PAPER 2 EXAM QUESTIONS

Question 1

Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in this process [4]

Answer 1

1. Chemoreceptors detect rise in
   CO2/H+/acidity/carbonic acid/fall in pH
   OR
   Baro/pressure receptors detect rise in blood
   pressure
2. Send impulses to cardiac centre/medulla
3. More impulses to SAN
4. By sympathetic (nervous system for chemoreceptors/CO2)
   OR
   By parasympathetic (nervous system for baro/pressure receptors/blood pressure)

Question 2

The solution that the student used to produce a chloroplast suspension had the same water potential as the chloroplasts.
Explain why it was important that these water potentials were the same [2]

Answer 2

1. Osmosis does not occur
2. Chloroplast/organelle does not
   burst/lyse/shrivel/shrink

Question 3

Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds. [2]

Answer 3

1. Less/no ATP produced
2. Less/no reduced NADP produced
3. Less/no GP reduced/converted to TP

Question 4

Suggest one way in which an increase in the uptake of phosphate could increase plant growth. [1]

Answer 4

Used to produce named phosphate compound in cells
e.g. ATP/ADP/phospholipids/DNA/RNA/RuBP/TP/GP etc.

Question 5

Suggest one way in which mycorrhiza fungus may benefit from their association with plants. [1]

Answer 5

Example of a carbon-containing biological
compound e.g. carbohydrate/ amino acid/vitamin

Question 6

Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity. [2]

Answer 6

1. Represents dry mass / mass of carbon
2. Represents gross production minus respiratory
   losses

Question 7

Each year, a few people with type I diabetes are given a pancreas transplant.
Pancreas transplants are not used to treat people with type II diabetes.
Give two reasons why pancreas transplants are not used for the treatment of type II diabetes. [2]

Answer 7

1. (Usually)Type II produce insulin
2. Cells/receptors less sensitive/responsive (to
   insulin)
   OR
   Faulty (insulin) receptors
3. (Treated/controlled by) diet/exercise

Question 8

Suggest how transcription factors can reprogramme cells to form induced pluripotent stem cells. [2]

Answer 8

1. Attach to gene/DNA/promoter region;
2. Stimulate/inhibit transcription/RNA polymerase;

Question 9

What is meant by the term phenotype? [2]

Answer 9

1. characteristic due to genotype/allele(s);
2. characteristic due to environment;

Question 10

Suggest one reason why DNA replication stops in the polymerase chain reaction (PCR). [1]

Answer 10

Limited number of primers/nucleotides

Question 11

Scientists have used the RT-PCR (reverse transcriptase-polymerase chain reaction) 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. [2]

Answer 11

1. Base sequences differ;
2. (Different) complementary primers required;

Question 12

What is a gene pool? [1]

Answer 12

All the alleles in a population

Question 13

Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two
species are different.
Using this information, suggest how these two species of palm tree arose by sympatric speciation. [5]

Answer 13

1. Occurs in the same habitat/environment/population
2. Mutation/s cause different flowering times
3. Reproductive separation/isolation
   OR
   No gene flow
   OR
   Gene pools remain separate
4. Different allele/s passed on/selected
   OR
   Change in frequency of allele/s
5. Disruptive (natural) selection
6. Eventually different species cannot (inter)breed
   to produce fertile offspring

Question 14

In the brain of a person with Alzheimer’s disease there is a lower concentration of acetylcholine. This affects communication between nerve cells and initially results in memory loss and confusion. Some of the symptoms of AD that are associated with communication between nerve cells are reduced by taking the drug donepezil. Donepezil inhibits the enzyme acetylcholinesterase.
Explain how donepezil could improve communication between nerve cells. [3]

Answer 14

1. Less/no acetylcholine broken down;
2. Acetylcholine attaches to receptors;
3. (More) Na+ enter to reach threshold/for
   depolarisation/action potential/impulse;

Question 15

Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction. [2]

Answer 15

1. (Less/no) ATP;
2. (Less/no) reduced NADP;

Question 16

An effect of heat stress is a decrease in the activity of the enzyme rubisco. A decrease in the activity of an enzyme means that the rate of the reaction it catalyses becomes slower. A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis.
Explain why. [2]

Answer 16

1. (Less/no) carbon dioxide (reacts) with RuBP;
2. (Less/no) GP;

Question 17

Where precisely is rubisco found in a cell? [1]

Answer 17

1. Stroma (of/in chloroplast);

Question 18

Describe how alterations to tumour suppressor genes can lead to the development of tumours. [3]

Answer 18

1.Increased methylation of tumour suppressor genes;
2.Mutation in tumour suppressor genes;
3. Tumour suppressor genes are not transcribed/expressed
OR
Amino acid sequence/primary structure altered;
4. Results in rapid/uncontrollable cell division;

Question 19

Describe how you would determine the mean percentage cover for beach grass on a
sand dune. [3]

Answer 19

1. Method of randomly determining position of
   quadrats e.g. random numbers table/generator;
2. Large number/sample of quadrats;
3. Divide total percentage by number of quadrats/samples/readings;

Question 20

Furosemide is a drug used to remove excess fluid from the body. Furosemide is sometimes used to treat high blood pressure.
Suggest how furosemide would cause a decrease in blood pressure. [1]

Answer 20

1. Lower volume of blood;

Question 21

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. [3]

Answer 21

1.Water potential of filtrate/tubule decreased;
2. Less water (reabsorbed) by osmosis (from
filtrate/tubule);
3. Collecting duct (is where osmosis occurs);

Question 22

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest two reasons why. [2]

Answer 22

1. Small sample size;
2. Fusion/fertilisation of gametes is random;
3. Linked Genes;
4. Epistasis;

Question 23

Dopamine is a neurotransmitter released in some synapses in the brain. The transmission of dopamine is similar to that of acetylcholine. Dopamine stimulates the production of nerve impulses in postsynaptic neurones.
Describe how.
Do not include in your answer the events leading to the release of dopamine and the events following production of nerve impulses at postsynaptic neurones. [3]

Answer 23

1. Dopamine diffuses across synapse;
2. Attaches to receptors on postsynaptic membrane;
3. Stimulates entry of sodium ions and depolarisation/action potential;

Question 24

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. [2]

Answer 24

1. Morphine attaches to opioid receptors;
2. More dopamine released to provide pain relief;

Question 25

GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABA causes negatively charged chloride ions to enter postsynaptic neurones. Explain how this inhibits postsynaptic neurones. [3]

Answer 25

1. Inside of postsynaptic neurone becomes more negative/hyperpolarisation/inhibitory postsynaptic potential; 2. More sodium ions required to reach threshold OR Not enough sodium ions enter to reach threshold; 3. For depolarisation/action potential;

