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A2 Biology 1 > Coordination and Control > Flashcards

Coordination and Control Flashcards

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1
Q

Define photoperiod

A

the relative length of days and nights

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2
Q

define short day plants

A

plants that flower when day length is short and night length is long (winter)

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3
Q

define long day plants

A

Plants that flower when days are long and nights are short (summer)

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4
Q

What pigment controls flowering?

A

phytochrome

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5
Q

what colour is phytochrome?

A

light blue

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6
Q

what are the two forms of phytochrome?

A

P660 and P730

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7
Q

How can P730 and P660 be converted to each other?

A
  • When P660 absorbs red light (of wavelength 660nm), it is rapidly converted to P730.
  • P730 is unstable and so is converted slowly back to P660 in darkness.
  • When P730 absorbs far red light (wavelength 730nm) it is rapidly converted to P660.
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8
Q

What form of phytochrome accumulates during the day?

A

P730 as daylight has proportionally more red light for P660 to be converted by

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9
Q

What is the physiologically active form of phytochrome?

A

P730 - concentration will determine whether the plant flowers

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10
Q

What does P730 do to LDPs?

A

stimulates flowering

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11
Q

What does P730 do to SDPs?

A

inhibits flowering

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12
Q

What is required for an SDP to flower?

A

a critically long period of uninterrupted darkness - allows enough time for accumulated P730 to be converted to P660, therefore removing inhibitory effect of P730.

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13
Q

What is required for an LDP to flower?

A

the night length has to be short enough to prevent too much P730 being converted to P660, and there not being a high enough concentration of stimulatory P730 to stimulate flowering.

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14
Q

What is the phytochrome response to and effect of an LDP on a short day-long night regime?

A

P660 converted to P730 during the day. Dark period is long enough for sufficient P730 to be slowly converted back to P660 to prevent P730 reaching critical level needed for flowering
Effect: no flowering

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15
Q

What is the phytochrome response to and effect of an LDP on a long day-short night regime?

A

Long day length causes P660 to be converted to P730 in high concentrations. The night is too short for enough P730 to be converted back to P660. P730 builds up to critical level.
Effect: flowering

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16
Q

What is the phytochrome response to and effect of an SDP on a short day-long night regime?

A

P660 is converted to P730 during the day. Dark period is long enough for a sufficient level of P730 to be converted to P660 to remove the inhibitory effect of P730.
Effect: flowering

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17
Q

What is the phytochrome response to and effect of an SDP on a long day-short night regime?

A

P660 is converted to P730 during the day, but the dark period is not long enough for a sufficient level of P730 to be converted to P660 to remove the inhibitory effect of P730.
Effect: no flowering

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18
Q

Why would the photoperiod be manipulated by plant growers?

A

to match consumer demand and provide year-round flowers

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19
Q

Give the names of three classes of plant hormones

A

auxins
gibberellins
cytokinins

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20
Q

What are auxins?

A
  • plant hormones involved in phototropism
  • causes cell elongation and maintains teh structures of cell walls
  • in high concentrations can inhibit growth
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21
Q

Describe how auxins move through the plant

A
  • Transport occurs in one direction - away from the tip

- short distance movement relies on diffusion, long distance movement relies on the phloem

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22
Q

What do gibberellins do?

A
  • elongate the internodal distance - increases overall length of stem
  • have been used to promote growth in dwarf species of plants
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23
Q

What do cytokinins do?

A
  • promotes cell division (but only in presence of auxin)

- prevents senescene - the process of ageing and breakdown of chlorophyll in older leaves

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24
Q

Describe the stages of how auxin works in elongation of cells

A
  1. Auxin produced in cells of the apical meristems (zone of elongation)
  2. Diffuses down the shoot to the zone of elongation
  3. Binds to receptors in the cell membranes of the newly formed cells in the zone of elongation (as newly formed cells, the cell walls are also thinner and more flexible)
  4. Cells pump H+ ions into the cellulose cell walls
  5. This acidification loosens the cross links in the cellulose microfibrils, making the wall more flexible
  6. As the cells absorb water by osmosis, the cell walls stretch more readily due to the hydrostatic pressure exerted
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25
Q

What will auxin cause in a plant that is exposed to differential illumination?

