Topic 8 Grey matter

Question 1

Describe the functions of the enzymes used to genetically modify bacteria. (4)

Answer 1

-Restriction endonuclease used to cut plasmid/isolate gene.
-Forming sticky ends.
-Ligase enzyme used to join isolated gene to plasmid.
-Ligase forms phosphodiester bonds between nucleotides.
-Recombinant DNA/plasmid produced.

Question 2

Explain how an enzyme is involved in joining two different genes together in genetic modification. (3)

Answer 2

-DNA ligase joins the two genes.
-By joining phosphate to sugar/forming phosphodiester bonds.
-By condensation reactions.

Question 3

What enzyme is used to cut open plasmids in genetic modification? (1)

Answer 3

-Restriction endonuclease.

Question 4

Explain how human genome sequencing can be used to identify the mutations associated with a genetic condition. (3)

Answer 4

-Sequence genome of people with genetic condition.
-Sequence genome of people without genetic condition.
-Compare the base sequences to identify mutations found only in individuals with genetic condition.

Question 5

The neurones of the central nervous system contain TAU proteins. These proteins help to maintain cell structure. Scientists are studying the effect of these different TAU proteins in animal models.

Describe how Drosophila flies could be genetically modified to produce one form of the human TAU protein. (4)

Answer 5

-Extract mRNA for one form of the TAU protein.
-Copy mRNA into DNA.
-Use restriction enzymes to create sticky ends/cut DNA and a vector.
-Ligate/insert the TAU DNA into the vector DNA.
-Introduced vector into fertilised egg.

Question 6

Describe how bacteria can be genetically modified to produce a cytokine for treatment of neurological and mental disorders. (4)

Answer 6

-Isolate gene for the cytokine.
-Use a bacterial plasmid as a vector.
-Cut human DNA and plasmid using same restriction enzyme.
-Splice/join gene and plasmid together using DNA ligase.
-Put modified plasmids into bacterial cells.

Question 7

Describe how positron emission tomography (PET) scans can be used to investigate brain structure. (2)

Answer 7

-PET makes use of radioactive tracers/markers/glucose.
-PET scan detects emission of positrons/production of gamma rays.
-Provides 3D image.

Question 8

When a child is shown a cheeseburger they produced a large mass of saliva. The child was then shown a cheeseburger eight more times. After the sixth time the mass of saliva decreased by a significant amount.

Explain what happens at the synapse to cause a decrease in saliva production when the child was shown a cheeseburger on more than six occasions. (4)

Answer 8

-Reduced permeability of presynaptic membrane to calcium ions/fewer calcium ions enter pre-synaptic neurone.
-So fewer vesicles fuse with presynaptic membrane.
-Therefore less neurotransmitters binds to receptors on post-synaptic membrane.
-Action potential may not occur in post-synaptic neurone/membrane may not be depolarised.

Question 9

Visual development requires exposure of the visual cortex to environmental signals during a critical period.

Describe the role of visual stimulation on the development of the visual cortex during the critical period. (3)

Answer 9

-Ocular dominance columns develop in visual cortex.
-Neurones form synapses with these cells/columns.
-Stimuli/action potentials along neurones required to strengthen connections with cells of ocular dominance columns.
-Stimulation during critical period is needed to form effective connections in visual cortex.

Question 10

Describe the process that occurs at a synapse that leads to habituation. (4)

Answer 10

-Repeated stimulus decreases permeability of pre-synaptic membrane/calcium channels not opening.
-So fewer/no calcium ions move into pre-synaptic neurone.
-So fewer/no vesicles fuse with pre-synaptic membrane.
-So less/no neurotransmitter released/can diffuse across gap.
-Action potential/depolarisation less likely to occur in post-synaptic neurone.

Question 11

What are two types of scans that can be used to identify brain tumors? (2)

Answer 11

-CT.
-MRI.

Question 12

What changes does fMRI detect to measure brain activity? (1)

Answer 12

-Changes in blood flow.

Question 13

What type of scanner uses X-Rays? (1)

Answer 13

-CT.

Question 14

What is the term that describes a change in response as a result of repeated stimulation? (1)

Answer 14

-Habituation.

Question 15

The retina of the human eye contains rod cells, these cells detect light energy as photons. The light energy is converted to a nerve impulse that is interpreted by the brain.

Describe how ions and neurotransmitter molecules are involved in the transmission of an impulse. (4)

Answer 15

-Calcium ions enter presynaptic neurone so vesicles with neurotransmitter can fuse with presynaptic membrane.
-Neurotransmitter molecules diffuse across the syanpse.
-Neurotransmitters bind with receptors on postsynaptic membrane.
-Sodium ions diffuse into post-synaptic cell leading to a depolarisation/an action potential.

Question 16

What area of the brain interprets images? (1)

Answer 16

-Visual cortex.

