* Prokaryotic cells: These are the simplest form of cells, lacking a nucleus and other membrane-bound organelles. They are considered the most primitive type of cell.

* Protists: These are a diverse group of eukaryotic organisms, meaning they have a nucleus and other organelles. They are more complex than prokaryotes but are still considered relatively simple compared to plants, animals, and fungi.

* Yeast: Yeast is a type of fungus. Fungi are eukaryotes and are more complex than protists.

* Heterotrophic: This is a mode of nutrition, not a specific type of cell. Heterotrophs obtain their food from other organisms, unlike autotrophs who produce their own food (like plants).

Conclusion:

Prokaryotic cells are considered the most primitive because they lack the complex internal structure found in eukaryotic cells.

Here's a simple way to think about it:

1. Prokaryotes: Simplest, most ancient.

2. Protists: More complex than prokaryotes.

3. Yeast (fungi): Even more complex than protists.