Students filled up five test tubes with milk, which contains lactose sugar. They added methylene blue, which is an oxygen indicator to each test tube. The students left one test tube without yeast. They put 2ml of yeast, 3ml yeast, 4ml of yeast and Sml of yeast in the next 4 test
tubes. They timed how long it took for the yeast to deplete the oxygen in each test tube.
What is the independent variable in this experiment?

Dis the

By water evaporation from the leaves is created a negative pressure at the top of the tree that promotes the ascension  of the water through channels that are called xylem. there are also two molecule forces that are involved: the intra-water molecules cohesion (water molecules stick to each other) and the adhesion when the water molecules stick to the channels they are running in. this is what enables water to go from the roots to the top of a tall tree.