Unit 4: Cells Learning Goal D: Explain how the structure of the cell membrane relates to how materials are transported through it and identify those modes of transportation.

Cell Membrane  The cell membrane regulates what enters and leaves the cell and also provides protection and support. Composed of a double-layered sheet called a lipid bilayer (two layers of lipids). Contains many different molecules.  Proteins, carbohydrates, etc. The different molecules help regulate what enters and leave a cell.

Cell Wall  A strong supporting layer around the membrane found in some types of cells. The main function of the cell wall is to provide support and protection for the cell. Most cell walls are porous enough to allow water, oxygen, carbon dioxide, and certain other substances to pass through the cell wall.

Diffusion:  A particle moving from an area of higher concentration to an area lower concentration until it reaches equilibrium. Equilibrium is when the concentration of a solute is the same throughout a system.

Diffusion  Diffusion depends upon random particle movements; substances diffuse across membranes without requiring the cell to use energy.  Particles still move after equilibrium is reached. They move at an equal rate in each direction.

Osmosis  The diffusion of water across a selectively permeable membrane.

Osmosis  Isotonic means that there is an equal concentration on both sides of the membrane.  Hypertonic means there is a higher concentration of the solute than of the water (strong solution).  Hypotonic means there is more water molecules than other molecules (weak solution).

Facilitated Diffusion  Some molecules are too big or too strongly charged to pass through the membrane. There are protein channels that allow certain molecules to pass through the membrane. This is a fast process, but it is specific to the molecules it lets through. This does not require energy.

Active Transport  Requires energy to move molecules into or out of the cell. Molecules are moved from an area of low concentration to an area of high concentration.  Proteins act as pumps forcing molecules into or out of cells.

Endocytosis  The process of taking material into the cell by means of enfolding, or pockets, of the cell membrane. Phagocytosis is when food particles are taken in by an organism surrounding the food and breaking off in the cell. Pinocytosis is when liquid is taken in by an organism surrounding the liquid and breaking off in the cell.

Exocytosis  The membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.