Biology Unit 1 Chapter 6 - Immunity

Explain why each of the following means that a vaccine might not be effective against HIV. (i) HIV rapidly enters host cells. (2) (ii) HIV shows a lot of antigenic variability. (2)

(i) Enters cells before secondary immune response caused; So no antibodies present to attack HIV (ii) Many antigens present on HIV; Not possible to make a vaccine for all antigens

(Refer to ) The graph shows the number of new cases of two diseases which occurred in two different human populations. (Salmonella food poisoning and influenza). Explain the shape of the curve for (i) Salmonella food poisoning (ii) influenza. (2)

(i) single source of infection; (ii) transmitted from individual to individual

(Refer to June 2010 paper) Cervical cancer occurs in the neck of the uterus. Scientists investigated the link between cervical cancer and infection with some types of Human Papilloma Virus (HPV). The graph shows the frequency of five different types of HPV in women who had cervical cancer. A local newspaper published an article about cervical cancer with the headline 'HPV causes cervical cancer'. Do the data shown in the graph support this claim? Explain your answer. (3)

(yes): Many women with cervical cancer have HPV 16, 18 and 31; (no): Few women with cervical cancer have HPV 6 and 11; HPV infection does not mean causation of cervical cancer because it could be caused by another factor

(Refer to exam q) A test has been developed to find out whether a person has antibodies against the mumps virus. The test is shown in the diagram. Explain why this test will detect mumps antibodies, but not other antibodies in the blood. (1)

2nd antibodies specific to mumps antibody

Scientists have developed vaccines against HPV. One of the vaccines contains HPV antigens. What is an HPV antigen? (2)

A protein; Which causes immune response

How does a B cell respond when a pathogen enters the blood or tissue fluid? (6)

An antibody protein on a specific B cell has a complementary shape and fits exactly onto the antigens of the pathogen; The antigens of the pathogen are taken up by the specific B cells and they present them on their surfaces; T helper cells attach to the processed antigens on the B cells thereby activating them; Once activated the B cell divides by mitosis to form clones of identical B cells, all of which produce an antibody that is specific and complementary to the pathogen's antigen; The antibodies on the cloned B plasma cells attach to the antigens on the pathogen and destroy them. They are responsible for immediate immunity (known as primary immune response); Some cloned B cells are memory cells that do not produce antibodies directly, but respond to future infections by the same pathogen by dividing rapidly to form plasma cells that produce antibodies and more memory cells. They are therefore responsible for long-term immunity (secondary immune response)

What is the difference between an antigen and an antibody? (2)

An antigen is a molecule that triggers an immune response by lymphocytes; whereas an antibody is a molecule that has a complementary shape to the antigen and is produced in response to it

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. (2)

Antibodies have a specific tertiary structure; Antigens are complementary to antibody

Some new tests use monoclonal antibodies. Explain why these antibodies are referred to as monoclonal. (1)

Antibodies produced from the same B cell

Imatinib is taken up by blood cells by active transport. Explain how the data for the two different temperatures support this statement. (2)

At every concentration, uptake is faster at a higher temperature; Due to faster ATP production in respiration

What are the two types of lymphocytes and what are their roles? (2)

B cells; involved in humoral immunity, produce antibodies, responds to foreign material outside body cells, responds to bacteria and viruses; T cells; involved in cell-mediated immunity, responds to foreign material inside body cells, responds to own cells altered by viruses or cancer and to transplanted tissues

It will be many years before it can be shown that this vaccination programme has reduced cases of cervical cancer. Suggest two reasons why. (2)

Cancer takes years to develop; Only teenagers are vaccinated

Smear tests will continue to be offered to women, even if they have been vaccinated. Suggest why women who have been vaccinated still need to be offered smear tests.

