spec papers

Question 1

the decrease in the percentage of light passing through the water between 25C and 60C is caused b the release of the red pigment from cells of the beetroot. suggest how the increase in temperature of the water causes the release of the red pigment. (2)

Answer 1

1. Damage to (cell surface) membrane;
2. (membrane) proteins denature;
3. Increased fluidity / damage to the phospholipid bilayer;

Question 2

multiple copies of the AMY1 gene is an adaptation to a high- starch diet. use your knowledge of protein synthesis and enzyme action to explain the advantage of this adaptation. (3)

Answer 2

1. More mRNA / more transcription;
2. More translation / enzyme;
3. So reaction faster;

Question 3

NMO is a disease that leads to damage to nerve cells in the spinal cord. a person with NMO produces anti-AQP4 antibody that attacks only these nerve cells. explain why the anti- AQP4 antibody only damages these cells. (4)

Answer 3

1. antibody has a specific tertiary structure;
2. Has binding site complementary to one antigen;
3. Antigen to this antibody (only) found on these nerve cells;
4. So, forms antigen-antibody complex with these nerve cells (causing damage);

Question 4

a new treatment for NMO involves using a monoclonal antibody. the structure of the variable region of this monoclonal antibody is identical to the variable region of an anti- AQP4 antibody, but the rest of its structure is different. use this info and your knowledge of antigen-antibody complexes to suggest how this monoclonal antibody prevents anti-AQP4 damaging nerve cells. (2)

Answer 4

The monoclonal antibody forms antigen- antibody complex with nerve cell antigen so less / no anti-AQP4 can bind;
2. When monoclonal antibody binds it doesn’t cause damage to nerve cell;

Question 5

a student investigated the effect of lipase concentration on the hydrolysis of lipids. he took a beaker containing a suspension of lipids. he placed a pH probe attached to a data logger into the beaker. after 5 mins he added the lipase solution. give a suitable control for this investigation. (1)

Answer 5

boiled lipase solution

Question 6

Explain the advantages of lipid droplet and micelle formation (3)

Answer 6

1. Droplets increase surface areas (for lipase / enzyme action);
2. (So) faster hydrolysis / digestion (of triglycerides / lipids);
3. Micelles carry fatty acids and glycerol / monoglycerides to / through membrane / to (intestinal epithelial) cell;

Question 7

Explain the role of the heart in the formation of tissue fluid (2)

Answer 7

1. Contraction of ventricle(s) produces high blood / hydrostatic pressure;
2. (This) forces water (and some dissolved substances) out (of blood capillaries);

Question 8

Explain how the chromosome number is halved during meiosis. (2)

Answer 8

1. Homologous chromosomes (pair);

2. One of each (pair) goes to each (daughter) cell / to opposite poles

Question 9

Crossing over greatly increases genetic diversity in this species of moss.
Describe the process of crossing over and explain how it increases genetic diversity.

Answer 9

1. Homologous pairs of chromosomes associate / form a bivalent;
2. Chiasma(ta) form;
3. (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
4. Producing new combinations of alleles;

Question 10

define Species richness (1)

Answer 10

Species richness = the number of (different) species in a community;

Question 11

Suggest and explain why AZT does not destroy HIV in the body but stops or slows the development of AIDS (lines 3–4).

Answer 11

1. Person (infected with HIV) has HIV DNA (in their DNA);
2. New HIV (particles) still made;
3. (AZT) inhibits reverse transcriptase;
4. (AZT) stops these (new HIV particles) from forming new HIV DNA;
5. Stops destruction of more / newly infected T cells;
6. So immune system continues to work (and AIDS does not develop);

Question 12

Give two reasons why it was important that the student counted the number of stomata in several parts of each piece of leaf tissue. (2)

Answer 12

• So it is a representative sample;

- To obtain a (reliable) mean;

Question 13

The species of tubifex worm in Figure 3 has 50% saturation of their haemoglobin with oxygen at 0.08 kPa. Explain how this enables this species to survive in water polluted with sewage.(2)

Answer 13

1. High/50% saturation (with oxygen) below (pO2 of) 0.2 kPa;
2. (Oxygen) for respiration;

Question 14

The chilling requirement of seeds of certain plant species is considered to be an adaptation for survival in countries with seasonal changes in environmental conditions. Suggest how this adaptation may enable these plant species to survive and respond to seasonal changes. (3)

Answer 14

1. Seeds/embryo remain dormant/inactive in winter/cold OR Growth/development of seed/embryo during winter/cold;
2. Seeds/plants develop in spring/summer OR Seeds/plants develop when temperature/light increases;
3. Plant photosynthesise (in spring/when warm);
4. Produce (more) seeds/offspring in spring/growing season;

Question 15

The frequency of the CCR5 mutation is highest in Europe. Scientists have collected data on the history and number of HIV infections in Europe. Using these data, scientists have concluded that the high frequency of the CCR5 mutation is not due to natural selection in response to HIV. Suggest two reasons why scientists reached this conclusion (2)

Answer 15

1. Low/lower exposure to HIV (in Europe) OR Low/lower number of HIV/AIDS (infections/cases);
2. (HIV relatively) recently evolved;
3. Mutation/CCR5 has been around for many years;
4. Mutation/CCR5 is advantageous (for something else);

