Note the vacuole at each end of the Closterium cell. There are refractile* crystals (red arrow) in each vacuole. These crystals made of CaSO₄ are in motion.
Are the crystals living?
Do they leave the vacuole?
Do they move in a specific direction?
What kind of movement do they exhibit?

*Light bends when it passes through these crystals giving them a green appearance.

Read about the Diffusion in Agar experiment.

Read about the Osmosis experiment.