a level. bio q 2

Question 1

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

Answer 1

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

Question 2

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 2

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

Question 3

Arbuscular mycorrhiza fungi (AMF) are fungi which grow on, and into, the roots of
plants. AMF can increase the uptake of inorganic ions such as phosphate.

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

Answer 3

Used to produce named phosphate compound in
cells

Question 4

Suggest one way in which AMF may benefit from their association with plants

Answer 4

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

Question 5

Explain the role of DNA polymerase in RT-PCR.

Answer 5

Joins nucleotides to produce (complementary
strand/s of) DNA;

Question 6

Any DNA in the sample is hydrolysed by enzymes before the sample is added to
the reaction mixture.
Explain why.

Answer 6

1. To remove any DNA present;
2. As this DNA would be amplified/replicated;

Question 7

Suggest one reason why DNA replication stops in the polymerase chain reaction.

Answer 7

Limited number of primers/nucleotides;

Question 8

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 8

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

Question 9

What is a gene pool?

Answer 9

All the alleles in a population;

Question 10

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.

Answer 10

1. Occurs in the same
   habitat/environment/population;
2. Mutation/s cause different flowering times;
3. Reproductive separation/isolation
4. Different allele/s passed on/selected
5. Disruptive (natural) selection;
6. Eventually different species cannot (inter)breed
   to produce fertile offspring;

Question 11

What is meant by the term phenotype?

Answer 11

1. (Expression / appearance / characteristic due
   to) genetic constitution/genotype/allele(s);
2. (Expression / appearance / characteristic due
   to) environment;

Question 12

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

Answer 12

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

Question 13

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 13

1. Compete (with fertile males) to mate/for
   food/resources
2. Do not reproduce/breed

Question 14

Describe how the mark-release-recapture method could be used to determine the
population of A. aegypti at the start of the investigation

Answer 14

1. Capture/collect/sample, mark and release;
2. Leave time for mosquitoes/Aedes to disperse
   before second sampling/collection;
3. (Population =) number in first sample × number
   in second sample divided by number of marked
   in second sample/number recaptured;

Question 15

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

Answer 15

(Radiation) affects their ‘attractiveness’/courtship
/survival/ life span;

Question 16

PT1 is a channel protein that transports fatty acids into mitochondria.
Using Figure 1, explain the benefit of activation of AMPK during exercise

Answer 16

1. Less/no malonyl-CoA;
2. (More) fatty acids transported/moved into
   mitochondria;
3. Respiration/oxidation of fatty acids provides
   ATP;

Question 17

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

Answer 17

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

Question 18

Another 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.

Answer 18

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

Question 19

Where precisely is rubisco found in a cell?

Answer 19

Stroma

Question 20

There are different types of gene mutation.
Put a tick () in the box next to the statement which describes incorrectly the effect
of the mutation in an exon of a gene.
[1 mark]
A substitution may not result in a change to the
encoded amino acid.
An inversion will result in a change in the number of
DNA bases.
A deletion will result in a frame shift.
An addition will result in a frame shift.

Answer 20

Box 2.
An inversion will result in a change in the number
of DNA bases

Question 21

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

Answer 21

1.(Increased) methylation (of tumour suppressor
genes);
2.Mutation (in tumour suppressor genes);
3. Tumour suppressor genes are not
transcribed/expressed

Question 22

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 22

1. (So the) oxygen is used/absorbed/respired;

Question 23

Explain why a log scale is used to record the number of cells.

Answer 23

Large range/difference/increase in numbers;

Question 24

Many yeast cells die during the death phase.
Suggest one reason why.

Answer 24

. Decrease/no glucose/substrate

Question 25

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

Answer 25

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 26

The scientists concluded that the results shown in Figure 5 were due to succession
taking place.
Use Figure 5 to explain why the scientists reached this conclusion.

Answer 26

1. Beach grass is the pioneer (species);
2. Pioneers/named species change the (abiotic)
   environment/habitat/conditions/factors;
3. (So) less hostile for named species
4. Conifer/hardwood trees represent climax
   community;

Question 27

Furosemide and CVT are drugs used to remove excess fluid from the body.
Scientists investigated the effect of these drugs on the volume of urine produced by
human volunteers. The scientists used the following method.
* They divided volunteers into three groups, A, B and C at random.
* They gave all the volunteers the same food for 3 days.
* After 3 days, they gave the volunteers in group A a tablet containing furosemide,
the volunteers in group B a tablet containing CVT and the volunteers in group C a
placebo (a tablet that did not contain either drug).
* They then found the mean volume of urine produced by each group in the 4 hours
after taking the tablets.
Some of the results the scientists obtained are shown in Table 1.
A value of ± 2 standard deviations from the mean includes over 95% of the data.

Answer 27

All the volunteers were given the same food for 3 days.
Suggest and explain one reason why they were given the same food.

Question 28

Furosemide is sometimes used to treat high blood pressure.
Suggest how furosemide would cause a decrease in blood pressure.

