Unfortunately, they're all the same page. Scientific writing must be accurate . Although writing instructors may tell you not to use the same word twice in a sentence, it's okay for scientific writing, which must be accurate. Make sure you say what you mean . I injected the drug into the rat.
Temperature affects the reaction.
I used solutions in various concentrations. I used solutions in varying concentrations. The erythrocytes, which are in the blood, contain hemoglobin. The erythrocytes that are in the blood contain hemoglobin. Write at a level that's appropriate for your audience.