Question 26

What is meant by a genome? [1]

Answer 26

1. All the DNA in a cell/organism;

Question 27

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. [1]

Answer 27

1. Binds to P34 gene/DNA/mRNA OR Binds to transcription factor gene/DNA OR Binds to promoter;

Question 28

Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids. [2]

Answer 28

1. Restriction (endonuclease/enzyme) to cut plasmid/vector; 2. Ligase joins gene/DNA to plasmid/vector;

Question 29

Suggest two features of the structure of different proteins that enable them to be separated by gel electrophoresis. [2]

Answer 29

1. Mass/number of amino acids/polypeptides; 2. Charge; 3. R groups (differ);

Question 30

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. 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. [4]

Answer 30

1. LP due to mutation OR Allele due to mutation; 2. Milk provides named nutrient; 3. Individuals with LP more likely to survive and reproduce OR Individuals with advantageous allele more likely to survive and reproduce; 4. Directional selection; 5. Frequency of allele increases (in the offspring/next generation);

Question 31

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. One hypothesis for LP in humans suggests that the selective pressure was related to some human populations farming cattle as a source of milk. Use the information provided to explain why the number of people showing LP would rapidly increase once selection for this condition had been established. [2]

Answer 31

1.Dominant allele; 2.Always expressed/shown when present in phenotype/offspring OR Expressed when only one dominant allele present;

Question 32

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. [2]

Answer 32

1. Mutation in promoter (DNA/gene) for transcription factor OR Mutation in promoter (region/DNA) for the gene OR Mutation in gene for transcription factor; 2. Lactase gene continues to be transcribed/active;

Question 33

Complete achromatopsia is a form of complete colour blindness. It is caused by having only rods and no functional cone cells. People with complete achromatopsia have difficulty in seeing detail. Explain why. [3]

Answer 33

1. No functional cones OR Only rods; 2. Cones are connected to a single neurone OR Several rods connected to a single neurone; 3. (Cones) Separate (sets of) impulses to brain OR (Rods) Single (set of) impulse/s to brain;

Question 34

One form of red-green colour blindness is caused by a sex-linked recessive allele which affects more men than women. Red-green colour blindness affects more men than women. Explain why. [2]

Answer 34

1. Gene/allele is on the X chromosome; 2. Females require two alleles/females can be heterozygous/carriers and males require one allele;

Question 35

People with red-green colour blindness are unable to distinguish between red and green, and also between other colours. They have green-sensitive cones but the photoreceptive pigment they contain does not function. Explain why people with tis colour blindness cannot distinguish between colours. [3]

Answer 35

1. Green sensitive pigment/cones non-functional OR Cones that detect green light non-functional; 2. Three different types of pigment/cone; 3. Other/different colours (‘seen’) due to stimulation of more than one cone/pigment;

Question 36

Current research into the treatment of red-green colour blindness involves the use of induced pluripotent stem cells (iPS cells). Suggest how iPS cells could correct red-green colour blindness.

Answer 36

1. (iPS cells) divide; 2. (iPS cells) develop/differentiate into (green sensitive) cones;

Question 37

Succession occurs in natural ecosystems. Describe and explain how succession occurs. [4]

Answer 37

1. Colonisation by pioneer species; 2. Pioneers/species/organisms change the environment/habitat/conditions/factors; 3. Environment becomes less hostile for other/new species OR Environment becomes more suitable for other/new species OR Environment becomes less suitable for previous species; 4. Change/increase in diversity/biodiversity; 5. To climax community;

Question 38

Sickle cell disease (SCD) is a group of inherited disorders. People with SCD have sickle-shaped red blood cells. A single base substitution mutation can cause one type of SCD. This mutation causes a change in the structure of the beta polypeptide chains in haemoglobin. Explain how a single base substitution causes a change in the structure of this polypeptide. Do not include details of transcription and translation in your answer. [3]

Answer 38

1. Change in sequence of amino acid(s)/primary structure; 2. Change in hydrogen/ionic/disulfide bonds; 3. Alters tertiary/30 structure;

Question 39

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. Use this information to explain how HSCT is an effective long-term treatment for SCD. [3]

Answer 39

1. Produce healthy (red blood) cells OR Produce (normal) polypeptide/haemoglobin; 2. No sickle/faulty/SCD (red blood) cells (produced) OR No defective polypeptide/haemoglobin; 3. Stem/marrow cells (continuously) divide/replicate OR Less chance of rejection (from brother/sister);

Question 40

A student investigated the effects of indoleacetic acid (IAA) on the growth of oat seedlings (young plants). The student: * removed the shoot tip from each seedling and cut out a 10mm length of shoot * placed 10 lengths of shoot into each of 5 Petri dishes * added to each Petri dish an identical volume of 5% glucose solution * added to each Petri dish 40 cm3 of a different concentration of IAA solution * left the Petri dishes at 20°C in the dark with their lids on for 5 days * removed the shoots after 5 days and measured them * determined the mean change in length of shoot at each concentration of IAA. Explain why the student removed the shoot tip from each seedling. [2]

Answer 40

1. Tip produces IAA; 2. Affects concentration of IAA OR Affects (shoot) length/growth/elongation; 3. Mitosis/division occurs in shoot tips; 4. Affects (shoot) length/growth/elongation;

Question 41

A student investigated the effects of indoleacetic acid (IAA) on the growth of oat seedlings (young plants). The student: * removed the shoot tip from each seedling and cut out a 10mm length of shoot * placed 10 lengths of shoot into each of 5 Petri dishes * added to each Petri dish an identical volume of 5% glucose solution * added to each Petri dish 40 cm3 of a different concentration of IAA solution * left the Petri dishes at 20°C in the dark with their lids on for 5 days * removed the shoots after 5 days and measured them * determined the mean change in length of shoot at each concentration of IAA. Explain why the student added glucose solution to each Petri dish. [2]

Answer 41

1. For respiration; 2. Provide ATP/energy (for growth);

Question 42

A student investigated the effects of indoleacetic acid (IAA) on the growth of oat seedlings (young plants). The student: * removed the shoot tip from each seedling and cut out a 10mm length of shoot * placed 10 lengths of shoot into each of 5 Petri dishes * added to each Petri dish an identical volume of 5% glucose solution * added to each Petri dish 40 cm3 of a different concentration of IAA solution * left the Petri dishes at 20°C in the dark with their lids on for 5 days * removed the shoots after 5 days and measured them * determined the mean change in length of shoot at each concentration of IAA. Explain why the lids were kept on the Petri dishes. [2]

