Diseases and Immunity: Biology 0610 (Cambridge O Level / IGCSE)

A gardener is tidying a flower bed using a pair of secateurs (pruning shears). Earlier that day, a neighbour used the same secateurs to trim a rose bush, without realising that a small, infected cut on his hand had left bacteria on the blades. The gardener does not clean the secateurs before using them, and a few days later she develops a similar bacterial skin infection at a small cut on her own hand.

Which statement correctly classifies how the bacterium was transmitted to the gardener, and gives the correct reason?

St. Aldric's boarding school has a single drinking-water dispenser in one of its dormitories. During one term, staff failed to clean the dispenser's tap for several weeks, and a thin film of grime built up around the spout. In the same week, twenty-three students who drank from this dispenser developed vomiting and diarrhoea. Students in other dormitories, who used a separate, regularly-cleaned dispenser, remained healthy. Laboratory tests showed that all of the ill students were infected with the same species of bacterium.

(a) State what is meant by: (i) a pathogen (ii) a transmissible disease. [2]

(b) State whether the bacterium was transmitted to the students directly or indirectly, and explain your answer using information from the scenario. [2]

(c) Once swallowed in the contaminated water, the bacteria still had to overcome some of the body's defences before they could cause illness in a student. State two of the body's defences against pathogens that these bacteria would have had to overcome, and explain how each defence normally protects the body. [4]

A university health clinic is trialling a new nasal-spray vaccine against one particular strain of influenza (flu) virus, called strain P. Volunteers are given the nasal spray, which contains a weakened form of strain P.

Several months later, some of the vaccinated volunteers are exposed to strain P and do not become ill. However, other volunteers are separately exposed to a different strain of flu virus, strain Q, whose antigens have a different shape from those of strain P. Several of these volunteers do become ill with strain Q, even though they were vaccinated against strain P.

(a) Explain what is meant by active immunity, referring to the nasal-spray vaccine in your answer. [2]

(b) Explain, in terms of antigens and antibodies, why volunteers who were protected against strain P were not protected against strain Q. [3]

(c) Outline the sequence of events that occurs inside a volunteer's body, from the moment the nasal-spray vaccine is given, that leads to long-term protection against strain P. [4]

A foal (baby horse) is born prematurely and fails to suckle enough of its mother's first milk (colostrum) in the hours after birth. Because of this, a veterinarian injects the foal with a solution containing ready-made antibodies against tetanus, extracted from the blood of another, already-immune horse.

Which statement correctly describes the type of immunity the foal gains from this injection, and whether memory cells are produced as a result?

A remote island community experiences an outbreak of whooping cough, a bacterial disease of the airways. Public health workers begin a mass vaccination programme for all children over two months old. Babies younger than two months are too young to be vaccinated, so health workers instead encourage mothers to breastfeed their babies, since the mothers themselves were vaccinated against whooping cough years earlier.

(a) State what is meant by: (i) active immunity (ii) passive immunity. [2]

(b) Explain how the vaccination programme is expected to give the older children long-term protection against whooping cough, referring to memory cells in your answer. [3]

(c) Explain how breastfeeding can give an unvaccinated young baby short-term protection against whooping cough, and state one way this protection differs from the protection gained by the vaccinated children. [3]

(d) Suggest why vaccinating a large proportion of the island's population, rather than only the children at greatest risk, helps to control the spread of whooping cough for the whole community, including people who cannot be vaccinated. [2]

A dust storm blows across a farm. James, a farm worker, spends the afternoon outdoors, breathing in air that is thick with dust, some of which carries fungal spores that could cause a lung infection if they reach his airways.

Which statement correctly describes how James's nose and airways help to protect him from these spores?

A village has no sewage treatment system. Untreated waste from village toilets flows directly into the river, and this same river is also used by villagers as a source of drinking water and for washing food before it is cooked. Many villagers also prepare and sell food from open stalls beside the river, without any handwashing facilities nearby. Over one month, a large number of villagers become ill with a disease that causes vomiting and diarrhoea.

(a) Explain why allowing untreated sewage to enter the river that is also used for drinking water increases the risk of this disease spreading through the village. [2]

(b) State three measures, other than sewage treatment, that could be introduced in the village to help control the spread of this disease, and for each one explain how it helps to reduce transmission. [6]

Priya gets a splinter of wood stuck under the skin of her finger while gardening. She removes the splinter, but does not clean the small wound. Bacteria on the splinter had already entered the wound. Two days later, the area around the wound is red, swollen and slightly painful, and a small amount of thick, yellowish-white fluid (pus) has collected at the site.

(a) State the name of the process by which white blood cells engulf and destroy pathogens such as the bacteria in Priya's wound. [1]

(b) Describe how Priya's white blood cells respond to the bacteria that entered through the wound in her finger. [3]

(c) Suggest what the pus that has collected at the wound site is made of. [2]

Ranjit receives his first vaccination against tetanus at age 5. His body responds by producing antibodies against the tetanus antigen; the level of these antibodies in his blood rises over the following weeks, then gradually falls over the following months and years. At age 15, Ranjit receives a booster vaccination containing the same tetanus antigen. This time, the level of antibodies in his blood rises much faster and reaches a much higher peak than it did after the first vaccination, and Ranjit does not become ill at any point.

(a) Explain, in terms of what happens inside Ranjit's body over time, why the level of antibodies after the first vaccination at age 5 does not stay high indefinitely. [2]

(b) Explain, in terms of memory cells, why the antibody response to the booster vaccination at age 15 is faster and reaches a higher level than the response to the first vaccination at age 5. [3]

(c) Explain why the protection Ranjit gains from the booster vaccination is described as active immunity, even though he received it by injection from a doctor rather than through natural infection. [2]

In a region near a large area of stagnant water, many villagers become ill with malaria, a disease caused by a single-celled organism that lives inside red blood cells. Investigators find that villagers who sleep under mosquito nets are far less likely to become ill than those who do not, even though none of the villagers who fell ill had any direct contact with each other.

Which statement correctly identifies the type of pathogen that causes malaria, and correctly explains how it is transmitted between villagers?