A Scientist Isolates a Microbe from a Contaminated Water Source

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 × 103 cells of the new organism and then incubates the inoculated medium at 37oC. 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 medium that did not contain any lead. She decides to repeat the experiment using lower concentrations of lead than those she used initially.
-Select which of the following is the hypothesis being tested by the scientist.

A) The newly isolated microbe can grow in the presence of lead.
B) The newly isolated microbe is a bacteria.
C) Lead can be placed into tubes of growth medium.
D) Bacteria must be incubated for 72 hours before they grow.
E) Lead is a good nutrient for all bacterial growth.