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Biology Edexcel A Alevel > Topic 8 > Flashcards

Topic 8 Flashcards

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1
Q

Draw a sensory neurone

A
  • Dendrites
  • Axon
  • Terminal branches
  • Cell body external in between Schwann cells
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2
Q

Draw a Relay neurone

A
  • Dendrites
  • Axon
  • Terminal branches
  • Cell body not external in between Schwann cells
  • Large number of connections to other nerve cells
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3
Q

Draw a Motor neurone

A
  • Dendrites around cell body which is at end of cell
  • Axon
  • Terminal branches at end
    *
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4
Q

Function of sensory neurones

A

Carry impulses from sensory cells to the CNS

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5
Q

Function of Relay neurones

A

Connect neurones

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6
Q

Function of motor neurone

A

Conducts impulses from CNS to effectors

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7
Q

Role of Schwann cells

A

To speed up the rate of transmission

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8
Q

What is the myelin sheath?

A

A fatty insulating layer around the axon

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9
Q

Describe the route of nerve impulses

A
  1. Receptors detect a stimulus and generate a nerve impulse.
  2. Sensory neurones conduct a nerve impulse to the CNS along a sensory pathway.
  3. Sensory neurones enter the spinal cord through the dorsal route.
  4. Sensory neurone forms a synapse with a relay neurone.
  5. Relay neurone forms a synapse with a motor neurone that leaves the spinal cord through the ventral route.
  6. Motor neurone carries impulses to an effector which produces a response.
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10
Q

What causes the pupil to dilate?

A

Radial muscles contract and the circular muscles relax

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11
Q

What causes the pupil to constrict?

A

Radical muscles relax and the circular muscles contract

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12
Q

What is the resting potential for an axon? (what is the charge of the inside of the axon compared the the outside)

A

-70mV

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13
Q

How is the resting potential maintained?

A
  1. Na+/K+ pump creates a concentration gradient across the membrane.
  2. K+ diffuse out of the cell down the K+ concentration gradient, making the outside of the membrane positive and the inside negative creating a potential difference.
  3. The potential difference will pull K+ back into the cell
  4. At -70mV potential difference, the two gradients counteract each other and there is no net movement of K+ ions.
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14
Q

What are the 4 types of channels in a cell surface membrane?

A
  1. Na+ gated channel
  2. Na+/K+ pump
  3. K+ channel
  4. K+ gated channel
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15
Q

Why is the charge inside of the membrane of a neurone more negative than the outside?

A

As the inside of the membrane has a higher K+ concentration and a lower Na+ concentration. (Vice versa outside)

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16
Q

Why is the axons resting potential -70mV?

A
  1. Potassium ions diffuse out of the cell due to the concentration gradient.
  2. The more potassium ions that diffuse out of the cell the larger the potential difference across the membrane.
  3. The increased negative charge inside the cell attracts potassium ions back across the membrane into the cell.
  4. When the potential difference across the membrane is -70mV, the electrical gradient exactly balances the chemical gradient. So there is no net movement of K+ which maintains the potential difference.
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17
Q

What happens when a nerve is stimulated?

A
  1. If a threshold level due to stimulus is met the voltage dependant Na+ channels open. Na+ flows into axon depolarising the membrane.
  2. Voltage dependant Na+ channels close. Voltage dependant K+ channels open. K+ leave the axon repolarising the membrane.
  3. The membrane is hyperpolarised. The voltage dependant K+ channels close. K+ diffuse back into the axon to recreate the resting potential.
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18
Q

What is the refractory period and how long does it last?

A

The period when new action potential cannot be generated in the same section of membrane for about 5 milliseconds.

It lasts until all the voltage dependent sodium and potassium channels have returned to their normal resting state and the resting potential is restored.

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19
Q

What is saltatory conduction?

A

When the impulse jumps from one node to the next due to myelination of the membrane increasing the speed of conduction.

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20
Q

Describe how an impulse travels along a membrane.

