7:3 Movement Through the Membrane

Cell Membrane Every cell has a cell membrane Regulates what enters and leaves the cell. Provides protection & support The middle section is called a lipid bi-layer, a double layer lipid sheet.

Lipid Bi-layer Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains Go to Section:

Diffusion Liquids are present both in and out of the cell The membrane monitors what enters or exits the cell The cytoplasm has various solutes within it The concentration of a solution is the mass of solute in a given volume (mass/volume) Diffusion is when molecules move from one area of concentration to another (usually through a membrane)

Diffusion causes many substances to move across a cell membrane but does not require the cell to use energy! Equilibrium is reached when the concentration of the solute is the same throughout a solution of a system.

High Concentration Low Concentration Cell Membrane Protein channel

Osmosis Osmosis is the diffusion of water through a selectively permeable membrane Selectively permeable means the membrane allows certain substances to pass by and others not. Osmosis allows water molecules to pass through a biological membrane easily. Osmosis is the movement of water from an area of high concentration of water molecules to an area of low concentration of water molecules. When a cell membrane does not allow substances in, it is said to be impermeable. Water will move across a membrane until there is equilibrium.

Biological membranes are permeable to water, but impermeable to larger molecules such as sugar. Membranes may be selectively permeable, allowing only substances of their choice into the cell. When a cell is at equilibrium with the surrounding solution, the cell is isotonic. Cell membranes are completely permeable to water, therefore, the environment the cell is exposed to can have a dramatic effect on the cell.

3 types of solutions: Isotonic, Hypotonic and Hypertonic Osmosis in cells Let’s take a look!

Facilitated Diffusion During facilitated diffusion, molecules such as glucose that cannot cross the cell membrane’s lipid bilayer directly move through protein channels instead. Hundreds of different protein channels have been found that allow ions, sugars and salts to cross various membranes.

Active Transport When materials move across a membrane AGAINST concentration differences. Requires the input of energy Some types of active transport move materials through the cell membrane. Endocytosis – taking in through pockets of cell membrane (process is called phagocytosis) Exocytosis – exits the cells via the membrane

7-4 The Diversity of Cellular Life UNICELLULAR – one celled MULTICELLULAR – many cells Multicellular organisms have cell specialization. They are specialized to perform specific functions within the organisms. LEVELS OF ORGANIZATION IN AN ORGANISM: Cells  Tissues  Organs  Organ Systems  Organism