A scientist isolates a microbe from a contaminated water source. She thinks that

Question

A scientist isolates a microbe from a contaminated water source. She thinks that the organism might be a new bacteria that is capable of surviving in the presence of lead, a heavy metal. She makes tubes of growth medium containing either no lead, 0.1 mg lead, 0.25 mg lead, 0.5 mg of lead or 1 mg of lead. She inoculates each tube with the 10 x 10e3 cells of the new organism and then incubates the inoculated medium at 37-degree Celsius. After 48 hours, she examines the tubes of medium and finds that there is no growth in any of them. However, she finds that the bacteria grew fine in a medium that did not contain any lead. She decides to repeat the experiment using lower concentrations of lead than those she used initially. Which of the following is the hypothesis being tested by the scientist?

1) bacteria must be incubated for 72 hours before they grow

2) lead can be placed into a tube of growth medium

3) the newly isolated microbe is a bacteria

4) lead is a good nutrient for all bacterial growth

5) the newly isolated microbe can grow in the presence of lead

Explanation / Answer

The hypothesis she is testing for is

"lead is a good nutrient for all bacterial growth". The basis of her hypothesis is that she found a microbe and she was not confirmed whether it was bacteria or any other microbe. But she tests these microbes obtained for being bacteria and which are able to survive in the presence of heavy metal i.e lead. But her hypothesis somehow failed at the end as no bacteria grew in the presence of lead.

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