CELL TRANSPORT Homeostasis Membrane permeability Equilibrium Transport

Homeostasis: Maintaining a Balance Organisms must adjust to changes in their environment. If not…DEATH!

What Maintains Homeostasis? The PLASMA MEMBRANE maintains the proper concentrations of materials by controlling the passage.

Characteristics of the Cell Membrane

Selectively Permeable aka Semipermeable 1.Water, oxygen, nitrogen, carbon dioxide and other small nonpolar molecules can diffuse directly 2.Allows some things in and others not

Plasma Membrane-Structure 1.Phospholipid Bilayer- 2.2 fatty acids and 1 phosphate group attached to a glycerol 3. Polar Heads (water soluble) 4. Non Polar -Fatty acid chain (not water soluble) REVIEW NOTES FROM THE CELL!

The cell membrane also has proteins floating in it that do many things. Some are gates to let substances in and out.

Protein in membrane

Plasma Membrane Function-Proteins The cell membrane's function, in general, revolves around membrane proteins. 1.Receptor proteins which allow cells to communicate 2. Transport or channel proteins regulate what enters or leaves the cell 3. Marker proteins which identify the cell

Cellular Transport NO ENERGY REQUIRED Diffusion (passive) Facilitated Diffusion (passive) Osmosis-Diffusion of Water (passive) ENERGY REQUIRED Active Transport

Diffusion  Diffusion - the process by which molecules spread from areas of high concentration, to areas of low concentration.  Passive Transport-requires no energy

Concentration gradient - a difference between concentrations in a space. C. When the molecules are even throughout a space - it is called Dynamic EQUILIBRIUM

About this diagram: this represents a cell in a solution. The cell will not let the red particles pass through the membrane. The green molecules can pass through, as can water molecules. The arrows show the direction of particle movement. The green particles are moving in to the cell where their concentration is lower, and water is moving out of the cell because its concentration is higher inside osmosis diffusion

Osmosis A.Osmosis - the diffusion of water molecules through a selectively permeable membrane. Passive Transport Ex.Water will move in the direction where there is a high concentration of solute (and hence a lower concentration of water).

Isotonic Solution Concentration of solute in cell and solution is equal No net movement into or out of cell

Hypotonic Solution  There are less solute (salt) molecules in the solution.  Water will move into the cell.  Cell will swell  Cell could burst  Plant cells have vacuoles to collect extra water

Hypertonic Solution A.There are more solute (salt) molecules in solution, which causes the water to leave the cell B.Plants wilt and animal cell shrink-Plasmolysis. In both cases, the cell may die.

Crenated red blood cells in hypertonic salt solution X 1000 Notice that the cells have shrunk.

Red blood cells in isotonic solution X 1000 Note that all the cells appear normal.

Red blood cells in hypotonic solution X 1000 Note that the pinkish cells have swollen (the little dip in the middle of a normal rbc is not visible and one side bows out).

Facilitated Diffusion (Transport Proteins, passive) Moves substances down the concentration gradient without using cell’s energy Use of carrier proteins located in membrane

Animations of cell processes: Diffusion & Osmosis: Osmosis Examples Hypotonic, Hypertonic, Isotonic Interactive Quiz

Active Transport Move particles from a region of lesser concentration to a region of greater concentration. Move against the concentration gradient. Must use energy (ATP)

Sodium-Potassium Pump Sodium/Potassium pump: 3 Na+ out of cell 2 K + into cell Here the energy of a phosphate (shown in red) is used to exchange sodium atoms for potassium atoms.

Endocytosis and Exocytosis Cells can also move things in and out by using pieces of membrane. Look at the animations on the link to view these processes: Endocytosis: pinocytosis – cellular drinking phagocytosis – cellular eating Exocytosis: - can involve getting rid of waste, or can involve secreting cell products (such as hormones or other important compounds)

Active Transport Exocytosis Exocytosis- substances inside a vesicle are released from a cell as the vesicle fuses with the cell membrane Requires Energy

Endocytosis Substances are moved into a cell by a vesicle that pinches off from the cell membrane Phagocytosis-cell “eating” engulfs food Pinocytosis- cell “drinking” Requires energy ATP