The protists Trypanosoma brucei, Naegleria fowleri, and Toxoplasma gondii
a. invade host cells to cause cellular damage.
b. are only infective in the flagellated form.
c. have a nucleus and are eukaryotic.
d. have all of the above characteristics.

Verified step by step guidance

1. Step 1: Understand the nature of the organisms mentioned. Trypanosoma brucei, Naegleria fowleri, and Toxoplasma gondii are all protists, which means they are eukaryotic microorganisms with a defined nucleus.
2. Step 2: Analyze whether these protists invade host cells to cause cellular damage. For example, Toxoplasma gondii is known to invade host cells, and Naegleria fowleri invades brain tissue causing damage, while Trypanosoma brucei affects the bloodstream and tissues.
3. Step 3: Consider the infective forms of these protists. Trypanosoma brucei is infective in its flagellated form, Naegleria fowleri also has a flagellated stage that is infective, and Toxoplasma gondii has different life stages but is not solely infective in a flagellated form.
4. Step 4: Evaluate the statements given: (a) invasion and cellular damage, (b) infective only in flagellated form, and (c) having a nucleus and being eukaryotic. Since all are eukaryotic, (c) is true; (a) is generally true; (b) is partially true but not for all.
5. Step 5: Conclude which option best fits all three protists based on the above analysis, focusing on their cellular structure and pathogenic mechanisms.

Key Concepts

Eukaryotic Cell Structure

Protists like Trypanosoma brucei, Naegleria fowleri, and Toxoplasma gondii are eukaryotic organisms, meaning they have a defined nucleus and membrane-bound organelles. This distinguishes them from prokaryotes such as bacteria and is fundamental to understanding their cellular complexity and life processes.

Infective Forms and Motility

Many protists have different life stages, some of which are flagellated and motile, aiding in infection and movement within the host. However, not all infective forms are flagellated; for example, Toxoplasma gondii infects as a non-flagellated form, highlighting the diversity in infective strategies among protists.

Pathogenesis and Host Cell Invasion

These protists cause disease by invading host cells, leading to cellular damage. Understanding how they enter, survive, and replicate within host cells is key to grasping their pathogenic mechanisms and the resulting clinical symptoms.