Cellular Transport 8.1 Notes

I. Plasma Membrane maintains homeostasis in the cell Controls the passage of materials into and out of the cell.

Plasma membrane is selectively permeable because it allows some materials to pass through while keeping others out

Plasma Membrane

II. Diffusion DIFFUSION: All objects in motion have energy called kinetic energy. A. Process of diffusion 1. Diffusion – net movement of particles from an area of higher concentration to

Diffusion

an area of lower concentration. Example: perfume Diffusion results from random movement of particles. B. The selectivity of membranes- 1. Only molecules of water, oxygen, nitrogen, carbon dioxide, and a few other small,

nonpolar molecules can diffuse directly across the lipid bilayer. III. Osmosis How osmosis occurs 1. Osmosis is the diffusion of water molecules through a selectively permeable

Osmosis

membrane from an area of higher water concentration to an area of lower water concentration. 2. Unequal distribution of particles, called a concentration gradient, is

one factor that controls osmosis. B. Cells in an isotonic solution- 1. Isotonic solution – the concentration of dissolved substances (solute) in the solution is the same as the concentration of dissolved substances inside the cell;

therefore, the concentration of water in the solution is the same as the concentration of water inside the cell. 2. Cells in an isotonic solution do not experience osmosis and they retain their normal shape.

Isotonic Solution

Most solutions (immunizations your doctor gives) are isotonic so that cells are not damaged by the loss or gain of water. C. Cells in a hypotonic solution-

Hypotonic, Hypertonic, and Isotonic Solutions

1. Hypotonic solution – concentration of dissolved substances is lower in the solution outside the cell than the concentration inside the cell; therefore, there is more water outside the cell than inside.

2. In a hypotonic solution, water enters a cell by osmosis. 3. The cell swells. 4. Turgor pressure, which is the pressure inside a cell, increases in a hypotonic solution.

Hypotonic Solution

5. The rigid property, due to the cell wall, produced by turgor pressure gives plant cells their shape and support. As the pressure increases inside the cell, the plasma membrane is pressed against the cell wall. They do not burst when placed in a hypotonic solution. Instead of bursting, the plant cell becomes more firm.

6. Animal cells in a hypotonic solution may swell and burst. (The plasma membrane may be unable to withstand the pressure.) 7. An adaptation that some animals have to keep their cells from rupturing is called a contractile vacuole.

How do they work? Like medicine droppers; they collect excess water from the cell, contract, and squeeze water out. D. Cells in a hypertonic solution 1. Hypertonic solution – concentration of dissolved substances outside the cell is higher than the concentration

inside the cell; therefore, there is less water outside the cell than inside. 2. In a hypertonic solution, water leaves a cell by osmosis. 3. The cell shrinks. 4. Turgor pressure decreases when a cell is placed in a hypertonic solution.

Hypertonic Solution

5. Plant cells lose water in a hypertonic solution, mainly from the central vacuole. The plasma membrane and cytoplasm shrink away from the cell wall. The process in which plants wilt due to a loss of turgor pressure in a hypertonic solution is called plasmolysis.

Plasmolysis

6. Animal cells will shrivel in a hypertonic solution because of decreased pressure. 7. You should not salt meat before cooking because the salt forms a hypertonic solution on the meat’s surface; water inside the meat cells diffuse out, leaving the cooked meat dry and tough.

IV. Passive Transport – Movement of particles across membranes by diffusion. A.Passive transport requires NO energy. B. Examples of passive transport include: diffusion, osmosis, facilitated diffusion

Passive Transport

C. Passive transport by proteins- 1. Transport proteins are embedded in the lipid bilayer of the plasma membrane, and they allow needed substances or waste materials to move across the plasma membrane.

2. Facilitated diffusion is the passive transport of materials across the plasma membrane with the aid of transport proteins. Transport proteins provide convenient openings for particles (ions) to pass through.

Passive and Facilitated Diffusion

3. Facilitated diffusion helps move sugars and amino acids across membranes. V. Active transport – Movement of particles across membranes from areas of lower concentrations (the environment) to higher concentrations (inside the cell); Moves against a concentration gradient

Active Transport

A. Active transport requires energy. B. Examples of active transport: endocytosis, exocytosis, sodium-potassium pump C. Endocytosis –process by which a cell surrounds & takes in material from its environment. This material does not pass directly through the

membrane. Instead, it is engulfed and enclosed by a portion of the cell’s plasma membrane. That portion of the membrane then breaks away, and the resulting vacuole with its contents moves inside the cell.

(Example: Amoebas feed by phagocytosis, which is an example of endocytosis.)

D. Exocytosis – expulsion or secretion of materials from a cell. Cells use exocytosis to expel wastes, such as indigestible particles, from the interior to the exterior environment. Substances such as hormones are secreted by this process.

Exocytosis

E. Sodium-Potassium Pumps a. Uses energy stored in the form of ATP b. Moves sodium ions (Na+) out through the cell’s membrane c. Help to transport food particles into cells

d. Pumps potassium ions (K+) in e. Example: Nerve cells use the differences in sodium and potassium ion concentrations produced by sodium-potassium pumps to send signals throughout the body, like electrical signals passing over wires.