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

Algae are different from protozoans in that they are photosynthetic and thus make their own food. Protozoa on the other hand are animal like and do not possess mechanisms for making their own food an so they feed on ready made food materials from their environment..

Algae are different from plants because they have no vascular tissue like that found in plants. They also lack roots, stems and leaves, which plants have. Examples of algae are seaweed, kelp, and brown, red and green algae.