A

phototropism
will result in auxin concentration being higher on the shaded side, resulting in greater cell elongation on the shaded side (higher conc auxin = more elongation), which results in curvature of the shoot towards the light source

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26
Q

What type of phototropism does auxin aid in?

A

positive phototropism - growing towards the light

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27
Q

why is positive phototropism due to auxin significant?

A

it allows the shoots and leaves to be angled towards the light, maximising the surface area of plant exposed to light and therefore the amount of light absorbed. This increases the rate of photosynthesis, meaning the plant can maximise its growth rate and aid it in competition

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28
Q

Name three scientists who performed experiments related to phototropism

A
  • darwin (1880)
  • boysen-jenson (1913)
  • paal (1919)
  • went (1928)
  • briggs (1957)
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29
Q

What are the common features of neurones and what are their functions?

A
  • cell body/centron - where most organelles (inc nucleus) are found
  • dendron(s) - fine threads of cytoplasm that deliver impulses TOWARDS cell body
  • axon(s) - fine threads of cytoplasm that carry impulses AWAY from the cell body
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30
Q

Name the three types of neurones

A
  • sensory neurones
  • motor neurones
  • association/relay/connector neurones
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31
Q

Describe the general structure of a sensory neurone

A

tend to have dendrons and axons of a similar long length, so cell body is normally centrally placed in diagrams

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32
Q

describe the general structure of a motor neurone

A

have long axons and many short dendrons (often referred to as dendrites)

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33
Q

describe the general structure of an association/relay/connector neurone

A

are shorter in overall length compared to other types of neurone, and have shorter dendrons and axons

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34
Q

What is a myelinated neurone?

A

A neurone that is wrapped in Schwann cells, creating an electrically insulating myelin sheath
(most nerves in mammals are myelinated)

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35
Q

What are the nodes of Ranvier?

A

small exposed patches of the myelinated neurone’s membrane between each Schwann cell

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36
Q

What is the function of myelination?

A

greatly speeds up nerve impulse transmissions

protects the neurone

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37
Q

define the potential difference (in neurones)

A

the difference in charge between two regions (eg. inside and outside the neurone membrane)

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38
Q

what is the name for cells which have a potential difference across their membrane and what causes a potential difference in cells?

A

polarised cells are caused by an uneven distribution of charged ions across the cell membrane.

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39
Q

Describe the state of a neurone during the resting potential

A

Neurones have an excess of Na+ surrounding them, resulting in a potential difference of -70mV and therefore an electrochemical gradient.
The ions cannot flow across the membrane as the required transmembrane proteins are closed.
This is because there are more positively charged ions outside the cell, and the cell contains many proteins, most of which tend to be negatively charged.

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40
Q

What is an electrochemical gradient?

A

a diffusion gradient whereby charged ions want to move across a membrane to their oppositely charged region.

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41
Q

Describe how a neurone initiates depolarisation from a resting potential.

A

When a stimulus is applied to a neurone, the transmembrane proteins open and Na+ ions flood into the cell - the cell’s potential difference rises (becomes less negative).

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42
Q

What is the threshold potential value?

A

-55mV

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43
Q

describe how reaching the threshold potential leads to an action potential being fired.

A
  • If enough transmembrane proteins open and enough positive ions enter the membrane. the threshold potential will be reached
  • At this point more voltage gated ion channels open and the neurone becomes rapidly depolarised - the potential difference across the membrane reaches a peak - this is known as the action potential
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44
Q

What is the value of the action potential?

A

+40mV

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45
Q

Describe what happens to a neurone that doesn’t reach the threshold potential.

