The immune system

* The three photomicrographs, D, E and F, show three different types of muscle tissue.

State which photomicrograph shows cardiac muscle, which shows involuntary (smooth) muscle and which shows skeletal muscle.

Describe the evidence that supports your identification of each type of muscle tissue.

Extra answer space if required.

The table lists events that occur during muscle contraction. Each event is represented by a letter.

Give the sequence of letters that shows the correct order of events during muscle contraction.

The first letter has been done for you.

Myasthenia gravis (MG) is a disease that causes muscle weakness.

In MG, antibodies bind to acetylcholine receptors in neuromuscular junctions which prevents acetylcholine from binding to the receptors.

The diagram shows this process.

Acetylcholine

State the name given to diseases such as MG.

Explain how the binding of antibodies to acetylcholine receptors in the neuromuscular junction reduces the rate at which Ca²⁺ ions bind to troponin.

Pathogens are transmitted to animals and plants by a variety of methods.

A group of scientists collected and analysed data about climate change and the number of cases of diseases transmitted by animal vectors.

The scientists wanted to know whether the number of cases of each disease had increased as a result of climate change.

They found that the number of cases had increased for 103 different animal vector‑transmitted diseases.

The scientists concluded that climate change has increased the transmission of pathogens by animal vectors.

Suggest one additional piece of information that is needed to assess the validity of the scientists’ conclusion.

Suggest why climate change might result in more cases of diseases caused by animal vector‑transmitted pathogens.

Neutrophils are white blood cells that contribute to the immune response against infection.

Neutrophils produce oxidative bursts as part of their response to infection.

An oxidative burst is the rapid production of highly reactive particles, including hydrogen peroxide (H₂O₂), inside the cell.

State the location of the stem cells that differentiate into neutrophils.

The graph shows the change in hydrogen peroxide concentration in a neutrophil during an oxidative burst.

Use the graph to calculate the initial rate of increase of H₂O₂ concentration in the neutrophil during an oxidative burst.

Suggest how an oxidative burst helps neutrophils to perform their function.

Antibodies can bind to receptors on the cell surface membrane of a neutrophil.

The binding of an antibody to a receptor causes the neutrophil to engulf the pathogen that is bound to the antibody.

State the name given to antibodies that act in this way.

Plants lack immune cells, but they have other defences against pathogenic infection.

The sentences describe one form of plant defence against pathogens.

Complete the sentences using the most appropriate word or phrase.

When a pathogen is detected in plant tissue, a plant increases the production of a

polysaccharide called........ This polysaccharide is deposited

in channels called........, which pass through cell walls. This

deposition stops the pathogen moving between cells. The polysaccharide is also

deposited in the small gaps between sieve tube elements. These gaps are known as

........ This deposition stops the pathogen moving between

different regions of the plant.

Type 1 diabetes mellitus is characterised by a lack of insulin production. Type 2 diabetes mellitus can involve reduced production of insulin and a decreased response to insulin.

* Scientists analysed the occurrence of diabetes in identical and non-identical twins.

Identical twins have the same DNA. Non-identical twins share approximately 50% of each other’s DNA.

The scientists selected 614 pairs of twins in which at least one of the individuals had diabetes: 109 pairs had type 1 diabetes; 505 pairs had type 2 diabetes.

The scientists calculated the percentage probability of an individual having diabetes when their twin has the disease.

The table shows the percentage probability of both individuals in a pair of twins developing either type 1 or type 2 diabetes.

Explain what conclusions can be drawn from the data in the table about the influence of the environment and genetics on the probability of developing diabetes.

Extra answer space if required.

Insulin is secreted from cells in the pancreas.

This is a photomicrograph of pancreatic tissue.

Identify the structures labelled A, B and C.

The graph shows the changes in the rate of insulin secretion in a person with type 2 diabetes after consuming glucose.

The table shows the changes in the rate of insulin secretion in a person with normal glucose tolerance after consuming glucose.

Plot the data from the table on the graph and draw a line of best fit.

The table lists statements about a molecule of insulin.

Complete the table by stating the level of protein structure (primary, secondary, tertiary or quaternary) to which the statement relates.

Bacteria can be genetically modified to produce insulin.

State how a plasmid containing the gene coding for insulin can be transferred into a bacterial cell.

Suggest how bacterial cells can be screened to check if they have taken up a recombinant plasmid.

In the future, type 1 diabetes could be treated by giving patients new pancreatic -cells that have been produced in a laboratory from stem cells.

State a feature of stem cells that allows them to be used to produce pancreatic -cells.