Answer 28

1. Lower volume of blood;

Question 29

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 29

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

Question 30

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

Answer 30

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

Question 31

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.

Answer 31

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

Question 32

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 32

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

Question 33

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

Answer 33

1. (Inside of postsynaptic) neurone becomes more
   negative/hyperpolarisation/inhibitory
   postsynaptic potential;
2. More sodium ions required (to reach threshold)
3. For depolarisation/action potential;

Question 34

Explain why the antibody binds to the transcription factor.

Answer 34

1. (Transcriptional factor/antibody) has a
   specific/tertiary structure/shape;
2. Complementary (shape/structure

Question 35

Describe the roles of two named types of enzymes used to insert DNA fragments into
plasmids

Answer 35

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

Question 36

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 36

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

Question 37

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.

Answer 37

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

Question 38

Use the information provided to explain why the number of people showing LP would
rapidly increase once selection for this condition had been established.

Answer 38

1. Dominant allele;
2. (Always) expressed/shown (when present in
   phenotype/offspring)

Question 39

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 39

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

Question 40

Succession occurs in natural ecosystems. Describe and explain how succession
occurs.

Answer 40

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

Question 41

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.

Answer 41

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

Question 42

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

Answer 42

1. Produce healthy (red blood) cells
2. No sickle/faulty/SCD (red blood) cells (produced)
3. Stem/marrow cells (continuously) divide/replicate

Question 43

Explain why the student removed the shoot tip from each seedling

Answer 43

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

Question 44

Explain why the student added glucose solution to each Petri dish

Answer 44

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

Question 45

Explain why the lids were kept on the Petri dishes

Answer 45

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

Question 46

escribe and explain the results shown in Table 1 and suggest how the results might
have differed if lengths of root had been used.

Answer 46

1. Increase in IAA concentration the higher/greater
   the mean (change in) length;
2. (High) IAA stimulates cell elongation;
3. In roots, growth/elongation less/inhibited

Question 47

Another 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.

Answer 47

1. (Less/No) tropomyosin moved from binding site
2. (Fewer/No) actinomyosin bridges formed;
3. Myosin head does not move

Question 48

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.

Answer 48

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

Question 49

n photosynthesis, which chemicals are needed for the light-dependent reaction?

Answer 49

NADP, ADP, Pi and water;

Question 50

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

Answer 50

. Chlorophyll absorbs light
. Electron/s are lost

Question 51

Explain why the student marked the origin using a pencil rather than using ink.

Answer 51

ink and (leaf) pigments would mix

Question 52

Describe the method the student used to separate the pigments after the
solution of pigments had been applied to the origin

Answer 52

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

Question 53

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

Answer 53

(Absorb) different/more wavelengths (of light) for
photosynthesis;

Question 54

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.
0 9 . 1 Describe how you could estimate the size of a population of sundews in a small
marsh.

Answer 54

1. Use a grid
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 55

Suggest and explain how digesting insects helps the sundew to grow in soil with very
low concentrations of some nutrients

Answer 55

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

Question 56

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

Answer 56

1. (Refers to) saltatory conduction
2. (Nerve) impulses slowed/stopped;
3. (Refers to) neuromuscular junctio

Question 57

Suggest and explain one way epigenetics may affect the age when symptoms of
Huntington’s disease start.

Answer 57

1. (Increased) methylation of
   DNA/gene/allele;
2. Inhibits/prevents transcription;

Question 58

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

Answer 58

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

Question 59

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.

Answer 59

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

Question 60

The binding of testosterone to an 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.

Answer 60

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

Question 61

Other than the thermometer, explain how two features of the calorimeter shown in
Figure 2 would enable a valid measurement of the total heat energy released.

Answer 61

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

Question 62

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

Answer 62

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 63

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.

Answer 63

1. ATP;
2. Reduced NADP;

Question 64

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

Answer 64

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

Question 65

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

Answer 65

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

Question 66

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.

Answer 66

1. Restriction endonucleases/enzymes cuts
   plasmid;
2. Ligase joins gene/DNA and plasmid

Question 67

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.

Answer 67

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

Question 68

Describe the process of glycolysis.

Answer 68

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

Question 69

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

Answer 69

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

Question 70

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

Answer 70

1. Myelination provides (electrical) insulation;
2. (In myelinated) saltatory (conduction
3. In non-myelinated depolarisation occurs along
   whole/length (of axon);

Question 71

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

Answer 71

1. No/less ATP produced;
2. No/less active transport
3. Electrochemical gradient not maintained

Question 72

Use your knowledge of indoleacetic acid (IAA) to explain the growth curvature shown
in Figure 1

Answer 72

1. Tip produces IAA;
2. IAA diffuses (into shoot);
3. (More) elongation of cells on one side (than
   other);

Question 73

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

Answer 73

1. Males have one allele;
2. Females need two recessive alleles

Question 74

A female fruit fly with white eyes was crossed with a male fruit fly with red eyes to
produce a large number of offspring.
Tick ( ) one box next to the statement which correctly describes the phenotypes
produced from this cross.

