One type of density change is mass over volume.
Paramecia feed on microorganisms like bacteria, algae, and yeasts. To gather food, the Paramecium makes movements with cilia to sweep prey organisms, along with some water, through the oral groove, and inside the mouth opening. The food passes through the cell mouth into the gullet.
FF no freckles
Ff no freckles (F dominates over f so there are no freckles)
ff freckles
Installing more flashing (strobe) lights would help reduce accidents.
Hope this helps!