Question 16

Suggest two variables the student should control in using the filter paper discs in this investigation. (2)

Answer 16

1. (Same) size;
2. (Same) material/absorbency;
3. In solution for same time period;

Question 17

Some people produce a much higher ventricular blood pressure than normal. This can cause tissue fluid to build up outside the blood capillaries of these people. Explain why. (2)

Answer 17

1. More fluid forced/filtered out of capillary/blood (due to high pressure);
2. Less return of fluid (into capillary/blood) due to pressure

Question 18

Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer. (3)

Answer 18

1. mRNA binds to ribosome;
2. Idea of two codons/binding sites;
3. (Allows) tRNA with anticodons to bind/associate;
4. (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules);
5. Moves along (mRNA to the next codon)/translocation described;

Question 19

Suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients. (2)

Answer 19

1. Membrane folded so increased/large surface area; OR Membrane has increased/large surface area for (fast) diffusion/facilitated diffusion/active transport/co-transport;
2. Large number of protein channels/carriers (in membrane) for facilitated diffusion;
3. Large number of protein carriers (in membrane) for active transport;
4. Large number of protein (channels/carriers in membrane) for co-transport

Question 20

High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid.
Explain how. (2)

Answer 20

1. (Higher salt) results in lower water potential of tissue fluid;
2. (So) less water returns to capillary by osmosis (at venule end);

Question 21

Bacteria are often used in industry as a source of enzymes. One reason is because bacteria divide rapidly, producing a large number of them in a short time.
Describe how bacteria divide. (2)

Answer 21

1. Binary fission;
2. Replication of (circular) DNA;
3. Division of cytoplasm to produce 2 daughter cells;
4. Each with single copy of (circular) DNA;

Question 22

Some proteases are secreted as extracellular enzymes by bacteria. Suggest one advantage to a bacterium of secreting an extracellular protease in its natural environment.
Explain your answer (2)

Answer 22

1. To digest protein;
2. (So) they can absorb amino acids for growth/reproduction/protein synthesis/synthesis of named cell component; OR (So) they can destroy a toxic substance/protein

Question 23

The scientists incubated the flasks containing the leaf discs at 26 °C and gently shook the flasks. Suggest one reason why the scientists ensured the temperature remained constant and one reason why the leaf discs were shaken. (2)

Answer 23

1. Shaking -> So all surfaces of the leaf discs are exposed (to water)/so all submerged;
2. Maintain temperature -> so that the rate of diffusion (of ions out of cells) remains constant

Question 24

Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen. [3 marks]

Answer 24

1. Helper T cell/TH cell binds to the antigen (on the antigen-presenting cell/phagocyte);
2. This helper T/TH cell stimulates a specific B cell;
3. B cell clones OR B cell divides by mitosis;
4. (Forms) plasma cells that release antibodies;

Question 25

Collagen is a protein produced by cells in joints, such as the knee. Rheumatoid arthritis (RA) is an auto-immune disease. In an auto-immune disease, a person’s immune system attacks their own cells. RA causes pain, swelling and stiffness in the joints. Scientists have found a virus that produces a protein very similar to human collagen. Suggest how the immune response to this viral protein can result in the development of RA. [2 marks]

Answer 25

1. The antibody against virus (antigen) will bind to collagen; 2. This results in the destruction of the (human) cells/collagen;

Question 26

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. [3 marks]

Answer 26

1. Tracheoles have thin walls so short diffusion distance to cells; 2. Highly branched/large number of tracheoles so short diffusion distance to cells; 3. Highly branched/large number of tracheoles so large surface area (for gas exchange); 4. Tracheae provide tubes full of air so fast diffusion (into insect tissues)

Question 27

The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water. Some other species of insect have larvae that are a similar size and shape to damselfly larvae and also live in water. These larvae do not actively hunt prey and do not have gills. Explain how the presence of gills adapts the damselfly to its way of life. [2 marks]

Answer 27

1. Damselfly larvae has high(er) metabolic/respiratory (rate); 2. (So) uses more oxygen (per unit time/per unit mass);

Question 28

No organelles are visible in the cytoplasm of this red blood cell. Suggest why.[1 mark]

Answer 28

Cytoplasm of red blood cell filled with haemoglobin

Question 29

Describe how substances move across cell-surface membranes by facilitated diffusion. [3 marks]

Answer 29

1. Carrier/channel protein; 2. (Protein) specific/complementary to substance; 3. Substance moves down concentration gradient;

Question 30

The scientists decided to collect animals from the soil samples for 40 minutes. Suggest how the scientists decided that 40 minutes was an appropriate time. [2 marks]

Answer 30

1. Repeat soil sorting for different times and record number of species collected; 2. Find optimum time / time beyond which further sorting does not lead to increase in animal species found;

Question 31

The saliva of most humans contains α-amylase. The gene encoding α-amylase is called AMY1; it is located on chromosome 1. The number of copies of the AMY1 gene is unlikely to affect people’s ability to digest starch. Explain why. [3 marks]