All offspring red-eyed
All females red-eyed, all males white-eyed
All males red-eyed, all females white-eyed
All males white-eyed, females red-eyed and
females white-eyed

Answer 74

1. Box 2.
   All females red-eyed, all males white-eyed.

Question 75

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.

Answer 75

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

Question 76

A coral reef is an underwater ecosystem formed as a ridge of mainly calcium
carbonate deposits. Algae are photosynthesising organisms. Some algae grow on coral reefs. Succession results in a wide variety of fish living on coral reefs.

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.

Answer 76

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 77

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

Answer 77

1. Increase in variety/diversity of
   species/plants/animals;
2. Provides more/different habitats/niches

Question 78

During photosynthesis, plants produce (1) compounds which contain
carbon, such as carbohydrates, lipids and proteins. Most of the sugars synthesised
by plants are used by the plant in (2) . The rest are used to make other
groups of biological molecules. These biological molecules form the biomass of the
plants. Biomass can be measured in terms of mass of (3) per given area
per given time. The chemical energy store in dry biomass can be estimated
using (4) .

Answer 78

1. Organic
2. Respiration
3. Carbon
4. Calorimetry;

Question 79

Describe the light-independent reaction of photosynthesis.

Answer 79

1. Carbon dioxide
   combines/reacts with ribulose
   bisphosphate/RuBP;
2. Produces two glycerate (3-
   )phosphate/GP using
   (enzyme) Rubisco;
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 80

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

Answer 80

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

Question 81

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

Answer 81

1. Volume of (stock) bacteria (culture);
2. Concentration of (stock) bacteria
   (culture);
3. Concentration of glucose
4. Volume of ammonium chloride;
5. Time (bacteria/culture left to divide);
6. Concentration/volume of oxygen;
7. Concentration/volume of nitrogen;

Question 82

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

Answer 82

1. Less/no ATP/energy required/used
2. ATP/energy can be used for
   growth/synthesis/replication

Question 83

Put a tick ( ) in the box next to the process that occurs in anaerobic respiration but
does not occur in aerobic respiration.

Answer 83

Phosphorylation of glucose
Reduction of NAD
Reduction of pyruvate
Substrate-level phosphorylation

Question 84

Using all the information, suggest how speciation happened to produce two species of
lemur.

Answer 84

1. Geographical isolation
2. Reproductive separation/isolation
3. Different selection pressures
4. (Variation due to) mutation(s) (in different populations)
   5.(Different/advantageous) allele/s passed on/selected

Question 85

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

Answer 85

1. (Only) the presynaptic
   neurone/knob/membrane releases/has
   neurotransmitter/acetylcholine;
   2.(Only) the postsynaptic
   neurone/membrane has receptor

Question 86

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.
0 7 . 3 Suggest and explain how MG can weaken contraction of muscles.
Do not include details of myofibril or muscle contraction in your answer.

Answer 86

1. Less/no acetylcholine/neurotransmitter
   binds to receptor/s;
2. Less/no depolarisation

Question 87

Mestinon can help in the treatment of MG. Explain how

Answer 87

1. Less/no acetylcholine/neurotransmitter
   broken down;
2. (More) acetylcholine attaches to
   receptors;
3. Depolarisation (of sarcolemma) occurs

Question 88

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.

Answer 88

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/stop (from glassware) before solvent
   reaches end (of chromatography paper)

Question 89

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.

Answer 89

1. No/fewer calcium ions enter synaptic knob
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 90

When the patients recorded the intensity of pain, suggest two reasons why it was
important to use a statistically valid scale.

Answer 90

1. (Sensation of) pain is subjective
2. To ensure that differences (in pain detection)
   were (statistically) significant

Question 91

The tomato seeds were planted into sterilised soil.
Suggest two reasons why the soil was sterilised

Answer 91

1. Kill/remove/no (other) mycorrhizae/fungi;
2. Kill/remove/no nitrogen-fixing
   /nitrifying/denitrifying/saprobiotic bacteria;
3. Kill/remove/no pathogens;
4. Kill/remove/no pests;
5. Kill/remove/no competitors;
6. Kill/remove/no seeds/spores;
7. Is a (controlled) variable;

Question 92

The soil used in this investigation had the recommended concentration of fertiliser.
Suggest two reasons why the soil contained the recommended concentration of
fertiliser.

Answer 92

1. So mycorrhizae/water is the only 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 93

An ecosystem supports a certain size of population of a species, called
the (1) capacity. There are often numerous habitats within an ecosystem.
Within a habitat, a species occupies a (2) governed by an adaption to
both (3) and biotic conditions. Populations of different species form
a (4) .
Write the correct biological term beside each number below that matches the space in
the passage..

Answer 93

1) carrying
(2) niche
(3) abiotic
(4) community;

Question 94

Suggest two reasons for conserving rainforests

Answer 94

1. Conserve/protect
   species/plants/animals/organisms

Question 95

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

Answer 95

1. Heat (loss) from respiration;
2. (Food) not digested