1. B1.1.2 How our bodies defend themselves against infectious disease
   
B1.1.2 How our bodies defend themselves against infectious disease
GCSE items that can be used to define successful outcomes for peer and self assessment activities.

2. Using Exam pro items to support successful outcomes
Evaluating slimming claims
Using Exam pro items to support successful outcomes
Learners will be able to test their progress against learning outcomes using questions taken from past AQA GCSE examinations.
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3. After 24 hours, the students measured the amount of bacterial growth.
1. Some students investigated the effect of pH on the growth of one species of bacterium.
They transferred samples of bacteria from a culture of this species to each of eight flasks. Each flask contained a solution of nutrients but at a different pH.
After 24 hours, the students measured the amount of bacterial growth.
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4. a) It was important that the flasks in which the bacteria grew were not contaminated with other microorganisms.
Describe two precautions the students should have taken to prevent this contamination.
(2 marks)
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5. (c) The graph shows the results of the investigation.
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6. The students wanted to find the best pH for the growth of this species of bacterium.
(i) Use the graph to estimate the pH at which the bacteria would grow best.
pH (1 mark)
(ii) What could the students do to find a more accurate value for the best pH for growth of the bacteria?
(1 mark)
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7. Mark scheme Q 1 (a) any two from: 2 • sterilise / kill microorganisms
(b) any two from:
ignore ‘cleaning’ / ‘disinfect’
• temperature
ignore ‘germs’
ignore references to time / type of bacterium
• method of sterilisation eg apparatus / media sterilised in oven / autoclave
• concentration / amount of nutrients / ions
• type of nutrient
allow pressure cooker / boiling water
• volume / amount of solution
• pass flask mouth / pipette tip / loop / test tube mouth through flame
• amount of bacteria added
• agitation or amount of oxygen
• work near a flame
• minimise opening of flask / test tube or hold non-vertical
(c) (i) 7.5
allow idea of sealing / covering or prevent entry of air
accept in range 7.4 – 7.6 1
(ii) use more pH values around / close to pH 7.5 / between 7 and 8
[6]
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8. The graph shows the number of people with measles in the UK between 1940 and 2010.
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9. ……………………………………………………………………………………………………………………
(a) Compare how effective introducing the measles vaccine was with introducing the MMR vaccine.
Use data from the graph.
……………………………………………………………………………………………………………………
…………………………………………………………………………………………………...………………
(3 marks)
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10. (b) To see the effect of pH on the growth of the bacteria, other conditions should be kept constant.
Suggest two conditions which should have been kept constant for all eight flasks.
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11. b) The MMR vaccine was introduced in 1988.
Other than measles, which two diseases does the MMR vaccine protect against?
(2 marks)
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12. ……………………………………………………………………………………………………………………
(c) To immunise someone against measles, a small quantity of the inactive measles pathogen is injected into the body.
Describe what happens in the body after immunisation to stop a person catching measles in the future.
……………………………………………………………………………………………………………………
(3 marks)
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13. Mark scheme Q2
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14. After an incubation period of two days, the dish looked like this.
An investigator placed paper discs containing different concentrations of an antibiotic onto a culture of bacteria in a petri dish.
After an incubation period of two days, the dish looked like this.
(a) Explain why there are areas around some of the paper discs where no bacteria are growing.
(2 marks)
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15. The concentration of the antibiotic on the paper discs is given in the table, along with the diameter of the circles where no bacteria are growing.
Disc
Concentration of the antibiotic in units
Diameter of circle where no bacteria are growing, in mm A B 2 8 C 4 14 D 6 26 E 10
What effect does an increase in the concentration of the antibiotic have on the growth of the bacteria?
(2)
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16. The precautions include: • passing inoculating loops through a flame
(c) When students carry out this experiment, they need to take several safety precautions.
The precautions include:
• passing inoculating loops through a flame
• sealing the lid of the petri dish with tape
• incubating at a maximum temperature of 25 °C.
Explain why each of these precautions is necessary.
To gain full marks in this question you should write your ideas in good English. Put them into a sensible order and use the correct scientific word (4 Marks)
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17. Suggest two ways by which this problem could be limited.
Scientists are concerned that many bacteria are developing resistance to antibiotics.
Suggest two ways by which this problem could be limited.
(2 marks)
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18. (a) antibiotics diffuse / pass (into agar) do not allow into dish 1
Lid taped
kill / prevent growth of bacteria or destroy cell wall / bacteria accept bacteria are dead 1
prevent bacteria getting in / out or prevent someone touching bacteria
accept microorganisms/fungi for bacteria do not accept viruses or germs 1
(b) it / higher concentration kills more bacteria or causes less growth do not accept anything referring to size of circle 1
25°C
levels off (at 6 units) accept above 4 units 1
prevents / reduces growth of / reproduction 1
(c) Quality of written communication: for correct sequencing or linking of ideas or points this mark can only be awarded for a plausible attempt (not necessarily biologically correct) to link a precaution to a purpose
harmful bacteria / microorganisms or pathogens 1
(d) any two from:
• to avoid over-use of antibiotics or use no / less / low concentration antibiotics
Q √ or Q ×1
Loop flamed
• select antibiotic that is most effective
to sterilise it / kill unwanted microorganisms
• finish the course
accept so no bacteria present do not accept to clean it 1
• don’t give or use for animals
• develop new antibiotics or alternatives 2
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