chapter 4 - Membrane Structure and Function

Selectively Permeable Membrane

cell membrane only allows some substances in/out, not all.

Passive Transport

movement of molecules WITHOUT energy (high → low).

Diffusion

movement of molecules from high concentration to low concentration.

Osmosis

diffusion of WATER across a membrane.

Facilitated Diffusion

passive transport that uses protein channels to help move molecules.

Active Transport

movement of molecules against concentration gradient (low → high) and requires ATP energy.

Sodium-Potassium Pump

active transport protein that moves 3 Na⁺ out and 2 K⁺ into cell using ATP.

Endocytosis

cell taking material INTO the cell by forming vesicles

Exocytosis

cell releasing material OUT of the cell using vesicles.

What direction do molecules move during passive transport?

from high concentration → low concentration.

Why does active transport require ATP?

because it moves substances against their concentration gradient.

Hypertonic Solution

higher solute outside the cell → water moves out → cell shrinks.

Hypotonic Solution

lower solute outside the cell → water moves in → cell swells

Isotonic Solution

equal solute inside and outside → no net water movement.