Topic 8 exam questions Flashcards
habituation n that
Describe the interaction of the muscles in the eye that led to this dilation of the pupils (3)
-Antagonistic interaction of muscles
-In the iris
-Radial muscles contract and circular muscles relax
Decreasing the intensity of light entering the eye causes pupil dilation
Describe the roles of the circular and radial muscles in pupil dilation (2)
-Muscles work antagonistically
-Circular muscles relax
-Radial muscles contract
Suggest why the pupil appears black (1)
-Pigment at the back of the eye absorbs light / no light is reflected out
There are two sets of iris muscle, the radial muscle and the circular muscles. They work antagonistically to alter the size of the pupil
Explain why these two sets of muscles need to be antagonistic (3)
-Circular muscles contract and radial muscles relax constrict to constrict pupil
-Radial muscles contract and circular muscles relax to dilate the pupil
-These muscles can only shorten
-Antagonistic muscles have opposite effects
Describe the differences in the structure of a myelinated sensory neurone and a myelinated motor neurone (3)
-Sensory neurone has longer dendron
-Sensory neurone has dendron myelinated
-Axon is shorter in sensory neurone
- Sensory neuron has cell body containing nucleus on the side / towards the middle
Describe the role of the myelin sheath in the conduction of nerve impulses (4)
-Myelin sheath plays a role in electrical insulation
-Depolarisation at nodes
-Impulse jumps from node to node
-Saltatory conduction
-Leads to faster conduction
Name the type of cell that forms the myelin sheath (1)
Schwann cell
Describe the role of myelination in the conduction of a nerve impulse (2)
-Provides electrical insulation
-Enables saltatory conduction
Explain why there is a difference in the conduction velocity of these neurones (5)
-Schwann cells cover the axon in myelinated neurone
-Schwann cells / Myelin provide insulation
-Action potential / depolarisation at nodes of Ranvier
-Saltatory conduction in myelinated neurone
-Which means impulse jumps from node to node, leading to faster velocity of the nerve impulse
Describe the role of the dendrites in a neurone (3)
-Forms synapses with other neurones
-Receive impulses from other neurones
-Involved in summation
-Dendrites propagate a signal / initiate an action potential to the cell body / axon
Explain how the structure of the axon cell membrane is related to the conduction of nerve impulses (3)
-Phospholipid restricts ion movement
-Proteins span the membrane
-Sodium / Potassium pump moves ions
-protein gates / channels allow diffusion movement of ions
Explain how myelination increases the speed of transmission of nerve impulses in a sensory neurone (5)
-Neurone cell surface membrane exposed at nodes of Ranvier
-Nodes are the site of clusters of sodium-gate channel proteins
-Which open / close when impulse arrives
-Allowing depolarisation at nodes
-Myelin acts as an electrical insulator on neurone surface between nodes
-Myelin sheath are made of Schwann cells
-Impulse ‘jumps’ from node to node
-This is called saltatory conduction
-Saltatory conduction happens between the myelin layers of the Schwann cell
Describe the role of ion channels in the conduction of a nerve impulse (5)
-Sodium ion channels open
-Sodium ions diffuse in
-Causing depolarisation of the membrane
-Sodium ion channels close and potassium ions channels open
-Then potassium ions diffuse out
-Causing repolarisation of the membrane
Explain the role of ATP in the transmission of impulses along neurones (2)
-ATP required for sodium / potassium pumps
-To move ions against concentration
-To maintain potential difference across axon membrane
Describe how the neurotransmitter crosses this synapse (2)
-Vesicles fuse with presynaptic membrane by exocytosis
-The neurotransmitter crosses the synapse via diffusion
Describe how the arrival of a nerve impulse at a synapse causes the release of neurotransmitters (3)
-Ca2+ enters the synaptic knob / bouton
-Vesicles containing neurotransmitters
-Fuse with the presynaptic membrane and are released into the synaptic cleft
Describe and explain the sequence of events that occurs at the synapse after a neurotransmitter has been released (5)
-Neurotransmitter diffuses across the gap
-It binds to receptors on the post synaptic membrane
-Gated-channels opening / Na+ travels through post-synaptic membrane
-Causing depolarisation
-An action potential is set up in post-synaptic membrane
-Leads to temporal / spatial summation
-Information from neurotransmitter travels one way in the synapse
-Neurotransmitter integrates in the post-synaptic cell
-Neurotransmitter is broken down by enzymes so there is no prolonged action potential in post-synaptic membrane
-Neurotransmitter can be reabsorbed through pre-synaptic membrane
Explain how MDMA could affect levels of serotonin in the brain (3)
-Higher levels of serotonin
-In the synapse
-Inhibits reabsorption into neurone
Drugs called SSRI’s are used to reduce depression. They work by inhibiting the reabsorption of serotonin at a synapse.
