How did cyanbacteria undergo photosynthesis without a chloroplast?
While lacking chloroplasts cyanbacteria still contain chlorophyll and use carbon fixation to convert carbon dioxide to sugar.
Guess they gotta they make do with what they have
How do we know that cellular respiration has occurred due to evolution?
That’s a really good question although I wouldn’t worry too much about it for the exam. You might want to know other progressions and processes of evolution but the way cellular respiration in particular came to be, probably won’t be a focal point you should worry about.