Lesson 3Text Selection – Section 7.4 (pp. 201-207)

At the conclusion of this lesson students should be able to:

Explain the processes of diffusion, facilitated diffusion, osmosis, and active transport.

Identify dynamic equilibrium in a diffusion demonstration.

Predict the effect of a hypotonic, hypertonic, or isotonic solution on a cell.

Discuss how large particles enter and exit cells.

Food coloring demonstration Drops of red and

blue food coloring are added to opposite ends of a container of water.

What will happen when the food colorings are added?

What will happen a few minutes later?

Substances dissolved in water (solutes) move constantly in random motion

Causes diffusion net movement of particles from an area

where there are many particles of the substance to an area where there are few particles of the substance

How can you tell this is happening/has happened in our experiment?

What happened to our food colorings? How can this result be explained?

Figure 7.20 © Glencoe-McGraw Hill (2007)

Once a uniform purple color is reached, the food coloring particles continue to move randomly.

However, at some point, all particles of a substance (in this case food coloring) will be as spread out as they can and there will no longer be areas of high and low concentration.

When this occurs, dynamic equilibrium has been reached.

This looks like a

multiple choice

question!

Three main factors affect the rate (speed) of diffusion: Concentration of the diffusing particles Temperature Pressure

If any of these three increases, the diffusion rate will increase. Why?

Passive transport – movement of a substance across the plasma membrane without the use of the cell’s energy.

Active transport – requires the use of the cell’s energy to move substances into or out of a cell across the cell membrane.

Requires Energy

No Energy Required

Water can diffuse easily across the plasma membrane – most other substances cannot.

In facilitated diffusion, special transport proteins move ions and small molecules across the plasma membrane

Click here for

videoFigure 7.21 © Glencoe-McGraw Hill (2007)

The diffusion of water across a selectively permeable membrane. Cells must regulate this in order to

maintain homeostasis. One of three

situations exists.

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Cell is in a solution that has the same concentration of water and solutes

Iso – Greek meaning “equal”

cell is in dynamic equilibrium with environment

Water enters and leaves the cell at the same rate.

Figure 7.23 © Glencoe-McGraw Hill (2007)

Cell is in a solution that has a lower concentration of solute than the cell hypo – Greek meaning

“under” Net movement of water

is into the cell Causes osmotic pressure

In animals – cell could burst

In plants, cell wall prevents bursting; cell becomes firmer

Figure 7.24 © Glencoe-McGraw Hill (2007)

Cell is in a solution that has a higher concentration of solute than the cell. hyper – Greek meaning

“above” Net movement of water is

out of the cell Results:

In animals – cells shrivel In plants, central vacuole

pulls away from cell wall; plant wilts

Figure 7.25 © Glencoe-McGraw Hill (2007)

Is your blood pure water?

What would happen to your red blood cells if pure water were to be injected into your blood stream?

Reread pp. 201-207

Complete the Section 7.4 Study Guide

Requires the cell’s energy Moves substances across the plasma

membrane against a concentration gradient.

Concentration Gradient

Passive Transport

Active Transport

Amount of a substance

commonly called pumps

Figure 7.26 © Glencoe-McGraw Hill (2007)

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video

Enzyme that uses cellular energy to pump 3 Na+ out of the cell and 2 K+ into the cell.

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The sodium-potassium ATPase pump sets up concentration gradients of these two ions across the plasma membrane.

Other substances can use this gradient to get into the cell through a process called coupled transport.

Figure 7.28 © Glencoe-McGraw Hill (2007)

Used for substances that are too large to move through the plasma membrane by diffusion or carrier proteins. Endocytosis – process by which a

cell surrounds a substance with its plasma membrane and brings it inside.

Exocytosis – process by which vesicles fuse with the plasma membrane and secrete their contents outside the cell.▪ Used for expelling waste▪ Secreting cell products (i.e tears, hormones)

Figure 7.29 © Glencoe-McGraw Hill (2007)

Complete the Transport through Membranes worksheet

Study for QUIZ on Tuesday. You should be able to: Match terms with their definitions Draw a plasma membrane and label its parts Identify the tonicity of a solution and explain its

effect on a cell. Read a short passage and explain what cellular

transport mechanisms (diffusion, osmosis, etc.) are occurring and why.