Past paper questions

An antigen in a vaccine leads to the production of antibodies. Describe the part played by

B lymphocytes in this process.

1 macrophages present antigens to B lymphocytes;

2 antigen binds to / is complementary to receptors on lymphocyte;

3 binds to a specific lymphocyte;

4 lymphocytes become competent / sensitised;

5 (B) lymphocytes reproduce by mitosis / (B) lymphocytes cloned;

6 plasma cells secrete antibodies;

Hepatitis B vaccine contains a viral antigen produced by genetically modified bacteria.

Describe how the isolated gene that codes for a protein in the virus's coat could be

transferred to the bacterial cells.

1 restriction enzyme / endonuclease;

2 to cut plasmid / to form sticky ends in plasmid;

3 (use) ligase(to join) gene to plasmid;

4 culture bacteria with (in medium containing) plasmids

5 to allow uptake of plasmids / transformation;

6 use of cold shock / chemical treatment (to enhance uptake) / heat

shock;

Give two factors, other than cost, that should be considered when selecting an antibiotic to

treat a bacterial disease.

side effects / allergic reactions / low toxicity to cells;

interaction with other drugs / effective in conditions of use / reasonably stable;

should only act on the problem bacteria / narrow spectrum;

how much resistance the bacteria have built up;

The table describes the effects of two antibiotics on bacteria.

Tetracycline prevents tRNA binding

Chloramphenicol prevents peptide bonds forming

(i) Explain how each of these antibiotics slows down the rate of growth of bacteria.

tetracycline

prevents tRNA binding to ribosomes / amino acid / mRNA;

amino acids not available / brought / picked up;

chloramphenicol

prevents amino acids being joined / prevents primary structure forming;

no enzymes / no structural proteins formed;

Suggest why tetracycline has no effect on human cells.

only prevents tRNA binding to 70S / prokaryotic / bacterial

ribosomes / human ribosomes are different sizes / shapes / structure;

Describe how bacteria are destroyed by phagocytes.

1. (Phagocyte engulfs) to form vacuole / vesicle / phagosome;

Accept surrounds bacteria with membrane

2. Lysosome empties contents into vacuole / vesicle / phagosome;

Accept joins / fuses

3. (Releasing) enzymes that digest / hydrolyse bacteria;

Ignore breakdown / destroy / lytic enzymes

Give two structures a bacterial cell may have that a white blood cell does not have.

1. Cell wall;

2. Capsule / slime layer;

3. Circular DNA;

Reject "circular chromosome"

4. Naked DNA / DNA without histones;

5. Flagellum;

6. Plasmid;

7. Pilus;

8. 70s / smaller ribosomes;

9. Mesosome;

Salmonella typhimurium causes food poisoning in humans but not in other mammals.

Explain why these bacteria attach to human cells but not to the cells of other mammals.

bacteria have ligands / antigens / proteins / glycoproteins / polysaccharides (on membrane

/ wall);

complementary to receptors / fits / binds / attaches to specific receptor

Salmonella bacteria release toxins that cause the body temperature to rise. Although a

small increase in body temperature can be beneficial, a large increase can cause serious

harm.

Explain how a large increase in a person's body temperature can cause harm.

enzymes denatured / tertiary / secondary structure altered / altered

active sites / breaks hydrogen bonds;

prevents named chemical reactions / metabolic pathways;

Some species of bacteria, which live in soil and decompose organic material, release

exotoxins. Suggest how the release of exotoxins benefits the bacteria.

inhibits / kills other bacteria / fungi / decomposers / reduces competition;

The MV + MMR group had more measles antibodies in their blood before vaccination

than the MMR only group. Suggest an explanation for this.

still have maternal antibodies;

Scientists tested a claim that modified citrus pectin (MCP) increased the production of antibodies

by the immune system.

• They divided a large number of mice into five groups.

• They gave the mice in each group a different amount of MCP in their food.

• The scientists then stimulated antibody production in the mice. They did this by injecting

them with a solution containing sheep red blood cells.

