Chp. 3.3 – 3.4 Cell membrane Diffusion & Osmosis

Cell Membrane Composed of 2 phospholipids with other molecules dispersed between them. Phospholipid is composed of 3 basic parts: – A charged phosphate group – Glycerol – Two fatty acid chains The charged phosphate group and the glycerol make the ‘head’. The fatty acids form the ‘tail’.

Fluid Mosaic Model This describes the arrangement of the molecules that make up the cell membrane. First, the membrane is flexible not rigid. This allows it to behave like a fluid. Secondly, the variety of molecules in the membrane is like an arrangement of colorful tiles and patterns that make up a mosaic.

Selective Permeability It allows some not all materials to cross. This allows the cell to maintain homeostasis, no matter the changing conditions.

Passive Transport Movement of molecules across a cell membrane without energy.

2 Types of Passive Transport Diffusion – movement of molecules from a region of higher concentration to lower concentration. Osmosis – movement of water across a semi-permeable membrane from higher concentration to lower concentration.

Effects of Osmosis Isotonic – has the same amount of solute as the cell. Equal amounts of water enter and exit the cell. Hypertonic - higher concentration of solute than the cell. More water exits the cell, causing it to shrivel or even die. Hypotonic – lower concentration of solute than the cell. More water enters the cell, causing it to expand or burst.

Facilitated Diffusion The diffusion of molecules across a membrane through transport proteins. These make it easier to enter or exit a cell.

Active Transport A cell uses energy to move substances from a lower concentration to a higher concentration.

Endocytosis The process of taking liquids or large molecules into a cell by engulfing them in a membrane. Example: Phagocytosis The cell membrane engulfs large particles. “cell eating”

Exocytosis The release of substances out of a cell by the fusion of a vesicle with the membrane.

Lab Report T. Green09/17/13 Title: Diffusion Across the Membrane Background Info. Hypothesis Materials Procedure Data Results Conclusion

Background Info Isotonic –Equal amounts of water enter and exit the cell. Hypertonic - More water exits the cell, causing it to shrivel or even die. Hypotonic –More water enters the cell, causing it to expand or burst.

Hypothesis Which solution is hypotonic, or hypertonic to the egg?

Materials Cups Vinegar 3 eggs Water Glucose solution (corn syrup)

Procedure Copy Handout

Data See Handout

Conclusion Questions on Handout # 1-6