Incorrect Answers For Paper 2 Flashcards

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1
Q

When explaining the benefit if an enzyme involved in respiration, what should you always mention?

A

That the processes the enzyme aids provides ATP.

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2
Q

Dengue is a serious disease that is caused by a virus. The virus is carried from
one person to another by a mosquito, Aedes aegypti. One method used to try to
reduce transmission of this disease is the Sterile Insect Technique (SIT). This
involves releasing large numbers of sterile (infertile) male A. aegypti into the
habitat. These males have been made infertile by using radiation.
0 2 . 1 Explain how using the SIT could reduce transmission of dengue.

A

-Males are infertile, so there is more infraspecific competition between the males.
-Do not reproduce.

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3
Q

The release of radiation-sterilised A. aegypti has not been very successful in
controlling the transmission of dengue.
Suggest one reason why.

A

Radiation affects their courtship.

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4
Q

If there are more mitochondria, what will there also be an increase in?

A

Increase in aerobic respiration.

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5
Q

The scientists then compared the length of time that the control mice and the
trained mice could carry out prolonged exercise. The trained mice were able to
exercise for a longer time period than control mice.
Explain why.

A

-More aerobic respiration produces more ATP
-Anaerobic respiration delayed.
-Less lactate.

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6
Q

The solution that the student used to produce the chloroplast suspension had the
same water potential as the chloroplasts.
Explain why it was important that these water potentials were the same.

A

-So that osmosis did not occur.
-So that the chloroplasts did not lyse.

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7
Q

In an investigation using DCPIP to investigate the light dependent reaction, why would a test tube with no chloroplasts and only DCPIP solution be set up?

A

-To show that chloroplasts are required for the light dependent reaction.
-To show that light does not affect DCPIP.

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8
Q

Explain why a test tube containing chloroplasts and DCPIP solution would turn colourless after 30 minutes in light.

A

-Reduction of DCPIP by electrons.
-From chlorophyll/light dependent reaction.

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9
Q

The student evaluated the effectiveness of different chemicals as weed-killers by
assessing their ability to prevent the decolourisation of DCPIP in chloroplast
suspensions.
He added different concentrations of each chemical to illuminated chloroplast
suspensions containing DCPIP. He then determined the IC50 for each chemical.
The IC50 is the concentration of chemical which inhibits the decolourisation of
DCPIP by 50%.
Explain the advantage of the student using the IC50 in this investigation.

A

It provides a standard reference point.

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10
Q

When linking a slow LDR to the LIR, what must you always say?

A

Less ATP produced
Less NADPH produced
Less GP is reduced to TP

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11
Q

Explain why an increase in shoot biomass can be taken as a measurement of
net primary productivity.

A

-It represents the mass of carbon produced by the plant.
-Represents the gross production minus respiratory losses.

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12
Q

What is meant by phenotype?

A

-Expression due to the genotype.
-Expression due to the environment as well.

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13
Q

One way to detect and measure accurately the amount of RNA in a tissue sample
is by RT-PCR (reverse transcriptase-polymerase chain reaction).
RT-PCR uses a reaction mixture containing:
• the sample for testing
• reverse transcriptase
• DNA nucleotides
• primers
• DNA polymerase
• fluorescent dye.
Any DNA in the sample is hydrolysed by enzymes before the sample is added to
the reaction mixture.
Explain why.

A

-To remove any DNA present.
-As this DNA would be amplified and replicated.

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14
Q

Scientists have used the RT-PCR method to detect the presence of different RNA
viruses in patients suffering from respiratory diseases.
The scientists produced a variety of primers for this procedure.
Explain why.

A

Base sequences differ.
So different complementary primers are required.

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15
Q

In an isolated population, why might there be a high frequency of a certain mutation?

A

-Isolated so there is inbreeding/low genetic diversity.
-Allele is inherited through generations from a common ancestor.

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16
Q

This autosomal dominant mutation involves a change in triplet 280 from GAA to
GCA. Scientists analysed chromosome 14 from 102 individuals from Yaramul.
They recorded a sample size of 204 and detected 75 E280A mutations but only
74 potential AD cases. The scientists identified individuals with the mutation by
whole genome sequencing. They had decided that a DNA probe would not be a
suitable method to detect the E280A mutation.
Suggest why a DNA probe for the mutated triplet was not considered a suitable
method for detection of the E280A mutation

A

GCA triplet is common and found in other places.
Would be unable to determine if it was the mutation or a false positive.

