4.1.1 communicable diseases

Evaluate the use of antibody–drug conjugates (ADCs) as a treatment for cancer compared with traditional chemotherapy, which kills all rapidly dividing cells. (4 marks)

Supporting points:

• ADCs are specific to cancer cells / bind to tumour antigens SO drugs are targeted to tumour/cancer cells

• Treatment is targeted SO less damage to healthy/non-cancerous cells / fewer side effects

• Treatment is targeted SO smaller dose required

Opposing points (award a maximum of 3):

• Cancer cells may develop resistance OR P-glycoprotein may reduce effectiveness of ADCs

• Not all tumour cells may express the target antigen / expression of antigen may vary SO some cancer cells may not be affected

• ADCs might still cause side effects if the antigen is present on some normal cells / if the drug is released before reaching the tumour cell

• Monoclonal antibodies may be recognised as foreign and trigger an immune response

• Producing monoclonal antibodies and linking them to a cytotoxic drug is complex/expensive SO limiting treatment availability

State why it is important to have T lymphocytes with different specific receptors. (2 marks)

• each is specific/ complementary to a different antigen

• the immune system is able to recognise/ respond to many different pathogens/ toxins

Describe what happens to a T lymphocyte when it comes into contact with the right pathogen. (2 marks)

• the lymphocyte receptor binds/attaches to the complementary antigen

• the T-lymphocyte is activated

Explain what is happening to the T cell numbers in Figure 1.2 during the early days after the start of an infection (1 mark)

• clonal expansion/mitosis/cloning themselves

Explain the relationship between T cell numbers and pathogen numbers in Figure 1.2 during the early days after infection. (2 marks)

increasing T cell numbers lead to decreased pathogen numbers because

• increased helper T cell numbers lead to increased production of cytokines/ stimulation of B lymphocytes/ plasma cell production/ antibody production/ activity of phagocytes

• increased killer T cell numbers lead to more destruction of pathogen cells/ toxins secreted into pathogens/ holes punched in the cell membranes of pathogens

The English elm tree, Ulmus procera, was once widespread in Britain. The English elm is much less common now because of a disease known as Dutch elm disease.

• The disease is caused by a fungus that first arrived in Britain in 1967.

• Beetles living under the bark pick up fungal spores while feeding.

• Within a few years approximately 25 million trees were dead.

Suggest two reasons for the rapid spread of the fungus in the elm population. (2 marks)

• mobile vector (insect) moving/ flying from tree to tree

• low genetic diversity/ lack of resistance

• fungal spores carried by the wind

• climate favouring fungal growth/ spread of vector

• overcrowding of trees/ small distance between trees

The pathogen that causes malaria is called .................... . This organism belongs to the kingdom .................... . The pathogens that cause malaria and Dutch elm disease are both in the domain .................... . (3 marks)

• plasmodium

• protista/ protoctista

• eukaryota/ eukarya

Plague is caused by the bacterium, Yersinia pestis.

The bacterium is a rod-shaped cell that is approximately 3 μm long. Yersinia pestis is viewed using a light microscope with a magnification of 1250.

Photographs taken of the image obtained by the light microscope could be further enlarged using a projector. Why might the enlarged image be unable to tell us more about the structure of Yersinia pestis? (1 mark)

with light microscope no further resolution at x1250

Outbreaks of plague still occur occasionally. Plague is transmitted by several methods including droplet infection, close contact between people and fleas moving between infected rats and people. Suggest two ways to minimise the spread of an outbreak of plague. (2 marks)

• stay/ keep indoors/ wear masks

• measure to not attract/ kill rats/ fleas

• strict/ immediate quarantine for persons with symptoms

Suggest why it is important to use clones in an investigation such as this. (2 marks)

• reduced/ no genetic variation

• control more variables

• increases validity

State how a clone of potatoes could be produced for this investigation and explain why it is important to carry out this procedure under aseptic conditions. (2 marks)

procedure: tissue culture/ micropropagation

asepsis important because: reduces microorganisms/ contamination

The sweet potato is a plant that is a staple food in countries such as China. The sweet potato is susceptible to a group of viruses known as potyviruses.

It is difficult for the virus to enter the sweet potato cell. Suggest a barrier that makes it difficult for potyviruses to enter the sweet potato cell. (1 mark)

cellulose cell wall

The sweet potato is a plant that is a staple food in countries such as China. The sweet potato is susceptible to a group of viruses known as potyviruses.

