OCR GCSE Biology B (Twenty First Century)
OCR GCSE Biology B B2.4 How can we identify the cause of an infection? Exam Questions
Free OCR GCSE Biology B exam questions for B2.4 How can we identify the cause of an infection?, with a mark scheme for every pack. Covers diagnosing infections, culturing microorganisms, aseptic technique, zones of inhibition, monoclonal antibodies, testing kits and identifying plant diseases.
B2.4 How can we identify the cause of an infection? exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR GCSE Biology B B2.4 How can we identify the cause of an infection?
B2.4 looks at how scientists and doctors find out which pathogen is causing an infection so it can be treated correctly. You need to describe how microorganisms are grown on agar plates using aseptic technique, how antibiotics and antiseptics are tested by measuring clear zones, and how monoclonal antibodies are made and used in diagnostic tests. Plant diseases are identified by symptoms, lab tests and testing kits. This links pathogens in B2.1 with treatment in B2.6. Examiners frequently ask about practical method, safety and calculating the area of a zone of inhibition.
What you need to know
- Culturing microorganisms Bacteria are grown on nutrient agar in Petri dishes. Sterilise equipment, flame the inoculating loop, lift the lid only slightly, tape the lid on and incubate at 25 °C in school to reduce the chance of growing human pathogens.
- Testing antimicrobials Paper discs soaked in different antibiotics or antiseptics are placed on a bacterial lawn. A larger clear zone of inhibition suggests a more effective substance. Area of the zone = πr².
- Bacterial growth Bacteria reproduce by binary fission. Number of bacteria = starting number x 2^n, where n is the number of divisions.
- Monoclonal antibodies Antibodies from one clone of cells are identical and bind only to one antigen. They are made by fusing a lymphocyte with a tumour cell to form a hybridoma that divides and secretes the antibody.
- Diagnostic uses Monoclonal antibodies can detect specific pathogens or hormones (as in pregnancy tests) and can be labelled to locate molecules in the body.
- Identifying plant disease Look for symptoms such as stunted growth, spots, decay, growths or discolouration, compare with reference sources, and use lab tests or kits containing monoclonal antibodies.
Common mistakes in B2.4 How can we identify the cause of an infection?
- Using the diameter instead of the radius in πr². Halve the diameter first.
- Writing that plates are incubated at 37 °C in schools. Incubate at 25 °C to avoid growing human pathogens.
- Saying the lid is taped all the way round to stop air getting in. Tape it partly so oxygen can enter and anaerobic pathogens are not encouraged.
- Describing monoclonal antibodies as made by the patient. They are made by hybridoma cells in a lab.
- Concluding the bigger zone always means the best antibiotic without considering concentration. Concentrations and disc sizes must be controlled for a fair comparison.
Try three B2.4 How can we identify the cause of an infection? exam-style questions
1. Give one reason why Petri dishes are incubated at 25 °C rather than 37 °C in school labs. (1 mark)
Show the mark scheme answer
To reduce the risk of growing pathogens that infect humans.
2. A zone of inhibition has a diameter of 12 mm. Calculate its area. Use π = 3.14. (2 marks)
Show the mark scheme answer
Radius = 6 mm; area = 3.14 x 6^2 = 113 mm2 (113.04).
3. Describe how monoclonal antibodies are produced. (4 marks)
Show the mark scheme answer
A mouse is injected with an antigen; lymphocytes that make the specific antibody are collected; they are fused with tumour (myeloma) cells to make hybridoma cells; hybridomas divide rapidly and the identical antibodies are collected and purified.
B2.4 How can we identify the cause of an infection? FAQs
What does OCR GCSE Biology B B2.4 cover?
It covers culturing bacteria with aseptic technique, testing antibiotics and antiseptics, monoclonal antibodies and how plant and animal infections are identified.
Which paper is B2.4 examined in?
J257 has two papers at each tier, Breadth in Biology and Depth in Biology, and content from any chapter, including B2, can be assessed on either one. Expect it to be linked to ideas about science and to other chapters.
Which calculations come up in B2.4?
Practise the area of a circle (πr²) for zones of inhibition and bacterial numbers after a number of divisions using 2^n, including converting times into numbers of generations.