Answer 42

1. To prevent/reduce evaporation; 2. (Which) alters concentration of (IAA) solution OR (Which) alters water potential;

Question 43

A group of scientists suggested that a decrease in the force of muscle contraction is caused by an increase in the concentration of inorganic phosphate, Pi, in muscle tissues. Their hypothesis is that an increase in the concentration of Pi prevents the release of calcium ions within muscle tissues. Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction. [3]

Answer 43

1. (Less/No) tropomyosin moved from binding site OR Shape of tropomyosin not changed so binding site not exposed/available; 2. (Fewer/No) actinomyosin bridges formed; 3. Myosin head does not move OR Myosin does not pull actin filaments OR (Less/No) ATP hydrolase activation;

Question 44

In muscles, pyruvate is converted to lactate during prolonged exercise. Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration. [2]

Answer 44

1. Regenerates/produces NAD OR oxidises reduced NAD; 2. (So) glycolysis continues;

Question 45

Describe the role of glucagon in gluconeogenesis. Do not include in your answer details on the second messenger model of glucagon action. [2]

Answer 45

1. Attaches to receptors on target cells and activates/stimulates enzymes; 2. Glycerol/amino acids/fatty acids into glucose;

Question 46

Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration. [2]

Answer 46

1. (More) insulin binds to receptors; 2. (Stimulates) uptake of glucose by channel/transport proteins OR Activates enzymes which convert glucose to glycogen;

Question 47

Metformin is a drug commonly used to treat type II diabetes. Metformin’s ability to lower the blood glucose concentration involves a number of mechanisms including: * increasing a cell’s sensitivity to insulin * inhibiting adenylate cyclase. Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration. [3]

Answer 47

1. Less/no ATP is converted to cyclic AMP/cAMP; 2. Less/no kinase is activated; 3. Less/no glycogen is converted to glucose OR Less/no glycogenolysis;

Question 48

Describe what happens during photoionisation in the light-dependent reaction. [2]

Answer 48

1. Chlorophyll absorbs light OR Light excites/moves electrons in chlorophyll; 2. Electron/s are lost OR Chlorophyll becomes positively charged;

Question 49

Explain why the student marked the origin for the chromatogram using a pencil rather than using ink. [1]

Answer 49

Ink and (leaf) pigments would mix OR (With ink) origin/line in different position OR (With pencil) origin/line in same position OR (With pencil) origin/line still visible;

Question 50

Describe the method used to separate the pigments after the solution of pigments had been applied to the origin. [2]

Answer 50

1. Level of solvent below origin/line; 2. Remove/stop before (solvent) reaches top/end;

Question 51

The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves. [1]

Answer 51

Absorb different/more wavelengths of light for photosynthesis;

Question 52

What is a DNA probe? [2]

Answer 52

1. (Short) single strand of DNA; 2. Bases complementary (with DNA/allele/gene);

Question 53

Describe how the DNA is broken down into smaller fragments before adding a DNA probe. [2]

Answer 53

1. Restriction endonuclease/enzyme; 2. (Cuts DNA at specific) base sequence OR (Breaks) phosphodiester bonds OR (Cuts DNA) at recognition/restriction site;

Question 54

before adding DNA probes, the DNA on the nylon membrane is treated to form single strands. Explain why. [1]

Answer 54

So DNA probe binds/attaches/anneals;

Question 55

Describe how you could estimate the size of a population of sundews in a small marsh. [5]

Answer 55

1. Use a grid OR Divide area into squares/sections; 2. Method of obtaining random coordinates/numbers e.g. calculator/computer/random numbers table/generator; 3. Count number/frequency in a quadrat/section; 4. Large sample and calculate mean/average number (per quadrat/section); 5. Valid method of calculating total number of sundews, e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in marsh;

Question 56

The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes. The soil in bogs and marshes is acidic and has very low concentrations of some nutrients. The sundew can trap and digest insects. Suggest and explain how digesting insects helps the sundew to grow in soil with very low concentrations of some nutrients. [2]

Answer 56

1. Digestion/breakdown of proteins; 2. Provides amino acids OR (Sundew can) produce a named (organic) nitrogen-containing compound e.g. proteins, amino acids, DNA, ATP; 3. Digestion/breakdown of named (organic) phosphate-containing compound e.g. DNA, RNA; 4. Provides named (organic) phosphate-containing product e.g. nucleotides OR (Sundew can) produce a named phosphate-containing compound e.g. ATP, DNA;

Question 57

Damage to the myelin sheath of neurones can cause muscular paralysis. Explain how. [3]

Answer 57

1. (Refers to) saltatory conduction OR (Nerve) impulses/depolarisation/ions pass to other neurones OR Depolarisation occurs along whole length (of axon); 2. (Nerve) impulses slowed/stopped; 3. (Refers to) neuromuscular junction OR (Refers to) sarcolemma;

Question 58

Guillain–Barré syndrome is a rare disease in which the immune system damages the myelin sheath of neurones. Sometimes, neurones of the autonomic nervous system are affected, causing heart rate irregularities. Sometimes Guillain–Barré syndrome causes heart rate irregularities. Suggest and explain why. [3]

Answer 58

1. Slower/fewer impulses along sympathetic/parasympathetic pathway/neurones; 2. Impulses from cardiac centre OR Impulses from medulla; 3.To SAN;

Question 59

To treat Huntington's disease, a drug was injected at the base of the spine into the cerebrospinal fluid bathing the brain and spinal cord. The drug contains single-stranded DNA molecules. These single-stranded molecules inhibit the mRNA needed to produce huntingtin. Suggest and explain how this drug could cause a reduction in the concentration of the protein huntingtin. [3]

Answer 59

1. It/DNA is complementary to (m)RNA; 2. Binds to mRNA for huntingtin; 3. Prevents translation;

Question 60

To treat Huntington's disease, a drug was injected at the base of the spine into the cerebrospinal fluid bathing the brain and spinal cord. Suggest two reasons why people had the drug injected into the cerebrospinal fluid rather than taking a pill containing the drug. [2]

Answer 60

1. Drug will directly/quickly reach brain OR Cerebrospinal fluid bathes the brain; 2. Drug not destroyed by acid OR Drug not digested by enzymes;

Question 61

Symptoms of Huntington’s disease can start at any time, but usually develop between 30 and 50 years of age. The likelihood and age when symptoms start are linked to the number of CAG base sequence repeats in the gene for Huntington’s disease. However, recent studies have suggested that epigenetics may also affect the age when symptoms first start. Suggest and explain one way epigenetics may affect the age when symptoms of Huntington’s disease start. [2]

