Question 1
1
Exposure to organophosphorus pesticides (OP) is a cause of serious nerve damage. It disrupts synaptic transmission by inhibiting the enzyme acetylcholinesterase, causing death due to cardiovascular and respiratory failure. Recombinant human acetylcholinesterase ( RAChE ) was obtained by genetic engineering and produced in Nicotiana benthamiana plants. It was tested as a new therapeutic treatment in mice that were exposed to OP. The following graph shows the severity of the symptoms shown by each mouse at different ratios of RAChE to OP.
11 marks
Question 1(a)
1(a)
State the minimum ratio at which some mice showed no symptoms.
Easystructured1 marks
Answer
0.38 (allow any value in the range 0.37-0.39)
Question 1(b)
1(b)
Analyse the effect of increasing the ratio of RAChE to OP on the symptoms in mice.
Mediumstructured3 marks
Answer
as the ratio increases, the symptoms decrease; between 0 and 0.16 (accept 0.14-0.18 ) symptoms decrease/are moderate; between 0.16 (accept 0.14-0.18 ) and 0.4 (accept 0.38-0.42 ) symptoms are mild; between 0.38 and 0.41 mice may have mild or no symptoms; after 0.4 (accept 0.38-0.42 ) there are no symptoms;
Question 1(c)
1(c)
Predict what would happen if a mouse received 300 mg of RAChE and 600 mg of OP.
Mediumstructured2 marks
Answer
a. (ratio would have been) 0.5/1 to 2; b. no symptoms;
Question 1(d)
1(d)
To test the effect of OP damage on synapses, mice were treated with RAChE, OP or both. Their diaphragms were dissected 10 days after treatment. The area of the synapse between axons and the diaphragm was measured. When the synapses are damaged by OP there is a greater area. The box plot shows the effect of different treatments on the area of the synapse. Calculate the difference in median area of synapse between the control mice and mice treated with rAChE and OP, giving the units.
Mediumstructured1 marks
Answer
\(90 \mu \mathrm{~m}^{2}\) (accept 75-100 )(units required)
Question 1(e)
1(e)
Describe the evidence for damage to synapses by OP provided by data in the box plot.
Mediumstructured2 marks
Answer
higher/highest median area of synapses; higher/highest maximum/minimum area of synapses; higher/highest \(25{ }^{\text {th }} / 75^{\text {th }}\) percentile;
Question 1(f)
1(f)
Using the data from both graphs, evaluate the hypothesis that plant-produced RAChE could be used to protect humans or other mammals from damage caused by exposure to OP .
Hardstructured2 marks
Answer
the higher the rAChE, the milder the symptoms/damage (first graph); with or without OP, rAChE decreases area of synapses / rAChE reduces the damage to synapses (second graph); (but still) some increase in area/damage to synapses (with OP) even with rAChE; the study was done on mice with no evidence that its results extend to humans;
Question 1
1
Solutions of ions, for example NaCl dissolved in water, can be used to investigate the concentration of solutes in plant tissues. After immersion in solutions of varying concentration, the percentage changes in mass of potato samples were measured. The graph shows the results.
0 marks
Question 1(b)
1(b)
Ions move across the plasma membrane of a neuron during an action potential. The oscilloscope trace shows voltage changes generated in a neuron during three action potentials. Explain the movement of ions which causes the voltage changes observed during the interval labelled X on the graph.
Hardstructured3 marks
Answer
a. at the peak the sodium channels close b. the potassium channels open c. potassium ions flow out d. repolarization occurs e. delay in closing of potassium channels f. hyperpolarization results g. sodium and potassium pump re-starts to restore ions to resting/previous potentials/concentrations Accept \(\mathrm{Na}^{+}\)and \(\mathrm{K}^{+}\)ions. Award [2 max] if answer refers to part of graph before X. 3 max
Question 1
1
Common pesticides used by gardeners contain neonicotinoids. What is the effect of a neonicotinoid pesticide on the transmission of a nerve impulse between neurons in an insect? A. It prevents the release of acetylcholine from the presynaptic membrane. B. It widens the synaptic cleft so diffusion of acetylcholine across the gap is slower. C. It irreversibly binds with acetylcholine receptors on the postsynaptic membrane. D. It interferes with the enzymatic breakdown of acetylcholine by acetylcholinesterase.