Cervical cancer can be caused by other factors

Why is it difficult to control cholera by vaccination? (2)

Cholera is an intestinal disease and therefore not easily reached by the immune system; The antigens of the cholera pathogen change rapidly, making it difficult to develop an effective and lasting vaccine

Suggest one possible problem in injecting people with antivenom made in this way. (1)

Could transfer disease

What are the features of a successful vaccination programme? (4)

Economically available in sufficient quantities to immunise all the vulnerable population; Few side-effects, if any; Vaccine must be administered properly by trained staff at the appropriate time; It must be possible to vaccinate the majority of the vulnerable population

Some scientists have suggested that people should be vaccinated to prevent infection by chlamydia. Evaluate this suggestion. (3)

FOR Prevents heart disease; AGAINST Vaccination costly; Research in mice might not be replicated in humans

Most cases of cervical cancer are caused by infection with Human Papilloma Virus (HPV). This virus can be spread by sexual contact. There are many types of HPV, each identified by a number. Most of these types are harmless but types 16 and 18 are most likely to cause cervical cancer. A vaccine made from HPV types 16 and 18 is offered to girls aged 12 to 13. Three injections of the vaccine are given over six months. In clinical trials, the vaccine has proved very effective in protecting against HPV types 16 and 18. However, it will be many years before it can be shown that this vaccination programme has reduced cases of cervical cancer. Until then, smear tests will continue to be offered to women, even if they have been vaccinated. A smear test allows abnormal cells in the cervix to be identified so that they can be removed before cervical cancer develops. The Department of Health has estimated that 80% of girls aged 12 to 13 need to be vaccinated to achieve herd immunity to HPV types 16 and 18. Herd immunity is where enough people have been vaccinated to reduce significantly the spread of HPV through the population. HPV vaccine is offered to girls aged 12 to 13. Suggest why it is offered to this age group. (1)

Few girls are sexually active at this age

Where are B cells formed? Where do they mature? (2)

Formed from stem cells in the bone marrow; Mature in the bone marrow

Where are T cells formed? Where do they mature? (2)

Formed from stem cells in the bone marrow; Mature in the thymus gland

(Refer to Jan 2012 paper) The diagram shows an antibody molecule. What is the evidence from the diagram that this antibody has a quaternary structure? (1)

Has more than one polypeptide chains

In areas where there are repeated outbreaks of cholera, most people who become infected by cholera bacteria do not become ill. Suggest and explain one reason why. (2)

Have produced memory cells; After previous infection

Identify three ethical issues associated with vaccination programmes. (3)

How can any individual health risks from vaccination be balanced against the advantages of controlling a disease for the benefit of the entire population?; The development of new vaccines often involves the use of animals; There are issues associated with who the vaccine should be tested on and how such trials should be carried out

Casein is a protein used to screen strains of bacteria for protease production. Describe how the bacteria break down casein. (3)

Hydrolysis; of peptide bonds; into amino acids

Explain why the secondary immune response is much more rapid than the primary one. (4)

In the primary response, the antigens on the pathogen have to be ingested, processed and presented by B cells; They then need to divide by mitosis to produce plasma cells and memory cells; Whereas in the secondary immune response, memory cells are already present; so the only process is dividing by mitosis to produce plasma cells and memory cells

So far, these types of vaccine have not been considered safe to use in a mass vaccination programme. Suggest why they have not been considered safe. (3)

Inactive virus may become active; Genetic information from HIV may harm cells; People may become HIV positive after vaccine used

What is vaccination? (2)

Injection of antigens; Antigens from dead microorganisms

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. (2)

Memory B cells do not recognise new antigens; Antibodies previously produced are not effective

A vaccine can be used to produce immunity to HPV. Describe how memory cells are important in this process. (3)

Memory cells produced from previous infection; When individual comes into contact with virus again; More antibodies are produced rapidly; Destroying virus before it can cause harm

(Refer to exam q) The drawings show the changes in a B lymphocyte after stimulation by specific antigens. Explain how the changes shown in the drawings are related to the function of B lymphocytes. (4)

Mitochondria provide more energy; More RER to synthesise proteins; More Golgi apparatus to modify and package proteins; These are necessary because B lymphocytes produce antibodies

Three injections of the vaccine are given. Use your knowledge of immunity to suggest why. (2)

More memory cells; So antibodies produced quicker if infected

Explain why there will be no colour change if mumps antibodies are not present in the blood. (2)

No antibodies to bind to antigen; Therefore 2nd antibody with the enzyme wont bind

Scientists have carried out trials of a drug to treat coeliac disease. Suggest two factors that should be considered before the drug can be used on patients with the disease. (2)

No serious side effects; Cost of drug

What are the two types of defences in the human body? (2)

Non-specific mechanisms; Such as a barrier to the entry of pathogens and phagocytosis; These respond to all pathogens in the same way and act immediately; Specific mechanisms; Such as cell-mediated responses involving T lymphocytes and humoral responses involving B lymphocytes; These distinguish between different pathogens and provide long-lasting immunity but responses are less rapid

What is immunity? (1)

Once the body's immune system has overwhelmed a pathogen, it is better prepared for a second infection from the same pathogen because it has produced memory cells and can repel it before it can cause any harm.