A

If a stimulus doesn’t result in enough ion channels being opened, and the threshold potential is not reached, then an action potential is not fired and the stimulus would be referred to as a ‘sub threshold stimulus’

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46
Q

what is the all or nothing pronciple?

A

an action potential always peaks at the same value, regardless of the intensity of the stimulus. More intense stimuli will result in a more frequent firing of action potentials.

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47
Q

How does a neurone reestablish the resting potential after firing an action potential?

A
  • The neurone must actively re-establish the resting potential - this process is known as repolarisation.
  • The period of time taken for depolarisation is known as the refractory period and the neurone can’t be stimulated during this time. During this time the positive ions both diffuse and are actively pumped out of the neurone into the surrounding fluid.
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48
Q

Why is the refractory period significant?

A

it limits the speed at which action potential fires, and therefore allows the coordinator (brain/spinal cord) to detect each action potential as a discrete event. It also ensures that impulses can only travel in one direction

49
Q

define impulse

A

the propagation of action potentials along the neurone

50
Q

what type of transmembrane proteins are found in neurones?

A

voltage-gated ion channels

51
Q

How does an impulse travel along a neurone?

A
  • There are localised circuits generated along the length of the membrane. Areas where there are excess negative charges attract positive charges and vice versa.
  • These localised circuits flow in both directions but due to the refractory period, can only result in action potentials in areas of the membrane that have had the resting potential returned (so regions still in the refractory period cannot react).
  • Voltage gated ion channels are able to sense these localised changes in charge and respond by opening their ‘gates’ (changing shape in response to a change in localised charge).
  • As a result the cations flow into the cell, resulting in depolarisation (therefore making an action potential more likely)
  • This sequence of events continues along the length of the neurone, resulting in an impulse
52
Q

What is saltatory conduction?

A

In myelinated neurones, the speed of impulse transmission is greatly increased as local current can only exist at the nodes of Ranvier. Therefore the localised currents jump from one node to the next.

53
Q

How do organisms without myelin sheaths speed up impulse transmission?

A

larger diameter of neurones (eg. in squid)

54
Q

What factors speed up the rate of impulse transmission in neurones?

A

saltatory conduction
diameter of neurone
temperature

55
Q

how does temperature affect impulse transmission?

A

the rate of diffusion is directly affected by temperature

56
Q

Describe the process of synaptic transmission of an impulse.

A
  1. Impulse arrives at synaptic bulb
  2. Ca2+ ion channels open, calcium ions diffuse into synaptic bulb
  3. Vesicles fuse with presynaptic membrane, releasing acetylcholine by exocytosis into synaptic cleft
  4. Acetylcholine diffuses across cleft and binds to receptors in postsynaptic membrane
  5. Na+ ion channels open in postsynaptic membrane, cations diffuse in, membrane becomes gradually depolarised and EPSP is generated
  6. EPSP reaches threshold intensity (given sufficient depolarisation) and produces action potential in postsynaptic membrane
  7. Acetylcholinesterase breaks down acetyl choline and products are released into cleft
  8. Products diffuse across cleft, are reabsorbed into synaptic bulb and are resynthesised into acetylcholine.
57
Q

explain why a large number of mitochondria are present in the presynaptic cell

A

there needs to be energy provided in the form of ATP for the resynthesis of acetylcholine from its breakdown products of choline and ethanoic acid, after it was broken down by acetylcholinesterase.

58
Q

how do synapses allow for unidirectionality?

A

impulses can only pass from the presynaptic to the postsynaptic membrane, as the neurotransmitter is only resynthesised in the presynaptic cell, and its receptors are only present on the postsynaptic membrane.

59
Q

name some neurotransmitters involved in generating EPSPs

A

acetylcholine and noradrenaline

60
Q

how does acetylcholine generate an EPSP?

A

they make depolarisation more likely

61
Q

what does EPSP stand for?

A

excitatory post synaptic potential

62
Q

name a neurotransmitter associated with IPSPs

A

GABA

63
Q

what does IPSP stand for?

