Cell Membranes, Diffusion, and Transport

Ms. KlinkhachornDecember 7, 2010

Homework

• Finish Concept Check 6.3 p 122 – #1-5

• Complete Chapter 6 Review p 132– #s 1, 3, 4, 11, 12, 13, 20, 21– Answers must be written in complete sentences

Cell Membrane Function

• How does the cell membrane act as a protective barrier?– It is selectively permeable. It selects what is going

to go in and out of the cell.• Oxygen, Carbon Dioxide, Waste, Nutrients

• Why is it important that the membrane is selectively permeable?

Cell Membrane: Analogy

• The cell membrane is like a window screen.• How?

How do different materials get into and out of the cell?

Background Information

• Concentration: the number of molecules of a substance in a given area/volume– Examples:

• The concentration of 5th period is 29 students/classroom

• There are 40 grams of sugar per 1 liter bottle of Coke• Chicago has 100,000 people living in it per square mile

Practice

Period Number of Students

1 29

2 28

5 29

7 22

8 26

• Which period has the highest concentration of students in the classroom?

• Which period has the lowest?

Where are the areas of high and low concentration?

This is an example of a concentration gradient.

Concentration Gradient

• A concentration gradient is established when, in a given area/volume, there is a difference in concentration

Diffusion

• Diffusion is the movement of molecules from a high concentration to a low concentration– Does NOT require energy– Molecules stop moving when they hit equilibrium

• No concentration gradient exists anymore

Examples of Diffusion

1. Food coloring in water2. Baking cookies3. Spraying air freshener

• What are other examples of diffusion that you encounter regularly? Explain your answer using the terms concentration and concentration gradient.

What is the role of diffusion in cells?

• Diffusion across a cell membrane is known as passive transport.

• Can use a protein but doesn’t always.

Outside of CellOutside of Cell

Inside of CellInside of Cell

Cell MembraneCell Membrane

Passive Transport

Cell MembraneCell Membrane

Passive Transport

Cell MembraneCell Membrane

• What do you notice about this picture? Look carefully.

Active Transport

• Active Transport is the movement of molecules from low to high concentration– Since it is going up concentration gradient, it

requires energy (ATP)– Always needs a protein to help with this

Compare and Contrast Passive and Active Transport