Exam questions · Biology
Culturing Microorganisms and Developing Medicines
- 30 exam questions
- 92 marks
- 45 quick checks
Aseptic Technique and Culturing Microorganisms
Just this lesson-
1 State [1 mark]
State what is meant by an aseptic technique.
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Model answer
A method that prevents unwanted microorganisms from contaminating the culture.
Mark scheme
- Preventing contamination by unwanted microorganisms — 1 mark
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2 Describe [2 marks]
Describe how an autoclave is used to prepare agar and petri dishes for culturing microorganisms.
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Model answer
The agar and glass dishes are heated by steam under pressure, at about 121 °C, for about 15 to 20 minutes, which kills all microorganisms and their spores, so they are sterile.
Mark scheme
- Steam under pressure at about 121 °C — 1 mark
- Kills all microorganisms, so they are sterile — 1 mark
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3 Explain [3 marks]
Explain why an inoculating loop is held in a flame and then cooled before it is used.
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Model answer
The flame kills any microorganisms on the loop, so that only the microorganisms being studied are transferred. It is then cooled because a hot loop would kill the bacteria that it picks up.
Mark scheme
- Flame kills microorganisms on the loop — 1 mark
- So only the wanted microorganisms are transferred — 1 mark
- Cooled so that it does not kill the bacteria picked up — 1 mark
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4 Explain [3 marks]
A student taped the lid on a petri dish with four short pieces of tape and put it in an incubator at 25 °C. Explain why the lid was not sealed completely, and why the temperature was 25 °C.
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Model answer
The lid is not sealed completely so that oxygen can enter, and harmful anaerobic bacteria cannot grow. The temperature is 25 °C because human pathogens grow best at body temperature, so fewer of them will grow at this lower temperature.
Mark scheme
- Oxygen can get in — 1 mark
- Prevents growth of anaerobic pathogens — 1 mark
- 25 °C is too low for most human pathogens — 1 mark
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5 Calculate [3 marks]
A bacterium divides every 30 minutes. Calculate the number of bacteria after 5 hours, starting with one cell, assuming that none die.
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Model answer
5 hours is 300 minutes, so there are 300 ÷ 30 = 10 divisions. The number is 2 to the power 10, which is 1024 bacteria.
Mark scheme
- 10 divisions — 1 mark
- 2 to the power 10 — 1 mark
- 1024 — 1 mark
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6 Evaluate [6 marks]
A technician found that a petri dish she had prepared contained several different colonies, when only one type of bacterium should have been present. Suggest three ways in which the dish could have been contaminated, and say how each could be avoided.
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Model answer
The loop may not have been sterilised, which can be avoided by heating it until red hot before use. The dish may have been left open for too long, so that microorganisms in the air landed on it, which can be avoided by lifting the lid only slightly and for as short a time as possible. The agar or the dish may not have been sterile, which can be avoided by using an autoclave. The neck of the culture bottle may not have been flamed, or the bench and hands may not have been clean, which can be avoided by flaming the neck, and using disinfectant and washing hands.
Mark scheme
- Unsterilised loop — 1 mark
- Flame until red hot — 1 mark
- Lid open too long — 1 mark
- Lift the lid only slightly and briefly — 1 mark
- Non-sterile agar or dish — 1 mark
- Use an autoclave, or flame the bottle neck — 1 mark
Quick check
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1
What does an autoclave use to sterilise equipment?
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C: Steam under pressure
Steam under pressure, at about 121 °C, kills all microorganisms.
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2
Why is an inoculating loop heated in a flame?
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A: To kill microorganisms on it
To kill any microorganisms on it, so only the wanted ones are transferred.
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3
Why is a dish stored upside down?
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D: So that condensation does not drip onto the agar
Condensation then falls on the lid, not on the agar.
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4
Why is the lid of a petri dish not completely sealed?
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B: To let oxygen in
Oxygen must get in, so that anaerobic pathogens do not grow.
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5
At which temperature are school cultures usually incubated?
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A: 25 °C
25 °C or below, which is too cool for most human pathogens.
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6
What is agar?
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C: A jelly used as a growth medium
A jelly, made from seaweed, that forms a solid medium.
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7
What does the word sterile mean?
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D: Free from all living microorganisms
Sterile means free from all living microorganisms.
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8
One bacterium divides every 20 minutes. How many are there after 1 hour?
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B: 8
60 ÷ 20 = 3 divisions, and \(2^3 = 8\).
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9
Why is aseptic technique especially important when culturing bacteria in a school laboratory?
