Pearson Edexcel International A Level Biology: Adaptive Immunity and Antibiotics (YBI11) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover statements 6.10 to 6.15 (B and T cells, types of immunity, evasion by pathogens, antibiotics, Core Practical 14 and hospital-acquired infections) of the Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology specification (YBI11), Issue 2. Topic 6 is International A2 (IA2) and there are no tiers. Learn the content in the study guide and revision notes first. The course hub, checklist and diagnostics show the wider course.

Questions

1. State one function of each of the following cells in the immune response: T helper cells, T killer cells and T memory cells. [3]

2. Compare B effector cells and B memory cells. [4]

3. Name the type of immunity in each case. (a) A newborn receives antibodies in its mother’s milk. [1] (b) A hiker bitten by a snake is injected with antivenom. [1] (c) A child recovers from chickenpox and cannot catch it again. [1] (d) An adult is given a toxoid vaccine against tetanus. [1] (e) Explain why the protection in (b) is short-lived. [2]

4. A volunteer is given a vaccine dose on day 0 and a second dose on day 35. The table shows antibody concentration in arbitrary units (AU).

Day	7	14	21	28	35	42	49	56
Antibody (AU)	0	5	12	8	4	40	95	70

(a) Calculate the mean rate of increase in antibody concentration between day 35 and day 49. [2] (b) Express the second peak as a multiple of the first peak, to 2 significant figures. [1] (c) Explain the difference between the two responses. [3]

5. Explain how antigenic variation in influenza viruses, and the effect of HIV on T helper cells, each support the theory of an evolutionary race between pathogens and hosts. [5]

6. Penicillin prevents bacteria from building their cell walls. Tetracycline binds to bacterial ribosomes and stops protein synthesis. (a) Distinguish between a bactericidal and a bacteriostatic antibiotic. [2] (b) Decide which type each of the two antibiotics is most likely to be, and explain how its action leads to that effect. [2]

7. A culture of bacteria contained 2.0 × 10⁶ viable cells per cm³. After 8 hours the counts were: no antibiotic, 6.4 × 10⁸; antibiotic X, 2.1 × 10⁶; antibiotic Y, 4.0 × 10³. (a) Calculate the percentage change in viable cells for X and for Y. [2] (b) Classify each antibiotic as bacteriostatic or bactericidal, giving a reason. [2] (c) The culture with Y still looked cloudy. Explain why, and suggest how to measure the effect properly. [2]

8. Four discs, each 6 mm in diameter, were placed on a lawn of bacteria. Disc U contained sterile water. The table shows the diameters of the clear zones (including the disc) in mm.

Disc	Repeat 1	Repeat 2	Repeat 3
S	19	21	20
T	10	9	11
U	6	6	6
V	15	16	14

(a) Calculate the mean zone diameter and the zone area for T. [2] (b) Calculate how many times greater the clear area beyond the disc is for S than for V. [3] (c) Explain the purpose of disc U and what its result shows. [2]

9. Describe how you would investigate the effect of three different antibiotics on a species of bacteria, including how you would reduce the risks. [7]

10. Antibiotic-resistant bacteria have become common on a hospital ward. (a) Explain how this could have happened. [3] (b) Describe two prescribing practices that reduce the risk, and explain how each works. [4]

11. A hospital ward recorded 48 infections in 16 000 patient-days. After new procedures, it recorded 27 infections in 15 000 patient-days. (a) Calculate the infection rate per 1000 patient-days before and after, and the percentage reduction in the rate. [3] (b) Give two causes of hospital-acquired infections and, for each, a hospital practice that reduces the risk. [4]

Answers

1. T helper cells release cytokines that activate B cells, T killer cells or phagocytes [1]. T killer cells destroy body cells showing the antigen, such as infected cells [1]. T memory cells stay in the body and form T helper and T killer cells quickly on a second exposure [1]. [3] Examiner insight: A function means what the cell does. “Helps” or “kills” alone is too vague; say what it acts on.

2. Both form from a selected B cell that divided by mitosis, and carry the same receptor for the antigen [1]. B effector cells (plasma cells) secrete antibody [1]; B memory cells do not secrete antibody now [1]. Effector cells are short-lived, whereas B memory cells persist and respond if the antigen returns [1]. [4] Examiner insight: A comparison needs both cells in each sentence. Writing about each cell in a separate paragraph leaves the link to the reader.

3. (a) Natural passive [1]. (b) Artificial passive [1]. (c) Natural active [1]. (d) Artificial active [1]. (e) The injected antibodies are not made by the hiker’s own B cells, so no memory cells form [1], and the antibodies are broken down and not replaced [1]. [6] Examiner insight: Use the two-word names. Define active as “makes own antibodies”, and artificial as “medical treatment”, if a question asks for a reason.

4. (a) 95 − 4 = 91 AU [1]; 91 / 14 = 6.5 AU per day [1]. (b) 95 / 12 = 7.9 times [1]. (c) The first dose produced B memory cells [1]. They were already selected and more numerous than the original matching B cells, so they divided quickly into plasma cells [1]. More plasma cells made more antibody, sooner, so the peak was higher [1]. [6] Examiner insight: Take values from the table and show the subtraction. Say “memory cells” rather than “the body remembers”.

