Quick Quiz
1. How would each of the following
molecules cross the phospholipid
membrane?
 Testosterone (large lipid)
 Sodium
 Oxygen
2. What is this diagram an example of?
3. What are the main differences between
active & passive transport?
4. Why does temperature affect the rate of
diffusion?
Transport across membranesACTIVE
 DESCRIBE & EXPLAIN WHAT IS MEANT BY ACTIVE
TRANSPORT, ENDOCYTOSIS & EXOCYTOSOIS
Active vs. Passive Transport
Active
Passive
Energy
needed?
Energy
needed?
 Does not
require E in the
form of ATP
Needs E in the
form of ATP
Active vs. Passive Transport
Active
Passive
When
 If diffusion is not
quick enough
When
 To transport
molecules across
cell membrane
high-low conc.
 To maintain
homeostasis
How does active transport help
homeostasis?
Example: Paramecium in fresh water
90% water
10% solute
99% water
1% solute
How does active transport help
homeostasis?
Example: Paramecium in fresh water
Contractile
vacuole
Pushes water
Out of the cell
How does active transport help
homeostasis?
Videos
 https://www.youtube.com/watch?v=pahUt0RCKYc
 https://www.youtube.com/watch?v=MPnXIvprb_w
Active Processes
 Active Transport
 Bulk Transport
What is active Transport?
Which part of the membrane does
this?
Carrier Proteins-PUMPS!
 What direction is transport?
Against the conc. Gradient (low-high
conc.)
 What do they need to operate?
Energy in the form of ATP

Active Transport
 Carrier protein is a specific shape to fit a specific molecule
Active pumps only pump each molecule in one direction.
The Sodium Potassium Pump
 Most famous active transport in animals
 The sodium potassium pump
 This pump uses ATP to pump:
 3 Sodium ions (Na+) out of the cell
 2 Potassium ions (K+) into the cell
Math example
Sodium Potassium Pump
Sodium Potassium Pump Movie
 https://www.youtube.com/watch?v=fxOIcWwdl-o
Why do cells do this?
 To lower salt concentration in the cell
 They are pumping more ions (salt) out than in, so the overall
salt concentration stays lower

This keeps it in balance with the outside environment
 To maintain an electrical charge in the cell
 This lets the cell get electrical signals from nerves
Diagram it yourself
 With your partner, use your book on
page 82 to diagram the four steps of the
sodium potassium pump on a
whiteboard.
 Be prepared to be called on to explain
any part of the process.
Bulk Transport-Moving large amounts
 Sometimes
cells have to move really large
molecules or objects into or out of cells
Molecules like extra-large proteins or
polysaccharides are too big to be transported even
with the help of a protein
The cell has to use bulk transport instead
Endocytosis
Bulk transport into a cell
is called endocytosis.
Steps
 First the membrane folds in to make a pouch.
 Then the objects to be transported enter the pouch.
 The pouch folds in on itself.
 Finally it pinches off to make a vesicle inside the cell.
Exocytosis
Bulk transport out of a
cell is called exocytosis.
Steps
 Cells package a molecule (like a hormone) into a
vesicle.
 When the molecule is needed the vesicle goes to the
cell membrane
 It fuses with the cell membrane and then opens up
on the outside to let the molecule out of the cell
Copy & complete the table
Summary of transport Processes:
Name of Description E
Protein
process of process
needed? needed?
Passive
Processes
Active
Processes