Unit 4: Homeostasis and Transport

Homeostasis and Transport How the structure of the plasma membrane allows it to function as a regulatory structure and/or protective barrier Plasma membrane: A thin, phospholipid and protein molecule bilayer that encapsulates a cell and controls the movement of materials in and out of the cell through active or passive transport. Concentration gradients: The graduated difference in concentration of a solute per unit distance through a solution. The lipids are fluid and allow small molecules to diffuse across. Larger molecules pass through the proteins embedded in the plasma membrane (either through facilitated diffusion or active transport).

Homeostasis and Transport Passive transport: The transportation of materials across a plasma membrane without using energy. Diffusion: The movement of particles from an area of high concentration to an area of low concentration; a natural result of kinetic molecular energy. Osmosis: The movement of water or another solvent through permeable membranes from an area of higher water concentration (dilute) to an area of lower water concentration (concentrated). Facilitated diffusion: A process in which substances are transported across a plasma membrane with the concentration gradient with the aid of carrier (transport) proteins; does not require the use of energy. Carrier proteins: Proteins embedded in the plasma membrane involved in the movement of ions, small molecules, and macromolecules into and out of cells; also known as transport proteins.

Homeostasis and Transport Active transport: the movement of particles from an area of low concentration to an area of high concentration that uses energy provided by ATP or a difference in electrical charges across a membrane. Pumps: actively pump specific molecules across the membrane Sodium potassium pump: a method of active transport that allows cells to have a high concentration of potassium but low concentrations of sodium. This imbalance is how nerve cells are able to transmit impulses and respond to stimuli. Endocytosis: A process in which a cell engulfs extracellular material through an inward folding of its plasma membrane. Exocytosis: A process in which a cell releases substances to the extracellular environment by fusing a vesicular membrane with the plasma membrane, separating the membrane at the point of fusion and allowing the substance to be released.

Homeostasis and Transport Membrane bound cellular organelles facilitate transport of materials. Endoplasmic reticulum: An organelle, containing folded membranes and sacs, responsible for the production, processing, and transportation of materials for use inside and outside a eukaryotic cell. There are two forms of this organelle: rough ER that has surface ribosomes and participates in the synthesis of proteins mostly destined for export by the cell and smooth ER that has no ribosomes and participates in the synthesis of lipids and steroids as well as the transport of synthesized macromolecules. Golgi: An organelle found in eukaryotic cells responsible for the final stages of processing proteins for release by the cell.

Homeostasis and Transport How organisms maintain homeostasis Homeostasis: The regulatory process in which an organism regulates its internal environment. Negative feedback loops are a way to help maintain homeostasis. They sense the change and cause a response to the change. Thermoregulation: how organisms regulate temperature. (i.e. Sweating, shivering) When body temperature drops the blood vessels constrict to limit blood to extremities and muscles shiver. When body temperature increases, blood vessels near the skin open up and the body begins to sweat. Water regulation: how organisms regulate water levels. (i.e. Osmosis, contractile vacuoles) A fish in freshwater urinates constantly to remove excess water. Oxygen regulation: Gas exchange to regulate oxygen As you exercise, your breathing increases to bring more oxygen to your cells.

Video Review Plasma Membrane

Video Review Diffusion vs. Osmosis

Video Review Sodium-Potassium Pump

Video Review Passive and Active Transport