The results are shown in the graph.

The data obtained in this investigation have been plotted on a graph. How would you join

the points? Give a reason for your answer.

Straight lines point to point as not possible to predict intermediate values / values between

points;

Use the graph to describe the effect of MCP on mean antibody production

increases then levels / falls;

Maximum antibody production 180 units / at dose of 0.25 g per kg;

The dose of MCP given to the mice was calculated in g per kg body mass. Explain why the

dose was calculated per unit mass.

Takes into account different masses of mice / allows comparison;

Explain how antibodies were produced when the mice were injected with sheep red blood

cells.

Sheep red blood cells have antigens (on their surface);

Antigens are proteins foreign to mice / are non-self;

Stimulate B cells to produce antibodies;

A newspaper suggested that these data show that taking MCP will give people increased

resistance to disease. With reference to the data give two reasons why this conclusion

may not be valid.

Response only observed in mice;

Disease organisms not investigated;

Not all disease caused by pathogens / cured by antibodies;

Different cells in the body have different functions.

(a) Some white blood cells are phagocytic. Describe how these phagocytic white blood cells

destroy bacteria.

1. Phagocyte attracted to bacteria by chemicals / recognise antigens on bacteria as

foreign;

2. Engulf / ingest bacteria;

3. Bacteria in vacuole / vesicle;

4. Lysosome fuses with / empties enzymes into vacuole;

5. Bacteria digested / hydrolysed;

The epithelial cells that line the small intestine are adapted for the absorption of glucose.

Explain how.

1. Microvilli provide a large / increased surface area;

2. Many mitochondria produce ATP / release or provide energy (for active

transport);

3. Carrier proteins for active transport;

4. Channel / carrier proteins for facilitated diffusion;

5. Co-transport of sodium (ions) and glucose or symport / carrier protein for

sodium (ions) and glucose;

6. Membrane-bound enzymes digest disaccharides / produce glucose;

Changes to the protein coat of the influenza virus cause antigenic variability. Explain how

antigenic variability has caused some people to become infected more than once with

influenza viruses

memory B / T cells do not recognise (new antigens);

antibodies previously produced are not effective

as shape not complementary to new antigen;

The drawings show the changes in a B lymphocyte after stimulation by specific antigens

Describe the role of macrophages in stimulating B lymphocytes.

antigen in membrane presented to lymphocytes /

produce cytokinins;

Explain how the changes shown in the drawings are related to the function of B

lymphocytes.

mitochondria provide (more) ATP / energy;

(more) RER / ribosomes synthesise proteins;

(more) Golgi body secretes / modifies or packages proteins /

produces glycoproteins;

(B lymphocytes) produces antibodies;

What is the evidence from the diagram that this antibody has a quaternary structure?

Has more than one / four polypeptide chains / made up of polypeptide chains;

Scientists use this antibody to detect an antigen on the bacterium that causes stomach

ulcers. Explain why the antibody will only detect this antigen.

1. Antibody / variable region has specific amino acid sequence / primary structure;

2. The shape / tertiary structure of the binding site is complementary to / fits /

binds with these antigens;

2. Do not accept active site for this point.

3. Forms complex between antigen and antibody;

Clostridium difficile is a bacterium that is present in the gut of up to 3% of healthy adults

and 66% of healthy infants.

(i) C. difficile rarely causes problems, either in healthy adults or in infants. This is

because its numbers are kept low by competition with harmless bacteria that

normally live in the intestine.

Use this information to explain why some patients treated with antibiotics can be

affected by C. difficile.

Antibiotics kill other bacteria / Clostridium is resistant;

Less / no competition so (Clostridium)

reproduces / replicates / multiplies / increases in number;

Suggest why older people are more likely to be affected by C. difficile.

Immune system less effective / more likely to have other

infections / been in hospital;

Accept: 'Weak / lower' immune system'.

