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A student carried out an investigation to identify the presence of microbes in water from different sources - HSC - SSCE Biology - Question 16 - 2012 - Paper 1
Question 16
A student carried out an investigation to identify the presence of microbes in water from different sources. The student’s lab notes are shown. Inoculation of an a... show full transcript
Worked Solution & Example Answer:A student carried out an investigation to identify the presence of microbes in water from different sources - HSC - SSCE Biology - Question 16 - 2012 - Paper 1
Step 1
What can be inferred from these results?
Answer
To answer this question, we need to analyze the student's findings:
- The results for the Control show no successful inoculation while the bottled, tap, and tank water samples did show growth after incubation at 37°C.
- The agar plates did show growth due to the water samples but not in the control, indicating that the water samples were indeed contaminated.
- The agar plates were exposed directly to water samples from these sources. Since the control did not show any results, yet all water samples did, it strongly suggests contamination occurred from the samples rather than improper sterilization.
Therefore, the most logical inference is (D): The agar plates were contaminated prior to the beginning of the experiment.