Answer 31

1. Little digestion of starch by salivary amylase OR starch in mouth for a short period OR salivary amylase inactivated by stomach acid; 2. Amylase also secreted by pancreas; 3. So (most) starch digestion occurs in small intestine;

Question 32

Suggest the role of the mRNA stop codons. [2 marks]

Answer 32

1. Stop translation; | 2. Result in detachment of polypeptide chain from ribosome;

Question 33

The first molecule of oxygen to bind causes a change in the shape of the haemoglobin molecule. This change of shape makes it easier for other oxygen molecules to bind to the haemoglobin molecule. Explain how Figure 8 provides evidence for this. [2 marks]

Answer 33

1. At low partial pressure of oxygen, little increase in saturation as oxygen increases; 2. (then) rapid rise as it gets easier for oxygen to bind;

Question 34

Suggest how the scientists could adapt their method to determine which tissue carried the radioactively labelled sucrose. [2 marks]

Answer 34

1. Take thin (horizontal) sections of plant tissue/stem; | 2. Place against photographic film in dark for several hours / carry out autoradiography;

Question 35

A mother who was infected with HIV gave birth to a baby. The baby tested positive using this test. This does not prove the baby is infected with HIV. Explain why. [2 marks]

Answer 35

1. Children receive (HIV) antibodies from their mothers/maternal antibodies; 2. (So) solution will always turn blue/will always test positive (before 18 months);

Question 36

A control well is set up every time this test is used. This is treated in exactly the same way as the test wells, except that blood plasma is replaced by a salt solution. Use information from Figure 5 to suggest two purposes of the control well.[2 marks]

Answer 36

1. Only the enzyme/nothing else is causing a colour change; | 2. Washing is effective/all unbound antibody is washed away;

Question 37

During replication, the two DNA strands separate and each acts as a template for the production of a new strand. As new DNA strands are produced, nucleotides can only be added in the 5’ to 3’ direction. Use Figure 6 and your knowledge of enzyme action and DNA replication to explain why new nucleotides can only be added in a 5’ to 3’ direction. [4 marks]

Answer 37

1. Reference to DNA polymerase; 2. (Which is) specific; 3. Only complementary with/binds to 5’ end (of strand); 4. Only complementary with/binds with phosphate end (of the developing strand);

Question 38

Give two ways in which the hydrolysis of ATP is used in cells. [2 marks]

Answer 38

1. To provide energy for other reactions/named process; | 2. To add phosphate to other substances and make them more reactive/change their shape;

Question 39

What is the evidence in Figure 3 that the phospholipid bilayer shown is part of the cell-surface membrane? [1]

Answer 39

Cell wall forms outside cell-surface membrane/has cellulose on it (on the outside);

Question 40

A quantitative Benedict’s test produces a colour whose intensity depends on the concentration of reducing sugar in a solution. A colorimeter can be used to measure the intensity of this colour. The scientist used quantitative Benedict’s tests to produce a calibration curve of colorimeter reading against concentration of maltose. Describe how the scientist would have produced the calibration curve and used it to obtain the results in Figure 4. Do not include details of how to perform a Benedict’s test in your answer. [3 marks]

Answer 40

1. Make/use maltose solutions of known/different concentrations (and carry out quantitative Benedict’s test on each); 2. (Use colorimeter to) measure colour/colorimeter value of each solution and plot calibration curve/graph described; 3. Find concentration of sample from calibration curve;

Question 41

There is genetic diversity within HPV. Give two ways doctors could use base sequences to compare different types of HPV. [2 marks]

Answer 41

1. Compare (base sequences of) DNA; 2. Look for mutations/named mutations (that change the base sequence); 3. Compare (base sequences of) (m)RNA;

Question 42

Suggest why the development of a monopolar mitotic spindle would prevent successful mitosis. [2 marks]

Answer 42

1. No separation of chromatids/chromosomes/centromeres; 2. Chromatids/chromosomes all go to one pole/end/sides of cell/not pulled to opposite poles; 3. Doubles chromosome number in cell/one daughter cell gets no chromosomes or chromatids;

Question 43

Suggest how amyloid-precursor protein can be the substrate of two different enzymes, α-secretase and β-secretase (lines 3–5). [2 marks]

Answer 43

1. Different parts/areas/amino acid sequences (of amyloid-precursor) protein; 2. Each enzyme is specific /fits/binds/ complementary to a different part of the APP;

Question 44

Many people with Alzheimer’s disease have mutations that decrease α-secretase production, or increase β-secretase production (lines 8–9). Use the information provided to explain how these mutations can lead to Alzheimer’s disease. [3 marks]

Answer 44

1. Mutations prevent production of enzyme(s)/functional enzyme; 2. (Increase in β-secretase) leads to faster/more β-amyloid production OR (Decrease in α-secretase) leads to more substrate for β-secretase; 3. (Leads to) more/greater plaque formation;

Question 45

When some of these types of drugs were trialled on patients, the trials were stopped because some patients developed serious side effects (lines 11–13). Using the information provided, suggest why some patients developed serious side effects. [1 mark]

Answer 45

1. Some β-amyloid required/needed (to prevent side effects)