Cellular Transport
Section 7.4
Cellular Transport
How do substances move throughout the
cell?
Ever smelled cookies baking while you were
in your bedroom?
Two ways to transport substances:
Without energy= Passive Transport
With energy = Active Transport
Diffusion is Passive
 Diffusion (AKA Passive Transport)- net mvmt of particles
from an area where there are many to an area where
there are fewer
 Animation
 The amount of substances in a given area is called
concentration
 Substances diffuse from high to low concentrations
 Therefore, it doesn’t require energy!
 Fig. 7.20
 What if the concentrations are the same?
 When there is continuous movement of the particles, but no
overall change in concentration it is called Dynamic Equilibrium
Three Main Factors of Diffusion
1. Concentration- high concentration, fast
diffusion
2. Temperature- high temp, faster
movement
3. Pressure- high pressure, particles are
closer together and bounce into each
other more often, faster diffusion
 CHEMISTRY!!!
Diffusion Across the Plasma Membrane
Besides diffusing water across the cell,
other ions and small molecules get
diffused, too
Facilitated Diffusion- uses transport
proteins to move other ions and small
molecules across the plasma membrane
Types of Transport Proteins
Used in Diffusion
1. Channel proteins open and close the
P.M. to allow the substance to diffuse
that are polar
2. Carrier Proteins change shape as they
diffuse to help move substances through
the membrane
 Fig. 7.21
 Passive Transport
 Reading Check- How do Na ions get into
a cell?
Applications of Diffusion
Kidney dialysis
Question:
Do substances need a stimulus to diffuse
across a membrane?
Osmosis- Water’ You Doing?
Diffusion of Water
 Water passes freely through the P.M. and doesn’t need
transport proteins
 The diffusion of water is called osmosis
 Regulating water in the cell helps maintain homeostasis
 How it works:
 Solute/solvent – which is which?
 Solute is the thing being dissolved, solvent does the dissolving
 Water is the solvent
 If there is a lot of water, the concentration of the cell is low –
it’s dilute
 Fig. 7.22
 Reading Check- Compare and contrast osmosis and
diffusion
Types of Solutions- Egg Demo
1. Isotonic: Same concentration of water and solutes as
its cytoplasm -Cells maintain normal shape
 Fig. 7.23
2. Hypotonic: if cell is in a solution that has a lower
concentration of solute
 More water outside of cell than inside, so the water flows in
because of osmosis and the cell swells
 Too much swelling can lead to a burst!
 Because plants of rigid cell walls, they don’t burst in hypotonic
solutions


Grocers use this idea to keep veggies fresh by misting them
That’s how pickles are made
 Fig. 7.24
3. Hypertonic: the concentration of the solute
outside of the cell is higher than inside




Cells shrivel because the water is leaving the cell (less
pressure)
In plants, it causes wilting
Fig. 7.25
Evaluate the benefits of sports drinks that contain
electrolytes that athletes drink instead of water
 Is there any danger in consuming these drinks?
 Osmosis
Active Transport
What if a substance has to move from an
area of lower concentration to an area of
higher?
It requires energy and is called active transport
Occurs in pumps- carrier proteins that help
in transport
Carrier Proteins
Active Transport
Fig. 7.26 Why does active transport
require energy?
Na+/K+ ATPase Pump- A type of Carrier
Protein
 Found in PM of animal cells
 Maintains the level of sodium ions (Na+) and
potassium ions (K+) inside and outside of the cell
 What is it used for?
This protein pump is an enzyme to help with energy
storing molecules
 What’s it transport?
Three Na+ out of the cell, 2 K+ into the cell
 Why?
The cell needs to get rid of Na+ and needs more K+
But, since there’s lots of Na+ already on the outside of
the cell and lots of K+ already on the inside of the cell,
active transport has to be used
Na+/K+ ATPase Pump
Three Na+ bind to the transport protein to
move out of the cell
The transport protein requires ATP to
change the shape of the protein
After the protein changes shape, it
releases the Na+ to the outside of cell
In turn, the K+ on the outside of the cell
bind to the protein
The protein changes shape and releases
the K+ on the inside of the cell
Transporting Large Particles
 Sometimes diffusion or transport proteins don’t
get the job done because the particles are too
large
 Endocytosis is the process in which a cell
surrounds the substance outside of the cell and
engulfs it in the plasma membrane
 The membrane then pinches off and leaves the
substance inside the cell
 Endocytosis
 Movie
Transporting Large Particles
Exocytosis is the opposite of endocytosis
Cells use it to expel wastes and secrete
cell products, like hormones, that were
manufactured inside the cell
Both Endo and Exo require energy to
maintain homeostasis in the cell
Movie
Visualize It!
Look at figure 7.29
Make a Venn Diagram to compare and
contrast the processes of endocytosis and
exocytosis.
Questions to Ponder
In what ways can materials move across a
cell membrane?
What is the difference between osmosis,
diffusion and facilitated diffusion?
Why are channel proteins needed?
How do materials move against the
concentration gradient?
Pg. 208- Cutting Edge Biology