Future treatments for type 1 diabetes may be able to use stem cells from a patient’s body to produce new -cells.

Explain why patients receiving these new -cells would still need to be given immunosuppressant drugs.

The heart can be affected by a variety of disorders, some of which involve the immune system.

Fig. 1.1 shows the roles of three different types of antibody, labelled R, S and T.

R S

Harmful molecules released by pathogens Fig. 1.1

State the names of the three different types of antibody shown in Fig. 1.1.

A condition called rheumatic heart disease can occur when a person’s antibodies attack antigens on their own heart cells.

State the name of the type of disease represented by rheumatic heart disease.

Fig. 1.2 shows two electrocardiogram (ECG) traces:

• an ECG of normal heart activity

• an ECG of a person with a type of heart disease

Fig. 1.2

Describe how the ECG trace of the heart with heart disease is different from the ECG trace of a normal heart.

Gene therapy is a possible future treatment for heart disease.

The AC6 gene codes for one form of the enzyme adenylyl cyclase.

Clinical trials have tested the effect of increasing levels of the AC6 gene in heart cells.

Suggest how using gene therapy to increase levels of the AC6 gene in heart cells may improve heart function.

State one method for inserting the AC6 gene into the heart cells during gene therapy.

The results from gene therapy trials are published in peer-reviewed journals.

State why the results from gene therapy trials are published in journals.

Bread contains a mixture of polypeptides known as gluten.

Gluten consists of two types of polypeptide: gliadins and glutenins.

The table below contains statements about the structures of gluten polypeptides.

In the boxes next to each statement, write the level of protein structure (primary, secondary, tertiary, or quaternary) to which the statement refers.

Coeliac disease is caused by an immune reaction to gliadins in a person’s digestive system. The immune system produces antibodies that bind to part of the gliadin polypeptides, which causes inflammation.

Some people who stop eating foods that contain gluten still occasionally experience the symptoms of coeliac disease.

What can you conclude about:

• the structure of the antibody that causes coeliac disease; and

• what the antibody binds to when producing the symptoms of coeliac disease?

Gluten helps to trap carbon dioxide within bread dough. This enables bread to rise when it is baked.

The carbon dioxide is produced by baker’s yeast, Saccharomyces cerevisiae. This species of yeast is able to convert ethanol to acetyl CoA at low glucose concentrations.

Fig. 2 shows the oxygen consumption and carbon dioxide production of a population of S. cerevisiae grown in batch culture. The population was provided with glucose as their only initial source of carbon.

Fig. 2

Suggest and explain what conclusions can be drawn from Fig. 2 about the factors that affected the rate and type of respiration carried out by S. cerevisiae in this batch culture.

Describe two practical considerations to ensure the S. cerevisiae population grows successfully when the initial culture is established.

A group of students were designing an experiment to investigate the effect of temperature on the respiration rate of S. cerevisiae.

Their planned method included the following:

• S. cerevisiae yeast suspension will be divided into six equal volumes to form the experimental groups.

• Six temperatures will be tested: 15 °C, 20 °C, 25 °C, 30 °C, 35 °C and 40 °C.

• Beakers of S. cerevisiae will be placed in water baths to control the temperature.

• Respiration rate will be measured by using a pH probe to monitor changes in the pH of the suspensions.

• The experiment will be repeated four times.

Evaluate whether the students’ method is likely to produce valid results.

The students used a Student’s t-test to compare the results at 30 °C and 35 °C.

They calculated a t value of 2.200.

The critical value for p = 0.05 is 2.306.

Assuming their final method was valid, what can the students conclude from the result of the t-test?

Multiple sclerosis (MS) is an autoimmune disease that damages the nervous system.

Suggest how the immune system causes damage to the nervous system.

Fig. 5 on the insert shows three neurones of different sizes from a person with MS.

One of the neurones has been affected by MS.

MS causes changes to neurones, which reduce the speed at which nervous impulses are conducted.

Using information from Fig. 5, what can you conclude about how MS causes a reduction in the speed of nervous impulses?

Guillain–Barré syndrome is another autoimmune condition in which neurones are damaged and the rate of nervous impulses is reduced.

MS affects the central nervous system.

Guillain–Barré syndrome affects the peripheral nervous system.

Suggest two symptoms of MS that might not be present in people with Guillain–Barré syndrome.

Explain your answers.

Multiple sclerosis and Guillain–Barré syndrome both cause muscle weakness and loss of muscle function.

Suggest and describe how the function of neuromuscular junctions will be affected by multiple sclerosis and Guillain–Barré syndrome.