Incorrect Answers For Paper 2

Question 1

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

Answer 1

That the processes the enzyme aids provides ATP.

Question 2

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.

Answer 2

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

Question 3

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

Answer 3

Radiation affects their courtship.

Question 4

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

Answer 4

Increase in aerobic respiration.

Question 5

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.

Answer 5

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

Question 6

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.

Answer 6

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

Question 7

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?

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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.

Answer 9

It provides a standard reference point.

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

What is meant by phenotype?

Answer 12

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

Question 13

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.

Answer 13

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

Question 14

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.

Answer 14

Base sequences differ.
So different complementary primers are required.

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

AND performs the power stroke.

Question 18

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?

Answer 18

-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.

Question 19

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

Answer 19

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

Question 20

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

Answer 20

Divide the total percentage by the number of quadrats.

Question 21

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

Answer 21

They change the abiotic conditions to make them less hostile.

Question 22

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?

Answer 22

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

Question 23

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.

Answer 23

-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.

Question 24

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

Answer 24

-Fertilisation is random
-Epistasis
-Linked genes

Question 25

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?

Answer 25

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

Question 26

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?

Answer 26

9:3:3:1

Question 27

What must you always say when talking about neurotransmitter movement?

Answer 27

The neurotransmitter **diffuses** across the synapse.

Question 28

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.

Answer 28

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.

Question 29

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.

Answer 29

cDNA binds to the promoter region of the P34 gene.

Question 30

What is the prevention of transcription always related to?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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.

Answer 32

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

Question 33

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.

Answer 33

-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.

Question 34

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.

Answer 34

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

Question 35

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

Answer 35

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

Question 36

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

Answer 36

-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.

Question 37

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

Answer 37

-iPS cells divide. -**AND** differentiate.

Question 38

Benefits of using iPS cells over gene therapy?

Answer 38

-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.

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

-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.

Question 42

Describe and explain how succession occurs.

Answer 42

-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.

Question 43

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

Answer 43

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

Question 44

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

Answer 44

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

Question 45

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.

Answer 45

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

Question 46

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?

Answer 46

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.

Question 47

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

Answer 47

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

Question 48

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

Answer 48

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

Question 49

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

Answer 49

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

Question 50

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

Answer 50

-**Chlorophyll absorbs** light. -Electrons are lost.

Question 51

What is a DNA probe?

Answer 51

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

Question 52

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.

Answer 52

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

Question 53

What does a thicker medulla in the kidney mean?

Answer 53

-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.

Question 54

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.

Answer 54

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

Question 55

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.

Answer 55

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.

Question 56

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?

Answer 56

That that molecule acts as a **competitive inhibitor**.

Question 57

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

Answer 57

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

Question 58

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

Answer 58

-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.

Question 59

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.

Answer 59

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

Question 60

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

Answer 60

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

Question 61

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.

Answer 61

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

Question 62

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.

Answer 62

-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.

Question 63

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

Answer 63

-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.

Question 64

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.

Answer 64

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

Question 65

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.

Answer 65

-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.

Question 66

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.

Answer 66

-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.

Question 67

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.

Answer 67

-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.

Question 68

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

Answer 68

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

Question 69

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.

Answer 69

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

Question 70

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.

Answer 70

-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.

Question 71

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.

Answer 71

-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.

Question 72

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.

Answer 72

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

Question 73

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

Answer 73

-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.

Question 74

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

Answer 74

-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

Question 75

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

Answer 75

-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.

Question 76

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

Answer 76

-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.

Question 77

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

Answer 77

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

Question 78

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.

Answer 78

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

Question 79

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

Answer 79

-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).

Question 80

Explain the shape of a PCR curve.

Answer 80

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

Question 81

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

Answer 81

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

Question 82

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

Answer 82

-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**.

Question 83

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.

Answer 83

-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.

Question 84

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

Answer 84

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

Question 85

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

Answer 85

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

Question 86

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.

Answer 86

-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.

Question 87

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

Answer 87

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

Question 88

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

Answer 88

-The **oxygen** is used up by the seeds.

Question 89

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.

Answer 89

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

Question 90

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.

Answer 90

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

Question 91

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

Answer 91

-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**

Question 92

When is the Hardy Weinberg principal not valid?

Answer 92

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

Question 93

How do you know a graph is showing temporal summation?

Answer 93

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

Question 94

Name the part of the body which releases ADH

Answer 94

Posterior pituitary.

Question 95

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

Answer 95

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

Question 96

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.

Answer 96

-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.

Question 97

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.

Answer 97

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

Question 98

Treatment with drugs might be able to reverse the epigenetic changes that cause cancers. Suggest and explain how.

Answer 98

-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.