The vaccine is made from HPV types 16 and 18. Explain why this vaccine may not protect against other types of this virus. (2)

Other HPV types have different antigens; So the correct antibodies not produced

Injecting antivenom does not give a person lasting protection against the venom of box jellyfish. Explain why. (2)

Passive immunity; No memory cells produced

Outline the two types of immunity. (4)

Passive immunity; produced by the introduction of antibodies into individuals from an outside source so they are not replaced when they are broken down, do not produce memory cells and the immunity is short-lived; Active immunity; produced by stimulating the production of antibodies by the individual's own immune system, produces memory cells and is long-lasting

Outline the role of T cells in cell-mediated immunity. (5)

Pathogens invade body cells or are taken up by phagocytes; The phagocyte places antigens from the pathogen onto its own cell-surface membrane; Receptor proteins on specific T helper cells are complementary and fit exactly onto these antigens; This activates other T cells to divide rapidly by mitosis to form a clone; The cloned T cells kill infected cells, stimulate B cells to divide, and develop into memory cells that enable a rapid response to future infections by the same pathogen

When a pathogen enters the body it may be destroyed by phagocytosis. Describe how. (4)

Phagocyte attracted by chemicals; Engulfs pathogen; Pathogen enclosed in vesicle; Lysosome fuses with vesicle and empties enzymes into vesicle; Pathogen molecules hydrolysed

Different cells in the body have different functions. Some white blood cells are phagocytic. Describe how these phagocytic white blood cells destroy bacteria. (4)

Phagocyte attracted to bacteria by chemicals; Engulfs bacteria; Bacteria enclosed in vesicle; Lysosome fuses with vesicle and empties enzymes into vesicle; Bacteria molecules hydrolysed

How can T cells distinguish invader cells from normal cells? (2)

Phagocytes that have engulfed a pathogen, body cells invaded by a virus and cancer cells present some of the pathogen's antigens on their own cell-surface membrane

What are the two types of white blood cells? (2)

Phagocytes; Lymphocytes

Name the second line of defence. (1)

Phagocytosis

What is the first line of defence against disease? Give three examples. (2)

Physical or chemical barriers to prevent the entry of pathogens; such as the skin, hydrochloric acid in the stomach and epithelial cells covered in mucus

Some doctors suggested offering the vaccine to young men. Explain the advantage of vaccinating young men as well as young women. (2)

Prevents males being carriers of HPV; Prevents males passing on HPV to unvaccinated females

After an infection with chlamydia, cells of the immune system of the mice may attack the heart muscle cells. Explain why. (2)

Protein on heart muscle similar to chlamydia protein; So antibodies attack heart muscle cells

Chlamydia is a bacterium. Scientists have shown that infection with chlamydia can cause heart disease in humans. Infection with the bacterium can stimulate the formation of atheroma. This can lead to a heart attack. Other scientists have been working with mice. These scientists have suggested that chlamydia may cause heart disease in a different way. They have found a protein on the surface of chlamydia cells which is similar to a protein in the heart muscle of mice. After an infection with chlamydia, cells of the immune system of the mice may attack their heart muscle cells and cause heart disease. Using information from the passage, explain what is meant by an antigen. (2)

Protein on surface of chlamydia; That initiates an immune response in mice

The tests using monoclonal antibodies allow vets to identify brucellosis while they are still on a farm. Explain the advantages of this. (3)

Rapid treatment of infected cattle; Reduces spread of disease; Prevents the death of non-infected animals

Explain why it is important to wash the well at the start of Step 4. (2)

Removes unbound 2nd antibodies; Otherwise enzyme may be present and changes colour of the solution anyway

Explain how antibodies were produced when the mice were injected with sheep red blood cells. (3)

Sheep red blood cells have antigens on their surface; Antigens are foreign to mice; And stimulate B cells to produce antibodies

Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why. (3)

Specific primary structure; Specific tertiary structure; So only complementary to one antigen

