1. Facilitated Diffusion
B-2.5 Explain how active, passive, and facilitated transport serve to maintain the homeostasis of the cell.
Passive Trnasport
Diffusion
Osmosis
Facilitated Diffusion
Active Transport

2. Cell Transport & Homeostasis
All organisms have processes and structures which respond to stimuli in ways that keep conditions in their bodies conducive for life.
Homeostasis depends in part on appropriate movement of materials across the cell membrane.

3. How does cellular transport support life?
Materials needed for cellular processes must pass into cells so they can be utilized.
For example, oxygen and glucose are continuously needed for the process of cellular respiration.
Waste materials from cellular processes must pass out of cells as they are produced.
For example, carbon dioxide is continuously produced within the cell during the process of cellular respiration.

4. Cell Membrane
The cell membrane regulates the passage of material into and out of the cell.
Depending on the needs of the cell, excess substances must move out of the cell and needed substances must move into the cell.
Each individual cell exists in a fluid environment, and the cytoplasm within the cell also has a fluid environment.
The presence of a liquid makes it possible for substances (such as nutrients, oxygen, and waste products) to move into and out of the cell.
A cell membrane is semipermeable (selectively permeable), meaning that some substances can pass directly through the cell membrane while other substances can not.

5. Passive Transport
NO ENERGY REQUIRED to move substances across membrane -- water, lipids, and other lipid soluble substances.
Types:
Diffusion
Osmosis
Facilitated Diffusion

6. Diffusion
The spreading out of molecules across a cell membrane until they are equally concentrated.
It results from the random motion of molecules and occurs along a concentration gradient.
Molecules move from an area of higher concentration to an area of lower concentration
Substances that are able to pass directly across the cell membrane can diffuse either into a cell or out of a cell.

7. Diffusion
Molecules move down the concentration gradient until there are equal numbers of molecules on both sides ~ dynamic equilibrium.

8. Diffusion is controlled by
Temperature
Pressure
Concentration

9. Dynamic Equilibrium
Molecules continue to move randomly, but the overall concentration remains the same.

10. Osmosis
Diffusion of water from an area of greater concentration of water to an area of lesser concentration of water -- across a semipermeable membrane.
Three Types of Solutions
Isotonic Solutions
Hypertonic Solutions
Hypotonic Solutions

12. Isotonic Solution Iso=Same
Concentration of solutes in the solution is the same as inside the cell.
Cell is in dynamic equilibrium, i.e., no net gain or loss of water.
Plant Cell
Blood Cell

13. Hypotonic Solution
Concentration of solutes is higher inside of the cell
Net movement of water will be INTO the cell.
Plant Cell
Blood Cell
13,000x

14. Hypotonic Solution
Turgid– A condition when a plant cell is in a hypotonic environment and the cell wall keeps the cell from bursting.
This is why grocery stores spray vegetables -- crispness!
Plant Cell
Cytolysis – A condition when an animal cell is an hypotonic solution and it bursts
Animal Cell

15. Hypotonic Solutions

16. Hypertonic Solution
Concentration of solutes is greater outside of the cell
Net movement of water will be OUT OF the cell.
Plasmolysis –A plant cell loses a lot of water and the cell membrane shrivels and pulls away form the cell wall
Plant Cell
Blood Cell
13,000x

17. Facilitated Diffusion
Movement across the membrane with the help of transport proteins .
No energy required
Some substances have chemical structures that prevent them from passing directly through a cell membrane. Ex. Glucose
The cell membrane is not permeable to these substances.

18. Transport Proteins Types:
Carrier protein - its shape fits certain molecules.
Channel protein - molecules diffuse through channel.

19. Active Transport
Transport of materials against (low to high) a concentration gradient
REQUIRES ENERGY!
One process of active transport happens when cells pump molecules through the cell membrane.
Calcium, potassium, and sodium ions are examples of materials that must be forced across the cell membrane using active transport

20. Active Transport Sodium-Potassium Pump
transports sodium ions out of cell, potassium ions into cell.
High Potassium K+
High Sodium
Low Potassium
Na+
Low Sodium

21. Large Molecules
When molecules are too large to pass through a cell membrane even with the aid of proteins then vesicles are used to help them through the membrane.
Cellular Structure and Function
Endocytosis -Process by which the cell takes particles into the cell
Exocytosis -Secretion of material out of the plasma membrane

22. Review Types of Cellular Transport Passive (No Energy Required)
Diffusion: Movement of solute (high to low)
Osmosis: Movement of water (high to low)
Hypotonic, Isotonic, and Hypertonic
Facilitated Diffusion: Carrier and channel proteins
Active (Requires Energy)
Endocytosis,, Exocytosis, Some Carrier Molecules Sodium-Potassium Pump