A student grew bacteria on agar in a Petri dish.
The Table shows the student's method.
Table
| Step | Method |
|---|---|
| 1 | Pour sterile nutrient agar into a Petri dish that has been in an autoclave. |
| 2 | Dip an inoculating loop into a culture of bacteria. |
| 3 | Take the lid off the Petri dish and put the lid on the bench. |
| 4 | Spread the bacteria over the agar using the loop. |
| 5 | Put the lid back on the Petri dish and hold it in place with two pieces of tape. |
| 6 | Incubate the Petri dish at 25 ∘C25\ ^\circ\text{C}25 ∘C for two days. |
State why the agar and the Petri dish were put in an autoclave.
Describe what the student should do to the inoculating loop before step 2.
Explain why step 3 could affect the results.
Explain why the Petri dish was incubated at 25 ∘C25\ ^\circ\text{C}25 ∘C and not at 37 ∘C37\ ^\circ\text{C}37 ∘C.
45 exam-style questions on Edexcel GCSE Biology 5.3 Immune system and medicines, covering 5.3.1 The specific immune system, 5.3.2 Response to immunisation, 5.3.3 Advantages and disadvantages of immunisation, 5.3.4 Antibiotics and bacterial infections, 5.3.5 Aseptic techniques in culturing, 5.3.6 Cross-sectional areas of cultures, 5.3.7 Stages of developing new medicines, and 5.3.8 Production of monoclonal antibodies. Each one has a worked solution and a mark scheme showing where the marks go.