5. Influenza viruses mutate, changing surface antigens [1]. Memory cells from an earlier infection no longer recognise the new antigen, so the variant survives and reproduces [1]. HIV infects T helper cells [1] and destroys them, so B cells and T killer cells are not activated [1]. In both cases the pathogen variants that evade the immune response are selected, and hosts then need new defences, which is an evolutionary race [1]. [5] Examiner insight: Connect each example to selection. Listing the examples without saying why they spread earns less than a linked chain.

6. (a) Bactericidal antibiotics kill bacteria [1]; bacteriostatic antibiotics stop them growing or reproducing without killing them [1]. (b) Penicillin is bactericidal because, with no cell wall, water enters by osmosis and the cell bursts [1]. Tetracycline is bacteriostatic because, without protein synthesis, the bacteria cannot grow or divide, but they are not necessarily killed [1]. [4] Examiner insight: “Most likely” signals that you should give the mechanism. A named type with no reason gains little.

7. (a) X: (2.1 − 2.0) / 2.0 × 100 = +5 % [1]. Y: (4.0 × 10³ − 2.0 × 10⁶) / 2.0 × 10⁶ × 100 = −99.8 % [1]. (b) X is bacteriostatic, as viable cells are the same while the control grew [1]. Y is bactericidal, as viable cells fell [1]. (c) Dead cells still scatter light, so the turbidity stays high [1]. Use a viable count, such as dilution plating [1]. [6] Examiner insight: Give the sign of a percentage change and the figures used. A fall quoted without a minus sign is ambiguous.

8. (a) Mean = (10 + 9 + 11) / 3 = 10.0 mm [1]; area = π × 5² = 78.5 mm² [1]. (b) S: π × 10² = 314 mm²; minus the disc, π × 3² = 28.3 mm², gives 286 mm² [1]. V: π × 7.5² = 177 mm², minus 28.3 gives 148 mm² [1]. 286 / 148 = 1.9 times [1]. (c) U is a control disc [1]; the zone is the size of the disc, so water and the disc do not inhibit growth, and the zones are due to the antibiotics [1]. [7] Examiner insight: Halve the diameter before squaring. Say whether your area includes the disc, so a reader can follow the method.

9. Wash hands, disinfect the bench and use sterile equipment and aseptic technique [1]. Spread a standard volume of a harmless bacterial culture over sterile nutrient agar to make a lawn [1]. Place discs of each antibiotic with sterile forceps, with a control disc of sterile water [1]. Tape the lid at two points, invert the plate and incubate at a set temperature, for example 25 °C [1]. After the same time, measure the diameter of each clear zone [1]. Repeat and calculate means, keeping the density of bacteria, agar depth, disc size and concentration constant [1]. Do not open the plates; use a non-pathogenic strain and autoclave or disinfect plates afterwards [1]. [7] Examiner insight: Cover the independent variable, the measurement, the controls and the safety in turn. Write “the same volume of culture” rather than “a fair test”.

10. (a) A random mutation gave one bacterium a resistance allele [1]. Sensitive bacteria were killed by the antibiotic, leaving resistant individuals to reproduce with less competition [1]. Offspring inherited the allele, and plasmids may have carried it into other bacteria, so resistant bacteria became common [1]. (b) Prescribe antibiotics only when they are needed [1], so fewer bacteria are exposed and there is less selection for resistance [1]. Test which antibiotic the bacteria are sensitive to before choosing one [1], so a narrow, effective antibiotic can be used and the others are saved for resistant infections [1]. [7] Examiner insight: Use “selection” and “allele” rather than “the bacteria become resistant”. For each practice, add the reason it lowers risk.

11. (a) Before: 48 / 16 000 × 1000 = 3.0 [1]. After: 27 / 15 000 × 1000 = 1.8 [1]. (3.0 − 1.8) / 3.0 × 100 = 40 % [1]. (b) Hands carry bacteria between patients [1], so wash hands or use alcohol gel [1]. Surgical wounds and devices let bacteria in [1], so use aseptic technique or remove devices early [1]. [7] Examiner insight: Use rates, not raw counts, when the patient-days differ. Pair each cause with a practice that targets that cause.

Where marks are usually lost

• Writing that T cells make antibodies, or that plasma cells are memory cells.
• Describing the second response as “better” without saying faster, higher and why.
• Mixing up natural and artificial, or active and passive, and forgetting that passive gives no memory cells.
• Saying bacteria “become resistant” or “get used to” an antibiotic.
• Treating a clear zone as proof that an antibiotic kills the bacteria.
• Using diameter in place of radius in area calculations, or leaving out the squared term.
• Missing the control disc, the inverted plate or the safety measures in a method.
• Quoting infection counts when the number of patient-days is different.
• Naming a hospital practice with no link to the cause it addresses.

Next steps

• Revision notes
• Study guide
• Edexcel A Level Biology hub
• Printable checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology (YBI11) specification, Issue 2, published by Pearson Education Limited.