Download Plasma membrane

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