Membrane Function Learning Target: I can explain how cell membranes interact with their environment

Entry Task: Predict what will happen when the mint plant is moved from regular water to salt water. Draw a picture to explain your thinking.

Mint plants after 2 hours in salt water

Mint plants transferred back into freshwater (4 hours later)

When you think osmosis, think: Water Follows Salt!

Osmosis Salt concentration of solution lower than inside the cell Water enters the cell causing it to lyse (burst) Salt concentration of solution the same as inside the cell The amount of water in the cell stays the same Salt concentration of solution higher than inside the cell Water leaves the cell causing it to shrivel

These are red onion cells These are red onion cells. The purple stuff is the cytoplasm inside the cell.

After adding salt, look what happens After adding salt, look what happens. What is happening to the amount of purple cytoplasm inside the cell?

What do you think is causing that to happen? After adding EVEN MORE salt, look what happens. What is happening to the amount of purple cytoplasm inside the cell? In osmosis: water follows salt! - Wherever there is more salt, water will go because it loves salt! What do you think is causing that to happen?

Definitions Hypotonic solution: lower concentration of solutes outside the cell than inside the cell Isotonic solution: same concentration of solutes outside the cell and inside the cell Hypertonic solution: higher concentration of solutes outside the cell than inside the cell

More Definitions Solute: the minor component in a solution, dissolved in the solvent Solvent: the liquid in which a solute is dissolved to form a solution Question: In a salt water solution, is the salt the solute or solvent? What about the water? How do you know?

Direction of water molecule movement

Movement of Matter Across the Cell Membrane The cell membrane is made of a phospholipid bilayer, with many protein channels allowing certain molecules to pass through.

Movement of Non-Polar Molecules Across the Cell Membrane Some small molecules like carbon dioxide and oxygen are able to move through the phospholipid bilayer without going through a protein channel.

Movement of Polar Molecules Across the Cell Membrane Water molecules are polar. That means they have a positive (+) side and a negative (-) side. Because they are polar, they cross the cell membrane by moving through a protein channel called aquaporin.

Aquaporins transport water molecules across the cell membrane by facilitated diffusion

Can Vinegar Get Inside Cells? Vinegar is 5% acetic acid and 95% water Like water, acetic acid is a polar molecule: Do we have any evidence of acetic acid entering egg cells? If so, how would it get there? http://mcb.asm.org/content/27/18/6446