Answer 61

1. (Increased) methylation of DNA/gene/allele; 2. Inhibits/prevents transcription; OR 3. Decreased methylation of DNA/gene/allele; 4. Stimulates/allows transcription; OR 5. Decreased acetylation of histone(s); 6. Inhibits transcription; OR 7. Increased acetylation of histone(s); 8. Stimulates/allows transcription;

Question 62

Suggest and explain how the interaction between circular muscles and radial muscles in the iris could cause the pupil to constrict (narrow). [2]

Answer 62

1. Circular muscle contracts; 2. Radial muscle relaxes;

Question 63

The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea. Explain how the fovea enables an eagle to see its prey in detail. Do not refer to colour vision in your answer. [3]

Answer 63

1. High visual acuity; 2. Each cone is connected to a single neurone; 2. Cones send separate (sets of) impulses to brain;

Question 64

The retina of an owl has a high density of rod cells. Explain how this enables an owl to hunt its prey at night. Do not refer to rhodopsin in your answer. [3]

Answer 64

1. High (visual) sensitivity; 2. Several rods connected to a single neurone; 3. Enough (neuro)transmitter to reach/overcome threshold OR Spatial summation to reach/overcome threshold;

Question 65

Steroid hormones are hydrophobic. Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane. [2]

Answer 65

1. Lipid soluble; 2. Diffuse through phospholipid bilayer;

Question 66

In the cytoplasm, testosterone binds to a specific androgen receptor (AR). An AR is a protein. Suggest and explain why testosterone binds to a specific AR. [2]

Answer 66

1. Has a (specific) tertiary structure/shape; 2. (Structures are) complementary;

Question 67

The binding of testosterone to an androgen receptor (AR) changes the shape of the AR. This AR molecule now enters the nucleus and stimulates gene expression. Suggest how the AR could stimulate gene expression. [2]

Answer 67

1. (AR is) a transcription factor; 2. Binds to DNA/promoter; 3. (Stimulates) RNA polymerase;

Question 68

Other than a thermometer, explain how two features of a calorimeter could enable a valid measurement of the total heat energy released from a sample. [2]

Answer 68

1. Stirrer distributes heat (energy); 2. Insulation/space/air reduces loss/gain of heat OR Insulation/space/air reduces conduction/convection; 3. Water has high (specific) heat capacity;

Question 69

In natural ecosystems, most of the light falling on producers is not used in photosynthesis. Suggest two reasons why. [2]

Answer 69

1. Light is reflected; 2. Light is wrong wavelength; 3. Light misses chlorophyll/chloroplasts/photosynthetic tissue; 4. CO2 concentration or temperature is a limiting factor.

Question 70

The light absorbed by chlorophyll is used in the light-dependent reaction. Name the two products of the light-dependent reaction that are required for the light-independent reaction. [2]

Answer 70

1. ATP; 2. Reduced NADP;

Question 71

Creatinine is produced in muscle tissues. Creatinine diffuses into the blood. The kidneys then excrete creatinine. A calibration curve can be used to determine the concentration of creatinine in urine. One method of producing a calibration curve needs: * creatinine solution of known concentration * distilled water * creatinine-detecting solution * a colorimeter. Creatinine-detecting solution reacts with creatinine to produce an orange colour. Use the information provided to describe how you could produce a calibration curve for creatinine. Do not include details on the use of glassware in your answer. [4]

Answer 71

1. Use distilled water and creatinine solution to produce dilutions series; 2. Addition of creatinine-detecting solution to each solution; 3. Using a known/specified/constant volume of a solution (e.g. diluted creatinine solution); 4. Record absorbance/transmission of solution/s using a colorimeter; 5. Plot dilution/concentration of creatinine solution against absorbance/transmission;

Question 72

Describe the sequence of events involved in transmission across a cholinergic synapse. Do not include details on the breakdown of acetylcholine in your answer. [5]

Answer 72

1. Depolarisation of presynaptic membrane; 2. Calcium channels open and calcium ions enter synaptic knob; 3 Calcium ions cause synaptic vesicles to move to/fuse with presynaptic membrane and release acetylcholine/neurotransmitter; 4 Acetylcholine/neurotransmitter diffuses across synaptic cleft; 5. Acetylcholine attaches to receptors on the postsynaptic membrane; 6. Sodium ions enter postsynaptic neurone leading to depolarisation;

Question 73

Mutation is one cause of genetic variation in organisms. Give two other causes of genetic variation. [2]

Answer 73

1. Crossing over; 2. Independent segregation/assortment (of homologous chromosomes); 3. Random fusion of gametes OR Random fertilisation;

Question 74

In a species of flowering plant, the T allele for tallness is dominant to the t allele for dwarfness. In the same species, two alleles CR (red) and CW (white) code for the colour of flowers. When homozygous red-flowered plants were crossed with homozygous white-flowered plants, all the offspring had pink flowers. Name the relationship between the two alleles that code for flower colour. [1]

Answer 74

Codominance;

Question 75

A scientist determined the dry mass of spinach plants. First, he heated each sample at 80 °C for 2 hours. Suggest what the scientist should do to ensure that he has removed all the water from the sample. [2]

Answer 75

1. Weigh and heat; 2. Until mass is constant;

Question 76

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. [2]

Answer 76

1. Affects/damages basement membrane OR More protein channels/carriers in basement membrane; 2. Proteins can pass into the (glomerular) filtrate/tubule;

Question 77

A scientist produced transgenic zebrafish. She obtained a gene from silverside fish. The gene codes for a growth hormone (GH). She inserted copies of this GH gene into plasmids. She then microinjected these recombinant plasmids into fertilised egg cells of zebrafish. Describe how enzymes could be used to insert the GH gene into a plasmid. [2]

Answer 77

1. Restriction endonuclease enzymes cut plasmid; OR Restriction endonuclease enzymes produce ‘sticky ends’; 2. Ligase joins gene/DNA and plasmid OR Ligase joins ‘sticky ends’;

Question 78

A scientist produced transgenic zebrafish. She obtained a gene from silverside fish. The gene codes for a growth hormone (GH). She inserted copies of this GH gene into plasmids. She then microinjected these recombinant plasmids into fertilised egg cells of zebrafish. 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 GH gene could produce offspring of transgenic fish without the desired characteristic. [2]

Answer 78

1. Cell division has occurred before gene added; 2. Cells producing gametes do not receive the gene;

Question 79

North American black bears can hibernate for up to 7 months without food or water. The bears survive using the fat stores in their bodies. The bears build up the fat stores during the summer. During hibernation, the heart rate of black bears decreases from a summer mean of 55 beats per minute to 14 beats per minute. Their metabolic rate falls by 75%. Black bears can hibernate for up to 7 months without food or water. Suggest and explain how. [3]