A
  1. At resting potential there is a positive charge on the outside of the membrane and negative change on the inside, with high sodium ion concentration outside and high potassium ion concentration inside (membrane No.1).
  2. When stimulated, voltage dependant sodium ion channels open. Sodium ions flow into the axon depolarising the membrane.
  3. Sodium ions move to the adjacent polarised (resting) region (membrane No.2) causing a change in the electrical charge (PD) in this part of the membrane (membrane No.2).
  4. The change in the potential difference in (membrane No.2) initiates a second action potential in (membrane No.3).
  5. In (membrane No.1) the voltage dependant sodium ion channels close and the voltage dependant potassium ion channels open. Potassium ions leave the axon repolarising the membrane and the membrane becomes hyperpolarised.
  6. A third action potential (in membrane No.3) is initiated by the second (in membrane No.2). The local electrical currents cause the nerve impulse to move along the axon. (In membrane No.1) potassium ions diffuse back into the axon, restoring the resting potential.
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21
Q

How does a synapse transmit an impulse?

A
  1. An action potential arrives
  2. The membrane depolarises. Ca+ channels open. Ca+ enter the neurone.
  3. Ca+ cause the synaptic vesicle containing neurotransmitter to fuse with the presynaptic membrane
  4. Neurotransmitter is released into the synaptic cleft
  5. Neurotransmitters bind with receptors on the post synaptic membrane. Cation channels open. Na+ flow through the channels.
  6. The membrane depolarises and initiates an action potential.
  7. When released from the receptor the neurotransmitter will be taken up across the presynaptic membrane (whole or broken down) or it can diffuse away and be broken down.
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22
Q

What is acetylcholine?

A

a neurotransmitter

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23
Q

Draw and describe Spatial summation

A

Impulses from different synapses, usually from different neurones. The number of different sensory cells stimulated can be reflected in the control of the response.

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24
Q

Draw and describe Temporal summation

A

Several impulses arrive at a synapse having travelled along a single neurone one after the other. Their combined release of neurotransmitter generates an action potential in the postsynaptic membrane.

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25
Q

Describe the key features of nervous control

A
  • electrical transmission by nerve impulses and chemical transmission at synapse.
  • fast acting
  • usually associated with short term changes eg muscle contraction.
  • action potential carried by neurones with connections to specific cells.
  • response is often very local, such as specific muscle cell or gland.
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26
Q

Describe the key features of hormonal control

A
  • chemical transmission through the blood
  • slower acting
  • can control long term changes eg growth
  • blood carries the hormone to all cells but only target cells are able to respond
  • response may be widespread, such as in growth and development.
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27
Q

What is indoleacetic acid (IAA)?

A

an auxin

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28
Q

What effect did IAA and illumination have on plants?

A
  • Its role is to stimulate growth and its response is cell elongation.
  • They found that more auxin had passed down the shaded side of the plant when it was illuminated from one side.
  • The reduced concentration on the illuminated side inhibited cell elongation.
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29
Q

How do auxins cause changes such as cell expansion, division and differentiation?

A
  1. The auxins bind to protein receptors in the target cells.
  2. This activates intracellular second messenger signal molecules, which activate transcription factors.
  3. These control the transcription of auxin-regulated genes and proteins produced bring about metabolic changes
  4. These metabolic changes result in responses such as cell expansion, division and differentiation.
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30
Q

Rods

A

Rods only give black and white vision but work in dim light as well as bright light.

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31
Q

Cones

A

Allow colour vision in bright light but don’t work in dim light.

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32
Q

Rhodopsin

A

A purplish photochemical pigment that absorbs the light in rod cells resulting in a chemical changes.

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33
Q

What happens to rod cells in the dark?

