Final answer:
Balantidium coli, Microsporidia, and helminths all represent parasitic organisms that can infect humans or other hosts, causing various diseases. Specifically, Giardia lamblia, Trypanosoma brucei, and Plasmodium falciparum are parasites with unique characteristics like evading the immune system or showing a distinctive blue halo under UV microscopy.
Step-by-step explanation:
The organisms listed as a), b), and d) in the student's question are indeed parasites. Balantidium coli is a protozoan parasite that can infect the digestive system of humans. Microsporidia are a group of spore-forming unicellular parasites. They can infect a variety of hosts, including humans, causing a range of illnesses. A helminth is a term that refers to parasitic worms, and they feed off their hosts. Each of these can have adverse effects on their hosts, exhibiting characteristics typical of parasitic organisms.
To address the specific multiple-choice questions: Giardia lamblia, referenced in figure 23.30, is known for its unique appearance with a blue halo, visible when using ultraviolet fluorescence microscopy. Trypanosoma brucei and Plasmodium falciparum are both well-known for their ability to evade host immune systems by altering surface proteins with each generation.