1. How substances move into and out of the cell
Cell Membranes
How substances move into and out of the cell

2. Objectives: 1. Identify the main functions of the cell membrane
2. Describe what happens during diffusion
3. Explain the processes of osmosis, facilitated diffusion, and active transport

3. Cell Membrane
Regulates what enters and leaves the cell and also provides protection and support
In: food and water, Out: waste
Lipid bilayer = strong, flexible barrier
Lipids – hydrophobic tails face each other
Proteins – some are channels and pumps
Carbohydrates – attached to surface of some proteins for recognition

4. Diffusion Moves substances across the membrane without use of energy
The cytoplasm inside of cells is a solution (liquid mixture of substances)
Substances dissolved in liquid = solutes

5. Diffusion
Concentration = amount of solute per volume of solution (example: g/L)
Molecules are moving, and diffuse from high concentration to low concentration = diffusion
Equilibrium = same concentration of solute throughout solution

6. Osmosis
Membranes are “selectively permeable” = some substances can pass through, others cannot
Osmosis = the diffusion of water through a selectively permeable membrane (through proteins called “aquaporins”)
Water moves in both directions, but the net movement is in the direction of the most solute particles

7. Osmosis

8. Osmosis Osmotic pressure is handled in a number of ways…
Cells are surrounded by isotonic solution (blood)
Cells are surrounded by a cell wall (plants)
Cells use a contractile vacuole to pump excess water out of the cell (single-celled organisms)

9. Movement of Substances Across the Membrane
Protein channels allow substances to cross that normally could not
Ions, sugars, salts, etc.
Net movement from higher to lower concentration
No energy required
Movement against the concentration gradient
Requires energy input
“Pumps” (for small molecules or ions)
Endocytosis = taking in large amount of material by folding inward
Exocytosis = removal of large amounts of material by a vacuole fusing with the membrane
Facilitated Diffusion
Active Transport