A

inhibitory post synaptic potential

64
Q

how do neurotransmitters that cause IPSPs generally work?

A
  • hyperpolarising the neurone membrane, resulting in a potential difference across the membrane lower than the usual -70mV resting potential.
  • This in turn reduces the likelihood of an action potential as many more positive ions have to move in to reach the threshold potential
65
Q

how does GABA specifically work to generate an IPSP?

A

open chloride ion channels rather than sodium channels. This means the negative chloride ions will enter the neurone and lower the potential difference.

66
Q

what is the benefit of the CNS using IPSPs and EPSPs?

A

allows us to provide coordinated responses to a range of stimuli. IPSPs are also central in reducing anxiety by reducing the number of impulses that reach the brain

67
Q

Describe synaptic summation

A

At the synapse of a cholinergic neurone, the arrival of the contents of a single vesicle of acetylcholine may not be sufficient to trigger an action potential in the post synaptic membrane - it merely makes it more likely in the immediate future (facilitates it), but as the contents of more vesicles arrive, the threshold of stimulation is quickly achieved

68
Q

name and describe the two types of synaptic summation.

A
  • Temporal summation is when the vesicles come from the same presynaptic neurone in quick succession
  • Spatial summation is when the vesicles come from different sources - when a post synaptic neurone has multiple neurones synapsing with it.
69
Q

How can the amount of light entering the eye be controlled and why is this important to allowing vision in very bright or very dim light?

A
  • The size of the pupil is altered by the circular and radial muscles in the iris working antagonistically.
  • Bright light needs a smaller pupil size to prevent any damage to the light sensitive cells of the retina
  • Dim light needs a larger pupil size to allow more light to enter the eye, ensuring enough light reaches the light sensitive cells to form an image.
70
Q

Describe the pupillary reflex in the case of bright light

A
  • photoreceptor cells of retina are stimulated
  • more impulses sent to the brain via sensory neurones
  • impulses sent by brain along parasympathetic system
  • circular iris muscles contract, radial iris muscles relax
  • pupil constricts
  • amount of light entering the eye is reduced
71
Q

Describe the pupillary reflex in the case of dim light

A
  • fewer photoreceptor cells of retina are stimulated
  • less impulses sent to the brain via sensory neurones
  • impulses sent by brain along sympathetic system
  • circular iris muscles relax, radial iris muscles constrict
  • pupil dilates
  • amount of light entering the eye is increased
72
Q

define accommodation

A

the ability of the eye to change the shape of the lens in order to focus on both near and distant objects

73
Q

What is required to form a sharp image?

A

the light rays have to be refracted to a single point on the retina

74
Q

Where does refraction occur in the eye?

A

A lot of refraction happens at the cornea, and the lens completes the refraction by bending the rays by an appropriate amount depending on the distance the object being viewed is away from the eye

75
Q

describe what happens to form a sharp image of a distant object

A
  • Ciliary muscles relax
  • Tension in wall of eyeballs transferred to the suspensory ligaments, pulling them taut
  • Lens is pulled into a thinner shape
  • Refractive power of lens is reduced (a distant object’s light rays will arrive at the eye in a more parallel position, requiring less refraction to be focused onto a single point)
76
Q

describe what happens to form a sharp image of a nearby object

A
  • Ciliary muscles contract
  • Tension of the eyeball is not transferred to the suspensory ligaments, so they slacken
  • Less pressure is exerted on the lens, so it bulges becoming thicker (more convex)
  • Refractive power of the lens is increased (a close object’s light rays will be more diverging as they reach the eye, so will require more refraction to be focused to a single point on the retina).
77
Q

name some cell types present in the retina

A

rods, cones, ganglion cells, bipolar cells

78
Q

describe the structure of rods and cones

A
  • rods - inner segment with nucleus and many mitochondria, rod shaped outer segment containing membrane discs packed with light sensitive pigment
  • cones - inner segment with nucleus and many mitochondria, cone shaped outer segment containing membrane discs packed with light sensitive pigment
79
Q

name the light sensitive pigments found in rods and cones

A
  • rods - rhodopsin

- cones - iodopsin (1 of each of the three types found in each cell)

80
Q

how many types of rods and cones are there?