Question 17

Explain how fMRI can be used to identify the part of the brain involved in interpreting information from the visual cortex. (3)

Answer 17

-fMRI detects blood flow in brain.
-Increased brain activity results in increased blood flow in area of activity.
-Oxyhemoglobin absorbs fewer radio waves/fMRI detects areas where less signal absorbed.

Question 18

The muscles of the earthworm contract when it is touched. This is known as the withdrawal response.
Contraction of the muscle in the withdrawal response is stimulated by nerve impulses. These nerve impulses can be detected using electrodes.

Explain the electrical changes in an axon that allow these nerve impulses to be detected. (4)

Answer 18

-Potential difference across axon changing.
-Due to increased permeability to sodium ions/voltage gated sodium channels open.
-Sodium ions move into axon/cause depolarisation.
-Followed by an increased permeability to potassium ions/potassium channels open.
-Potassium ions move out of axon/cause repolarisation of membrane.

Question 19

Describe the role of the dendrites in a neurone. (3)

Answer 19

-Forms synapses/connections with other neurones.
-Integrate/receive impulses from other neurones.
-Involved in summation.
-Propagate a signal/initiate an action potential to cell body/axon.

Question 20

Compare and contrast the structure of a sensory neurone and a motor neurone. (4)

Answer 20

-Both have a cell body containing a nucleus.
-Both have an axon.
-Both have dendrites at one end of neurone and terminal branches at other end.

-Motor neurone cell body is at one end of axon but sensory neurone cell body is located along axon.

Question 21

Acetylcholinesterase is an enzyme involved in regulating the transmission of nerve impulses across some synapses.
Alzheimer’s disease is associated with the loss of neurones that produce acetylcholine.
It has been suggested that inhibitors of acetylcholinesterase may be useful in the treatment of Alzheimer’s disease.

Explain why inhibitors of acetylcholinesterase could be useful in the treatment of Alzheimer’s disease. (3)

Answer 21

-Acetylcholinesterase breaks down acetylcholine.
-Inhibitor prevents break down of acetylcholine.
-So more acetylcholine is available to bind to postsynaptic membrane.
-Therefore compensating for reduced production of acetylcholine.

Question 22

Describe the role of sodium ions in the functioning of a mammalian rod cell. (3)

Answer 22

-Sodium ions are pumped out of rod cell.
-In light/when stimulated sodium ions don’t move back into rod cell.
-In dark/when not stimulated sodium ions can move back into rod cell.
-In light the rod cell is hyperpolarised/in dark rod cell is depolarised.

Question 23

Phytochromes and IAA (indole acetic acid) are important substances that bring about growth responses in plants.
Cells in the tip of the oat plant release IAA.

Explain how the IAA affects the growth of the plant. (4)

Answer 23

-IAA diffuses from tip of plant.
-Therefore can be taken up by cells in zone of elongation.
-Which causes cells to elongate.
-Leads to lowering of pH in cellulose cell wall.
-Therefore causes plant to grow towards light/increase in height.

Question 24

Describe what a phytochrome is. (1)

Answer 24

-Photosensitive pigment of light.

Question 25

Describe the role of IAA (auxin) in the phototropic response of plants. (4)

Answer 25

-IAA produced in tip of shoot.
-IAA accumulates on dark side of shoot.
-IAA stimulates cell elongation.
-Causing shoot to grow towards light source.

Question 26

Describe how dopamine acts as a neurotransmitter. (4)

Answer 26

-Dopamine released from presynaptic membrane and diffuses across synaptic gap.
-Binds to receptors on post synaptic membrane.
-Alters permeability of post synaptic membrane/opens sodium ion channels in post synaptic membrane.
-Initiating depolarisation/action potential in post synaptic membrane.

Question 27

The use of drugs such as MDMA (ecstasy) can cause an imbalance of chemicals in the brain.
Describe how the use of MDMA could affect the transmission of impulses in the brain. (2)

Answer 27

-MDMA stimulates release of serotonin.
-Blocking pre synaptic receptors.
-Nerve pathways using serotonin more likely to be stimulated.

Question 28

Individuals who use MDMA may develop the symptoms of depression.
Explain how the use of MDMA could result in the development of these symptoms. (2)

Answer 28

-MDMA use results in depletion of serotonin.
-Post synaptic membrane becomes less responsive to serotonin/loss of receptors on post synaptic membrane.
-Serotonin levels affects mood/lack of serotonin associated with depression.

Question 29

Describe how low serotonin levels in an individual can affect the transmission of impulses in their brain. (2)

Answer 29

-Serotonin is a neurotransmitter/there will be less neurotransmitters.
-Less serotonin results in fewer depolarisations of post synaptic membrane.
-Threshold not achieved/less chance of action potential being produced in postsynaptic neurone.

Question 30

Explain how the treatment of Parkinson’s disease overcomes the difficulty of drugs passing from the blood into the brain. (2)

Answer 30

-L Dopa can be used to cross blood brain barrier.
-L Dopa converted into dopamine.