Answer 79

1. Fat (store) used in respiration/metabolism; 2. Less energy/food (store) is required due to low respiration/metabolism OR Less energy/food (store) is required due less movement; 3. Gluconeogenesis; 4.Low surface area to volume reduces heat loss OR Fat (layer/insulation) reduces heat loss; 5. Long loop of Henle so less water lost; 6. Water provided from respiration; 7. Reduced/no urination; 8. Less evaporation;

Question 80

North American black bears can hibernate for up to 7 months without food or water. The bears survive using the fat stores in their bodies. The bears build up the fat stores during the summer. During hibernation, the heart rate of black bears decreases from a summer mean of 55 beats per minute to 14 beats per minute. Their metabolic rate falls by 75%. During hibernation, the heart rate and the metabolic rate of black bears decrease. Use your knowledge of the nervous control of heart rate to describe how these are linked. [4]

Answer 80

1. Lower metabolism so less/low CO2 (in blood); 2. Detected by chemoreceptors; 3. Chemoreceptors located in aorta/medulla OR Chemoreceptors located in carotid artery; 4. Fewer impulses to cardiac centre; OR Fewer impulses to medulla (oblongata); 5. More impulses along parasympathetic/vagus pathway/neurones/nerve OR Fewer impulses along sympathetic pathway/neurones/nerve; 6. To SAN;

Question 81

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. In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation. Suggest and explain how. [2]

Answer 81

1. Allow passage of protons/H+; 2. Energy released as heat;

Question 82

Snowshoe hares within a population moult at different times. Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats. [4]

Answer 82

1. Hares which moult earlier more likely to survive; 2. Hares which moult earlier more likely to reproduce; 3. Pass on advantageous allele; 4. Frequency of allele increases in future populations;

Question 83

Describe the process of glycolysis. [4]

Answer 83

1. Phosphorylation of glucose using ATP; 2. Oxidation of triose phosphate to pyruvate; 3. Net gain of ATP; 4. NAD reduced;

Question 84

Malonate inhibits a reaction in the Krebs cycle. Explain why malonate would decrease the uptake of oxygen in a respiring cell. [2]

Answer 84

1. Less/no reduced NAD/coenzymes OR Fewer/no hydrogens/electrons removed (and passed to electron transfer chain); 2. Oxygen is the final electron acceptor;

Question 85

Explain how a resting potential is maintained across the axon membrane in a neurone. [3]

Answer 85

1. Higher concentration of potassium ions inside and higher concentration of sodium ions outside the neurone OR potassium ions diffuse out OR sodium ions diffuse in; 2. Membrane more permeable to potassium ions leaving than sodium ions entering OR Membrane less permeable to sodium ions entering than potassium ions leaving; 3. Sodium ions actively transported out and potassium ions in;

Question 86

Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon. [3]

Answer 86

1. Myelination provides electrical insulation; 2. In myelinated, saltatory conduction occurs OR In myelinated, depolarisation at nodes of Ranvier; 3. In non-myelinated, depolarisation occurs along whole/length of axon;

Question 87

A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV. Explain why. [3]

Answer 87

1. No/less ATP produced; 2. No/less active transport OR Sodium/potassium pump inhibited; 3. Electrochemical gradient not maintained OR Facilitated diffusion of ions causes change to 0 mV OR (Results in) same concentration of sodium and potassium ions either side of membrane OR No net movement of sodium and potassium ions;

Question 88

In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r. Male fruit flies are more likely than female fruit flies to have white eyes. Explain why. [2]

Answer 88

1. Males have one allele; 2. Females need two recessive alleles OR Females must be homozygous recessive OR Females could have dominant and recessive alleles OR Females could be heterozygous/carriers;

Question 89

Neonatal diabetes is a disease that affects newly born children. The disease is caused by a change in the amino acid sequence of insulin. This change prevents insulin binding to its receptor. Explain why this change prevents insulin binding to its receptor. [2]

Answer 89

1. Changes tertiary structure; 2. No longer complementary (to receptor);

Question 90

Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes. [3]

Answer 90

1. High concentration of glucose in blood/filtrate; 2. Not all the glucose is (re)absorbed at the proximal convoluted tubule; 3. Carrier/co-transport proteins are working at maximum rate OR Carrier/co-transport proteins/ are saturated;

Question 91

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. For some patients, HSCT is an effective treatment for MDS. Explain how. [3]

Answer 91

1. Produce healthy (blood) cells; 2. No MDS/faulty/cancerous (blood) cells; 3. Stem cells divide/replicate;

Question 92

Myelodysplastic syndromes (MDS) are a group of malignant cancers. In MDS, the bone marrow does not produce healthy blood cells. MDS can develop from epigenetic changes to tumour suppressor genes. In some patients, the drug AZA has reduced the effects of MDS. AZA is an inhibitor of DNA methyltransferases. These enzymes add methyl groups to cytosine bases. Suggest and explain how AZA can reduce the effects of MDS in some patients. [3]

Answer 92

1. AZA reduces methylation of DNA/cytosine/gene; 2. Tumour suppressor gene is transcribed/expressed; 3. Prevents rapid/uncontrollable cell division OR Cell division can be controlled/stopped/slowed;

Question 93

One method of transferring RNAi molecules into cells involves combining these molecules with a lipid. Suggest why this increases uptake of RNAi molecules into cells. [1]

Answer 93

(Cell/membrane has a) phospholipid bilayer OR No channel/carrier protein (for uptake) OR No need for channel/carrier protein (for uptake);

Question 94

Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment. [4]

Answer 94

1. (Requires DNA fragment) DNA polymerase, DNA nucleotides and primers; 2. Heat to 95 °C to break hydrogen bonds and separate strands; 3. Reduce temperature so primers bind to DNA/strands; 4. Increase temperature, DNA polymerase joins nucleotides and repeat method;

Question 95

Describe a method that could be used to determine the mean percentage cover of algae on a coral reef. Do not include information on the difficulties of using your method underwater. [3]

Answer 95

1. Method of randomly determining position of quadrats e.g. random numbers table/generator; 2. Large number/sample of quadrats; 3. Divide total percentage by number of quadrats/samples/readings;

Question 96

Explain how succession results in a wide variety of fish living on coral reefs. Do not describe the process of succession in your answer. [2]

Answer 96

1. Increase in variety/diversity of species/plants/animals; OR Increase in number of species/populations; 2. Provides more/different habitats/niches OR Provides greater variety/types of food;

