Passive Transport (7-3 part I)

Passive Transport A. Substances crossing the cell membrane without energy. Diffusion A. Movement of molecules from higher concentration to lower concentration. 1. The difference of molecules across a space is called the concentration gradient. B. Driven by kinetic energy of the molecules. C. Will eventually reach equilibrium, remember cells never stop moving.

3. Diffusion across membranes A. Size and type of the molecule depends on if it will cross through the cell membrane. Osmosis A. Movement of WATER across a cell membrane from an area of higher concentration to an area of lower concentration. B. Since water moves down the concentration gradient it doesn’t use any energy. It is a passive diffusion.

b. Plants live in this environment. C. Direction of osmosis 1. Hypotonic – concentration of solute molecules outside the cell is lower than the concentration in the cytosol, ( inside the cell) a. Water rushes into the cell to reach equilibrium (swelling of the cell). b. Plants live in this environment.

2). Hypertonic – concentration of solute molecules outside the cell is higher than the concentration in the cytosol, (inside the cell) a. Water rushes out of the cell to reach equilibrium ( shrinking of the cell)

3. Isotonic –when concentrations are equal inside and outside. a. Water diffuses in and out equally.

5. Water’s influence on plants and animals 1. Contractile vacuoles – organelles found in unicellular organisms that controls water inside it’s body, releasing any excess. 2. Cytolysis - without contractile vacuoles a cell will burst, killing the cell.

B. Plants- 1. Turgor pressure – pressure exerted when water pushes on the cell membrane and wall of a plant cell. 2. Plasmolysis – shrinking of a plant cell due to water loss.

6. Facilitated diffusion A. Movement of larger molecules across the cell membrane and are assisted by specific proteins in the membrane. 1. Called carrier proteins 2. Carry molecules from higher concentrations to lower concentrations. 3. Uses the concentration gradient so it doesn’t use any energy. 4. Will eventually reach equilibrium.

7. Diffusion through ion channels A. Many ions are not soluble in the lipid bi-layer of the cell membrane so they need help entering the cytosol of the cell. 1. The ion channels are specific to the ion they are allowing to pass through the membrane. B. Reasons these ion gates may open or close. 1. Stretching of the membrane 2. Electrical signals 3. Chemical in the environment

Summary Passive Transport Diffusion - Osmosis – Facilitated diffusion and ion channels 1. Movement from high to low down the concentration gradient. 2. NO energy is used (kinetic energy) 3. Eventually will reach equilibrium