Cells and energy

Everything in biology happens inside or between cells, so this topic is the foundation for the rest. It starts with organelles and their jobs, where students often give the right name the wrong job, or put chloroplasts in animal cells. Next is movement across membranes: diffusion moves particles from high to low concentration, and osmosis is the special case for water. The usual mistake is getting the direction of water movement backwards. Then comes enzymes, and why raising the temperature speeds them up only until they denature and stop working. Enzymes are not killed, because they were never alive. The topic ends with photosynthesis and cellular respiration, two processes that mirror each other. Plants do both, and that surprises many students. Read each page's common mistake carefully, since the wording in biology answers matters as much as the idea. Then try explaining the concept out loud in one or two sentences before you check the practice answers.