Mediummcq1 marks
Answer
C
Question 1
1
Mice (Mus musculus) have various defence systems against predators such as foxes (Vulpus vulpus) or stoats (Mustela erminea). The mice release specific alarm compounds when under threat that serve as danger signals for other mice. Predators also release scents that the mice can detect. In one study, mice were exposed to paper soaked in compounds taken from other mice, foxes or stoats in a test chamber. The scientists then measured the reaction of three different groups of neurons used in smelling: G1, G2 and G3, as shown in the diagram. The percentage of G1, G2 and G3 neurons responding to the mouse, fox and stoat compounds, as well as a control compound, are shown in the chart.
14 marks
Question 1(a)
1(a)
State the percentage of G2 neurons in the mice that respond to the fox scent.
Easystructured1 marks
Answer
10-25 «\%»
Question 1(b)
1(b)
Using evidence from the chart, identify, giving a reason, which group of neurons responded most to the chemicals. The scientists recorded the neural traces (action and resting potentials) of six G1 neurons exposed to the compounds from the different animals. The horizontal bar beneath each trace corresponds to the time of exposure to the test compound.
Mediumstructured1 marks
Answer
G1 always respond more than 25\% «except control», while G2 and G3 always respond 25\% or less G1 always responds more than G2 and G3/all of the others \(\boldsymbol{}\) OWTTE
Question 1(c)
1(c)
State the name of the instrument used to make these traces.
Easystructured1 marks
Answer
oscilloscope
Question 1(d)
1(d)
Distinguish between the effects of the mouse alarm compound and the effects of the control compound on the G1 neurons.
Mediumstructured1 marks
Answer
mouse chemicals cause action potentials «in all six neurons» while control ones cause none «remain in resting potential»/mouse chemicals cause greater responses OWTTE
Question 1(e)
1(e)
Compare and contrast the effects of the mouse alarm compound and stoat scent on the G1 neurons.
Mediumstructured2 marks
Answer
a. both chemicals cause action potentials OR both chemicals respond in the majority of/five/most neurons b. stoat scent causes a higher action potential/longer/bigger response than mouse alarm compound «in each neuron» OR neuron 2 reacts strongly to the stoat scent but has a minimal/no response to the mouse alarm compound
Question 1(f)
1(f)
Deduce whether there is a correlation between the neural traces and the percentage of responding G1 neurons.
Hardstructured2 marks
Answer
a. there is a positive relationship/correlation between the size of neural traces and the percentage of responding G1 neurons OR the chemicals that cause stronger/higher neural traces also cause the greatest percentage of responding G1 neurons b. fox and stoat scents have «approximately» the same/similar neural traces and the same percentage of responding neurons/>75\% c. mouse alarm compounds cause smaller neural traces and smaller percentage of responding neurons/25-75\% d. control chemicals have no response in both cases OR no percentage of «G1 neurons» response and no action potential «in neural traces» Accept vice versa.
Question 1
1
Honeybees (Apis mellifera) are key pollinators in most ecosystems. The worldwide use of neonicotinoid pesticides has caused concern because they may be contributing to the decline of honeybee populations. Scientists measured the concentration of five neonicotinoids (acetamiprid, clothianidin, imidacloprid, thiacloprid and thiamethoxam) in honey samples from 198 different locations across the world. Each pie chart shows the relative frequency of neonicotinoids in honey samples from a continent.
15 marks
Question 1(d)
1(d)
Deduce the conclusions that can be drawn from the data in the graph.
Mediumstructured2 marks
Answer
a. reduced acetylcholine does not affect larval survival in the first two days b. reduced acetylcholine causes increased mortality from day 3 onwards V c. 90\% versus 40\% survival/other valid numerical comparison by day 5 OR (much) greater decrease in survival occurs between days 4 and 5/by day 5 for the reduced group Do not accept answers without times/ days 2 max
Question 1(e)
1(e)
Suggest a reason for the effect of a diet reduced in acetylcholine on the larval survival rate.
Hardstructured1 marks
Answer
(larvae lacking acetylcholine/with reduced AcH cannot survive because) acetylcholine is a neurotransmitter taking message from one neuron to another in synapses of nervous tissues OR messages would not pass from one neuron to the other OR (larvae) unable to synthesise/produce AcH, so need it from their diet OWTTE
Question 1(f)
1(f)
The concentration of acetylcholine was measured in royal jelly produced by honeybees that had never been exposed to neonicotinoids (control) and honeybees that had been exposed for three weeks to two neonicotinoids; clothianidin and thiacloprid. Compare and contrast the effect of clothianidin and thiacloprid treatments on the concentration of acetylcholine in royal jelly.
