Rotifers are microscopic animals that feed on algae, protozoa, organic wastes, and dead bacteria.
To investigate the effects of light intensity on the feeding response of rotifers, a student placed 100 newly-hatched rotifers in an environmentally-controlled tank and introduced a quantified amount of algae. After ten minutes, she counted the number of rotifers that exhibited a positive feeding response (i.e., algae were found in their guts).
The student repeated the procedure for various light intensities while holding all other factors constant, including the temperature, which was kept at 25°C.
The data from her investigation is shown below.
Light Intensity Number of Rotifers with
Positive Feeding Response
100,000 lx
(direct sunlight) 97
10,000 lx
(sunny day) 96
1,000 lx
(cloudy day) 98
500 lx
(sunrise) 94
1 lx
(full moon) 97
What is the independent variable in this investigation?
A.
light intensity
B.
the number of rotifers with a positive feeding response
C.
the amount of algae
D.
water temperature