Culturing microorganisms

A student investigated the effect of antibiotics on the growth of bacteria.

The student prepared an agar gel plate.

Figure 5 shows some of the equipment the student used.

Describe a method the student could use to:

• prepare a sterile agar gel plate

• grow an uncontaminated sample of bacteria on the agar gel plate.

Use the equipment in Figure 5 in your answer.

The student used an agar gel plate to test three antibiotics, A, B and C.

Figure 6 shows how the agar gel plate was set up.

The student incubated the agar gel plate at 25 °C.

Why should the temperature not be higher than 25 °C?

What was the purpose of the paper disc soaked in water?

Tick () one box.

The student removed the agar gel plate from the incubator after 48 hours.

Antibiotic A was the most effective at killing the bacteria. Antibiotic C was the least effective at killing the bacteria.

Figure 7 shows the results for the disc soaked in antibiotic B.

Complete Figure 7 to show the results you would expect.

You should:

• draw a ring around the disc soaked in antibiotic A

• draw a ring around the disc soaked in antibiotic C.

The student repeated the investigation with antibiotic D.

The bacteria were resistant to antibiotic D.

What effect would antibiotic D have had on the bacteria?

Tick () one box.

Figure 10 shows a bacterial cell and a yeast cell.

Which statement about bacterial cells and yeast cells is correct?

Tick () one box.

Give two features of a yeast cell that are not found in a bacterial cell.

Use Figure 10.

A scientist investigated the effect of different antibiotics on one type of bacterium.

The scientist:

• used three samples of culture medium

• added a different antibiotic to each sample

• added equal numbers of bacteria to each sample.

Figure 11 shows the results.

Compare the effectiveness of the antibiotics shown in Figure 11.

It was not possible for the scientist to count the total number of bacteria per cm³ of culture medium.

The cells were too close together to be counted accurately.

The scientist took 10 samples from the culture medium. Each sample had a volume of 0.02 cm³.

Describe how the scientist could use the samples to estimate the number of bacteria

Salmonella bacteria cause outbreaks of food poisoning in humans. To prevent food poisoning in humans, farmers vaccinate their animals against Salmonella bacteria.

How do Salmonella bacteria in food cause the symptoms of vomiting and diarrhoea?

During a food poisoning outbreak, scientists identified the farm where the food came from. The farmer had not vaccinated the farm animals against Salmonella bacteria.

The food poisoning outbreak could have been prevented if the farm animals had been vaccinated. Explain how:

• the immune systems of animals respond to a vaccination

• the immune response in farm animals prevents an outbreak of food poisoning in humans.

Most cases of food poisoning do not need to be treated with antibiotics. However, some patients may need to take antibiotics to recover. Scientists investigated the effectiveness of five different antibiotics on the Salmonella bacteria in the outbreak. Antibiotics A, B, C, D and E were used in the investigation. Figure 4 shows the results.

Describe two aseptic techniques the scientists should have used in the investigation.

The scientists incubated the bacteria at 37 °C. Students in school laboratories incubate bacteria at 25 °C. Explain why scientists use 37 °C but students must use 25 °C to incubate bacteria.

What is the purpose of the paper disc with no antibiotic in Figure 4 ?

The scientists concluded that either antibiotic A or antibiotic B should be prescribed to patients with food poisoning. Why should antibiotic A or antibiotic B be prescribed?

The scientists wanted to be more certain about which antibiotic should be prescribed. Describe how the results in Figure 4 could be used to obtain a quantitative comparison of antibiotics A and B.

One year later, there was another outbreak at the farm involving Salmonella bacteria. Antibiotic B did not have an effect. Suggest why antibiotic B no longer had an effect.

Antibiotics treat food poisoning because they kill Salmonella bacteria inside the human body. Some antibiotics work because they damage the bacterial cell wall. The bacteria die because the cells burst. Explain why the cells burst.

Plant cells and fungal cells are similar in structure.

Figure 10 shows a fungal cell.

Name one structure in Figure 10 which is present in both plant cells and fungal cells but not in animal cells.

Which disease is caused by a fungus?

Tick (✓) one box.

