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 reaction of the bacteria to the antibiotic
D.
the presence of the Streptococcus bacteria