Hardstructured2 marks
Answer
a. both neonicotinoids reduce the concentration of acetylcholine in royal jelly (compared to control) b. clothianidin reduces the concentration of acetylcholine in royal jelly more than thiacloprid (but perhaps not statistically different) c. clothianidin is used in smaller concentrations (than thiacloprid) so no firm conclusion can be obtained Need one similarity and one difference. 2 max
Question 1(g)
1(g)
Explain how neonicotinoids affect synaptic transmission in insects. (h) Companies that manufacture neonicotinoid pesticides have argued that they do not
Hardstructured3 marks
Answer
a. neonicotinoids bind to the (acetylcholine) receptor (in insects) b. (binding happens) in (cholinergic) synapses/at motor end plate/between motor neuron and muscles c. neonicotinoids bind irreversibly (to receptors) OR (receptors are blocked so) acetylcholine is unable to bind d. acetylcholinesterase/enzymes cannot break down neonicotinoids e. (synaptic) transmission prevented f. (causing) insect paralysis/death 3 max
Question 1
1
There is growing evidence of a decrease in bee populations. This decrease is a serious problem because of their valuable role as pollinators in the ecosystems where they live. Neonicotinoid pesticides have been implicated in this decrease because they have been found at trace levels in the nectar and pollen of crop plants and in the bee colonies. Scientists placed colonies of a species of bumblebee, Bombus terrestris, in the laboratory to test the effects of different levels of a neonicotinoid on their development. They divided the colonies into three groups: - The control colonies were given a solution of water and sugar that resembled nectar produced by flowers. - A second group of colonies was given the same sugar solution containing a neonicotinoid dissolved in it at low concentrations, similar to those found in nature. - A third group of colonies was given the same sugar solution containing a neonicotinoid dissolved in it at high concentrations, similar to those found in nature. After two weeks, all colonies were placed in the field to allow the bumblebees to feed naturally.
12 marks
Question 1(a)
1(a)
5 marks
Question 1(a)(i)
1(a)(i)
Describe the effect of neonicotinoid pesticides on the nervous system of insects.
Mediumstructured1 marks
Answer
a. blocks synaptic transmission at (cholinergic synapses); b. binds to (acetylcholine) receptors; 1 max
Question 2
2
What is happening at the structure labelled X ?
Mediummcq1 marks
Answer
A
Question 2
2
How does potassium move across the membrane of a neuron during repolarization? A. Simple diffusion B. Facilitated diffusion C. Endocytosis D. Active transport
Mediummcq1 marks
Answer
B
Question 2
2
Cholinergic synapses use acetylcholine as their neurotransmitter. They are widespread in the body, passing on signals to muscle cells. These synapses are affected by neonicotinoid pesticides. The diagrams, which are not drawn to scale, show the synapse between two neurons and a detail of the synaptic cleft.
0 marks
Question 2(a)
2(a)
On the diagrams, label:
0 marks
Question 2(a)(iii)
2(a)(iii)
with a letter P a location where a neonicotinoid pesticide could bind.
Mediumstructured1 marks
Answer
any receptor protein on post synaptic membrane marked Must unambiguously be pointed to a receptor on the synapse side. Accept labels of acetylcholinesterase.
Question 2(b)
2(b)
Outline how depolarization of the membrane of an axon occurs.
Mediumstructured2 marks
Answer
a. (local depolarization) causes ion / sodium / voltage gated channels to open / b. altering membrane permeability to sodium ions/ \(\mathrm{Na}^{+} /\)positive ions \(/ \mathrm{Na}^{+}\)diffuses into the cytoplasm c. membrane potential (of the axon) changes from negative to positive d. a threshold potential is reached and an action potential is generated Do not accept sodium pumps. Mp b requires evidence that the student recognizes sodium is an ion. Numerical values indicating change from -70 to +30 /+40 /+55 can be accepted. 2 max
Question 2(c)
2(c)
Explain how acetylcholine initiates an action potential in a postsynaptic membrane.
Mediumstructured2 marks
Answer
a. acetylcholine binds to the receptor protein b. (causing a) change in tertiary structure / conformation of protein c. diffusion/entry of ions/ \(\mathrm{Na}^{+}\)through the receptor/channel protein allowed 2 max
Question 7
7
Which element or ion is required for transmission of a nerve impulse? A. Phosphorous B. Sodium C. Sulfur D. Iron
Mediummcq1 marks
Answer
B