Q

What do the membranes of sarcoplasmic reticulum have?

A

The membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR

108
Q

What is the structure of myofibrils?

A
  • Myofibrils are located in the sarcoplasm
  • Each myofibril is made up of two types of protein filament:
    thick filaments made of myosin and thin filaments made of actin
  • two types of filament are arranged in a particular order, creating different types of bands and lines
109
Q

H band

A
  • only thick myosin filaments present
110
Q

I band

A
  • only thin actin filaments present
  • light
111
Q

A band

A

areas where only myosin filaments are present + areas where thick myosin and some actin filaments overlap
- dark

112
Q

M line

A

attachment for myosin filaments
- middle of the myosin filaments and the sacromere

113
Q

Z line

A

attachment for actin filaments
- end of each sacromere where actin of neighbouring sacromeres can bind

114
Q

Sarcomere

A

section of myofibril between 2 Z lines
- Myosin and actin form repeating units called sarcomeres

115
Q

COMMON EXAM QUESTION

How does an individuals muscles get bigger from exercise?

A
  • the size of the fibres and not the number of fibres increase
  • An increase in the length and number of contractile units within each fibre causes this increase in size
116
Q

Smooth (involuntary) muscle

A
  • vital for the unconscious control of many body parts
  • contains both actin and myosin filaments but no banding or striation
  • consists of small elongated cells/spindle-shaped fibres that contain one nucleus
117
Q

Cardiac muscle

A
  • only present within the heart
  • specialised striated muscle
  • myogenic
    -does not tire or fatigue so it can contract continuously
  • cardiac muscle fibres form a network that spreads through the walls of the atria and ventricles
    connected to each other via specialised connections called intercalated discs
  • large number of mitochondria
118
Q

What are the 2 types of muscle fibres found within skeletal muscles?

A

Fast fibres
Slow fibres

119
Q

Fast muscle fibres

  • pale
A
  • Fast muscle fibres contract rapidly
  • low amounts of myoglobin - functions as a store of oxygen in muscles and increases the rate of oxygen absorption from the capillaries
  • rely on anaerobic respiration for ATP supply
  • fewer capillaries
  • fewer smaller mitochondria present
  • large store of calcium ions in SR
  • large amounts of glycogen and phosphocreatine present
  • faster rate of ATP hydrolysis in myosin heads
  • fatigues rapidly due to greater lactate formation
120
Q

Slow muscle fibres

  • very red
A
  • long contraction - relaxation cycle (contract slower)
  • high amounts of myoglobin - increases the rate of oxygen supply/absorption
  • denser network of capillaries
  • ATP supplied mostly from aerobic resp
  • many LARGE mitochondria present
  • small store of calcium ions in SR
  • small amounts of glycogen present
  • slower rate of ATP hydrolysis in myosin heads
  • fatigues more slowly due to reduced lactate formation
121
Q

Transmission across a neuromuscular junction

A
  • Striated muscle contracts when it receives an impulse from a motor neurone via the neuromuscular junction
  • Neuromuscular junctions work in a very similar way to synapses
  • located between a neurone and a muscle cell
  • an impulse travelling along the axon of a motor neurone arrives at the presynaptic membrane, the action potential causes calcium ions to diffuse into the neurone
    -This stimulates vesicles containing the neurotransmitter acetylcholine (ACh) to fuse with the presynaptic membrane
  • ACh that is released diffuses across the neuromuscular junction and binds to receptor proteins on the sarcolemma (surface membrane of the muscle fibre cell)
  • This stimulates ion channels in the sarcolemma to open, allowing sodium ions to diffuse in
  • This depolarises the sarcolemma, generating an action potential that passes down the T-tubules towards the centre of the muscle fibre
  • These action potentials cause voltage-gated calcium ion channel proteins in the membranes of the sarcoplasmic reticulum (which lie very close to the T-tubules) to open
  • Calcium ions diffuse out of the sarcoplasmic reticulum (SR) and into the sarcoplasm surrounding the myofibrils
  • Calcium ions bind to troponin molecules, stimulating them to change shape
  • causes the troponin and tropomyosin proteins to change position on the thin (actin) filaments
  • myosin-binding sites are exposed to the actin molecules
  • process of muscle contraction (known as the sliding filament model) can now begin
    -multiple neuromuscular junctions spread across several muscle fibres within the muscle
122
Q

How to stop muscle contraction?

A
  • to prevent the muscle from being continually stimulated by a single impulse, acetylcholinesterase enzyme present in the synaptic cleft breaks down the acetylcholine molecules
  • Ca ions are also pumped back into the sacroplasmic reticulum once the sarcolemma, T tubules (transverse) and SR are no longer polarised
  • movement of calcium ions terminates muscle contraction
123
Q

What region of the brain plays a role in controlling heart rate?

A

medulla

124
Q

Where is the medulla found?

A

The medulla is found at the base of the brain near the top of the spinal cord

125
Q

What 2 parts is the medulla made out of?

A

The acceleratory centre, which causes the heart to speed up
The inhibitory centre, which causes the heart to slow down

126
Q

How are both the centres connected?

