Do Now! Brainstorm: What parts of a house separate it from it’s external environment? What may enter through those parts?

Cell Membrane Controls movement in and out of the cell Selectively permeable Some substances can pass freely. Some substances can pass to an extent. Some not at all. Allow cells to maintain homeostasis.

View phospholipid animation

Lipids in the cell membrane The head is hydrophilic (love water) The tails are hydrophobic (hate it)

Phospholipids only let small molecules pass through How can the larger ones get in the cell?

Proteins in the CMB Proteins allow only certain molecules pass by based on their shape.

Carbohydrates in the cell membrane If you get a heart transplant can you get just anybodies heart? Allow cells to be recognized

Fluid Mosaic Model Show animation

Diffusion Collision of molecules Molecules move from a high concentration to low concentration This occurs because of a concentration gradient. Diffusion only occurs if their is a concentration gradient.

If the concentration gradient no longer exist it is said to be at equilibrium.

Diffusion animation

Active Transport Do you think molecules can ever move against their concentration gradients?