Question 97

Lake Malawi in East Africa has more species of fish than any other lake in the world. Many of these species have evolved from a common ancestor. Lake Malawi is one of the largest lakes in the world and was formed several million years ago. Since then, the water level has fluctuated greatly. As a result, what is now a large lake was at one time many smaller, separate lakes. Suggest and explain how this speciation may have occurred. [4]

Answer 97

1. Variation/differences due to mutation/s; 2. (Reference to) allopatric (speciation); 3. Smaller/different lakes have different environmental conditions OR Smaller/different lakes have different selection pressures; 4. Reproductive separation/isolation OR No gene flow OR Gene pools remain separate; 5. Different alleles passed on/selected OR Change in frequency of allele/s; 6. Eventually different species/populations cannot breed to produce fertile offspring;

Question 98

Deforestation and farming along the shores of Lake Malawi have caused increased soil erosion and loss of nutrients into the lake. This has resulted in a decrease in some fish populations. Loss of nutrients into Lake Malawi has resulted in a decrease in some fish populations. Explain why. [4]

Answer 98

1. (Growth/increase of) algae/surface plants/algal bloom blocks light; 2. Reduced/no photosynthesis so submerged plants die; 3. Saprobiotic microorganisms aerobically respire OR Saprobiotic microorganisms use oxygen in respiration; 4. Less oxygen for fish to respire;

Question 99

The mark-release-recapture method can be used to estimate the size of a fish population. Explain how. [4]

Answer 99

1. Capture/collect sample, mark and release; 2. Ensure marking is not harmful (to fish) OR Ensure marking does not affect survival of fish; 3. Allow time for fish to randomly distribute before collecting a second sample; 4. Population = number in first sample × number in second sample / number of marked fish in second sample;

Question 100

Suggest why the mark-release-recapture method can produce unreliable results in very large lakes. [1]

Answer 100

1. Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;

Question 101

Describe the light-independent reaction of photosynthesis. [6]

Answer 101

1. Carbon dioxide reacts with ribulose bisphosphate; 2. Produces two glycerate 3-phosphate using Rubisco enzyme; 3. GP reduced to triose phosphate; 4. Using reduced NADP; 5. Using energy from ATP; 6. Triose phosphate converted to glucose/hexose/RuBP/ribulose bisphosphate/named organic substance;

Question 102

Give the equation used to calculate the net production of consumers, N, where I represents the chemical energy store in ingested food F represents the chemical energy lost to the environment in faeces and urine R represents the respiratory losses to the environment. [1]

Answer 102

N = I - (F + R)

Question 103

Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain why. [2]

Answer 103

1. Energy lost between/at trophic/feeding levels; 2. Energy lost via respiration/excretion/faeces;

Question 104

Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 molecules of ATP for each molecule of nitrogen that is reduced. When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit. Explain how. [2]

Answer 104

1. Less/no ATP/energy required/used OR More ATP/energy available; 2. ATP/energy can be used for growth/synthesis/replication OR Lower (rate of) respiration required OR ATP for phosphorylation;

Question 105

Name the process that occurs in anaerobic respiration but does not occur in aerobic respiration. [1]

Answer 105

Reduction of pyruvate

Question 106

Name the statistical test you should use to determine if the observed frequencies of four phenotypes differed significantly from the frequencies expected according to the Hardy–Weinberg equation. State how many degrees of freedom should apply. [2]

Answer 106

1. Chi-squared; 2. 3;

Question 107

A scientist concluded that the observed frequencies of four phenotypes differed significantly from the expected frequencies. Use your knowledge of the Hardy–Weinberg principle to suggest two reasons why. [2]

Answer 107

1. Selection (against/for a blood group/phenotype/allele); 2. (High rate of) mutation; 3. Immigration/emigration; 4. No random mating.

Question 108

Give two reasons why transmission across a cholinergic synapse is unidirectional. [2]

Answer 108

1. Only the presynaptic neurone/knob/membrane releases/has neurotransmitter/acetylcholine; 2.Only the postsynaptic neurone/membrane has receptors OR No receptors in presynaptic neurone/membrane;

Question 109

Myasthenia gravis (MG) is an autoimmune disease caused when antibodies bind to the sarcolemma (postsynaptic membrane) of neuromuscular junctions. This can weaken contraction of muscles. Suggest and explain how MG can weaken contraction of muscles. Do not include details of myofibril or muscle contraction in your answer. [2]

Answer 109

1. Less/no acetylcholine/neurotransmitter binds to receptor/s; 2. Less/no depolarisation OR Fewer/no action potential(s) OR Fewer/no sodium ions enter to reach threshold;

Question 110

Myasthenia gravis (MG) is an autoimmune disease caused when antibodies bind to the sarcolemma (postsynaptic membrane) of neuromuscular junctions. This can weaken contraction of muscles. Mestinon is a drug that inhibits the enzyme acetylcholinesterase. Mestinon can help in the treatment of MG. Explain how Mestinon can help in the treatment of MG. [3]

Answer 110

1. Less/no acetylcholine/neurotransmitter broken down; 2. More acetylcholine attaches to receptors; 3. Depolarisation (of sarcolemma) occurs OR Action potential(s) produced OR (Enough) sodium ions enter to reach threshold OR Fewer/no antibodies attach;

Question 111

Scientists conducted an investigation using very high doses of (streptozotocin) STZ. This led to destruction of pancreatic cells. The scientists concluded that these rats would not be suitable for studying type II diabetes. Give two reasons why the scientists made this conclusion. [2]

Answer 111

1. (Type II) still produce/release insulin; 2. (Type II) cells/receptors less/not responsive/sensitive to insulin; 3. Pancreatic cells not destroyed (in type II diabetes); 4. Damage to pancreatic cells may affect processes/reactions (in the body);

Question 112

Name the part of the body which releases antidiuretic hormone (ADH) into the blood. [1]

Answer 112

Posterior pituitary;

Question 113

Alcohol decreases the release of ADH into the blood. Suggest two signs or symptoms which may result from a decrease in ADH. [2]

Answer 113

1. Dehydration/thirst; 2. Frequent urination OR Increase in volume of urine; 3.Less concentrated urine OR Dilute urine OR Urine paler/lighter in colour;

Question 114

Describe the effect of ADH on the collecting ducts in kidneys. [3]

Answer 114

1. (Stimulates) addition of channel proteins into membrane; 2. Increases permeability to water OR More water (re)absorbed; 3. By osmosis;

Question 115

BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins. Mutations in BRCA1 and BRCA2 can cause cancer. Explain how. [3]

Answer 115

1. Change in DNA base sequence/triplet; 2. Change in (sequence of) amino acids OR Change in primary/tertiary structure; 3. Results in rapid/uncontrollable cell division;

