Cell Transport and Homeostasis H Bio

Cell Transport and the Cell Membrane Functions: Regulates what enters and leaves the cell Selectively Permeable – allows only certain substances to enter and leave “selects” also called semi-permeable Aids in protection and support Contains and separates a cell from its environment Made of a phospholipid bilayer

Cell Transport and the Cell Membrane Molecules found in the cell membrane (biological membranes) Lipids, mainly phospholipids, animal cells also contain the steroid cholesterol to aid in membrane fluidity. Proteins (receptor, enzyme, transport/channel, carrier) Carbohydrates – chains that attach to membrane proteins (glycoproteins) or lipids (glycolipids) in the cell membrane serve as “name/ID tags” for cell to cell recognition

Cell Transport and the Cell Membrane Fluid Mosaic Model Bilayer is fluid in nature with proteins embedded throughout Phospholipid Bilayer Contain a hydrophilic head and a nonpolar hydrophobic tail H bonds form between the phospholipids head and the watery environment inside and outside of the cell Hydrophobic interactions force the tails to face inward Phospholipids are not bonded to each other, making the layer fluid Cholesterol embedded in the membrane makes is stronger and less fluid

Cell Transport and the Cell Membrane Passive Transport  down a concentration gradient, no E Diffusion Osmosis Facilitated Diffusion

7.3 Cell Transport DIFFUSION DIFFUSION A)Passive Transport – no energy required ex) DIFFUSION: movement of molecules from H  L concentrationDIFFUSION * across a semi-permeable membrane until equilibrium is reached FACILITATED FACILITATED DIFFUSION ex) FACILITATED DIFFUSION: use of protein channels (diffusion w/help)FACILITATED * to move charged molecules or large items move in/out * still from H  L concentration (no energy needed) * ex) glucose, certain ions OSMOSIS OSMOSIS * ex) diffusion of water (OSMOSIS) thru semi-permeable membraneOSMOSIS Different solution environments: HYPERTONIC HYPERTONIC = solution is high (hyper = above) in solute (ex: salt water) HYPOTONIC HYPOTONIC = solution is low (hypo = below) in solute (ex: fresh water) ISOTONIC ISOTONIC = solution is a equilibrium with outside environment 12 3

The Effect of Osmosis on Cells Cell shrinking = plasmolysis Cell swelling and bursting = cytolysis

Cell Transport and the Cell Membrane Active Transport  up/against gradient, required E (ATP) Membrane/Molecular Pumps Bulk Transport Endocytosis Exocytosis

B)Active Transport – energy needed to move items from L  H concentration (against/up the concentration gradient)Active Transport ex) molecular : small molecules and ions - moved through special protein channels Na/K pump - nerve cells use the Na/K pump (33% of all our energy!) ex) bulk: for very large itemsbulk - requires cell membrane to change shape a) endocytosis – cell membrane folds inward, brings item in * phagocytosis (cell eating) used by amoeba and WBC’s * pinocytosis (cell drinking): packets of fluid brought inside cell b) exocytosis – materials are released from the cell * vacuole fuses with membrane, contents released to outside * ex: hormones made in brain pituitary  released to bloodstream  travel to target organ

Homeostasis and Levels of Organization : Unicellular – ONE cell is the entire organism (ex: bacteria, protists) - internal cell environment is regulated by the whole cell Multicellular – cells depend on jobs of other cells to regulate internal environment - cells need to be specialized in certain functions - cells must have ways of communicating with each other Cell Communication: - chemical signals picked up by receptors on target cell (ex: hormones) - cell to cell connections (gap junctions) passageways for contents to share Levels of Organization: from simplest to most complex cell  tissue  organ  organ system  organism