Question

question 8 of 10
the ph indicator bromothymol blue turns yellow when co₂ gas is added to a
solution and blue when co₂ is removed from a solution. an experiment will
test how the intensity of light affects the rate of photosynthesis in algae.
which of these should be a control for this experiment?

a. algae that are placed in a blue solution and kept in the dark
b. algae that are placed in a yellow solution and kept in the dark
c. algae that are placed in a blue solution and kept in direct sunlight
d. algae that are placed in a yellow solution and kept in direct sunlight

Explanation:

To determine the control, we analyze the experiment: the independent variable is light intensity, and the dependent variable is photosynthesis rate (measured via CO₂ changes, indicated by bromothymol blue color). A control should have the independent variable at a baseline (no light, since the experiment tests light intensity effects) and the initial condition (yellow solution, as CO₂ is added initially, turning it yellow). Option A has a blue solution (CO₂ removed, not initial state), C and D have light (not baseline for independent variable). Option B has algae in a yellow solution (initial CO₂ - rich state) and kept in the dark (baseline light intensity, so no photosynthesis - related CO₂ change expected, serving as a control to compare with experimental groups with different light intensities).

Answer:

B. Algae that are placed in a yellow solution and kept in the dark