Explain how SSRI’s help to maintain a feeling of well-being (3)
-SSRIs bind to channel / reuptake proteins
-Serotonin levels remain high in the synapse
-Serotonin binds to receptor proteins in post-synaptic membrane
-Depolarisation of post-synaptic membrane
-Action potentials / impulses / transmission continues
Double blind trials give scientists confidence in the results collected.
Explain two ways the design of this trial could be improved in order to increase confidence in the results (4)
-Use more patients / increase sample size / repeat the trial
-To increase reliability
-Use statistical analysis
-To see if the differences are significant
-Consider sample selection to use the same age / gender / ethnicity … of patients
-To control biotic variables
Describe how low serotonin levels in an individual can affect the transmission of impulses in their brain (2)
-Serotonin is a neurotransmitter / there will be less neurotransmitter
-Less serotonin results in fewer depolarisations of post synaptic membranes
-Threshold not achieved / less chance of action potential being produced in post-synaptic neurone
Describe how the use of MDMA could affect the transmission of impulses in the brain (2)
-MDMA prevents re-uptake / increases concentration of serotonin
-Blocking pre-synaptic receptors by bindings to post synaptic receptors
-Nerve pathways using serotonin are more likely to be stimulated so more action potentials generated
Individuals who use MDMA may develop symptoms of depression
Explain how the use of MDMA could result in the development of these symptoms (2)
-MDMA use leads to depletion of serotonin
-Post synaptic membrane becomes less responsive to serotonin / loss of receptors on post synaptic membrane
-Serotonin levels affect mood / lack of serotonin associated with depression
Some early studies of schizophrenia included identical twins raised in separate families
Explain how the design of these studies allows the influence of environmental factors on the development of schizophrenia to be investigated (2)
-Identical twins being raised apart allows for environmental factors to be investigated separately from genetic factors
-Therefore may be able to determine relative amount of risk due to genetic variation / relative amount of risk due to environment
Schizophrenia has been linked to abnormally high levels of a neurotransmitter in the brain
Explain how the action of the drugs used to treat schizophrenia may lead some patients to experience symptoms similar to those of Parkinson’s disease (5)
-Parkinson’s symptoms arise due to low dopamine levels
-Transmission of nerve impulses disrupted causing lack of control of muscle movements
-Schizophrenia drugs lower dopamine levels
-Therefore less dopamine in synaptic knob secreted into cleft / diffuses across cleft
-Therefore less dopamine available to bind to receptors
-Therefore little charge in membrane structure
-Therefore fewer sodium ions enter postsynaptic cell
-Therefore less depolarisation of postsynaptic cell
Explain the effect of increasing light intensity on the current produced by a rod cell (5)
-Increasing light intensity decreases the current
-Because rhodopsin is broken down / opsin is released
-Therefore, more opsin binds to the channel proteins in the outer segment
-Sodium-gated voltage channels close
-Reducing / stopping the influx of sodium ions / making membrane impermeable to sodium ions
Rod cells form synapses with bipolar neurones
Describe how movement of sodium ions in a rod cell affects depolarisation in a bipolar neurone (4)
-In the dark, sodium ions move in through sodium ion channels into the outer segment
-Sodium ions removed / pumped out at inner segment
-So rod cells depolarises
-Causing neurotransmitter / glutamate to be released
-Inhibits depolarisation in the adjacent bipolar neurone
Which brain area controls coordination of movement (1)
Cerebellum
Explain the advantages of using MRI scanning to identify tumours compared to using CT scans (3)
-MRI gives better resolution
-Therefore more detail can be seen
-No use of X-rays
-Therefore safer / less risk of mutation
-Therefore can be used more often
Explain how fMRI scanning would help neuroscientists to identify the part of the brain involved in controlling a voluntary actions such as picking up a pen to write on paper (3)
-Increased neural activity of cerebellum / cerebrum
-More oxygen needed so increase in blood flow / oxyhaemoglobin
-Less radio wave signal absorbed
Describe how PET scans can be used to investigate brain structure (2)
-PET makes use of radioactive tracers / markers / glucose
-PET scan detects emission of positrons / production of gamma rays
-To provide a 3D image
Describe why a combined PET and CT scan may be better for diagnosing cancer than a PET or CT scans on its own (3)
-Using both provides information on function and structure
