Homeostasis and Cellular Transport

Cell Membrane

• A phospholipid bilayer that forms the outer membrane of a cell

• Is selectively permeable• Controls which substances pass into

or out of the cell

Lipids

• A type of organic molecule that is insoluble in water

• Ex. Fats, oils, waxes

Phospholipid

• A type of lipid found in the cell membrane. Has a phosphate group attached to it.

• Phospholipids have polar, hydrophilic heads and nonpolar, hydrophobic tails.

Hydrophilic

• Molecular attraction to water• (water loving)

Hydrophobic

• Molecular repulsion to water• (water fearing)

• The cell membrane is formed by a double layer of phospholipids arranged with their tails facing each other and their polar heads oriented toward the watery environment inside and outside the cell

Membrane Proteins

• Peripheral proteins- proteins located either on the inner surface or outer surface of the cell membrane

Membrane Proteins

• Integral proteins- proteins that are embedded within the cell membrane; extend from the outer surface to the inner surface; play an important role in transporting substances across the cell membrane

Fluid Mosaic Model

• States that the phospholipids and membrane proteins move with in the cell membrane. The movement of the phospholipids and proteins creates tiny pores where certain substances can diffuse into the cell.

Solution

• a mixture in which one or more substances are uniformly distributed

Solute

• The substance that is dissolved in a solution

Solvent

• The substance in which a solute is dissolved

Sample Problems

• Identify the solvent and solute in each of these solutions

• 1. sugar water solution• 2. salt water solution

Aqueous solution

• Solution in which the water is the solvent

Concentration

• Measurement of the amount of solute dissolved in a fixed amount of the solution

Isotonic solution

• The concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell

Hypertonic solution

• The concentration of solute molecules in the solution outside the cell is higher than the concentration inside the cell.

Hypotonic solution

• A solution where the concentration of dissolved substances in the solution is lower outside the cell than the concentration of solute molecules inside the cell

Diffusion

• The movement of molecules from an area of high concentration to an area of lower concentration

Osmosis

• The movement of water molecules across a membrane from an area of high concentration to an area of low concentration

Equilibrium

• Occurs when the concentration of a substance is the same throughout a space

• When a cell is placed in an isotonic solution, there is no net movement of water. The cell size remains the same

• When a cell is placed in a hypertonic solution, water diffuses out of the cell and the cell shrinks.

• When a cell is placed in a hypotonic solution, water diffuses into the cell and the cell swells and may burst.

Passive Transport

• Movement of substances across the cell membrane that does not require any energy.

• Substances move down their concentration gradient.

Types of Passive Transport

• Diffusion• Osmosis• Facilitated diffusion• Ion channels

Facilitated Diffusion

• Substances move down their concentration gradient across the cell membrane with the assistance of carrier proteins

Facilitated Diffusion

Carrier Proteins

• Proteins embedded in the cell membrane that aid in the transport of substances across the cell membrane

Ion channels

• Proteins embedded in the cell membrane that provide a passageway across the cell membrane for the diffusion of ions

Active Transport

• Movement of substances across the cell membrane that requires energy.

• Substances move against their concentration gradient from an area of low concentration to high concentration.

Types of Active Transport

• Sodium- Potassium Pump• Endocytosis• Exocytosis

Sodium- Potassium Pump

• Carrier proteins transport sodium (Na+) and potassium (K+) ions across the cell membrane against their concentration gradients.

• Moves Na+ out of the cell and K+ inside the cell

Sodium- Potassium Pump

Endocytosis• Process where cells ingest

substances. • The substances are enclosed by a

portion of the cell membrane that folds into itself to form a pouch that separates from the cell membrane.

Vesicle

• Membrane “pouch” containing either ingested substances or substances to be released from the cell.

Exocytosis

• Process where cells release substances to the outside of the cell.

• The substances are contained inside a vesicle that fuses with the cell membrane releasing the substance to the outside of the cell.

Exocytosis