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17
Q

What is always needed after saying the myosin heads binds to the actin-myosin head?

A

AND performs the power stroke.

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18
Q

The scientists first produced transgenic poplar trees. These trees all had a length
of foreign DNA inserted into them. This DNA led to the production of single-
stranded RNA that specifically inhibited expression of the gene for PIP1.
The scientists then measured the difference in the amount of PIP1 in leaves of
transgenic poplars and in leaves of wild type poplars without the foreign DNA. The
amount of PIP1 in the transgenic poplars was approximately 15% of that in the wild
type poplars.
Using this information, what can you conclude about the effect of the foreign DNA in
the transgenic poplar trees?

A

-Single stranded RNA has base sequence complementary to PIP1 mRNA.
-Binds to mRNA of PIP1 and leads to its destruction.
-Prevents translation of PIP1.
-Reduces photosynthesis.

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19
Q

Suggest one reason why it was important that the student left the apparatus for one
hour after the yeast culture reached a constant temperature.

A

So that the oxygen is absorbed/respired.
(Cannot say acclimatise).

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20
Q

What is the final step when determining the mean percentage cover of a species in a particular area?

A

Divide the total percentage by the number of quadrats.

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21
Q

What do pioneer species do when they inhabit an area of land?

A

They change the abiotic conditions to make them less hostile.

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22
Q

In an experiment investigating the kidney function, explain why it is important to give all of the volunteers the same food for several days before starting the experiment?

A

-It will affect the water potential of the blood.
-It will affect the volume of urine.

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23
Q

Furosemide inhibits the absorption of sodium and chloride ions from the filtrate
produced in the nephrons.
Explain how furosemide causes an increase in the volume of urine produced.

A

-Na+ and Cl- ions remain in the filtrate.
-Filtrate has a more negative water potential.
-Less water is reabsorbed via osmosis from the tubule.
-Collecting duct is where osmosis occurs.

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24
Q

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often
not the same as the expected ratios.
Suggest reasons why.

A

-Fertilisation is random
-Epistasis
-Linked genes

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25
Q

In a genetic cross with two genes, what causes there to be most of the dominant-dominant (1860) and recessive-recessive (580) phenotypes, and very low numbers of dominant-recessive (68 + 57) phenotype?

A

-The genes are linked.
-Produces fewer dominant-recessive offspring.
-This is because crossing over has occurred.

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26
Q

What is the expected phenotype ratio when a dihybrid is performed and the genes for height of plant and for the type of leaf were on
different homologous pairs of chromosomes?

A

9:3:3:1

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27
Q

What must you always say when talking about neurotransmitter movement?

A

The neurotransmitter diffuses across the synapse.

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28
Q

Dopamine has a role in numerous processes in the brain including pain relief. The
release of dopamine can be stimulated by chemicals called endorphins produced in
the brain. Endorphins attach to opioid receptors on presynaptic neurones that release
dopamine.
Morphine is a drug that has a similar structure to endorphins and can provide pain
relief.
Explain how.

A

Morphine has a similar tertiary structure to endorphins, so can bind to the same complementary opioid receptor on the pre synaptic membrane, which causes dopamine to be released.

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29
Q

Soybeans are used in a number of processed foods. However, soybeans contain a
protein known as P34 that causes an allergic response in some people. Scientists
have created transgenic soybeans that produce single-stranded cDNA, which
prevents transcription of the P34 gene. They used recombinant plasmids as vectors
to transform soybean cells. After they had screened these cells for production of the
P34 protein, they cultured the transformed cells to form soybean plants.
Suggest how single-stranded cDNA could prevent transcription of the P34 gene.

A

cDNA binds to the promoter region of the P34 gene.

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30
Q

What is the prevention of transcription always related to?

A

A transcription factor or protein binding to the promoter region of the DNA.

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31
Q

What is the prevention of translation of a gene always linked to?

A

The binding is siRNA or miRNA to the mRNA of that gene followed.

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32
Q

The soybean cells were screened for the presence of the P34 protein. This process
involved the use of gel electrophoresis to separate proteins extracted from soybean
cells.
Suggest two features of the structure of different proteins that enable them to be
separated by gel electrophoresis.

A

-They have a varying lengths of polypeptide chain.
-Charge.
-R groups differ.

