1. How does it move? It swims with one or two long whips, often green; or it is a rolling green ball

Alone or in a colony?

Single cells are small; use 400× to see the flagella. Colonies are easier at 100×.

1. A large hollow green ball of hundreds of cells, rolling, with darker balls inside→ Volvox
2. A small plate or ball of 4 to 32 green cells→ Small green colonies
3. A single cell→ next question

Not sure? How to judge size by the field of view · This step looks wrong