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A: It protects the culture from contamination and the students from pathogens
It stops contamination of the culture, and prevents pathogens being released or breathed in.
Investigating Antiseptics, Antibiotics and Plant Extracts
Just this lesson-
1 State [1 mark]
State what a clear zone around a disc shows.
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Model answer
The substance on the disc stopped bacteria growing, or killed them.
Mark scheme
- Bacteria were killed or did not grow — 1 mark
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2 Explain [2 marks]
A disc soaked in sterile water was included in the investigation. Explain why.
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Model answer
It is a control. If there is no clear zone around it, this shows that the water and the paper disc do not stop the growth of bacteria, so any zones round the other discs are due to the substances being tested.
Mark scheme
- A control for comparison — 1 mark
- Shows the zones are due to the substances tested — 1 mark
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3 Calculate [3 marks]
The clear zone around an antiseptic disc had a diameter of 20 mm. Calculate the cross-sectional area of the zone. Give your answer in mm squared to 3 significant figures.
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Model answer
Radius = 10 mm. Area = π × 10² = 314 mm².
Mark scheme
- Radius of 10 mm — 1 mark
- Use of π r² — 1 mark
- 314 mm squared — 1 mark
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4 Calculate [3 marks]
A student found that substance X gave a zone of diameter 18 mm and substance Y a zone of diameter 9 mm. Calculate how many times larger the area of the zone for X is than that of Y.
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Model answer
Area X = π × 9² = 254 mm². Area Y = π × 4.5² = 63.6 mm². 254 ÷ 63.6 = 4 times larger.
Mark scheme
- Area of X — 1 mark
- Area of Y — 1 mark
- 4 times — 1 mark
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5 Describe [4 marks]
Describe four precautions that should be taken to make this investigation safe.
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Model answer
Use harmless bacteria and not known pathogens. Use aseptic technique, so that other microorganisms are not grown. Tape the lid and do not open the dish after incubation. Wash hands, wipe the bench with disinfectant, and autoclave the dishes before disposal.
Mark scheme
- Harmless bacteria — 1 mark
- Aseptic technique — 1 mark
- Taped lid and not opened — 1 mark
- Hygiene, or autoclave for disposal — 1 mark
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6 Evaluate [6 marks]
A student tested an antibiotic, an antiseptic and a garlic extract on a lawn of bacteria. The areas of the clear zones were antibiotic 452 mm squared, antiseptic 314 mm squared and garlic 78 mm squared, and there was no zone around the control. Evaluate what the results show about the three substances, and suggest how the reliability of the investigation could be improved.
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Model answer
The antibiotic made the biggest zone, which shows that it was the most effective at stopping the bacteria from growing, followed by the antiseptic and then the garlic. The control had no zone, so the zones were caused by the substances. However, a bigger zone does not mean that a substance is safe or better as a medicine, because the antiseptic could harm human cells. The garlic extract works, but is weaker than the others, and it is not known what it contains, or whether it would be safe to take. Only one test was done, so the results might be a chance event. Repeating at least three times and calculating a mean area would make the results more reliable, and using the same concentration for each substance would make the comparison fairer.
Mark scheme
- Antibiotic biggest zone, most effective — 1 mark
- Order of effectiveness — 1 mark
- Control shows the zones are due to the substances — 1 mark
- Limit: antiseptic can harm human cells, or garlic is not known to be safe — 1 mark
- Repeat the investigation and find a mean — 1 mark
- Keep the concentration and the other variables the same — 1 mark
Quick check
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1
What is a zone of inhibition?
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B: A clear area around a disc where bacteria did not grow
It is a clear area where bacteria did not grow.
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2
Why is a sterile water disc used?
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C: As a control
It is a control that shows the zones are due to the substances.
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3
A clear zone has a radius of 5 mm. What is its area, to the nearest whole number?
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D: 79
\(\pi \times 5^2 = 78.5\), which is 79 mm squared.
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4
A clear zone has a diameter of 10 mm. Which calculation gives its area?
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A: \(\pi \times 5^2\)
The radius is 5 mm, so the area is \(\pi \times 5^2\).
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5
If the diameter of a clear zone doubles, what happens to its area?
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C: It becomes four times as large
Area depends on the radius squared, so it is four times as big.
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6
Why are the dishes not opened after incubation?
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B: To stop bacteria being released
The bacteria could be harmful, and would be released.
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7
Which is a control variable in this investigation?
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A: The temperature of incubation
The temperature of incubation must be the same for all of the discs.
