question: What allows some things to enter the cell while keeping other things out?
distractor3: cell vacuum
distractor1: cell substrate
distractor2: cell center
correct_answer: cell membrane
support: This window screen has a fly on it. In a way, the window screen is like a cell membrane. It lets some things pass through while keeping other things out. Air molecules and raindrops can pass through the screen, but larger objects like the fly cannot. In the first lesson of this chapter, you'll learn about different ways that substances can pass through the cell membrane. You'll find out how the cell membrane lets some substances pass through while keeping other substances out.