Question 116

Genetic testing, using DNA from saliva, can screen for all known harmful mutations in both BRCA1 and BRCA2 genes. Describe how this DNA could be screened for all known harmful mutations in both genes. [4]

Answer 116

1. Use of PCR to amplify (DNA/sample); 2. Cut DNA using restriction endonuclease enzymes; 3. Separate DNA fragments using electrophoresis; 4. Addition of labelled DNA probes and binding (by DNA hybridisation); 5. Mutations identified by fluorescence/radioactivity OR Compare positions/bands (to known) DNA sample with (all harmful) mutations;

Question 117

ER-positive breast cancers have receptors for the hormone oestrogen. These cancers develop as a result of increased oestrogen concentrations in the blood.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. [3]

Answer 117

1. Drug binds to oestrogen receptor; 2. Prevents binding of oestrogen/hormone; 3. No/fewer transcription factor(s) bind to promoter OR RNA polymerase not stimulated/activated;

Question 118

Men with prostate cancer have a high concentration of prostate-specific antigen (PSA) in their blood. Urinary infections and a naturally enlarged prostate can also increase concentrations of PSA. Blood tests can be used to test for cancers. However, the results of blood tests may not be conclusive when testing for prostate cancer. Explain why. [2]

Answer 118

1. High/increased concentration of PSA not always linked to prostate cancer OR High/increased concentration of PSA could be a false positive; 2.Could be due to urinary infection OR Could be due to enlarged prostate;

Question 119

Recent research has indicated that several cancers result from epigenetic abnormalities. Treatment with drugs might be able to reverse the epigenetic changes that cause cancers. Suggest and explain how. [3]

Answer 119

1. Drugs could increase methylation of oncogenes; 2. Drugs could decrease methylation of tumour suppressor genes; 3. Increased methylation of DNA/genes inhibits transcription/expression of genes OR Decreased methylation of DNA/genes stimulates transcription/expression of genes; 4. Decreased acetylation of histones inhibits transcription/expression of genes OR Increased acetylation of histones stimulates transcription/expression of genes;

Question 120

A student used chromatography to separate the different photosynthetic pigments in a chlorophyll solution. She had the following materials: Chromatography paper A ruler and pencil Suitable glassware A solvent (solvent A) 2 cm3 of the chlorophyll solution Describe how she could use these materials to separate the photosynthetic pigments by chromatography. [4]

Answer 120

1. Draw line/origin on chromatography paper using ruler and pencil; 2. Use pipette/tubing/dropper to add chlorophyll/solution to origin/line; 3. Add solvent/A below line/origin; 4. Remove before solvent reaches end of chromatography paper OR Mark (position) where solvent reaches/front;

Question 121

Using solvent A, the student separated five pigments. She then repeated her method using a different solvent, B. Using solvent B, she separated six pigments. Explain the difference between these results. [2]

Answer 121

For 2 marks = two pigments have same solubility in solvent A but different solubility in solvent B OR For 2 marks = one pigment is soluble in solvent B but not in solvent A OR For 2 marks = pigments have different solubilities in solvents A and B OR For 2 marks = one pigment is only soluble in solvent B OR For 2 marks = one pigment is insoluble only in solvent A;

Question 122

Glutamate is a neurotransmitter involved in the transmission of nerve impulses from pain receptors to the brain. Ziconotide is a drug that can reduce severe, constant pain. Ziconotide blocks the calcium ion channels at some of the synapses which use glutamate. The transmission of glutamate at synapses is similar to that of acetylcholine. Explain how ziconotide reduces severe, constant pain. [5]

Answer 122

1. No/fewer calcium ions enter synaptic knob OR No/less calcium enter synaptic knob via calcium ion channels; 2. No/fewer synaptic vesicles move to/fuse with presynaptic membrane and no/less glutamate is released; 3. No/less glutamate diffuses across synaptic cleft; 4. No/less glutamate attaches to receptors on the postsynaptic membrane; 5. No/fewer sodium ions enter postsynaptic neurone so no/fewer impulses sent to brain;

Question 123

Ziconotide is a polypeptide and acts on synapses in the spinal cord. Scientists investigated the effectiveness of ziconotide in reducing severe, constant pain. Ziconotide was injected into each patient’s cerebrospinal fluid that bathes the brain and spinal cord. Patients recorded the intensity of their pain using a statistically valid scale. Suggest two reasons why the patients had ziconotide injected into their cerebrospinal fluid rather than taking a pill containing the drug. [2]

Answer 123

1. Rapidly/quickly/directly reaches spinal cord; 2. Is broken down by enzymes OR Is broken down by acid OR Is too large to be absorbed;

Question 124

When the patients record the intensity of pain, suggest two reasons why it is important to use a statistically valid scale. [2]

Answer 124

1. (Sensation of) pain is subjective OR Pain sensitivity/threshold/tolerance varies; 2. To ensure that differences in pain detection were statistically significant OR For valid comparison;

Question 125

Water shortage can inhibit crop production. Scientists investigated the effect of the mycorrhizal species Glomus intraradices on the growth of tomato plants under conditions of water shortage and no water shortage. The tomato seeds were planted into sterilised soil. Suggest two reasons why the soil was sterilised. [2]

Answer 125

1. Kill/remove other mycorrhizae/fungi; 2. Kill/remove nitrogen-fixing/nitrifying/denitrifying/saprobiotic bacteria; 3. Kill/remove pathogens; 4. Kill/remove pests; 5. Kill/remove competitors; 6. Kill/remove seeds/spores; 7. Is a controlled variable;

Question 126

Water shortage can inhibit crop production. Scientists investigated the effect of the mycorrhizal species Glomus intraradices on the growth of tomato plants under conditions of water shortage and no water shortage. The soil used in this investigation had the recommended concentration of fertiliser. Suggest two reasons why the soil contained the recommended concentration of fertiliser. [2]

Answer 126

1. So mycorrhizae/water is the only variable OR So fertiliser is not a variable OR So fertiliser is a controlled variable; 2. Affects crop production/growth/mass; 3. Concentration of fertiliser would affect water potential of soil; 4. Does not affect pH of soil; 5. To provide usual soil/farming conditions;

Question 127

In cats, males are XY and females are XX. A gene on the X chromosome controls fur colour in cats. The allele G codes for ginger fur and the allele B codes for black fur. These alleles are codominant. Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoiseshell female. The two alleles, F and f of a different gene, which is not sex-linked, interact with the gene controlling fur colour. The allele F is dominant and stops the formation of pigment in the fur, resulting in white fur. The allele f is recessive and has no effect on fur colour. Name the type of interaction between the two genes affecting fur colour. [1]