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33
Q

Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase. Lactase is
essential to newborn mammals as milk is their only source of food. Most mammals
stop producing lactase when they start feeding on other food sources. Humans are
an exception to this because some continue to produce lactase as adults. The ability
to continue producing lactase is known as lactase persistence (LP) and is controlled
by a dominant allele. A number of hypotheses based on different selection pressures
have been put forward to explain LP in humans.

0 9 . 1 One hypothesis for LP in humans suggests that the selective pressure was related to
some human populations farming cattle as a source of milk.
Describe how farming cattle as a source of milk could have led to an increase in LP.

A

-LP is due to a mutation.
-Milk provides glucose.
-Individuals with allele are more likely to survive AND reproduce.
-Frequency of allele increases in the next generation.

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34
Q

Lactase persistence is caused by a mutation in DNA. This mutation does not occur in
the gene coding for lactase.
Suggest and explain how this mutation causes LP.

A

-Mutation in the gene for the transcription factor.
-Lactase gene continues to be transcribed.

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35
Q

When discussing how cones improve visual acuity, what must you always say?

A

That cones send separate sets of impulses to the brain, whereas rods send a single set of impulses the brain.

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36
Q

People with red-green colour blindness are unable to distinguish between red and
green, and also between other colours.
Explain why.

A

-Green sensitive pigment is non-functional.
-There are three different types of cone cell.
-Other colours are seen
Due to the stimulation of more than one cone.

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37
Q

When discussing pluripotent stem cells, what must always be stated about their growth?

A

-iPS cells divide.
-AND differentiate.

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38
Q

Benefits of using iPS cells over gene therapy?

A

-Use of iPS cells is long-term.
-Less chance of an immune response using iPS cells.
-Use of iPS cells is a single treatment.
-Harm/side effects from using viruses in gene therapy.

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39
Q

Why does the blinding of more insulin to muscle cells increase the rate of respiration?

A

-Insulin leads to more transport proteins for glucose.
-More glucose can be absorbed via facilitated diffusion for use in respiration.

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40
Q

What is the spearman’s rank used to test for?

A

To determine if there is a significant correlation between two variables.

41
Q

When discussing the effectiveness of fertilisers from graphical data, what main points should you always cover?

A

-State what mix of fertiliser caused the fastest growth (can be one fertiliser used by itself).
-State what mix of fertilisers caused the slowest growth.
-State what the different results suggests about the performance of fertilisers in those conditions.

42
Q

Describe and explain how succession occurs.

A

-Colonisation by the pioneer species.
-Pioneers change the environmental conditions.
-Environment becomes less hostile for new/other species.
-This change increases biodiversity as more species can inhabit the land.
-Climax community is reached eventually.

43
Q

Haematopoietic stem cell transplantation (HSCT) is a long-term treatment for SCD.
In HSCT, the patient receives stem cells from the bone marrow of a person who does
not have SCD. The donor is often the patient’s brother or sister. Before the treatment
starts, the patient’s faulty bone marrow cells have to be destroyed.
0 2 . 2 Use this information to explain how HSCT is an effective long-term treatment for SCD

A

-Produce healthy red blood cells.
-No SCD red blood cells are produced.
-Stem cells continuously divide and differentiate.
-Less chance of rejection.

44
Q

In an experiment investigating the effect is indoleacetic acid on growth of oat seedlings, why are the shoot tips removed from each seedling?

A

-IAA is produced in the shoot tip of the seedlings.
-It affects the shoot elongation.

45
Q

A student investigated the effects of indoleacetic acid (IAA) on the growth of
oat seedlings (young plants).
Explain why the lids were kept on the Petri dishes.

A

-To prevent evaporation.
-Which would alter the concentration of IAA.

46
Q

The student produced the different concentrations of IAA using a stock
1 g dm–3 solution of IAA (1 g dm–3 = 1 part per thousand) and distilled water.
What volumes of stock IAA and distilled water are required to produce 40cm3 of 10ppm IAA solution?

A

10 x 0.040 = 1 x V2
0.4 = V2
0.4 cm3 of stock IAA are required
40 - 0.4 = 39.6cm3
39.6cm3 of distilled water are required.

47
Q

Explain how a decrease in the concentration of calcium ions within muscle tissues
could cause a decrease in the force of muscle contraction.

A

-Less tropomyosin is moved form the binding site.
-Fewer actinomyosin cross bridges are formed.
-Myosin head does not pull actin filaments.
-Less ATP hydrolase activation.

48
Q

Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose
concentration.

