1. Cellular Transport
Section 7.4

2. Cellular Transport Two ways to transport substances:
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

3. 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

4. Three Main Factors of Diffusion
Concentration- high concentration, fast diffusion
Temperature- high temp, faster movement
Pressure- high pressure, particles are closer together and bounce into each other more often, faster diffusion
CHEMISTRY!!!

5. 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

6. Types of Transport Proteins Used in Diffusion
Channel proteins open and close the P.M. to allow the substance to diffuse that are polar
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?

7. Applications of Diffusion
Kidney dialysis
Question:
Do substances need a stimulus to diffuse across a membrane?

8. 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

9. Types of Solutions- Egg Demo
Isotonic: Same concentration of water and solutes as its cytoplasm -Cells maintain normal shape
Fig. 7.23
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

10. 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

11. 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 Why does active transport require energy?

12. 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

13. 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

14. 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

15. 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

16. Visualize It! Look at figure 7.29
Make a Venn Diagram to compare and contrast the processes of endocytosis and exocytosis.

17. 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 Cutting Edge Biology