300
A student wondered if different types of plants would produce different amounts of oxygen. A pea plant, a fern, and a cactus were growing in equal-sized containers with equal amounts of soil. The student measured the amount of oxygen produced by each.
Identify two control conditions that should be held constant besides the size of the container and amount of soil.
What is person performing the experiment, size of the plant, amount of water, light source, location, etc.