A
  1. Na+ diffuse in through open cation channels
  2. Na+ move down concentration gradient
  3. Na+ actively pumped out causing membrane to be slightly depolarised -40mV triggering neurotransmitter (glutamate) release.
  4. Inhibitory synapse, neurotransmitter released binds to bipolar cell, preventing it depolarising.
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34
Q

What happens to rod cells in the light

A
  1. Rhodopsin absorbs light and breaks down into retinal and opsin.
  2. Opsin activates a cascade of reactions that result in the closing of the non specific cation channels.
  3. As the cation channels have closed no Na+ can enter.
  4. Na+ actively pumped out causing membrane to e hyperpolarised.
  5. No neurotransmitter is released
  6. No inhibition so cation channels in bipolar membrane open and membrane becomes depolarised.
  7. Generating an action potential which is transmitted to the neurone of the optic nerve.
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35
Q

Opsin

A
  • When rhodopsin absorbs light and breaks down into retinal and opsin.
  • Opsin activates a cascade of reactions that result in the closing of the non-specific cation channels.
36
Q

Phytochromes

A

They absorb red and far-red light. Red light triggers germination and far-red inhibits.

37
Q

How do phytochromes switch processes on or off?

A
  1. Exposure to light causes phytochrome molecules to change from one form to another, bringing about a change in shape.
  2. The phytochromes may bind to the protein or disrupt the binding of a protein complex.
  3. These signal proteins may act as transcription factors or activate transcription factors that bind to DNA.
38
Q

How does gravity impact plants growth?

A

Ensuring that developing shoots reach the light while roots grow in the soil.

39
Q

What are the 4 lobes of the brain?

A
  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe
40
Q

Parietal lobe

A

Orientation, movement, sensation, calculation and some types of recognition and memory

41
Q

Occipital lobe

A

Processing information from the eyes, including vision, colour, shape, recognition and perspective.

42
Q

Temporal lobe

A

Auditory information: hearing, sound recognition and speech. Also memory.

43
Q

Frontal lobe

A

Higher brain functioning: decision making, reasoning, planning and consciousness of emotions.

Sends information to the body via the motor neurones to carry out movements.

44
Q

Where is the occipital lobe?

A

Back of head

45
Q

Where is the parietal lobe?

A

Top of head

46
Q

Where is the frontal lobe?

A

Front of head

47
Q

Where is the temporal lobe

A

By the ears

48
Q

Where is the hypothalamus?

A

It lies below the thalamus

49
Q

Function of the thalamus

A

Contains the thermoregulatory centre. Which monitors core body temperature and skin temperature. Also returning the body temp to optimum temperature.

Also controls sleep, thirst and hunger.

Also secrets hormones and acts as an endocrine gland

50
Q

Where is the cerebellum?

A

below the temporal and occipital lobe.

51
Q

What is the function of the cerebellum?

A

Maintenance of balance and posture

52
Q

Where is the medulla oblongata?

A

Just above the spinal cord

53
Q

What is the function of the medulla oblongata?

A

Transmitting signals between the spinal cord and the higher parts of the brain and in controlling autonomic activities, such as heartbeat and respiration.

54
Q

CT scans

A
  • Uses radiation but less than x-rays
  • Give a frozen moment picture
  • Look at structures rather than functions
  • Limited resolution so small structures cannot be distinguished.
55
Q

MRI scans

A
  • Magnetic field and radio waves
  • Examines tissues in small sections with thin slices which form 3D images.
  • Produce finely detailed images of brain structures with better resolution than CT scans.
56
Q

fMRI scans

A
  • Provides information about brain in action.
  • Can study memory, emotion, language and consciousness.
  • Places with higher oxygen consumption have higher activity levels
57
Q

PET scans

A
  • Patient injected with radiotracer.
  • More glucose is required in places with higher activity.
  • Only done once or twice a year.
  • Expensive.
58
Q

What happens during the critical period so that mammals can develop their visual capacities to the full?

A
  • At birth there is overlap between the territories of the different axons.
  • Axons compete for target cells in the visual cortex.
  • Every time a neurone fires onto a target cell, the synapse of another neurone sharing the target cell is weakened and they release less neurotransmitters.
  • If this happens repeatedly they will be cut back.
59
Q

What was Hubel and Wiesel’s study on monkeys about?

A

The monkey’s were deprived of light in one eye for 6 months. Monocular deprivation. After 6 months the eye was exposed to light. The monkey was blind in the light deprived eye. Retinal cells did respond, but the cells in the visual cortex did not.

Deprivation in adult monkeys had no effect. Visual deprivation in both eyes had much less effect than just one.