The antibiotic methicillin inhibits the enzyme transpeptidase. This enzyme is used by some

bacteria to join monomers together during cell wall formation. Methicillin has a similar

structure to these monomers. Use this information to explain how methicillin inhibits the

enzyme transpeptidase.

Attaches to active site (of enzyme);

(Methicillin) is a competitive inhibitor / prevents monomers / substrate

attaching (to enzyme);

MRSA is a variety of Staphylococcus aureus. It is difficult to treat infections caused by this

bacterium because it is resistant to methicillin and to some other antibiotics. As a result,

some patients who are already very ill may die if they become infected with MRSA. The

graph shows the number of deaths in England and Wales between 1994 and 2008 caused

by MRSA.

It may be difficult to identify MRSA as the actual cause of death. Explain why

Have other illness / medical condition / 'weak' immune system / disease /

infection;

Describe the change in the number of deaths caused by MRSA in England in the

period shown in the graph.

Increase up to 2006 / 20 (per 100 000) then decreases;

The graph shows the number of deaths from influenza per year in a developed country.

Suggest an explanation for the change in the number of deaths from influenza during

the first 10 years.

(decrease)

fall in deaths due to rise in number of people with immunity / better care / targeting

vaccination at vulnerable;

Suggest an explanation for the large increase in the number of deaths from influenza

in year 11.

mutation of virus / new strain;

mutant form not recognised by memory cells (allow antibodies);

The diagram shows some of the structures on the outside of an influenza virus

Haemagglutinin and neuraminidase are protein molecules. Haemagglutinin binds to

receptor molecules on the surface of epithelial cells in the breathing system.

Neuraminidase is an enzyme which breaks down molecules in the surface membrane of

epithelial cells and allows the viruses to be released from the cells.

Describe how T lymphocytes recognise and respond to the influenza virus.

T lymphocyte receptors recognise shape of haemagglutinin /

neuraminidase / viral antigen;

clone (once only);

destroy virus;

Describe how B lymphocytes respond to the influenza virus

clone (once only);

produce antibodies;

effect of antibody e.g. stimulation of phagocytosis /

precipitation of toxins;

New drugs have recently become available for treating influenza. One type is a

neuraminidase inhibitor. Explain how this type of drug would act as a treatment for

influenza.

alter shape of active site of neuraminidase / block active site;

virus unable to leave host cells;

The medical officer used a statistical test to assess the effectiveness of the five different

vaccines.

(i) What would be the null hypothesis?

there is no difference in the proportion / number of influenza cases

between the 5 vaccines;

The statistical test gave a probability of less than 0.05. What conclusion can be drawn

from this?

significant difference in proportion / number of cases of influenza

between the vaccines / the null hypothesis should be rejected;

It was suggested that the raw data showed that the type III vaccine was the most effective.

Give two reasons why this conclusion may not be reliable.

sample size small;

possible differences in exposure to infection;

exposure to different strains / mutants;

possible differences in existing immunity;

possible differences in sex / age;

possible differences in socio-economic status;

What is a pathogen?

(Micro)organism that causes disease / harm to body / an immune response;

When a pathogen enters the body it may be destroyed by phagocytosis.

Describe how.

1. Phagocyte attracted by a substance / recognises (foreign) antigen;

Accept named substance eg chemical / antigen

2. (Pathogen)engulfed / ingested;

Accept: description

3. Enclosed in vacuole / vesicle / phagosome;

4. (Vacuole) fuses / joins with lysosome;

5. Lysosome contains enzymes;

Accept named example of enzyme

6. Pathogen digested / molecules hydrolysed;

When a pathogen causes an infection, plasma cells secrete antibodies which destroy this

pathogen.

Explain why these antibodies are only effective against a specific pathogen.

1. Antigens (on pathogen) are a specific shape / have specific tertiary / 3D

structure;

1 / 3 Structure alone is insufficient

2. Antibody fits / binds / is complementary to antigen / antibody-antigen complex

forms;

Reject - active site

Give two ways in which pathogens can cause disease

1. (Releases) toxins;

2. Kills cells / tissues.

Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar.

Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria.

1. Water potential in (bacterial) cells higher (than in honey) / water potential in

honey lower (than in bacterial cells);

Q candidates must express themselves clearly

1. Must be comparative e.g. high WP in cell and low WP in honey

2. Water leaves bacteria / cells by osmosis;

3. (Loss of water) stops (metabolic) reactions.

3. Needs a reason why lack of water kills the cell

Whooping cough is a disease that affects some infants. Doctors collected data relating to

whooping cough between 1965 and 1996.

They collected data for:

• the number of cases of whooping cough reported

• the percentage of infants vaccinated against whooping cough.

The graph shows the data collected by the doctors.

Suggest two reasons why the percentage of infants vaccinated decreased between 1973

and 1975.

Any two from:

1. (Decrease linked to) few(er) cases of whooping cough;

2. (Decrease linked to) risk of / fear of side effects;

3. Insufficient vaccine available / too expensive to produce / distribute.

Between 1980 and 1990, there were three peaks in the number of reported cases of

whooping cough. After 1981, the number of cases of whooping cough in each peak

decreased.

Use the information from the graph to suggest why.

1. Vaccination rate increases;

2. Fewer people to spread the disease / whooping cough / more people immune /

fewer susceptible.

The percentage of the population vaccinated does not need to be 100% to be effective in

preventing the spread of whooping cough.

Suggest why.

1. More people are immune / fewer people carry the pathogen;

Herd immunity = 1 mark

Unvaccinated does not mean infected

(Do not accept disease for pathogen)

2. So susceptible / unvaccinated people less likely to contact infected people.

The diagram shows a human immunodeficiency virus (HIV).

Name structure P and enzyme Q.

(boarderand dot in middle)

P = membrane / lipid envelope / phospholipid bilayer;

Q = reverse transcriptase;

What is the function of the RNA molecules in this virus?

Carries genetic information / to make DNA

Describe how new viruses are produced after HIV has infected a T cell

DNA copy made (of viral RNA);

Inserted into host DNA / chromosomes;

(Uses viral DNA to) make viral proteins/particles;

Makes viral RNA;

(Host) cell makes new viruses;

"Budding off" / wrapped in cell membrane;

The diagram shows the human immunodeficiency virus (HIV).

Name A and B

(boarder and dot outline in the middle)

A = envelope/membrane/phospholipid (bilayer);

B = capsid / nucleocapsid / capsomere / protein;

The graph The graph shows changes in the number of T-cells and HIV particles in the blood of a person following infection.

Explain why the number of HIV particles in the blood

rises during the first few months after infection

(HIV is) invading cells which make new viruses; Cells release viruses into blood;

Explain why the number of HIV particles in the blood remains low between 1 and 7 years after infection

Virus remains dormant/exists as provirus/exists as DNA in host DNA;

This person developed a large number of infections about 9 years after he first became infected with HIV. Using information from the graph, explain why.

HIV destroys T cells; More (free) viruses produced leads to fall in T-cells; (So fewer) T-cells activate B-cells/memory cells;

Reduced/no antibody production; Immune system not working properly/inability to fight infection;

What is an antigen?

Molecule/protein/glycoprotein; Stimulates immune response; (That causes) production of antibodies;

Explain why antibodies against Salmonella do not normally bind to HIV.

Antigens on HIV are different (shape); So, antibody will not 'fit'/not complementary (to antigen); Receptor sites on antibody specific to one antigen;

Explain how the adaptor molecule allows anti-gal antibodies to associate with HIV.

(Has site with) same shape as salmonella antigen so binds to anti-gal antibodies; (Has site with) same shape as receptor molecule so that HIV will bind; Binds to both molecules;

Describe how humans produce antibodies against a pathogen such as Salmonella

Salmonella pathogen has specific antigen on surface; Salmonella pathogen engulfed by macrophage; T-cells activate B-cells; B-cell with complementary/specific receptor antibody activated/ clonal selection; B-cells divide/form clone/clonal expansion; Plasma cells make antibodies; Specific to antigen/bind to salmonella bacterial antigen;

HIV infects some human cells, such as T-cells, but not others. Suggest why.