The box jellyfish produces a poison (venom) which enters the blood when a person is stung. A person who has been stung can be treated with an injection of antivenom. This antivenom is produced by injecting small amounts of venom from box jellyfish into sheep, then extracting antibodies from the sheeps' blood. These antibodies are then injected into the person who has been stung. If a sheep is injected with the box jellyfish venom on more than one occasion a higher yield of antivenom is obtained. Explain why. (2)

Stimulates memory cells; So antibodies produced quicker

The human immunodeficiency virus (HIV) leads to the development of acquired immunodeficiency syndrome (AIDS). Eventually, people with AIDS die because they are unable to produce an immune response to pathogens. Scientists are trying to develop an effective vaccine to protect people against HIV. There are three main problems. HIV rapidly enters host cells. HIV causes the death of T cells that activate B cells. HIV shows a lot of antigenic variability. Scientists have experimented with different types of vaccine for HIV. One type contains HIV in an inactivated form. A second type contains attenuated HIV which replicates in the body but does not kill host cells. A third type uses a different, non-pathogenic virus to carry genetic information from HIV into the person's cells. This makes the person's cells produce HIV proteins. So far, these types of vaccine have not been considered safe to use in a mass vaccination programme. People with AIDS die because they are unable to produce an immune response to pathogens. Explain why this leads to death. (3)

Susceptible to other pathogens from environment; Pathogens cause diease in host; And damage cells

Influenza viruses and some other pathogens have many different strains. Why will we develop the symptoms of influenza even if we have already been infected by the virus? (4)

The antigens on the pathogen are constantly changing; so subsequent infections are likely to be caused by different varieties of the pathogen; Their antigens will not be complementary to the antibodies on the memory cells formed during previous infections and will not be recognised; With no appropriate memory cells to stimulate antibody production, the only means of overcoming the infection is by the primary response and the immune response is much slower

Why is it difficult to control tuberculosis by vaccination? (2)

The increase in HIV infection has led to more people with impaired immune system, making them more likely to contract TB; The proportion of elderly people in the population is increasing, and they often have less effective immune systems

After a pathogen gains entry to the body it is often a number of days before the body's immune system begins to control it. Why is this so? (1)

The lymphocytes that will control the pathogen need to build up their numbers and this takes time.

Scientists use this antibody to detect an antigen on the bacterium that causes stomach ulcers. Explain why the antibody will only detect this antigen. (3)

The variable region of the antibody has a specific amino acid sequence; So has a specific tertiary structure of the binding site; Which is complementary to these antigens

Why does vaccination not completely eliminate a disease? (4)

There may be many strains of a particular pathogen and so it is impossible to develop a vaccine that is effective against them all; Vaccination fails to induce immunity in certain individuals, e.g. people with defective immune systems; The pathogen may mutate frequently so that its antigens change suddenly, meaning that vaccines suddenly become ineffective because the new antigens on the pathogen are not recognised by the immune system; Individuals may have objections to vaccination for religious, ethical or medical reasons

State two similarities between T cells and B cells. (2)

They are both types of white blood cell; They both have a role in immunity

(Refer to June 2013 paper) Imatinib is a drug used to treat a type of cancer that affects white blood cells. Scientists investigated the rate of uptake of imatinib by white blood cells. They measured the rate of uptake at 4 ºC and at 37 ºC. Their results are shown in the table. The scientists measured the rate of uptake of imatinib in μg per million cells per hour. Explain the advantage of using this unit of rate in this investigation. (2)

To allow comparison; Because there are different number of cells in samples

Microfold cells take up antigens and transport them to cells of the immune system. Antigens are not able to pass through the cell-surface membranes of other epithelial cells. Suggest two reasons why. (2)

Too large to diffuse through the membrane; The antigens do not have the complementary shape of receptor proteins on the membranes of other epithelial cells

Scientists believe that it may be possible to develop vaccines that make use of microfold cells. Explain how this sort of vaccine would lead to a person developing immunity to a pathogen. (5)

Vaccine contains dead pathogen; Microfold cells take up and present antigen to T cells; T cells activate B cells; B cells produce antibodies; Memory cells are produced so that antibodies are produced faster in secondary response

Vaccines protect people against disease. Explain how. (5)

Vaccines contain antigens; Of dead pathogens; When injected with these memory cells are made; On second exposure memory cells produce antibodies; Antibodies destroy pathogens

Suggest one reason why vaccinating a large number of people would reduce significantly the spread of HPV through the population. (2)

Virus is not carried in vaccinated people; Non-vaccinated people more likely to contact vaccinated people