Pathogens

Biologists classify organisms into different groups. Two of these groups are bacteria and fungi.

Complete the passage about bacteria by writing a suitable word or words in each blank space.

Bacteria are small_........ celled organisms. They have a cell membrane and a cell_........ , made of peptidoglycan. Some bacteria are able to use the energy from the Sun to carry out _........ but other bacteria are_........ and feed on dead and decaying organisms. Bacterial cells do not have a nucleus but most of their genetic material is contained in a circular_........ of DNA. They also have small circles of DNA called_........ in their cytoplasm. Some bacteria are used by humans in food production. An example is using

Other bacteria, such as Pneumococcus, cause disease and so are called

A microscopic single-celled fungus, yeast, is used in the production of bread. Describe how yeast is used to produce bread.

1 (a) All living organisms share characteristics.

State two characteristics that all living organisms share.

Some organisms are pathogens. Which of these organisms can cause a bacterial disease in humans?

Viruses are pathogens but not living organisms.

Describe the effect of a named virus that infects plants.

Give three differences between the structure of viruses and bacteria.

Tobacco mosaic virus infects plant cells.

The photograph shows some of the virus particles.

(Source: © DR. JOHN FINCH/SCIENCE PHOTO LIBRARY)

Tobacco mosaic virus particles consist of a molecule of RNA surrounded by a coat.

Which substance is the coat made from?

The virus particle labelled P has an actual length of 0.3 μ m.

Calculate the magnification of this virus particle.

[1 mm = 1000 μ m]

magnification = ×_........

The photograph shows the leaves of a plant infected by tobacco mosaic virus.

Plants cells infected with the virus stop making chloroplasts.

Explain why plants that are infected with the virus grow more slowly than uninfected plants.

Rabies is a dangerous disease caused by a virus.

The rabies virus is a pathogen.

Which other groups of microorganisms include pathogens?

Rabies is transmitted to humans when they are bitten by an infected animal. Domestic dogs are dogs kept by people as pets or as working animals. Dogs and some wild animals are known to transfer rabies to humans.

In the 1940s, a rabies vaccine for animals was introduced in the United States and most domestic dogs were vaccinated.

The graph shows the number of cases of human rabies and domestic dog rabies in the United States from 1938 to 2018.

Number of domestic
Number of dog cases
human cases

The immune system of dogs works in a similar way to the immune system of humans.

Explain how the rabies vaccine prevents dogs from developing rabies.

Discuss the effects of the use of the rabies vaccine to immunise domestic dogs on the number of cases of rabies in humans.

Use information from the graph to support your answer.

A new RNA vaccine is being developed to treat rabies.

RNA that codes for parts of the rabies virus protein coat are injected into the body. Cells then take up the RNA and produce the viral proteins.

Describe how the cells use the RNA to produce the viral proteins.

Measles is a disease caused by a virus. The graph shows the number of cases of measles each year and the percentage of five year‑olds vaccinated between 1950 and 2016 in the United Kingdom.

percentage of five year-olds vaccinated

Determine the difference in the percentage change in the number of cases of measles between 1950 and 1965 and the percentage change in the number of cases of measles between 1968 and 1983.

Explain the relationship between the number of cases of measles and the percentage of five year‑olds vaccinated.

Use information from the graph in your answer.

Some children are receiving treatments that reduce the activity of their immune system.

Explain why vaccinations are not used on these children.

Yeast cells can be genetically modified to produce the proteins found on the outside of viruses.

Yeast is a single‑celled organism.

A yeast cell has a nucleus, and the cell wall is made of chitin.

Which group of organisms does yeast belong to?

Give a reason why viruses are not considered to be living organisms.

A species of yeast is genetically modified to produce a protein found on the outside of a hepatitis B virus.

This protein is used to make vaccines to prevent people being infected with hepatitis B.

The gene for this protein is inserted into a plasmid.

This plasmid is then used to modify the yeast cells.

Give the roles of two named enzymes used to produce plasmids containing the gene for the hepatitis B protein.

The diagram shows an industrial fermenter that can be used to grow large quantities of genetically modified yeast.

cooling water in air filter

Explain the function of the temperature monitor and cooling jacket.

Explain why air is needed in the fermenter.

Explain why the air is filtered before going into the fermenter.

Food items can often be spoiled if saprotrophic microorganisms such as mould fungi grow on them.

Describe how a saprotrophic fungus such as mould obtains its food.

A student uses this method to investigate ways of preventing peas from being spoiled.

• place three peas in each of three test tubes as shown in the diagram

• cover the peas in test tube A with water and keep at 37C

• cover the peas in test tube B with water and keep at 4C

• cover the peas in test tube C with vinegar, which is a weak acid,

• leave the peas for 24 hours

37C	4C	37C
A	B	C

The student observes the level of cloudiness of the solution to determine how spoiled the peas have become. The level of cloudiness can be used as a measure of fungal growth. The table shows the student’s results.

Suggest a problem with using the level of cloudiness of the solution to determine how spoiled the peas have become.

Explain the appearance of the peas in water at 4 °C.

Explain the appearance of the peas in vinegar at 37 °C.

Sickle cell anaemia is a condition in which some of the person’s red blood cells develop abnormally.

The diagram shows red blood cells from a healthy person and red blood cells from a person with sickle cell anaemia.

cells from a healthy person
cells from a person with sickle cell anaemia

(Source: © solar22/Shutterstock)

A person with sickle cell anaemia often suffers pain as some of their blood vessels become blocked by the sickle cells.

Suggest why the person’s blood vessels may become blocked.

People with sickle cell anaemia have symptoms of tiredness and joint pain that get worse if they are exposed to cold temperatures and high altitudes.

Suggest why these symptoms get worse.

Sickle cell anaemia is caused by a single recessive allele.

State what is meant by the term recessive.

A man and a woman who are both heterozygous for the sickle cell allele have a child.

Calculate the probability that the child will be female and not have sickle cell anaemia.

Sickle cell anaemia is more common in countries where malaria is found. This is because having an allele for sickle cell anaemia can reduce the likelihood of developing malaria.

Which type of organism causes malaria?

What is the name of the pigment found in red blood cells?

Give two differences in structure between red blood cells and white blood cells.

Human populations are at risk from infectious disease.

Describe the different types of pathogen. Refer to a disease that each type of pathogen causes in your answer.

Explain how vaccination protects humans from pathogens.

Organisms can be classified into groups based on their features.

State three differences between eukaryotic and prokaryotic organisms.

Give an example of a disease caused by a protoctist.

name of protoctist_........