A

-More insulin binds to receptors.
-This stimulates the uptake of glucose by transport proteins.
-Activates enzymes which convert glucose into glycogen.

49
Q

Explain how inhibiting adenylate cyclase may help to lower the blood glucose
concentration.

A

-Less ATP is converted to cAMP.
-Less kinase is activated.
-Less glycogen is converted into glucose.

50
Q

Describe what happens during photoionisation in the light-dependent reaction.

A

-Chlorophyll absorbs light.
-Electrons are lost.

51
Q

What is a DNA probe?

A

-Short single strand of DNA.
-Bases complementary with DNA/allele/gene.

52
Q

Guillain–Barré syndrome is a rare disease in which the immune system damages the myelin sheath of neurones.
Sometimes Guillain–Barré syndrome causes heart rate irregularities (lines 4–5).
Suggest and explain why.

A

-Slower/fewer impulses along the sympathetic/parasympathetic pathway.
-From the medulla.
-To the SAN.

53
Q

What does a thicker medulla in the kidney mean?

A

-A longer loop of Henle
-This increases sodium ion concentration.
-Therefore the water potential gradient is maintained for longer, so more water is reabsorbed from the loop and collecting duct.

54
Q

Mitochondrial DNA (mtDNA) is a small circular DNA molecule located in mitochondria.
It is 16 569 nucleotides long and contains 37 genes and a control region.
Sports scientists investigated whether a mutation in the control region of mtDNA in
human males was related to an ability to exercise for longer.
• The males in Group T had thymine at nucleotide position 16 519.
• The males in Group C had a mutation resulting in cytosine at
nucleotide position 16 519.
The mitochondrial DNA (mtDNA) control region is an area of mtDNA that is
non-coding. This region stimulates the synthesis of both mtDNA and mitochondrial
messenger RNA.
Use this information to suggest two reasons why the mutation at
nucleotide position 16 519 could lead to the differences seen in Figure 5. Group T had a larger percentage increase in VO2 max and CS activity than group C.

A

-Less mitochondrial replication and production.
-Less transcription of genes for mitochondrial proteins.

55
Q

When evaluating a conclusion, what must you always link the observation from the experiment to?
Use an increase in VO2 max and CS activity as an example.

A

The effect that the observation has.
E.g an increase in VO2 max and CS activity means more Krebs cycle activity and more oxygen is available.

56
Q

When a question is asking about a molecule that has a similar shape to a substrate for an enzyme, what should you always mention about that molecule?

A

That that molecule acts as a competitive inhibitor.

57
Q

Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane?

A

-Steroid hormones are lipids soluble as they are hydrophobic.
-This means that they can diffuse through the phospholipid bilayer.

58
Q

In natural ecosystems, most of the light falling on producers is not used in
photosynthesis.
Suggest reasons why.

A

-Some light is reflected off of the producers, so is not absorbed by the chlorophyll.
-Some lights misses the chlorophyll.
-CO2 concentration or temperature is the limiting factor.

59
Q

Alport syndrome (AS) is an inherited disorder that affects kidney glomeruli of both
men and women. Affected individuals have proteinuria (high quantities of protein in
their urine).
Suggest how AS could cause proteinuria.

A

-More protein channels in the basement membrane.
-Proteins can pass into the filtrate.

60
Q

The scientists carried out further work to investigate how the transplanted stem cells
developed after transplantation.
• The scientists transplanted stem cells from wild type male mice into
AS female mice.
• After 20 weeks, they found that the quantity of protein in the urine of these
female mice had significantly decreased.
• They examined cells from glomeruli in the female mice. Some of these cells
contained a Y chromosome.
Suggest how the transplanted stem cells reduce proteinuria

A

The stem cells divide and differentiate, which reduces the loss of proteins at the glomerulus.

61
Q

Microinjection of DNA into fertilised egg cells is a frequent method of producing
transgenic fish. However, the insertion of the transferred gene into nuclear DNA may
be delayed. Consequently, the offspring of transgenic fish may not possess the
desired characteristic.
Suggest and explain how delayed insertion of the Growth Hormone gene could produce offspring of
transgenic fish without the desired characteristic.

A

-Cell division has already occurred before the gene is added.
- So cells producing gametes to not receive the gene.

62
Q

An experiment uses a control group and has a large sample size. Explain how two features of the design of this investigation helped to ensure the
validity of any conclusions obtained.
Do not include calculating the mean or SD in your answer.