A

Both centres are connected to the sinoatrial node (SAN) by nerves

127
Q

The acceleratory centre

A
  • Once the acceleratory centre has been activated impulses are sent along the sympathetic neurones to the SAN
  • Noradrenaline is secreted at the synapse with the SAN
  • causes the SAN to increase the frequency of the electrical waves that it produces
  • increased heart rate
128
Q

The inhibitory centre

A
  • the inhibitory centre has been activated impulses are sent along the parasympathetic neurones to the SAN
  • Acetylcholine is secreted at the synapse with the SAN
  • This neurotransmitter causes the SAN to reduce the frequency of the electrical waves that it produces
  • reduces the elevated heart rate towards the resting rate
129
Q

Activation of the acceleratory and inhibitory centres

A

Exercise causes several internal conditions to change, creating internal stimuli:
- c02 conc in the blood increases
- initial fall in blood pressure caused by the dilation of muscle arterioles

  • internal stimuli can be detected by chemoreceptors and pressure receptors located in the aorta (close to the heart) and in the carotid arteries (they supply the head with oxygenated blood)
  • receptors release nerve impulses that are sent to the acceleratory and inhibitory centres (coordinators)
  • frequency of the nerve impulses increases or decreases depending on how stimulated the receptors are:
    Lower frequency impulses activate the inhibitory centre to slow down the heart rate
    Higher frequency impulses activate the acceleratory centre to speed up the heart rate
130
Q

Controlling the heart rate - the endocrine system

A

noradrenaline (neurotransmitter) and adrenaline are both secreted by the adrenal glands and they both cause an increase in heart rate

thyroxine, which is produced by the thyroid gland, also causes an increase in heart rate

131
Q

Structure of thick filaments in a myofibril

A

made up of myosin molecules
- fibrous protein molecules with a globular head
- fibrous part of the myosin molecule anchors the molecule into the thick filament
- in the thick filament, many myosin molecules lie next to each other with their globular heads all pointing away from the M line

132
Q

Structure of thin filaments in a myofibril

A

made up of actin molecules
- globular protein molecules
- many actin molecules link together to form a chain
- 2 actin chains twist together to form one thin filament
- fibrous protein- tropomyosin - is twisted around the two actin chains
- another protein- troponin - is attached to the actin chains at regular intervals

133
Q

How muscles contract – the sliding filament model

A
  • During muscle contraction sarcomeres within myofibrils shorten as the actin and myosin filaments move past each other (sliding filament model of muscle contraction)
134
Q

What is the process of sliding filament model of muscle contraction?

A
  • action potential arrives at the neuromuscular junction
  • Ca2+ are released from the sarcoplasmic reticulum into the sarcoplasm by diffusion
  • Ca2+ bind to troponin molecules, stimulating them to change shape
    this causes troponin + tropomyosin proteins to change position on the actin filaments
  • Myosin binding sites are exposed on the actin molecules
  • globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament
  • myosin heads bend and pull the actin filaments towards the centre of the sarcomere, causing the muscle to contract a very small distance
  • movement of the myosin heads is known as the power-stroke
  • When the myosin heads bend, it releases a molecule of ADP
    ATP binds to the myosin head, allowing it to detach from actin
  • myosin head acts as an ATPase enzme, hydrolysing ATP into ADP + Pi (the energy released during this reaction allows the myosin head to return to its original position)
  • myosin head can now bind to a new binding site on the actin filaments
  • myosin heads move again, pulling the actin filaments even closer to the centre of the sarcomere + causing the sarcomere to shorten further
  • As long as troponin and tropomyosin are not blocking the myosin-binding sites and the muscle has a supply of ATP, this process repeats until the muscle is fully contracted
135
Q

The role of ATP

A
  • supply of ATP is required for muscle contraction
    -> ATP binding allows myosin to detach from actin and ATP hydrolysis allows the myosin heads to return to their original shape; both of these processes are essential to allow the process described above to repeat
  • return of calcium ions to the sarcoplasmic reticulum occurs via active transport
    Resting muscles have a small amount of ATP stored that will only last for 3-4 seconds of intense exercise
    The mitochondria present in the muscles fibres are able to respire aerobically and produce ATP but this is slow and can take a considerable amount of time
    Anaerobic respiration, which is faster than aerobic, still takes 10 seconds before it even begins to produce any ATP
136
Q

The role of phosphocreatine

A

Phosphocreatine is a molecule stored by muscles that can be used for the rapid production of ATP
- A phosphate ion from phosphocreatine is transferred to ADP
- ADP + phosphocreatine → ATP + creatine
Diff muscle fibre types cont. diff limited amounts of phosphocreatine
It allows for muscles to continue contracting for a short period of time until the mitochondria are able to supply ATP
For prolonged activity, once the supply of phosphocreatine has been used up then the rate of muscle contraction must equal the rate of ATP production from both aerobic and anaerobic respiration

137
Q

Brewing

A
  • to make beer = need malt
    how to make the malt:
  • barley seeds germinate + the aleurone layer of seed produces amylase enzymes ( stored starch -> maltose)
  • giberellins switch on genes for amylase production + speeds up the process
  • malt is produced by drying and grinding up the seed

Biology (25 decks)

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