The best way to retain information is by repetition. If you'd like to remember answers until the end of exams, you should study the corresponding material every day and quiz yourself often to make sure you have still retained that information. It may also be helpful to link information to things you already know in real life (e.g., in HYPOtonic cells, there is more water outside the cell than inside the cell, so water flows into the cell and the cell swells like a HIPPO).