Answer 127

Epistasis

Question 128

Variation in flower colour is considered one of the factors involved in the evolution of the following two species of monkeyflower. * Erythranthe lewisii (Great Purple Monkeyflower), which has pink flowers, is mostly found at higher altitudes (1600 to 3000 metres) and attracts bumblebees. * Erythranthe cardinalis (Scarlet Monkeyflower), which has red flowers, is mostly found at lower altitudes (up to 2000 metres) and attracts hummingbirds. Bumblebees and hummingbirds are important in the pollination of flowers. Pollination involves the transfer of male gametes to female gametes. Explain the different processes that may have been involved in the evolution of these two species of monkeyflower. Use the information provided to justify your answer. [5]

Answer 128

1. Geographical isolation due to elevation/altitude; 2. Allopatric speciation due to isolation/ separation; 3. Different selection pressures OR Different environments; 4. However some overlap in distribution OR Both plants found in same area/habitat/altitude; 5. So possibly sympatric speciation; 6. Variation due to mutations; 7. Reproductive isolation due to different pollinators/distributions/altitudes OR Separate gene pools due to different pollinators/ distributions/altitudes; 8. Change in allele frequency in each population OR Different allele frequency in each population; 9. Different species can no longer interbreed to produce fertile offspring;

Question 129

Describe and explain how three features of the cells in the proximal convoluted tubule allow the rapid reabsorption of glucose into the blood. [3]

Answer 129

1. Microvilli provide a large surface area OR Folded cell-surface membrane provides a large surface area; 2. Many channel/carrier proteins for facilitated diffusion; 3. Many carrier proteins for active transport; 4. Many channel/carrier proteins for co-transport; 5. Many mitochondria produce ATP OR Many mitochondria for active transport; 6. Many ribosomes to produce carrier/channel proteins;

Question 130

Antidiuretic hormone (ADH) binds to V receptors found in cell-surface membranes in two parts of a nephron. Name the two parts of a nephron where V receptors are found. [1]

Answer 130

Collecting duct and distal convoluted tubule;

Question 131

V receptors only bind with ADH. Suggest and explain why. [2]

Answer 131

1. Has a (specific) tertiary structure/shape; 2. (Structures are) complementary;

Question 132

A decrease in blood pressure stimulates the release of ADH. Give the location of the receptors that detect a decrease in blood pressure and explain how the release of ADH will affect blood pressure. [3]

Answer 132

1. Aorta OR Carotid artery/sinus; 2. (ADH) increases (re)absorption of water; 3. Increases volume of blood and pressure increases OR Increases volume of blood and pressure returns to normal;

Question 133

Suggest two reasons for conserving rainforests. [2]

Answer 133

1. Conserve species/plants/animals/organisms OR For (bio)diversity; 2. Conserve/protect habitats/niches OR Provides/many habitats/niches; 3. Reduces climate change; 4. Source of medicines/drugs/wood; 5. Reduces erosion/eutrophication; 6. (For) tourism;

Question 134

Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem. [3]

Answer 134

1. Heat (loss) from respiration; 2. (Food) not digested OR Not all eaten; 3. Excretion;

Question 135

The KRAS gene codes for a protein called K-Ras. The protein relays signals from outside a cell to a cell’s nucleus, stimulating cell division. An alteration in the KRAS gene produces an oncogene which can cause a tumour to develop. Suggest and explain how an alteration in the KRAS gene can cause a tumour to develop. [3]

Answer 135

1. Mutation (in KRAS gene) OR Change in base sequence (of KRAS gene); 2. Change in (signalling) protein OR More (signalling) protein/K-Ras produced; 3. (Results in) rapid/uncontrollable cell division;

Question 136

Short tandem repeats (STRs) are short sequences of DNA, usually 2 to 7 base pairs. Describe how STRs could be removed from a sample of DNA. [2]

Answer 136

1. Restriction endonucleases/enzymes; 2. (Cut DNA) at specific base sequences/pairs OR (Cut DNA) at recognition/restriction sites;

Question 137

Genetic fingerprinting using short tandem repeats requires amplification of the STRs using the polymerase chain reaction (PCR). The short base sequences either side of a specific STR are known. Explain the importance of knowing these base sequences in PCR. [2]

Answer 137

1. (For) primers; 2. (To produce) a complementary base sequence OR (Primers provide starting sequence) for DNA/taq polymerase OR (Primers) stop (original) DNA strands re-joining;

Question 138

During genetic fingerprinting, different short tandem repeats are separated by gel electrophoresis. Give two features of STRs which enable them to be separated by gel electrophoresis. [2]

Answer 138

1. Number of nucleotides/repeats/bases OR Length/mass; 2. (Negative) charge;

Question 139

Describe the roles of ATP in muscle contraction. [2]

Answer 139

1. To break actinomyosin (bridges); 2. To move/bend the myosin head/arm; 3. (So) actin (filaments) are moved (inwards); 4. For active transport of calcium ions (into the sarcoplasmic/endoplasm

Question 140

Some studies have suggested that taking creatine supplements can improve muscle performance during intense short-term exercise. Eating more carbohydrate, known as ‘carbohydrate loading’, for a few days before exercise can improve muscle performance when exercising for a long time. Describe and explain how taking creatine supplements and ‘carbohydrate loading’ can improve performance of different types of muscle fibres during different types of exercise. [5]

Answer 140

1. Fast skeletal muscle fibres used during short-term/intense exercise; 2. Slow skeletal muscle fibres used during long-term exercise; 3. Creatine used to form phosphocreatine; 4. Phosphocreatine combines with ADP to form ATP; 5. Carbohydrate/glucose stored as glycogen OR Glycogenesis; 6. Glycogen hydrolysed to glucose OR Glycogenolysis; 7. Glucose for respiration;

Question 141

During aerobic exercise, calcium ions in muscle cells have several roles. They activate the inclusion of glucose transport proteins, GLUT4, in the cell-surface membrane and the inclusion of fatty acid transport proteins, CD36, in mitochondrial membranes. Suggest and explain how GLUT4 and CD36 transport proteins are beneficial during exercise [3]

Answer 141

1. More glucose enters muscle cells; 2. Glucose/fatty acids enter by facilitated diffusion; 3. Fatty acids used in Krebs cycle; 4. Respiration provides more ATP;

Question 142

An increase in muscle activity causes an increase in heart rate. Describe and explain how. [4]

Answer 142

1. Increase in CO2 detected by chemoreceptors; 2. Send more impulses to cardiac centre OR Send more impulses to the medulla; 3. More impulses (from centre/medulla) along sympathetic pathway/neurones/nerves OR Fewer impulses (from centre/medulla) along parasympathetic pathway/neurones/nerves; 4. To SAN;