What characteristics separate algae from a) protozoans and b) plants?

a.) Algae vs Protozoans

The main difference between Protozoans and Algae is that Algae are autotrophs, meaning they make their own food. Protozoans, on the other hand, are heterotrophs, they ingest other organisms or organic molecules.

b.) Algae vs plants

One of the more striking differences between algae and plants is their complexity. Algae can either be unicellular or multicellular, while plants are multi-cellular only. Plants have vascular systems, it allows the uptake and transport of nutrients and water. Algae needs to get all of its nutrients from water. Reproduction is also another difference between them. Plants have a more complex mode of reproduction. Algae reproduces through spores and replication.