Cell Transport
Learning Objectives
 Explain how passive transport works.
 Explain how active transport works.
Cell Transport
 Cells are kind of like countries
 A county has a border that
 Separates it from other countries
 Control what goes in and out
 Cells have a border called the cell membrane
 It separates it from other cells
 Controls what goes in and comes out
Cell Transport
 Cells need to maintain homeostasis to live
 Homeostasis is a state of relatively constant internal
physical and chemical conditions
 Cells maintain homeostasis by moving molecules from
one side of the membrane to the other
Passive Transport
 In passive transport, a cell moves materials
using diffusion
 Diffusion is the process by which molecules
move from an area of high concentration to
low concentration
 Diffusion does not require the cell to spend
energy
Passive Transport: Diffusion
Solutes
Outside Cell
Cell Membrane
Inside Cell
Higher concentration of solute
on one side of the membrane
than the other
Diffusion causes net movement
of solute particles from the side
of the membrane with the higher
solute concentration to the side
with the lower solute
concentration.
At equilibrium, particles move
equally in both directions, so
there is no net change.
Passive Transport: Facilitated Diffusion
 Not all molecules can
move through the cell
membrane
 In facilitated diffusion,
proteins help molecules
move through the cell
membrane
 No energy needed!
Passive Transport: Osmosis
aquaporin
sugar
water
cell membrane
Passive Transport: Osmosis
 Osmosis is the facilitated diffusion of water across the cell
membrane
 Sometimes sugar or salt builds up on one side of the cell
membrane
 Instead of moving the sugar or salt, the cell maintains
homeostasis by moving water
Osmosis
Passive Transport: Osmosis
 In osmosis, water moves from an area of HIGH
concentration to an area of LOW concentration
 Osmosis Vocab
 Solution: liquid with particles dissolved into it
 Solutes: particles dissolved in a liquid
Passive Transport: Osmosis
 Osmosis Vocab Continued
 Isotonic: when the concentration of 2 solutions is the
same
 Hypertonic: when comparing solutions, the solution
with the HIGH concentration of solutes
 Hypotonic: when comparing solutions, the solution with
the LOWER concentration of solutes
Osmosis in Cells
Isotonic
Hypertonic
Hypotonic
Active Transport
 Active Transport takes place when a cell uses energy to
move material across the cell membrane
 Two types of active transport
 Exocytosis
 Pushes materials out of the cell
 Uses protein pumps
 “Exo” means “out”
 Endocytosis
 Cell membrane wraps around molecule and pulls it
into the cell
 “Endo” means “in”
Active Transport
Protein pumps
Endocytosis
Exocytosis
Endocytosis