A

-A large sample size is used to ensure the results are accurate so they are representative.
-Use of a control group to allow a comparison.

63
Q

Black bears can hibernate for up to 7 months without food or water.
Suggest and explain how.

A

-They have built up fat stores in their body, which they can use in respiration.
-Less energy store is required due to low respiration.
-Gluconeogenesis.
-Low surface area to volume ratio reduces heat loss.
-Long loop of Henle so less water is lost.
-Water is provided from respiration.
-Reduced urination.
-Less evaporation.

64
Q

In many mammals, ‘uncoupling proteins’ help to maintain a constant body
temperature during hibernation. Uncoupling proteins are found in the inner
mitochondrial membrane and act as proton channels during chemiosmosis.
However, these proton channels do not generate ATP.
Suggest and explain how.

A

-Allow the passage of H+.
-Energy is released as heat.

65
Q

Guppies are small fish. Female guppies are dull in colour. Male guppies can be
bright or dull in colour.
Scientists investigated the effect of female brain size on choosing a mate. They used
laboratory-bred female guppies with large brains and with small brains.
They observed each female for 10 minutes and recorded which male they were
attracted towards. They repeated this with 45 large-brained females and
45 small-brained females.

Suggest three possible limitations of this investigation.

A

-The female fish are all laboratory bred, so their behaviours may be different in the wild.
-The females are separated by a transparent barrier, which may not allow for normal courtship behaviour.
-Do not know if the guppies have been used in previous experiments.
-10 minutes may not be long enough for females to make a choice.

66
Q

In northern India, there is a conflict of interests between farmers of livestock (eg cows)
and people trying to conserve ibex (a type of wild goat).
When livestock are given extra food, their populations can grow too large and
compete with ibex.
Livestock will outcompete ibex if they:
• are in the same habitat
• eat a similar diet.
Scientists investigated this conflict of interests.
Table 1 summarises some of the scientists’ findings.
Table 1
Type of
livestock
Difference between
livestock food and
ibex food*
Difference between
livestock habitat
and ibex habitat*
Cow 1.0 1.5
Horse 0.5 0.0
Yak 0.0 2.0
* A score of 0.0 indicates that the food or habitat is the same.
There must be a balance between the need for conservation of the ibex and the need
for farmers to keep livestock.
Using all the information, suggest and explain three actions that the farmers could
take to achieve this balance.

A

-Only grow crops so no competition.
-Keep the horses in enclosed areas, as they occupy the same habitat as the ibex.
-Do not farm horses as they have the same habitat and very similar food to the ibex.
-Farm cows as they have the least similar food and habitat to that of the ibex.
-Farm yaks, as despite eating the same food, they live in a very different habitat.
-Do not provide the livestock with extra food, as their populations will not grow large enough to cause competition.

67
Q

In Europe, viruses have infected a large number of frogs of different species.
The viruses are closely related and all belong to the Ranavirus group.
Previously, the viruses infected only one species of frog.
Suggest and explain how the viruses became able to infect other species of frog.

A

-Mutation in the viral DNA/RNA/genome/genetic material.
-Altered tertiary structure of viral attachment protein.
-Allows the attachment protein to bind to receptors of other species.

68
Q

Determining the genome of the viruses could allow scientists to develop a vaccine.
Explain how.

A

-Can identify the proteome of the virus.
-Determine possible base sequences that code for attachment proteins.

69
Q

Doctors investigated the link between high sodium concentrations in medicines and
hypertension (high blood pressure).
They analysed medical records of patients. 1 292 337 of these patients had taken
medicines containing high sodium concentrations. Each of these patients was paired
with a patient from a control group.
Give two factors that should have been the same for each pair of patients and
one factor that should have been different.

A

Factors: BMI, age, ethnicity, sex, previous medications, diet, exercise, health issues.
Different factor: Amount of Na+ in medicine.

70
Q

Increased methylation of the promoter region of a tumour suppressor gene causes
one type of human throat cancer.
In this type of throat cancer, cancer cells are able to pass on the increased
methylation to daughter cells. The methylation is caused by an enzyme called DNMT.
Scientists have found that a chemical in green tea, called EGCG, is a competitive
inhibitor of DNMT. EGCG enables daughter cells to produce messenger RNA
(mRNA) from the tumour suppressor gene.
Suggest how EGCG allows the production of mRNA in daughter cells.