Suggest how the potyviruses enter the sweet potato cell (1 mark)

damage/ wound OR carried by insects/ vectors

Some pathogens are carried between host organisms by animals, which are often insects. These animals suffer no symptoms of the disease and are known as ..................................... . Other pathogens, such as P. infestans that causes potato blight, produce reproductive structures called .................................... , which can be carried on air currents to infect other hosts. (2 marks)

• vectors

• spores

Plants produce callose in response to pathogenic infection, injury and changes in environmental temperature. Scientists wanted to investigate the effect of temperature on callose production. Outline a valid plan that could be used to investigate the effect of temperature on callose production in plants. You should include a suggestion for how callose production could be observed. (6 marks)

general experimental details

• a suitable range of temperatures (e.g. 0, 10, 20, 30, 40° C)

• a suitable sample size or the idea of repeats (e.g. 50 plants)

• idea of a baseline measure of callose levels before the experiment

control variables

• same species / size / genetics of plant (e.g. using cloned plants)

• light intensity and duration (e.g. 12 hours of light and 12 hours of dark)

• pH / nutrients / water regime (e.g. using the same soil and water supply)

• maintaining aseptic conditions and monitoring infections (and removing infected plants from the experiment)

callose observation

• use a microscope

• take tissue samples

• standardise the size and location of tissue samples

• take samples from different sites

• use of stain (e.g. aniline blue) • immunofluorescence

When their bark is damaged, trees in the genus Boswellia release the aromatic resin frankincense which soon hardens to cover the wound.

Suggest two ways in which frankincense contributes to defending the tree from pathogens. (2 marks)

• prevents pathogens entering wound

• aromatic compound is antibacterial

Frankincense is collected by cutting the bark of a tree and allowing the resin released to harden. It can be used to relieve the pain of rheumatoid arthritis. Frankincense works by blocking receptors for molecules called leukotrienes which cause inflammation. Leukotrienes are released by cells from the immune system.

Trees that are overused for harvesting frankincense do not live long and are becoming increasingly rare. Explain how traditional remedies, such as the use of frankincense, provide a strong argument for conservation of biodiversity. (2 marks)

• many plants/ microorganisms produce molecules that may have medical benefits OR many modern medicines have been developed from traditional remedies

• many such plants/ molecules yet to be discovered

The potato plant, Solanum tuberosum, is a staple food plant in many parts of the world. Potatoes are susceptible to infection by a pathogen called Phytophthora infestans, which causes a disease known as potato late blight. The most visible sign of the disease is a brown discolouration of the leaves. Some varieties of potato are resistant to infection by P. infestans. State two ways in which an individual S. tuberosum plant could respond to infection by P. infestans. (2 marks)

• production of callose

• release/ production of named chemical

• leaf drop/ abscission

• necrosis

The sweet potato is a plant that is a staple food in countries such as China. The sweet potato is susceptible to a group of viruses known as potyviruses. Sweet potato cells have a mechanism that recognises and destroys incorrectly formed mRNA or nonfunctional mRNA.

The nucleic acid in potyviruses is RNA. Suggest why this mechanism in sweet potato cells is able to counteract infection by a potyvirus. (2 marks)

• virus/ foreign RNA recognised as incorrect

• virus/ foreign RNA/ genome cut/ destroyed

• virus replication/ reproduction stopped

Sjogren’s syndrome is a rare condition that can reduce the production of mucus. Suggest how the upper respiratory tract of a person with Sjogren’s syndrome might be affected. (1 mark)

more infections/ irritation/ coughing

A cytoskeleton is present in all eukaryotic cells. One of its functions is to control the movement of organelles. Epithelial cells in the airways of mammals play an essential role in defences against pathogens. Explain the function of epithelial cells in the airways of mammals in the defence against pathogens and suggest the importance of the cytoskeleton in carrying out this function. (4 marks)

• goblet cells secrete/ release/ produce mucus

• mucus traps pathogens/ microorganisms/ bacteria

• ref. phagocytes/ neutrophils/ macrophages/ lysozyme

• cilia/ ciliated cells sweep/ move mucus

• cytoskeleton/ microtubules move/ makes up the cilia

Explain how the malarial parasite is able to bypass the body's primary defences. (2 marks)

• mosquito mouthparts pierce skin

• pathogen injected directly into blood

What is the role of an opsonin during this process? (1 mark)

opsonin binds to antigen on pathogen and assists binding/ binds to phagocyte

Other than having specific receptors, describe one way in which the structure of the neutrophil is specialised. (1 mark)

• well-developed cytoskeleton

• many lysosomes

• many mitochondria

• lobed nucleus

• Receptors on the cell membrane of a phagocyte recognise antibody molecules known as ............................., which are bound to pathogens and enhance phagocytosis.

