Plankton's Importance and Diatoms/Dinoflagellates

Many animals feed off of plankton, but too much can block sunlight and plants will die. However, phytoplankton produces much of the Earth's oxygen supply which is needed (obviously) for humans to survive. They show scientists where ocean currents provide nutrients for plant growth. The differences between diatoms and dinoflagellates is that diatoms have a silica cell wall, and dinoflagellates have flagella. 

Diatom

Dinoflagellate