Diffusion, Osmosis, Homeostasis and the Plasma Membrane

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

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

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

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

H. Facilitated Diffusion (Transport Proteins, passive)  Channel proteins simply act as a passive pore. Molecules will randomly move through the opening in a process called diffusion. This requires no energy, molecules move from an area of high concentration to an area of low concentration.

III. 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). H2O  conc. of solute (copy this)

Osmosis  Watch this animation of water molecules moving across a selectively permeable membrane. Water molecules are the small blue shapes, and the solute is the green.  The solute is more concentrated on the right side to start with, which causes molecules to move across the membrane toward the left until equilibrium is reached.

IV. Isotonic Solution- Equal on both Sides! If the concentration of solute (salt) is equal on both sides, the water will move back and forth but it won't have any result on the overall amount of water on either side. A."ISO" means the same Conc solution=Conc. of cell

V. Hypotonic Solution-Hypo means less! A.There are less solute (salt) molecules in the solution. Water will move into the cell. B.Salt “Sucks” or dehydrates the water C.C. The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting-Turgor Pressure D.D. In animal cells, the cell may be in danger of bursting, organelles called CONTRACTILE VACUOLES will pump water out of the cell to prevent this.

VI. Hypertonic Solution- "HYPER“ means more! 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.

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

B. Types of Active Transport 1. Exocytosis- To expel wastes, secrete substances- hormones.  Requires Energy

2. Endocytosis- Phagocytosis-cell “eating” engulfs food Pinocytosis- cell “drinking” cell surrounds and takes in material from its environment. Engulfed and enclosed by a portion of the cell’s plasma membrane. That portion breaks away and the resulting vacuole with its contents moves to the inside of the cell- requires ATP(ENERGY

C. Carrier Proteins Using ATP 1. Some proteins actively use energy from the ATPs in the cell to drag molecules from area of low concentration to areas of high concentration (working directly against diffusion) an example of this is the sodium/potassium pump. Here the energy of a phosphate (shown in red) is used to exchange sodium atoms for potassium atoms.