Here’s a nice article about the history of Kingdoms. It was written in 2011, so it’s only up through what we knew in 2011ish.
https://earthlingnature.wordpress.com/2011/12/05/a-brief-history-of-the-kingdoms-of-life/
When I took Botany as an undergrad, our professor was of retirement age and he taught us there were two Kingdoms: plants and animals. if it was green, it was a plant, if it wasn’t green it was an animal! He was a few decades behind even back in 1988. Looks like your college class is about 10-15 years behind current knowledge also.
An interesting thing about Paramecium (and other ciliates)…they evolved from ancestors that contained a chloroplast. Once we deduced that, it instantly required their reclassification. That happened not long after this discovery in 2008: https://doi.org/10.1016/j.cub.2008.06.031