Understanding Transport through Cell Membranes: Diffusion, Osmosis, and Protein Pumps, Summaries of Biological Sciences

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Transport Mechanisms

through Cell Membranes

Passive vs. Active Transport

Essential Questions

1. Define passive transport. (Related to Essential Skill 3-4)
2. Describe and give an example of

diffusion. (Related to Essential Skill 3-4)

3. Compare and contrast diffusion and

osmosis. (Related to Essential Skill 3-4)

4. Explain how facilitated diffusion differs

from diffusion in general.

1. Diffusion

 Movement of molecules from high concentration to low concentration.  Why can you smell popcorn from another room?  Why does food coloring mix by itself?  How does oxygen get into your blood?

Selectively Permeable = cell membrane

will only allow some things through!

 Large macromolecules

and charged ions can NOT get through the lipid bi-layer!!!

3. Osmosis

 Osmosis is the

Diffusion of

WATER!!!!!

 Water moves from

areas with more

water to areas with

less water

 Why do your fingers get wrinkles when you swim too long?  Have you ever put salt on a slug???

Solutions & Solutes

 A solution is a liquid with

another substance dissolved in it  Examples: salt water & sugar water

 A solute is the “stuff”

that is dissolved in a solution  Examples: salt & sugar

 In osmosis we trace the

movement of the water, not the solute

Solute + Solvent = Solution

Isotonic Environment

 Solution has the

SAME amount of “stuff” and water as the cell.

 There is no net gain

or loss of water from the cell.  Water moves equally in and out of the cell

Hypotonic Environment

 Solution has LESS

“stuff” and more water than the cell.

 Water will move INTO

cell.

Essential Questions

1. Define active transport. (Related to Essential Skill 3-4)
2. Describe and give an example of a

protein pump. (Related to Essential Skill 3-4)

3. Compare and contrast endocytosis and

exocytosis. (Related to Essential Skill 3-4)

4. Explain how protein pumps differ from

facilitated diffusion. (Related to Essential Skill 3-

Active Transport

 Movement of

molecules across the

membrane from low

to high

concentration.

 Requires ENERGY.

 3 Types of Active

Transport:

- **_Protein PUMPS

• Endocytosis
• Exocytosis_**

Riding a bicycle uphill = Active Transport analogy (NOT actual passive transport!)

Endocytosis

 Active transport of large particles INTO the cell, by

surrounding them with the cell membrane.

Exocytosis

 Active transport of substances OUT of the cell

using the cell membrane – Exiting the cell

Concentration Mountain – how to

remember Passive Transport

Active Transport Diffusion Osmosis Facilitated Diffusion

Protein pumps Endocytosis Exocytosis

No Energy^ Uses Energy

Concentration gradient

Summary