Final answer:
No, the blue tube does not always need to be filled completely; the specific experiment instructions, such as being one third full, should be followed. The experiment references osmosis and the equalization of water levels by adding solute.
Step-by-step explanation:
The question appears to be referring to the concept of osmosis, which is a biological process. In a test tube experiment simulating osmosis, it is not necessary for the blue tube to always be filled completely. The amount the tube should be filled will depend on the specific instructions provided for the experiment. According to the provided reference, the test tube should be about one third full, and this is valuable in experiments such as evaluating water potential and solute concentration effects on water movement across membranes.
Moreover, through the references provided, it is clear that water level can be equalized in tubes by the addition of a solute, which will cause water to move towards the area with higher solute concentration, potentially equalizing the levels as seen in osmosis or in demonstrating principles related to water potential and pressure.