Final answer:
It is important to underfill blood collection tubes to maintain the correct ratio of blood and additive for testing purposes.
Step-by-step explanation:
Biology:
In medical analysis, blood is collected into small diameter glass tubes using capillary action. It is important to underfill the tubes so that they are not completely full of blood. This is because an accurate ratio of blood and additive is needed for testing, and filling the tubes completely with blood can disrupt this ratio. By filling the tubes only about one third full, the correct ratio can be achieved, ensuring accurate test results.