60
Q

Give 2 reasons why animals should not be used in medical research?

A
  • Humans consent and as animals cannot consent they shouldn’t be used in trials
  • It is harmful to the animal, and no vertebrates should be used when there are non-animal alternatives
61
Q

Give 2 reasons why it is okay to use animals in medical research?

A
  1. Can certain animals suffer, do they have the mental ability to suffer?
  2. Utilitarianism is the belief that the right course of action is the one that maximised the amount of overall happiness or pleasure in the world. That animals can be used so long as the overall expected benefits are greater than the overall expected harms.
62
Q

What are the two ways memories are stored?

A
  1. the pattern of connections
  2. the strength of synapses
63
Q

How is habituation achieved?

A
  1. With repeated stimulation the Ca2+ channels become less responsive so less Ca2+ crosses the presynaptic membrane.
  2. Less neurotransmitter is released
  3. There is less depolarisation of the postsynaptic membrane so no action potential is triggered in the motor neurone.
64
Q

Why is habituation important?

A

It gives animals the ability to ignore unimportant repetitive stimuli so that limited sensory , attention and memory resources can be concentrated on more threatening or rewarding stimuli.

65
Q

How does IAA bring about responses in plants?

A

Increased concentration on the shaded side of the plant causes cell elongation. The reduced concentration on the illuminated side inhibited cell elongation.

66
Q

How does cell expansion as a result of auxins occur?

A
  1. The auxins cause the acidification of the cell wall by stimulating the activity of proton pumps that move H+ ions out of the cytoplasm and into the cell wall.
  2. The low pH in the cell wall disrupts the bonds that hold the cellulose microfibrils and hemicelluloses together.
  3. There is loosening of the cell wall: there is slippage of the polysaccharides relative to each other, bond reform in new locations, allowing bonds to reform in new locations.
67
Q

What are 5 features of nervous control in animals?

A
  1. Electrical transmissions by nerve impulses and chemical transmission at synapses
  2. Fast acting
  3. usually associated with short term changes eg muscle contraction
  4. Action potential carried by neurones with connections to specific cells
  5. Response is often very local such as a specific muscle cell or gland
68
Q

What are 5 features of hormonal control in animals?

A
  1. Chemical transmission through the blood
  2. Slower acting
  3. Can control long-term changes eg growth
  4. Blood carries the hormone to all cells but only target cells are able to respond
  5. Response may be widespread, such as growth and development.
69
Q

How do Inhibitory synapses work?

A

They make it less likely that an action potential will result in the post synaptic cell.

  1. Chloride ions move into the cell carrying a negative charge and potassium ions will move out carrying a positive charge.
  2. The result will be greater potential difference across the membrane as the inside becomes more negative than usual (hyperpolarisation).
  3. Making subsequent depolarisation less likely.
  4. More excitatory synapses will be required to depolarise the membrane.
70
Q

What causes Parkinson’s?

A

Dopamine secreting neurones in the basal ganglia die. These neurones normally release dopamine in the motor cortex.

Fewer sodium ion channels on the post synaptic membrane open, so the post synaptic cell is less likely to be depolarised. This means fewer action potentials are produced leading to symptoms such as tremors.

71
Q

What are the main symptoms of Parkinson’s?

A
  1. Stiffness of muscles
  2. Tremor of the muscles
  3. Slowness of movement
  4. Poor balance
  5. Walking problems
72
Q

How does L-dopa help patients with Parkinson’s?

A
  1. L-Dopa is a drug that is used to treat the symptoms of Parkinson’s disease.
  2. Its structure is very similar to dopamine
  3. When L-dopa is given its absorbed into the brain and converted into dopamine by the enzyme dopa-decarboxylase. This increases the level of dopamine in the brain.
  4. Higher level of dopamine means that more nerve impulses are transmitted across the synapse in the parts of the brain that control movement.
  5. This gives sufferers of Parkinson’s more control over their movements.
73
Q

Why can’t dopamine be given to treat parkinsons?

A

As dopamine cannot enter the brain.

74
Q

What causes depression?

A

Low levels of the neurotransmitter serotonin

75
Q

What does serotonin do?

