Osmosis & Diffusion

1-22-13

Key Question: How do you think things like water and food, which cells need to live, get into and out of cells?

Initial Thoughts:

Evidence #1 :Demos and Background Notes

What does “concentration” mean? For example: the concentration of salt in sea water.

Concentration: The number of “particles” in a given space. Which is more concentrated?

OR

Diffusion Demos

• Perfume• Food coloring and beaker• Food coloring and graduated cylinder

• Make a prediction.• Why did you predict what you did?

Diffusion• Diffusion is the natural

movement of any molecule from high concentration (where there’s lots of them)

to low concentration (where there’s not as much)

until they are equally spread out.

Osmosis• Diffusion of water from high to low

concentration

Vocabulary/Background• Osmosis – the movement of water molecules

from high concentration to low concentration

Diffusion

• Movement from high to low concentration until they are spread out equally in all areas

• Movement of ANY small uncharged molecules

• Osmosis is the diffusion of WATER.

Diffusion is a slow process because it relies on the random movement of atoms and molecules.

Why is this important to cells?

• This is how things like oxygen, food, and water get transported into and out of cells.

• http://molo.concord.org/database/activities/223.html

Do Now 1-25-12• Hand in your cell city project.• Digital projects:– Name your file your LAST NAME, FIRST NAME, PER

1, 2, OR 3.– Save to S:/ drive, Teachers, Mrs. Roberts, Inbox,

Cell City Project, your period.

Today: Set up Egg Lab

Egg Lab - Background• Osmosis – the movement of water molecules

from high concentration to low concentration

• Movement from high to low concentration until they are spread out equally in all areas

• Movement of ANY small uncharged molecules

• Osmosis is the diffusion of WATER.

Diffusion

Egg lab: Background

Egg Lab: Background

• Hypotonic: it causes it to swells up (think Hypo = Hippo)

• Hypertonic: it causes it to shrivel up(Think hyper skinny kid)

Egg Lab: Background

• Vinegar is an acid that will dissolve the hard shell, leaving only the thin membrane around the egg “cell”.

• Water is small enough that it can enter or leave through the egg membrane. (it is selectively permeable).

Evidence #2: Egg LabVariables:

Manipulated Variable:_____________Responding Variable:______________Controlled Variables:______________

Variables:• Manipulated Variable: Type of liquid• Responding Variables: Weight of egg and

Volume of liquid• Controlled Variables: same egg, same amount

of time in liquid, same amount of liquid

Evidence #2: Egg Lab#1 Testable Question: What will happen when

an egg is soaked in corn syrup?Hypothesis: If an egg is soaked in corn syrup, then

the egg will....because…..

#2 Testable Question: What will happen when an egg is soaked in colored water?Hypothesis: If an egg is soaked in colored water, then

the egg will....because…..

Analysis Questions1. Explain why diffusion and osmosis are important

to cells.

2. Why do grocery store owners spray fresh fruits and vegetables with water? Explain using what you learned about osmosis.

3. If a shipwrecked crew drinks sea water, they will probably die. Why?

SummaryWrite a summary of the Egg Lab. Remember to:1. restate your hypotheses (there were 2 in this

one) 2. Tell if it was supported or not. 3. Use your data to back up #24. Explain your data using the principles behind

Osmosis/Diffusion. Was the corn syrup and colored water hypotonic or hypertonic?

5. Further thoughts, improvements, extensions, etc.

Reflection

• Draw what happens when a cell is placed in sea water, using arrows to show the direction water is moving (in or out of the cell).

Big Idea

• Cells use diffusion and osmosis to get things like food & water into and out of cells.