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8
Why are antiseptics not used as medicines inside the body?
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D: They can harm human cells
They can damage human cells as well as microorganisms.
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9
A plant extract produces a large zone. Why can it not yet be called a medicine?
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B: It has not yet been tested for safety and effectiveness in humans
It must also be shown to be safe and effective in people, through further testing.
Developing New Medicines
Just this lesson-
1 State [1 mark]
State what is meant by a placebo.
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Model answer
A dummy treatment that does not contain the active drug.
Mark scheme
- A treatment with no active drug — 1 mark
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2 Name [2 marks]
Name the two stages of testing that come after the development stage of a new medicine.
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Model answer
Preclinical testing and clinical testing (clinical trials).
Mark scheme
- Preclinical testing — 1 mark
- Clinical testing — 1 mark
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3 Explain [3 marks]
Explain why a new medicine is tested on cells and animals before it is given to humans.
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Model answer
To check that it is not toxic, and does not cause harm that would put human volunteers at risk. Cells show whether it works, and animals show effects on a whole body, such as side effects and how it is absorbed.
Mark scheme
- Check for toxicity or harm before using humans — 1 mark
- Cells show whether it works — 1 mark
- Animals show whole-body effects — 1 mark
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4 Explain [3 marks]
Explain why clinical trials of a new medicine are double-blind.
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Model answer
Neither the patients nor the doctors know who is receiving the drug and who is receiving the placebo. This stops the patients' expectations, and the doctors' opinions, from affecting the results, so the results are fair and unbiased.
Mark scheme
- Neither the patients nor the doctors know — 1 mark
- Prevents the expectations of patients or the opinions of doctors affecting results — 1 mark
- So the results are unbiased — 1 mark
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5 Calculate [3 marks]
In a trial, 200 patients took a new drug and 160 of them improved. Of 200 patients who took a placebo, 60 improved. Calculate the percentage who improved in each group, and the difference between them.
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Model answer
Drug group: 160 ÷ 200 × 100 = 80%. Placebo group: 60 ÷ 200 × 100 = 30%. The difference is 50 percentage points.
Mark scheme
- 80% — 1 mark
- 30% — 1 mark
- 50 percentage points — 1 mark
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6 Evaluate [6 marks]
Some people think that it is wrong to test medicines on animals. Evaluate the use of animals in the testing of new medicines.
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Model answer
Testing on animals can show how a medicine affects a whole living body, including side effects that cells in a dish would not show, so it protects human volunteers from harm. The thalidomide disaster showed what can happen when testing is not thorough. However, animals can suffer pain and distress, and many people think it is wrong to cause this for human benefit. Animals are not the same as humans, so a medicine that is safe in an animal may still be harmful to a person, and the reverse. Scientists therefore use cells, tissues and computer models where possible, and tests on animals are strictly controlled. On balance, until there are alternatives that give the same information, limited and well-regulated testing is justified, to protect people.
Mark scheme
- Shows whole-body effects and side effects — 1 mark
- Protects human volunteers, or example of thalidomide — 1 mark
- Animals suffer — 1 mark
- Animals are different to humans, so results may not apply — 1 mark
- Alternatives such as cells and computer models — 1 mark
- A reasoned conclusion — 1 mark
Quick check
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1
Which is the correct order of the stages of developing a medicine?
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B: Discovery, development, preclinical testing, clinical testing
Discovery, then development, then preclinical testing, then clinical testing.
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2
What is preclinical testing?
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C: Testing on cells, tissues and animals
It is testing in the laboratory, on cells, tissues and animals, before people.
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3
What is a placebo?
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A: A treatment with no active drug
A dummy treatment with no active drug.
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4
Why are clinical trials double-blind?
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D: To stop bias in the results
Neither patients nor doctors know who has the drug, so the results are not biased.
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5
Who takes part in a phase 1 trial?
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B: A few healthy volunteers
A few healthy volunteers, to test for safety.
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6
What is the main aim of a phase 3 trial?
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C: To compare its effectiveness in a large group of patients
To find out whether it works better than a placebo or existing treatment in many patients.
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7
In a trial, 40 out of 80 patients improved on a drug. What percentage is this?
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A: 50%
\(40 \div 80 \times 100 = 50\%\).
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8
Why are new antibiotics needed?
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D: Bacteria become resistant to existing antibiotics
Bacteria evolve resistance, so older antibiotics stop working.
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9
In a trial, a group on a placebo showed a 30% improvement. What does this show?
