What is one characteristic that you could observe to distinguish diatoms and dinoflagellates

Diatoms have a cell wall that includes silica, while dinoflagellates have a cell wall that includes cellulose.

Explanation:

Diatoms are unicellular algae. Some of them can live in colonies forming filaments or ribbons, they are surrounded by a cell wall made of silica called a frustula.

They are microscopic animals, almost always single-celled. They have flagella. They can be divided into two large groups differentiated by the presence or absence of cellulosic plaques in the cell wall or amphysm.

this is a good question! i'll do some research and come back when i have the answer!