AP Biology Unit 2: Cell Structure and Function — Tips & Strategies

The cell membrane is a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins. Understand the role of each component for selective permeability.

If a substance moves DOWN its concentration gradient, it's passive (no ATP). If it moves AGAINST the gradient, it's active (requires ATP). Size and polarity determine which passive method is used.

Hypertonic, hypotonic, and isotonic describe the relative solute concentration OUTSIDE the cell compared to inside. Water moves toward the hypertonic side.

Mitochondria and chloroplasts have double membranes, their own circular DNA, 70S ribosomes, and reproduce by binary fission — all evidence supporting endosymbiosis.

Water moves up through xylem via transpiration pull, cohesion between water molecules, and tension created by evaporation from leaves. This is a classic FRQ topic combining multiple concepts.