A

-EGCG binds to the active site of DNMT
-DNMT cannot methylate the promoter region of the tumour suppressor gene.
-Transcription factor can bind to promoter region.
-RNA polymerase stimulated.

71
Q

GW1516 is a performance-enhancing drug. GW1516 activates AMPK and develops
slow muscle fibres at rest.
Use Figure 4 to justify why professional athletes are not allowed to take GW1516.
Do not include details of chemiosmotic theory in your answer.

A

-More Acetyl CoA enters the Krebs cycle.
-So the Krebs cycle generates more reduced enzymes.
-So more ATP is produced.
-Athletes could build more slow muscle fibres without exercising.
-More slow twitch fibres would increase endurance.

72
Q

The normal haematocrit for human males is 47(±5)%. For professional male cyclists,
the maximum haematocrit allowed is 50%.
A student suggested that professional male cyclists should be allowed to use EPO
until their haematocrit is 50%.
Give two reasons why this suggestion is not valid.

A

-Some males will gain a bigger advantage.
-Use of EPO can cause a heart attack.

73
Q

Explain how a resting potential is maintained across the axon membrane in a neurone.

A

-Higher concentration of K+ ions inside AND higher concentration of Na+ outside the neurone.
-Membrane is more permeable to K+ ions leaving than Na+ entering.
-3 Na+ ions actively transported out of the axon and 2 K+ ions into the axon.

74
Q

Explain why the speed of transmission of impulses is faster along the myelinated axon than along a non-myelinated axon.

A

-In myelinated axon, saltatory conduction occurs.
-Depolarisation occurs at the nodes of ranvier.
-Myelin sheath insulates the axon.
-In non-myelinated axon, depolarisation occurs along the whole length of the axon

75
Q

When talking about IAA in a phototropism, what must you always talk about?

A

-You must always talk about the movement of IAA, stating that it moves to the shaded side when light is exposed to the tip.
-When drawing a conclusion, you can say that IAA is not broken down by light or that is still produced in the dark.

76
Q

When explaining the results of a genetic cross where there is an autosomal linkage, what must you state?

A

-That there is an autosomal linkage between the two characteristics.
-State whether crossing over has occurred or not.
-State what gametes are produced/not produced by the parents.

77
Q

Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes.

A

-High concentration of glucose int he filtrate.
-Not all the glucose is reabsorbed at the proximal convoluted tubule
-Carrier proteins are fully saturated.

78
Q

Myelodysplastic syndromes (MDS) are a group of malignant cancers. In MDS, the
bone marrow does not produce healthy blood cells.
Haematopoietic stem cell transplantation (HSCT) is one treatment for MDS. In HSCT,
the patient receives stem cells from the bone marrow of a person who does not have
MDS. Before the treatment starts, the patient’s faulty bone marrow is destroyed.
0 6 . 1 For some patients, HSCT is an effective treatment for MDS.
Explain how.

A

-Produce healthy blood cells.
-No MDS/Faulty/cancerous blood cells.
-Stem cells divide/replicate.

79
Q

Describe and explain how the polymerase chain reaction (PCR) is used to amplify a
DNA fragment.

A

-Require DNA fragment, DNA polymerase, DNA nucleotides and primers.
-Heat strands to 95 to break the hydrogen bonds (and separate strands).
-Reduce temperature so that primers can anneal to DNA strands.
-Increase temperature, DNA polymerase joins nucleotides (and repeat method).

80
Q

Explain the shape of a PCR curve.

A

-Initially the number of molecules doubling is low.
-Plateaus as no more nucleotides.

81
Q

Explain how succession results in a wide variety of fish living on coral reefs.

A

-Increase in diversity of species.
-Provides more/different habitats/niches.

82
Q

Loss of nutrients into Lake Malawi has resulted in a decrease in some fish
populations. Explain why.

A

-Growth/ increase of algae/surface plants/algal bloom blocks the light.
-Reduced/no photosynthesis so submerged plants die.
-Saprobiotic microorganisms respire aerobically.
-Less oxygen for fish to respire.

83
Q

Lake Malawi in East Africa has more species of fish than any other lake in the world (line 1).
Suggest and explain how this speciation may have occurred.

A

-Variatioin/differences due to mutations.
-Allopatric speciation.
-Smaller/different lakes have different environmental conditions and selection pressures.
-Reproductive separation, no gene flow, gene pools remain separate.
-Different alleles passed on, change in frequency of alleles.
-Eventually different species/populations cannot breed to produce fertile offspring.