A fungal cell divides once every 90 minutes.

How many times would this fungal cell divide in 24 hours?

Some types of fungal cell are grown to produce high-protein food.

The high-protein food can be used to make meat-free burgers.

Where is protein digested in the human digestive system?

Tick (✓) one box.

Which chemical could be used to test if the burgers contain protein?

Tick (✓) one box.

Table 7 shows some information about burgers made from meat and meat-free burgers.

Evaluate the use of burgers made from meat compared with meat-free burgers in providing humans with a healthy, balanced diet.

Use information from Table 7 and your own knowledge.

Plant cells and fungal cells are similar in structure. Figure 2 shows a fungal cell.

Name one structure in Figure 2 which is present in both plant cells and fungal cells but not in animal cells.

Which disease is caused by a fungus? Tick (✓) one box.

A fungal cell divides once every 90 minutes. How many times would this fungal cell divide in 24 hours?

Some types of fungal cell are grown to produce high-protein food.

The high-protein food can be used to make meat-free burgers.

Where is protein digested in the human digestive system? Tick (✓) one box.

Which chemical could be used to test if the burgers contain protein? Tick (✓) one box.

Table 3 shows some information about burgers made from meat and meat-free burgers.

Evaluate the use of burgers made from meat compared with meat-free burgers in providing humans with a healthy, balanced diet. Use information from Table 3 and your own knowledge.

Turn over for next question

A student investigated the effectiveness of three different antibiotics. Figure 16 shows how the student set up an agar plate.

The student used aseptic techniques to make sure that only one type of bacterium was growing on the agar.

Describe two aseptic techniques the student should have used.

The student placed the agar plate in an incubator at 25 °C for 48 hours. Figure 17 shows the agar plate after 48 hours.

Which antibiotic is the least effective? Give a reason for your answer.

Calculate the area where no bacteria were growing for antibiotic C.

Give the unit.

Suggest one way the student could improve the investigation.

A student investigated the effectiveness of three different antibiotics.

Figure 3 shows how the student set up an agar plate.

The student used aseptic techniques to make sure that only one type of bacterium was growing on the agar.

Describe two aseptic techniques the student should have used.

The student placed the agar plate in an incubator at 25 °C for 48 hours.

Figure 4 shows the agar plate after 48 hours.

Which antibiotic is the least effective?

Give a reason for your answer.

Calculate the area where no bacteria were growing for antibiotic C.

Give the unit.

Suggest one way the student could improve the investigation.

A man has the following symptoms:

• yellow discharge from his penis

• pain when urinating.

The man has a bacterial infection.

What is the most likely cause of the man’s symptoms?

Tick (✓) one box.

The man took a full course of antibiotics.

The man’s symptoms did not improve.

Why did the antibiotics not cure the symptoms?

Tick (✓) one box.

Using a condom can stop the bacteria being passed to another person during sexual intercourse.

Suggest a different way the man could avoid passing the bacteria on to someone else.

A scientist investigated the effect of three different antibiotics on three different types of bacteria, A, B and C.

This is the method used.

1. Grow bacteria A on an agar plate.

2. Put three separate paper discs each containing one of the antibiotics (1, 2 and 3) onto the agar plate.

3. Put the agar plate into an incubator for 48 hours.

4. Repeat steps 1–3 for bacteria B and for bacteria C.

Figure 9 shows the scientist’s results.

Compare the effectiveness of the three antibiotics at killing the different types of bacteria.

Milk contains bacteria.

A small volume of raw milk was placed in a counting chamber in a special type of microscope slide.

Figure 10 shows what the counting chamber looked like when viewed using a microscope.

A scientist counted the number of bacteria in four samples of raw milk.

Table 4 shows the results.

Which milk sample is shown in Figure 10 ?

Tick (✓) one box.

Calculate the mean number of bacteria in the four samples in Table 4.

Calculate the mean number of bacteria per mm³ of milk in the samples.

Complete the following steps.

Calculate the total area of the counting chamber in Figure 10.

The depth of the counting chamber is 0.01 mm

Calculate the volume of the counting chamber in Figure 10.

