Question

An investigation was carried out to determine which of three antibacterial soaps is most effective. Four petri dishes labeled A, B, C, and D were set up. The same amount and type of bacteria was added to each dish. Next, 2 mL of a different brand of soap were added to dishes B, C, and D. Then, 2 mL of water were added to dish A, instead of soap. The dishes were incubated at 37°C for 24 hours. At the end of the investigation, the amount of bacteria in each dish was determined. Dish D had the least bacteria. It was concluded that the soap in dish D was the most effective soap to use against bacteria.
Which statement best describes the validity oF this conclusion?
A. The conclusion is not valid since the same
amount of bacteria was used in each dish.
B. The conclusion is valid since too small
a sample of bacteria was used in this
investigation.
C. The conclusion is valid since the amounts of
bacteria were measured at the end of the
D. The conclusion might not be valid since the
investigation was carried out only once.

Answer 1

Answer:

The correct answer is D. The conclusion might not be valid since the  investigation was carried out only once.

Explanation:

In a scientific experiment, a valid conclusion can be made by performing the experiment several times with the same experimental procedure because a single time experiment can have many defects or experimental errors.  

Therefore to reduce experimental errors in microbiology and to make a valid conclusion the same experiment is performed several times. So in this question, the experiment is performed only once so the chance of experimental errors is high and the conclusion made on this experiment could be wrong.  

So the statement best describes the validity of this conclusion is D.