• Once engulfed by a phagocyte, a pathogen is contained in a vacuole called a ............................. . Organelles called ............................. produce enzymes that digest the pathogen.

• opsonins

• phagosome

• lysosomes

Which of the two images, A or B, shows a non-specific immune response? Explain your answer. (1 mark)

A because nuclei of white blood cells are lobed (phagocytes)

Phagocytosis involves cytokines and opsonins. State the role of cytokines and opsonins in phagocytosis. (2 marks)

cytokines: attract phagocytes

opsonins: bind to pathogens/ foreign cells/ antigens and increase phagocytosis/ recognition by phagocytes

minimum of one light chain drawn on outside of heavy chain AND label to light (polypeptide) chain/ variable region/ antigen-binding site

Outline the processes that lead to the production of antibodies against an unfamiliar bacterium. (3 marks)

• B cells/ lymphocytes have antigen receptor/ carry antibody on surface specific/ complementary to only one antigen

• selected B cell clones/ divides by mitosis

• forms/ differentiates into plasma/ effector cells

• which secrete antibodies specific/ complementary to antigen

Explain how helper T cells act to speed up antibody production. (2 marks)

• helper T cells stimulated by antigen- presenting cells

• release cytokines/ interleukin

• stimulate B-cell/ mitosis/ clonal expansion

There are a number of different strains of the Clostridium botulinum bacterium. Different strains produce immunologically distinct forms of the toxin. Explain why the toxins produced by the different strains are described as being ‘immunologically distinct’ and how they will be dealt with by the immune system. (6 marks)

relevant points

• toxins produced by each strain will be (slightly) different

• each (botulinum) toxin will have different, 3D shape / amino acid sequence / DNA nucleotide coding sequence

• toxin, acts as / is, antigen

• immune response determined by shape of antigen

• different compounds will have different shapes

immune system

• antigen presenting cells ingest antigen and display antigen on their surfaces

• interaction between APCs and Thelper cells causes production of interleukins

• B cells activated by T-helper cells

• clonal selection and clonal expansion

• B cells differentiate into plasma cells

• plasma cells produce, antibodies / immunoglobulins

• by protein synthesis antibodies bind to and neutralise toxins.

Agammaglobulinemia and Vici syndrome are both genetic diseases. Agammaglobulinemia results in a lack of mature B lymphocytes in a person’s blood.

Suggest and explain one symptom of agammaglobulinemia. (2 marks)

• greater susceptibility to infection/ pathogens

• no/ fewer plasma cells/ effector cells/ antibodies

• antigens

• interleukins

• mitosis

• plasma

• antibodies

The specific immune response involves B and T lymphocytes. There is variation in specific immune responses between individual animals. Variation between immune responses can be influenced by genes and the environment. Using examples, explain how both genes and environment can cause animals to vary in their specific immune responses. (6 marks)

Genes

• inherit genes that code for immune cells / antibodies (from parents) examples: (B/T) lymphocytes, macrophages, etc

• different alleles code for different versions of immune cells/antibodies • ref. to gene segments recombining

• alleles code for many different variable regions

• reference to MHC alleles

• mutation produces new alleles (for antigens / immune cells )

• ref to autoimmune diseases examples: lupus, arthritis, allergies, SCID

Environment

• exposure to different pathogens determines immune response examples: measles, mumps, (produce) memory cells etc.

• vaccinations produce primary immune responses examples:MMR, BCG,HPV, (produce) memory cells etc.

• reference to environmental influence on allergies examples: pollen, hayfever, asthma, etc.

• poor diet can weaken immune system examples: low levels of protein / vitamins, (reducing) antibodies

• reference to epigenetic changes examples: as a result of diet, stress, chemical exposure

• (auto)immune diseases with an environmental component / trigger example: AIDS