A

Serotonin transmits nerve impulses across the synapse in the parts of the brain that control mood.

76
Q

How do SSRI’s work?

A

Selective serotonin reuptake inhibitors increase serotonin levels by preventing its reuptake at synapses.

77
Q

How does MDMA (ecstasy) work?

A
  1. MDMA increases the level of serotonin in the brain.
  2. Usually serotonin is taken back into a presynaptic neurone after triggering an action potential to be used again.
  3. MDMA increases the level of serotonin by inhibiting the reuptake of serotonin into presynaptic neurones. It binds and blocks the reuptake proteins on the presynaptic membrane.
  4. MDMA also triggers the release of serotonin from presynaptic neurones.
  5. This means that serotonin levels stay high in the synapse and cause depolarisation of the post synaptic neurones in parts of the brain that control mood.
  6. So the effect is mood elevation.
78
Q

How is information from the human genome sequencing project being used to create new drugs?

A

The HGP has identified all the genes found in human DNA. The data is used to identify genes and so proteins that are involved in disease.

Scientists use this information to create new drugs that target the identified proteins. eg scientists have identified an enzyme that helps cancer cells to spread around the body- a drug that inhibits this is being developed.

79
Q

How is information from the human genome sequencing project being used to create personalised medicines?

A

The HGP highlighted common genetic variations and its known that some variations make drugs less effective.

Drug companies can use this knowledge to design new drugs that are tailored to people with these variations.

Doctors can personalise a patients treatment by using their genetic information to predict how well they will respond to different drugs and only prescribe the ones that will be most effective.

80
Q

What social, moral and ethical issues arise from personalised medication?

A
  1. Research costs will increase which might mean drugs become more expensive and only the rich can afford.
  2. Some people may be refused an expensive drug as their genetic makeup indicates it wont be effective however it might be the only drug available.
  3. The information in a persons genome could be used to unfairly discriminate against them. And increase their life insurance.
  4. Revealing a drug is unlikely to help them might be psychologically damaging.
81
Q

How can genetically modified bacterium be used to produce drugs?

A
  1. Isolated human gene is then spliced with a plasmid that has been cut with the same restriction enzyme.
  2. The modified plasmid is put back into the bacterial cells.
  3. The cells multiply in fermenter
  4. This produces human insulin due to the protein production being switched on.
  5. Bacterial cell is destroyed and the insulin protein is extracted and purified.
82
Q

How can genetically modified plants be used to produce drugs?

A
  1. Identify a gene of interest and cut with restriction enzyme. Cut plasmid with same enzyme.
  2. Insert foreign gene into plasmid DNA along with a selectable antibiotic marker.
  3. Reinsert plasmid into bacterium.
  4. Allow bacterium to introduce plasmid vector with foreign DNA into plant cell.
  5. Foreign gene into the plant chromosome.
  6. Those plants that incorporate it into the chromosome grow on the antibiotic medium.
  7. These plants can either be purified or the protein could be delivered by eating the plant.
83
Q

Benefits of using genetically modified organisms

A
  1. Crops can be modified to have pest resistance so fewer pesticides are needed which reduces costs making food cheaper.
  2. Agricultural crops can be modified to produce higher yields and are more nutritious and therefore can reduce the risk of famine and malnutrition.
  3. Vaccines produced from plants do not need to be refrigerated making them more widely available.
84
Q

Risks of using genetically modified organisms

A
  1. Concerns over transmission of genetic material for example if herbicide resistant crops interbreed with wild plants it could create ‘superweeds’
  2. Some people are worried about the long term impacts of using GMOs, there may be unforeseen consequences.
  3. Some people may think its wrong to genetically modify animals purely for human benefit.
85
Q

How are genetically engineered animals used to produce drugs?

A
  1. Gene for protein is injected into the nucleus of a fertilised animal egg cell
  2. The egg cell is then implanted into an adult animal- it grows into an adult animal that contains a copy of the gene in every cell.
  3. The protein produced from the gene is normally purified from the milk of the animal.

Biology Edexcel A Alevel (15 decks)

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