84
Q

When describing the light-independent reaction, what must you always say about GP being converted to TP?

A

GP is reduced to TP using energy from ATP and NADPH synthesised in the light dependent reaction.

85
Q

Farming cattle for humans to eat is less efficient than farming crops because of
energy transfer.
Explain why.

A

-Energy is lost between trophies levels.
-Energy is lost in faeces, excretion, respiration.

86
Q

Nitrogen-fixing bacteria such as Azotobacter chroococcum use the enzyme
nitrogenase to produce ammonia from nitrogen gas in the air. A. chroococcum can
use ammonium chloride as a direct source of ammonia. When a source of ammonia
is not available this bacterium uses nitrogen fixation.
A scientist investigated the effect of an increase in the concentration of ammonium
chloride on the activity of nitrogenase in this bacterium. He prepared several liquid
medium cultures of the bacterium. Each liquid culture had the same volume.
He grew each culture in a different concentration of ammonium chloride.
In each culture:
• he recorded the nitrogenase activity in arbitrary units
• he removed the bacteria and then recorded the concentration of ammonium
chloride remaining in each liquid medium.

Apart from temperature and pH, give seven variables the scientist would have controlled
when preparing the liquid medium cultures.

A

-Volume of stock bacteria culture;
-Concentration of stock bacteria culture;
-Concentration of glucose;
-Volume of ammonium chloride;
-Time bacteria are left to divide;
-Concentration/volume of oxygen;
-Concentration/volume of nitrogen.

87
Q

In evaluation of conclusion questions, what can you always look for to argue against?

A

-If growth is due to another substance present in the experiment;
-How many species of organism the experiment was carries out in;

88
Q

In respirometer questions, when explaining why the bubble moved towards the seeds, what is always the first point in the explanation?

A

-The oxygen is used up by the seeds.

89
Q

Apart from time, give two measurements the student would have to make to determine the rate of aerobic respiration of these seeds in cm3 hour–1 in the respirometer.

A

-The distance moved by the bubble;
-Diameter of the lumen of the tube that the bubble is moving along.

90
Q

The student used the same apparatus to determine the volume of carbon dioxide the seeds produced during 48 hours.
Give the change the student would need to make to the contents of the apparatus and describe how he could calculate the volume of carbon dioxide produced.

A

-Remove the potassium hydroxide solution;
-Record the distance moved by the bubble;
-Use difference in distance liquid moves with KOH and without KOH.

91
Q

When explaining that a trait is dominant, what should you say?

A

-Individuals x and y, who had the trait produced a child who did not have the trait.
-Individuals x and y have the recessive allele

92
Q

When is the Hardy Weinberg principal not valid?

A

-Selection against the phenotype/allele;
-High rate of mutations;
-Immigration/emigration;
-No random mating.

93
Q

How do you know a graph is showing temporal summation?

A

Several repeated impulses in a short time provide enough neurotransmitter to reach threshold.

94
Q

Name the part of the body which releases ADH

A

Posterior pituitary.

95
Q

BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins. Mutations in BRCA1 and BRCA2 can cause cancer. Explain how.

A

-Change in DNA base sequence;
-Change in sequence of amino acids;
-Change in tertiary structure;
-Results in rapid uncontrollable cell division.

96
Q

Genetic testing, using DNA from saliva, can screen for all known harmful mutations in both genes. Describe how this DNA could be screened for all known harmful mutations in both genes.

A

-Use of PCR to amplify DNA sample;
-Cut DNA using restriction endonuclease;
-Separate DNA fragments using electrophoresis;
-Addition of labelled DNA probes and binding by DNA hybridisation;
-Mutations identified by fluorescence/radioactivity.

97
Q

Effective treatment of ER-positive breast cancers often involves the use of drugs which have a similar structure to oestrogen.

Suggest and explain how these drugs are an effective treatment of ER-positive breast cancers.

A

-Drug binds to oestrogen receptors;
-Prevents binding of oestrogen;
-Mo transcription factors bind to promoter and RNA polymerase not stimulated.

98
Q

Treatment with drugs might be able to reverse the epigenetic changes that cause cancers.

Suggest and explain how.

A

-Drugs can increase methylation of oncogenes;
-Drugs can decrease methylation of tumour suppressor genes;
-Increase methylation of DNA inhibits transcription of genes;
-Decreased acetylation of histones inhibits transcription of genes.