A
  • rods - only one, all contain rhodopsin- cones - 3 each with an iodopsin sensitive to a different wavelength of light
81
Q

describe the difference in sensitivity between rods and cones

A
  • rods - high sensitivity. Can operate in low light intensities due to retinal convergence, therefore used for night vision.
  • cones - low sensitivity. rewuire high light intensities to function and therefore are used for day vision.
82
Q

describe the difference in visual acuity between rods and cones

A

rods - low visual acuity

cones - high visual acuity

83
Q

describe the difference in colour perception between rods and cones

A
  • rods only provide monochromatic vision

- cones can sense blue, green or red light depending on the form of iodopsin present in membrane discs

84
Q

describe the layout of the retina

A

For light to reach the membrane discs containing the light sensitive pigments, it has to pass through the ganglion cells, bipolar cells and the bulk of the rod and cone cell. This is permitted due to the transparent nature of these cells but it does raise some interesting questions relating to evolutionary biology.

85
Q

define visual transduction

A

the process of converting light energy into an action potential

86
Q

how does light generate an impulse in rods that travels to the brain?

A

When light strikes rhodopsin it is broken down (bleached) into retinal and opsin. This change results in a change in membrane potential which is passed on to the neighbouring bipolar cell.

87
Q

why do rods have a high sensitivity and what does this mean?

A
  • many rods can synapse (3) onto one bipolar neurone. This is retinal convergence.
  • Therefore a small amount of neurotransmitter released from a few rod cells can be added together (spatial summation) to open enough ion channels in the bipolar cell to form an action potential.
88
Q

why do cone cells have a low sensitivity?

A

Cone cells do not display retinal convergence, so they require higher light intensities in order to release sufficient amounts of neurotransmitter as one cone synapses with one bipolar neurone.

89
Q

why do rods have a low visual acuity?

A

Rods will have decreased visual acuity due to retinal convergence - as one bipolar neurone synapses with three rods, the image formed in the brain is a result of a patch of cells being stimulated, rather than just one cell.

90
Q

why do cones have a high visual acuity?

A

Cones will have high visual acuity as each bipolar cell synapses to one cone. Therefore the brain can tell exactly which part of the retina is being stimulated.

91
Q

how can cones provide colour vision?

A

Cones also provide colour vision as different amounts of blue, green and red sensitive cone cells (each with a different kind of iodopsin that is sensitive to a different wavelength of light) can be stimulated. The relative amounts of each type that are stimulated will result in all the colours that we can perceive.

92
Q

describe the distribution of cells in the fovea (0º)

A

cone cells are most concentrated in the fovea
there are virtually no rods in the fovea as there are so many cones that there isn’t enough room for rods.
Therefore the fovea provides high detail colour vision in bright light in the centre of vision.

93
Q

Describe the distribution of cells in the peripheries of vision

A
  • Rods are in higher proportion than cones at the peripheries, gradually increasing towards the fovea, where they then decrease to 0.
  • There are no rod or cone cells at the blind spot (15-20º) where the optic nerve fibres are.
94
Q

why is it easier to view faint stars at night by looking at them with your peripheries?

A

it will mean that rod cells (not cone cells that are found in the fovea - the centre of vision) will be recognising the star, and as they are more sensitive, its dim light will be easier to see than if rod cells were being used.

