A scientist discovered a new antibiotic and wanted to know if it would be effective against group A Streptococcus bacteria. He designed a test experiment in a lab with ten different cultures of the bacteria. He introduced the antibiotic into five of the cultures, leaving the other five to grow without it. He recorded observations every three hours for a week.
What is the independent variable in this experiment?
A.
the presence of the new antibiotic
B.
the total number of bacteria cultures
C.
the presence of the Streptococcus bacteria
D.
the reaction of the bacteria to the antibiotic
A. the presence of the new antibiotic
The independent variable is the variable that is deliberately changed or manipulated by the scientist in an experiment. In this case, the scientist manipulated the presence of the new antibiotic in the cultures of Streptococcus bacteria to test its effectiveness.