Use the equation: volume = area depth

Calculate the mean number of bacteria per mm³ of milk in the samples.

Use the equation:

Milk is heated to reduce the number of bacteria it contains before it is sold for humans to drink.

Milk with more than 20 000 bacteria per cm³ cannot be sold for humans to drink.

Table 5 shows the number of bacteria per cm³ in four different samples of milk.

Which of the milk samples could not be sold for humans to drink?

Tick (✓) one box.

Why should milk sold for humans to drink not contain large numbers of bacteria?

Eating food containing Salmonella bacteria can cause illness.

Two symptoms of infection by Salmonella are vomiting and diarrhoea.

What causes these symptoms?

Give two ways a person with a mild infection of Salmonella can help prevent the spread of the bacteria to other people.

In very serious infections of Salmonella, a doctor can prescribe drugs to kill the bacteria.

What type of drug can the doctor prescribe to kill the bacteria?

A person with AIDS may take longer than a healthy person to recover from a Salmonella infection.

Explain why.

Salmonella bacteria can be transmitted from chickens to humans. Chickens can be vaccinated to prevent the transmission of Salmonella bacteria to humans.

Suggest one other way farmers could prevent the transmission of Salmonella from chickens to humans.

A restaurant owner employed a scientist to test the effectiveness of two kitchen cleaning liquids.

The scientist took samples from two work surfaces:

before the surfaces had been cleaned with the cleaning liquids

after the surfaces had been cleaned with the cleaning liquids.

The samples were then analysed for the number of bacteria they contained.

The results are shown in Figure 10.

Which cleaning liquid is the more effective?

Give a reason for your answer.

The scientist investigated the effect of cleaning liquid A and cleaning liquid B on Salmonella bacteria grown in a laboratory.

Figure 11 shows the way the investigation was set up.

The Petri dish was placed in an incubator at 25 °C for 48 hours.

After 48 hours, the scientist calculated the area around each paper disc where no bacteria were growing.

The results are shown in Table 4.

What measurement would the scientist need to take to calculate the area where no bacteria were growing?

Give one change to the investigation that would allow the scientist to check if the results are repeatable.

The scientist showed the results to the restaurant owner.

Both cleaning liquids cost the same per dm³.

Suggest one other factor the restaurant owner should consider when choosing which cleaning liquid to use.

Eating food containing Salmonella bacteria can cause illness.

Two symptoms of infection by Salmonella are vomiting and diarrhoea.

What causes these symptoms?

Give two ways a person with a mild infection of Salmonella can help prevent the spread of the bacteria to other people.

In very serious infections of Salmonella, a doctor can prescribe drugs to kill the bacteria.

What type of drug can the doctor prescribe to kill the bacteria?

A person with AIDS may take longer than a healthy person to recover from a Salmonella infection.

Explain why.

Salmonella bacteria can be transmitted from chickens to humans. Chickens can be vaccinated to prevent the transmission of Salmonella bacteria to humans.

Suggest one other way farmers could prevent the transmission of Salmonella from chickens to humans.

A restaurant owner employed a scientist to test the effectiveness of two kitchen cleaning liquids.

The scientist took samples from two work surfaces:

before the surfaces had been cleaned with the cleaning liquids

• after the surfaces had been cleaned with the cleaning liquids.

The samples were then analysed for the number of bacteria they contained.

The results are shown in Figure 1.

Which cleaning liquid is the more effective?

Give a reason for your answer.

The scientist investigated the effect of cleaning liquid A and cleaning liquid B on Salmonella bacteria grown in a laboratory.

Figure 2 shows the way the investigation was set up.

The Petri dish was placed in an incubator at 25 °C for 48 hours.

After 48 hours, the scientist calculated the area around each paper disc where no bacteria were growing.

The results are shown in Table 1.

What measurement would the scientist need to take to calculate the area where no bacteria were growing?

Give one change to the investigation that would allow the scientist to check if the results are repeatable.

The scientist showed the results to the restaurant owner.

Both cleaning liquids cost the same per dm³.

Suggest one other factor the restaurant owner should consider when choosing which cleaning liquid to use.