95
Q

Describe the process of dark adaptation

A
  • Before it can be reused, rhodopsin has to be resynthesised after bleaching. This process requires energy in the form of ATP (released by the mitochondria found in the inner segment of the rod cell)
  • In light conditions that rhodopsin is almost entirely broken down (cones are being used for vision in bright light) - the eye is said to be light adapted.
  • Upon entering an area of darkness it takes around 30 minutes for the rhodopsin to reform to allow rods to become sensitive. The eye is said to be dark adapted
96
Q

Define binocular vision

A

the use of 2 eyes to form an image, allowing better perception of distance

97
Q

define stereoscopic vision

A

the ability of the brain to form a 3D image, facilitated by binocular vision

98
Q

describe the general difference in the visual field of prey and predator species

A
  • Prey animals like rabbits will often have eyes on the side of their head to give them the widest possible visual field
  • Predator animals like humans will have eyes on the front of their heads to allow for very good depth perception
99
Q

Describe the structural framework of a skeletal muscle

A
  • Complete muscle covered in a tough outer coating of connective tissue
  • Muscle tissue is composed of many bundles of muscle fibres
  • Each muscle fibre is made of many myofibrils
100
Q

Describe the features of a muscle fibre

A
  • one large cell with many nuclei
  • large numbers of mitochondria present
  • outer membrane is called the sarcolemma
  • network of membranes called the sarcoplasmic reticulum
  • cytoplasm is called the sarcoplasm
101
Q

describe the features of the sarcolemma

A
  • It is here that the synapses of the motor neurones make contact in structures referred to as motor end plates.
  • Sarcolemma forms deep inholdings at intervals along the length of the muscle fibre - these are known as T-tubules
102
Q

what is the function of the sarcoplasmic reticulum?

A

storage site for calcium ions

103
Q

name the functional unit of the muscle

A

myofibril

104
Q

how do myofibrils cause muscle contraction?

A

The contraction of the whole muscle is brought about through the coordinated shortening of all the myofibrils.

105
Q

name and describe the two proteins in a myofibril

A
  • Myosin is a thicker fibrous protein with protruding heads at intervals along its length
  • Actin is a finer fibrous protein with binding sites for the myosin heads along its length
106
Q

what is the A band?

A

Section of the sarcomere that contains myosin (and actin in overlapping sections)

107
Q

what is the I band?

A

Section of sarcomere that just contains actin

108
Q

What is the M line?

A

Midpoint between Z lines

109
Q

What is the Z line?

A

Separates adjacent sarcomeres (beginning and end)

110
Q

What is the H zone?

A

Section of A band without actin

111
Q

describe the relaxed state of the sarcomere

A

Sarcomeres longer in length, less overlapping in A band, larger H zone, Z lines further from M line

112
Q

describe the contracted state of the sarcomere

A

sarcomeres shorter in length, more overlapping in A band, smaller H zone, Z lines closer to M line

113
Q

why does rigour mortis occur?

A

Rigour mortis occurs because the muscles are contracted and can’t relax as ATP is required to release the myosin heads from the actin, and ATP isn’t produced after death.

114
Q

Describe the process of muscle contraction

A
  1. Action potential travels through T-tubules and stimulates muscle fibre
  2. Action potential causes Ca2+ channels in sarcoplasmic reticulum to open
  3. Ca2+ diffuses into sarcoplasm down a concentration gradient
  4. Tropomyosin (normally covers actin binding sites) moves, myosin heads form actomyosin bridges
  5. Myosin heads change angle to pull actin filaments over myosin
  6. ATP attaches to each myosin head, and energy released allows the head to detach from actin
  7. Myosin repeats process of attachment, rotation and release as long as stimulation lasts.
115
Q

Describe the changes that occur in a sarcomere that goes from a relaxed to a contracted state

A
  • I band narrows
  • H zone narrows
  • sarcomere shortens
  • Z lines become close together
  • A band stays the same width
116
Q

Describe the features of skeletal muscle

A

striated
multinucleate fibres
attached to bone
conscious control

117
Q

describe the features of cardiac muscle

A

striated but banded with intercalated discs between cells
found in wall of heart
myogenic and involuntary control

118
Q

describe the features of smooth muscle

A

discrete uninucleate cells are spindle shaped, not striated
line gut and blood vessels, and iris and ciliary body in eye
involuntary control

A2 Biology 1 (5 decks)

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