A laboratory experiment was done to show the effects of organic waste on the dissolved oxygen (DO) content in water. Five tanks were set up, each containing fresh water and a small amount of single-celled green algae. Specified amounts of organic waste were added to the tanks. The results below show the amount of DO in each tank after a period of one week.

Tank 1 Tank 2 Tank 3 Tank 4 Tank 5
Initial DO 10 ppm 10 ppm 10 ppm 10 ppm 10 ppm
Amount of organic waste added 0 g 10 g 20 g 30 g 40 g
DO after one week 10 ppm 10 ppm 8 ppm 5 ppm 0 ppm

Which of the following would best improve the validity of the experiment?

For better results = Validity= we should maintain other parameters constant, like temperature, pH and sun light.

Explanation:

When making an experiment like this, we must control other parameters that can change our results.

Temperature: Dissolved Oxygen can change due temperature, for example: colder water, more dissolved oxygen and viceversa.

pH: Algae can change its function when changing water´s pH , so, we must maintain this condition controled.

Sunlight: Algae is activated through sunlight, in this case, we must investigate which are the conditions required for the algae that we are using .

it would be a gas formation