What does it mean to complement a substrate?

Asnail, elodea (aquatic plant), or both were added to the tubes and they were stoppered. tubes were placed under a grow light for 24 hours and the results recorded. the test tubes were then covered for 24 hours to produce a dark environment and the results recorded. which statement best explains the change in test tube d from the light setup to the dark setup.

According to this food web which of the following would be considered primary consumers

As the pea seeds respire, the level of coloured liquid in the left hand part of the capillary tube rises. by referring to what is happening in the apparatus, explain why the level of liquid changes