-PET scans shows areas that are more metabolically active / dividing more
-CT scan gives location / size
Describe why a region of the brain might appear lighter in an image obtained by a fMRI scan (3)
-Due to more activity
-An increase in oxygenated blood / blood flow to this region
-fMRI signals reflected / not absorbed by oxygenated blood
Explain how fMRI can be used to identify the part of the brain involved in interpreting information from the visual cortex (3)
-fMRI detects blood flow / oxygen use in the brain
-Increased brain activity results in increased blood flow / demand for oxygen / aerobic respiration in the area of activity
-Oxyhaemoglobin absorbs fewer radio waves / fMRI detects areas where less signal is absorbed
It is safer to use MRI than computed tomography (CT) because … (1)
CT scans use x-rays that can cause mutations in the DNA of muscle fibres
Describe the role of visual stimulation on the development of the visual cortex during the critical period (3)
-Ocular dominance columns develop in visual cortex
-Neurones form synapses with these cells / columns
-Stimuli / action potentials / impulses along with neurones required to strengthen connections with cells of ocular dominance columns
-Stimulation during the critical period is needed to form effective connections in the visual cortex
Describe how eyes relay visual information to the brain (5)
-Light is detected by rod cells
-Rod cell membrane is hyperpolarised
-Stopping the release of the inhibitory neurotransmitter glutamate
-Bipolar neurone is depolarised
-Impulse transmitted along optic nerve / ganglion neurone
-Impulse transmitted to visual cortex of the brain
Give one example of a growth response of a plant that is affected by phytochrome (1)
-Seed germination / flowering
Some plants only flower when the days are long and the nights are short, They are known as long-day plants
Describe the role of the photosensitive pigment phytochrome in the flowering of long-day plants (2)
-Increased red light due to a long day / short night
-Phytochrome red converted to phytochrome far red in the day / little conversion of far red form to red form during the short night
-Accumulation of high concentration of phytochrome far red stimulates flowering
Describe the role of IAA (auxin) in the phototropic response of plants (4)
-Auxin diffuses from the tip
-Therefore can be taken up by cells in zone of elongation
-Which causes cells to elongate
-Leads to lowering of the PH in the cellulose cell wall
-Therefore causes plant to grow towards the light / increase in height
Explain how the IAA affects the growth of a plant (4)
-Auxin diffuses from the tip of the plant
-Therefore can be taken up by cells in zone of elongation
-Which causes cells to elongate
-Details of action zone of elongation
-Therefore causes the plant to grow towards the light / increase in height / positive phototropism
Describe how bacteria can be genetically modified (4)
-Isolate the gene from human DNA
-Use a bacterial plasmid as a vector
-Cut the human DNA and the plasmid using the same restriction enzyme
-Splice the gene and plasmid together using DNA ligase
-Put the modified plasmids into bacterial cells
Beta-blockers are a type of drug with antihypertensive properties
Beta-blockers work by blocking the effects of a hormone called adrenaline
Adrenaline is produced by the adrenal glands located on top of each kidney
Adrenaline acts on the heart to cause changes in heart rate
Deduce how adrenaline can cause a change in heart rate (4)
-Adrenaline carried in the blood
-It acts on the sinoatrial node
-Increasing the frequency of impulses produced by the SAN
-Increasing the rate at which the heart contracts
Describe the role of enzymes involved in the synthesis of personalised proteins in GMOs (3)
-DNA helicase used to unzip DNA / break hydrogen bonds
-RNA polymerase involved in making mRNA / transcription of gene
-Joining nucleotides together forming phosphodiester bonds
-Enzymes join amino acids together forming peptide bonds
Explain how an inhibitory neurotransmitter works
-Neurotransmitter binds to chlorine ligand gated channels on the post synaptic neurone
-Chloride ion gates open and negatively charged chloride ions enter the cell
-Leads to hyperpolarisation
-Less chance of the action potential firing
Explain how acetylcholine can act as both an excitatory in skeletal muscles and an inhibitory neurotransmitter in the heart leading to our heart rate slowing down
Inhibitory:
-Acetylcholine binds to Cl- ligand gated channels on post synaptic membrane
-Chloride ion channels open and negatively charged chloride ions enter the membrane making it hyperpolarised
-Less chance of an action potential firing
Excitatory:
-Acetylcholine binds to Na+ ligand gated channel on post synaptic membrane
-Sodium ion channels open and positively charged sodium ions enter, causing the neurone to be come depolarised