HIV binds to specific receptor; Only present on certain cells / T-cells

Antibiotics are not used to treat viral infections, such as HIV. Explain why.

Antibiotics stop metabolism, viruses don't have metabolism; Viruses hide in cells, antibiotics can't reach;

When HIV, anti-gal and the adaptor molecule were added to a culture of human cells, 90% of the virus did not infect human cells. (lines 12-15). Explain why.

Adaptor molecule binds to HIV; (This) prevents the HIV binding to the receptor; Therefore few HIV available to infect cells;

Explain why a different type of adaptor molecule will have to be made to use against MRSA. (lines 16-17)

Would need to be complementary to MRSA (antigens); MRSA has different antigens; But would still need to have binding site for anti-gal;

After an infection with chlamydia, cells of the immune system of the mice may attack the heart muscle cells (lines 7-8). Explain why.

1. Antibodies / memory cells against chlamydia (protein / antigen) are present;

2. Protein on heart (muscle) similar to chlamydia protein / antigen so T cells / antibodies (attack heart muscle cells);

Some scientists have suggested that people should be vaccinated to prevent infection by chlamydia. Evaluate this suggestion.

FOR

1. Prevents / reduces heart disease / attacks;

2. Cheaper to vaccinate than treat heart disease;

AGAINST

3. Vaccination costly;

4. Don't know frequency of chlamydia infection;

5. Research in mice might not be replicated in humans / humans might have a different protein;

6. Vaccine could cause heart disease or immune response against heart (muscle);

Doctors use Zevalin to kill cancerous B-cells. Zevalin is a monoclonal antibody which has a highly radioactive substance called yttrium attached to it. The antibody binds to the surface of B-cells and the radioactivity kills the cells.

(a) Only B-cells are killed by Zevalin.

Explain why.

Zevalin/antibody binds to specific receptor/cell surface protein/antigen;

(Only found) on B-cells;

The doctors decided they could treat Patient P with Zevalin containing yttrium but not Patient Q. Suggest why Patient P could be treated with Zevalin containing yttrium and Patient Q could not.

Patient P treated with Zevalin/yttrium (no mark); Assume 'Zevalin' means 'with yttrium' unless they state otherwise

Where indium/antibody (only) on lymphatic system/groin and armpits;

So only (cancerous) B-cells killed;

In patient P high concentration of radioactivity/antibodies high enough to kill cancer cells;

Patient Q ‒ radioactivity in places where other body cells could be killed/ organs damaged/named example;

Could harm patient more than cancer;

Patient Q cancer has spread;

So too late to treat;

Suggest one reason for the difference in distribution of the radioactivity detected in these patients.

Patient Q ‒ (cancerous) B-cells outside of lymphatic system/metastasis;

So antibody bound in other parts of the body (as well);

Patient Q ‒ has different receptors/distribution of receptors compared to patient P;

Other body cells (than B-cells) have receptors for antibody;

The antibody in Zevalin comes from mice. Patients are tested for antibodies against Zevalin before treatment for their cancer. Suggest why.

Might be allergic to mouse antibody/protein;

(Mouse) antibody acts as an antigen;

Causes an immune response/antibody production;

Antibody destroys Zevalin;

Releases radioactivity into body/prevents activity against the cancer;

Describe how HIV is replicated after it has entered a human cell.

Reverse transcriptase; Accept integrase/description of action of

Enzyme uses (HIV) RNA to make DNA (copy);

DNA joined to (host) cell's DNA/chromosome;

DNA used to make HIV RNA (copies); Accept (HIV) DNA replicated when (T) cell divides

And HIV capsid proteins/enzymes;

Made at (host) ribosomes;

Assembly of new virus particles;

Budding off from membrane (of host cell);