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B: Some patients improve because they expect to, so the placebo group is needed
It is the placebo effect, which is why the drug group must be compared with a placebo group.
Making Monoclonal Antibodies
Just this lesson-
1 State [1 mark]
State what is meant by a monoclonal antibody.
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Model answer
An antibody produced by a clone of identical cells, all of which fit the same antigen.
Mark scheme
- Identical antibodies from a clone of cells — 1 mark
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2 State [2 marks]
Name the two types of cell that are joined together to make a hybridoma cell, and state one useful property that each gives to the hybridoma cell.
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Model answer
A lymphocyte, which makes the desired antibody, and a tumour cell, which divides quickly.
Mark scheme
- Lymphocyte, makes the antibody — 1 mark
- Tumour cell, divides rapidly — 1 mark
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3 Explain [3 marks]
Explain why a mouse is injected with an antigen when monoclonal antibodies are made.
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Model answer
The antigen stimulates the mouse's lymphocytes to make antibodies that fit it. These lymphocytes can then be collected, and are used to make the hybridoma cells that make this particular antibody.
Mark scheme
- Antigen makes lymphocytes produce antibodies — 1 mark
- The antibodies fit that antigen — 1 mark
- The lymphocytes are collected to make hybridomas — 1 mark
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4 Describe [4 marks]
Describe how monoclonal antibodies are made, from the injection of the mouse to the collection of the antibody.
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Model answer
A mouse is injected with an antigen. The lymphocytes that make the antibody are removed and joined with tumour cells to make hybridoma cells. The hybridoma cells that make the right antibody are selected, and grown in large numbers by cell division, and the antibody is collected and purified.
Mark scheme
- Mouse injected with antigen — 1 mark
- Lymphocytes fused with tumour cells — 1 mark
- Selected hybridomas grown in large numbers — 1 mark
- Antibody collected — 1 mark
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5 Calculate [3 marks]
A hybridoma cell divides once every 12 hours. Calculate the number of cells after 3 days, starting with one cell.
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Model answer
3 days is 72 hours, so there are 72 ÷ 12 = 6 divisions. 2 to the power 6 is 64 cells.
Mark scheme
- 6 divisions — 1 mark
- 2 to the power 6 — 1 mark
- 64 cells — 1 mark
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6 Explain [6 marks]
Explain why neither a lymphocyte nor a tumour cell can be used alone to make large amounts of a monoclonal antibody, and why hybridoma cells can.
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Model answer
A lymphocyte that makes the right antibody can produce it, but it does not divide in a laboratory, so only a very small number of cells, and little antibody, could be obtained. A tumour cell divides rapidly, but does not make the antibody that is needed, so it would produce none. A hybridoma cell is formed by fusing the two. It has the genes from the lymphocyte to make the specific antibody, and the property from the tumour cell of dividing continuously. It can therefore be grown in large numbers, as a clone, and every cell makes the same antibody, so a large supply can be collected.
Mark scheme
- Lymphocyte makes the antibody — 1 mark
- But does not divide — 1 mark
- Tumour cell divides — 1 mark
- But does not make the right antibody — 1 mark
- Hybridoma has both features — 1 mark
- Cloned in large numbers to make identical antibodies — 1 mark
Quick check
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1
What does a hybridoma cell do?
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B: Makes antibodies and divides
It makes the desired antibody and it divides.
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2
Which cell gives a hybridoma the ability to divide?
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C: A tumour cell
Tumour cells divide rapidly and for a long time.
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3
Why is the mouse injected with an antigen?
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A: So that it makes the desired lymphocytes
So that its lymphocytes make antibodies against the antigen.
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4
What does the word monoclonal mean?
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D: Identical antibodies from a clone of cells
The antibodies all come from one clone, so they are identical.
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5
Why can an ordinary lymphocyte not be used to make a large amount of antibody?
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C: It does not divide in a laboratory
It does not divide outside the body.
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6
A hybridoma cell divides once every day. How many cells will there be after 5 days from one cell?
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B: 32
\(2^5 = 32\).
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7
How are hybridoma cells made?
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A: By fusing a lymphocyte with a tumour cell
By fusing a lymphocyte with a tumour cell.
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8
What is done with the antibodies at the end of the process?
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D: They are collected and purified
They are collected and purified.
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9
Why do all of the antibodies from one hybridoma culture have the same shape?
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B: All of the cells are clones with the same genes
The cells are a clone, so they have identical genes, and make identical proteins.