-Increasing chances the action potential fire
Describe the role of ion channels in the conduction of a nerve impulse (5)
-Sodium ion channels open
-Then sodium ions diffuse in
-Causing depolarisation of the membrane
-Sodium ion channels close and potassium ion channels open
-Then potassium ions diffuse out
-Causing repolarisation of the membrane
Explain how low levels of dopamine contribute to symptoms of Parkinson’s disease
-Less dopamine is released into the synaptic cleft meaning less is able to bind with receptors on the postsynaptic membrane
-Fewer sodium channels on the membrane are opened so depolarisation of the postsynaptic neurone does not occur
-This leads to fewer action potentials which creates the symptoms such as tremors and slow movement
Treatments for Parkinson’s
Dopamine agonists:
Produce the same effect as dopamine by binding to and activating the dopamine receptors on the postsynaptic membrane
Dopamine precursors :
These are chemicals that can be converted into dopamine in the neurones. E.g. L-dopa
Effects of MDMA on the synapse
MDMA inhibits the reuptake of serotonin into the presynaptic neurone by binding to the specific proteins that enable serotonin reuptake, located on the presynaptic membrane; this increases the amount of serotonin present in the brain. Acts as a competitive inhibitor
Serotonin is usually reabsorbed into the presynaptic neurone to be recycled for future action potentials
MDMA also triggers the release of further serotonin from presynaptic neurones, further adding to the increase
When light stimulates a rod cell the pigment changes.
This pigment is … (1)
Rhodopsin
The cell that links a rod cell to a sensory neurone is … (1)
A bipolar neurone
When light reaches the rod cell the voltage across the cell surface membrane can change. This can lead to the formation of an action potential in an optic neurone
Describe how light causes a change in the voltage across the cell surface membrane of a rod cell (4)
-Reference to light intensity required
-Light absorbed by rhodopsin
-Rhodopsin changes shape
-Rhodopsin is converted to retinal AND opsin
-Opsin binds with cell surface membrane
-Idea of fewer sodium ions /Na+ enter rod cell
-Idea of sodium ions pumped out of rod cell ;
-Hyperpolarisation occurs leading to change in voltage
Suggest why a change in voltage across the cell surface membrane of a rod cell may not lead to the formation of an action potential in an optic neurone (2)
-Idea of not enough rhodopsin is converted /opsin binds to membrane
-So change in voltage is insufficient
-Neurotransmitter / glutamate still released from rod cell
-Depolarisation in bipolar neurone insufficient
-Bipolar neurone already depolarised
There are various ways of investigating brain structure and function
(a) Describe how scans from magnetic resonance imaging (MRI) may be used to
investigate brain tumours (2)
-Identification of location
-Size of tumour
-Type of tumour
-Reference to blood vessels
-Idea of monitoring treatment or growth of tumour
Suggest how fMRI was able to show that certain areas in the brain became
more active when people ate chocolate (3)
-Idea that fMRI can allow brain activity to be seen in real time
-Idea that fMRI uses radio waves / magnetic field
-Increase supply of oxygenated blood in active areas
-That {reflects/does not absorb} fMRI signals
-Idea of seen as a white area
-Idea of comparison with and without chocolate
Some of these more active areas were in the cerebral hemispheres of the brain.
The cerebral hemispheres have a number of functions.
State two functions associated with the cerebral hemispheres (2)
Think, learn, feel emotions, personality, ability to see, memory
Eugenol can be used to reduce pain.
Suggest an explanation for how eugenol affects the movement of sodium ions
and reduces pain (6)
-Higher concentration of Na+ outside of neurone
-Sodium ions move in causing a depolarisation
-Eugenol may affect Na+ / voltage-dependent gates
-Eugenol reduces influx of Na+
-So depolarisation less likely to occur
-No impulse transmitted along neurone
-Idea of no transmission to next neurone
-Idea of pain not being sensed as impulse stopped before entering CNS ;
IAA can interact with transcription factors to stimulate cells to produce proteins.
Suggest how the presence of IAA can cause cells to produce proteins.
(4)
-IAA at cell surface membrane e.g. binds to receptors
-Idea of movement within cell e.g. secondary messengers, IAA moves to the nucleus
-Detail of interaction with transcription factor
-Idea of switching on gene
-Activity at promoter region
-Allows formation of mRNA
-Idea of translation produces protein
Describe how the arrival of a nerve impulse at a synapse causes the release of neurotransmitters (3)
-Ca2+ enters synaptic knob
-Vesicles containing neurotransmitter
-Move towards / fuse with presynaptic membrane / reference to exocytosis of neurotransmitter
