I took two engineering courses that where not a lot people passed; static/dynamics and solid state electronics. I have to say eventhough it may appear that people are complaining that it is “too hard” it may not tell the entire story.
I agree however I will go beyond. This is an introductory course to not only biology but college as a whole. 20% is beyond reasonable expectation of failure at that level. That is something you would expect to see out of core courses and upper division. Physics for majors at the 100 level would(should) see a higher drop out rate than general courses. Beyond that I realize many believe that multiple choice is too easy it can be set up to be as tough as short answer(which BTW can be easier as you will likely get partial credit even if missing the question). Heck when I took animal physiology 361 we had multiple choice along with short answer and the multiple choice was far tougher as the answers were so similar to each other that it took excellent reading skills to notice the small things. I don’t know there is just a lot of missing in this story.
While getting my civil engineering degree there were two teachers who everybody tried to avoid because they were blatantly open about wanting to fail as many students as possible. One taught Chemistry II and the other taught thermodynamics. THANKFULLY I didn’t get the jerk for Chem II and never had to take thermo. I remember some of my engineering buddies literally being in tears when they found out they had to take thermo our junior year. Sucked to be them. LOL
My first chemical engineering class (sophomore level) had about a 4 in 5 drop out rate and was a real pressure cooker. Every math and science class had about a 1 in 5 or greater drop out rate. By the time I got into the core of my major classes at the junior level, they had pretty much completed the weeding out and the courses changed gears from weeding to increasingly going overboard for student retention via extra help from profs, study groups, etc. Senior level classes were a breeze by comparison to the sophomore level classes.
I am dual degreed in Microbiology and Chemical Engineering and confess to having to audit some of the math and chemistry classes. If your goal for a degree and career is strong enough, there is a way to tough it out, get stubborn and accomplish it. If you don't have these when needed then you'll drop to the wayside or switch to something else compatible with your capabilities.