Uses of Monoclonal Antibodies
Just this lesson-
1 State [1 mark]
State the name of the hormone that is detected by a pregnancy test.
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Model answer
hCG, human chorionic gonadotrophin.
Mark scheme
- hCG — 1 mark
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2 Explain [2 marks]
In a pregnancy test, a control line is found next to the test line. Explain why it is needed.
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Model answer
It shows that the test has worked, because it changes colour whether or not hCG is present. Without it, a lack of a test line could be because the test failed.
Mark scheme
- Shows the test has worked whether or not hCG present — 1 mark
- A missing test line could be due to a failed test — 1 mark
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3 Describe [3 marks]
Describe how a pregnancy test uses monoclonal antibodies to show that hCG is in the urine.
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Model answer
The urine moves along the strip and the hCG binds to mobile monoclonal antibodies that have a coloured bead. The hCG and its antibody are then caught by fixed antibodies on the test line, which changes colour.
Mark scheme
- hCG binds mobile antibodies — 1 mark
- Caught by fixed antibodies on the test line — 1 mark
- The line changes colour — 1 mark
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4 Explain [3 marks]
Explain how monoclonal antibodies can be used to find the position of a blood clot.
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Model answer
A monoclonal antibody that fits a protein found in the clot is labelled with a radioactive substance, and is injected into the patient. It binds only to the clot, so the radioactivity is detected by a scanner at that place.
Mark scheme
- Antibody fits a protein in the clot — 1 mark
- Radioactive label — 1 mark
- Detected by a scanner where it binds — 1 mark
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5 Explain [3 marks]
Explain why a monoclonal antibody can be used to deliver a drug to cancer cells and not to healthy cells.
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Model answer
The antibody has a shape that fits an antigen, called a tumour marker, on the surface of the cancer cells, and which is not on healthy cells. So it binds only to the cancer cells, and the drug that it carries is delivered to them.
Mark scheme
- Antibody shape fits an antigen on cancer cells — 1 mark
- Not found on healthy cells — 1 mark
- Drug delivered only to the cancer cells — 1 mark
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6 Evaluate [6 marks]
Evaluate the use of monoclonal antibodies, and of chemotherapy, in the treatment of a cancer.
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Model answer
Chemotherapy drugs travel around the whole body and kill cells that divide rapidly, so they damage healthy cells such as those in hair roots and the gut. This causes side effects such as hair loss, sickness and tiredness. Monoclonal antibodies bind only to cancer cells that have the right tumour marker, so they deliver the drug straight to the tumour, and healthy cells are mostly not harmed. This means fewer side effects, and a smaller dose of the drug can be used. However, monoclonal antibodies are expensive, they can still cause side effects such as fever or allergic reactions, and they only work on cancers that have a suitable antigen. Chemotherapy works for many types of cancer and is cheaper. Monoclonal antibodies are better when a suitable marker exists, but the choice depends on the cancer.
Mark scheme
- Chemotherapy damages healthy cells — 1 mark
- Side effects of chemotherapy — 1 mark
- Antibodies bind only to cancer cells — 1 mark
- Fewer side effects, smaller dose — 1 mark
- Expensive, or side effects, or needs a marker — 1 mark
- A reasoned conclusion — 1 mark
Quick check
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1
What does the control line in a pregnancy test show?
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C: That the test has worked
It shows that the test has worked.
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2
Which two lines show a positive pregnancy test?
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A: Test line and control line
Both the test line and the control line, because hCG is present and the test worked.
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3
What is a tumour marker?
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D: An antigen found on cancer cells
It is an antigen on cancer cells, which is not found on healthy cells.
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4
How do monoclonal antibodies target cancer cells?
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B: Their shape fits a tumour marker
Their shape fits an antigen found on the cancer cells.
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5
Which is a side effect of chemotherapy?
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A: Hair loss
Chemotherapy damages healthy dividing cells, which causes hair loss, sickness and tiredness.
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6
Why is chemotherapy more damaging than a monoclonal antibody treatment?
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C: It reaches healthy cells as well as cancer cells
The drug goes to all rapidly dividing cells, not only to cancer cells.
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7
What does a radioactive label on an antibody allow doctors to do?
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B: See where the antibody is
A scanner shows where the antibody has bound.
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8
Which is a disadvantage of monoclonal antibody treatments?
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D: They are expensive
They are expensive to make.
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9
A pregnancy test shows no lines at all. What should be concluded?
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B: The test has not worked
With no control line, the test has not worked, so it is invalid and should be repeated.