Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Protozoa
Name: Alex Beck
Location: N/A
Country: N/A
Date: N/A 

How many species of protozoa are there? How many are poisonous? What type is most deadly? How do they protozoa catch their food? How do protozoa digest their food? How big is the largest protozoa? How small is the smallest protozoa?

There are about 200,000 living species of protists. This is approximate because scientists do not agree on exactly what organisms should be classified as protists, and because all species have not been found yet. I don't know about poisonous ones except for a type called a dinoflagellate that causes the famous "red tide". It can kill fish when it is present in large numbers, and if eaten by clams and other shellfish, it can poison people who eat the shellfish. Protists capture their food in many ways. Some, like the ameba, surround it with their cell membranes. Other, like the paramecium, have a permanent groove in their membrane, and sweep food into it with little hairs called cilia. Digestion is inside the single cell, not inside a gut (which is actually outside your body if you think about it) like more advanced animals. I don't know sizes well enough to answer your last two questions. I checked all this information (most of which was in my head) in a college biology textbook called "Biology" by Solomon et al.


Click here to return to the Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory