Single-celled pond organisms have contractile vacuoles that maintain water balance within each cell. This is a an example of what scientific principle?

The correct answer is homeostasis.

Explanation:

A self-regulating procedure taking place within an organism, which permits them to sustain a stable internal condition level is termed as homeostasis. In case, if an organism fails to sustain homeostatic balance, the eventual result would be death. Water balance, temperature, salt concentration, and pH are some of the several internal conditions, which are required to maintain comparatively stability.

Some of the single-celled pond organisms like paramecium comprise contractile vacuoles, which remove additional water out of the cell. As water balance is a part of sustaining homeostatic balance for an organism, thus one can study homeostasis by witnessing the modifications within the contractile vacuole when the species is placed in distinct solutions.