Virus lifecycle

Figure 9 shows how adding fertiliser to the soil affects the yield of a food crop.

The area of a field is measured in hectares.

A farmer added 100 kg per hectare of fertiliser to a field.

Using Figure 9, calculate the increase in crop yield.

Explain why farmers should not add more than 40 kg per hectare of fertiliser to the soil.

Figure 10 shows part of a virus life cycle.

This virus infects bacterial cells.

Use Figure 10 to describe how new viruses are made.

Plants can be affected by pests such as insects.

Give one way that plant pests can affect the food available for the human population.

Stomach ulcers can be caused by bacteria.

Name the bacteria that cause stomach ulcers.

People with a stomach ulcer are treated with antibiotics and an alkaline medicine to reduce symptoms.

Give a reason why the alkaline medicine is used.

Antibiotics are used to treat stomach ulcers.

Bacteria have become resistant to some antibiotics.

A scientist has an agar plate spread with the bacteria that cause stomach ulcers and discs containing different antibiotics.

Describe how the scientist could use these to determine which antibiotic can kill the bacteria.

*(c) A bacteriophage is a type of virus that can infect bacterial cells.

Figure 12 shows a bacteriophage infecting a bacterial cell.

Scientists are investigating if a bacteriophage could be used as an alternative to antibiotics.

Describe the lytic lifecycle of a virus and suggest why a bacteriophage could be used as an alternative to antibiotics.

Figure 10 shows part of a method used to produce a bacterial culture on a Petri dish.

State why step 1 and step 2 are necessary.

Give one reason why step 3 is included.

*(iii) A student wanted to investigate how effective three different antiseptics were at killing bacteria.

The student was provided with:

• an inoculated Petri dish prepared using the method in Figure 10

• three different antiseptics

• filter paper discs

• sticky tape.

Devise a plan for the student to complete this investigation.

Include a control and any variables that the student would need to consider.

Viruses can cause disease.

Describe how the lytic pathway is involved in the reproduction of viruses.

Between 2013 and 2016 there was an outbreak of a disease called Ebola.

Ebola is estimated to have caused the deaths of more than 11 000 people.

Why is the number of deaths from Ebola only an estimate?

State how Ebola is spread from person to person.

The lytic pathway is part of the lifecycle of the Ebola virus.

After infection of the host cell, components of the virus are produced.

Describe the next stages of the lytic pathway.

The genetic material of a virus can also be inserted into the genome of the host.

Name this type of pathway.

State what is meant by the term genome.

Measles is a disease caused by a virus.

Describe the lytic pathway for a virus.

A measles infection can cause inflammation of the brain.

Figure 11 shows a brain.

Name the part of the brain labelled X.

The death rate from measles is 0.15%.

In 2015, 134 250 people died from measles.

Calculate the number of people infected with measles in 2015.

Give your answer in standard form.

Measles is prevented by immunisation.

State two reasons why people might not be immunised against measles.

The spread of measles is prevented by herd immunity.

Describe herd immunity.

A scientist was planning to compare the effectiveness of the antibiotic myxopyronin on two different species of bacteria.

Figure 18 shows the equipment the scientist can use.

agar plates
two species filter discs of
spreader
incubator of bacteria myxopyronin

Figure 18

Describe how the scientist could determine the effectiveness of myxopyronin on the two species of bacteria.

Myxopyronin inhibits bacterial RNA polymerase.

Explain why the antibiotic myxopyronin can be used to treat bacterial infections in humans.

*(b) Infections can also be caused by viruses.

Describe the lytic pathway of a virus and how this causes the spread of infection through a population.

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