The diagram shows a pathogen called Giardia - HSC - SSCE Biology - Question 4 - 2012 - Paper 1

Giardia is classified as a protozoan.
Protozoa are single-celled organisms that can exist in various environments and can sometimes be pathogenic to humans.

In analyzing the diagram provided, we observe membrane-bound organelles and the specific size range, which are characteristic features of protozoa. Other options like bacteria, prions, and viruses differ in structural and functional characteristics:

• Bacteria are unicellular organisms with a simpler structure without membrane-bound organelles.
• Prions are infectious proteins and do not have cellular structures.
• Viruses are much smaller and consist mainly of genetic material surrounded by a protein coat.

Thus, the correct answer is (C) Protozoan.