A student set up an experiment to show the effect of light color on photosynthesis in Elodea plants. She filled two test tubes with distilled water and placed a piece of Elodea in each of the tubes. She added a drop of phenol red, which turns red in a basic solution and yellow in an acidic solution. She blew in each tube before placing the volumeters on the top of the tube. Why did she blow into the tube? Multiple Choice

1) to add oxygen to the tube

2) to add carbon dioxide to the tube

3) to add carbohydrates to the tube

4) to add sodium bicarbonate to the tube