Cell Transport and Homeostasis H Bio Cell Transport
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 A) Passive Transport – no energy required molecules from H L concentration ex) DIFFUSION: DIFFUSION movement of * across a semi-permeable membrane until equilibrium is reached ex) FACILITATED DIFFUSION: DIFFUSION use of protein channels (diffusion w/help) * to move charged molecules or large items move in/out * still from H L concentration (no energy needed) * ex) glucose, certain ions * ex) diffusion of water (OSMOSIS) OSMOSIS thru semi-permeable membrane Different solution environments: HYPERTONIC = solution is high (hyper = above) in solute (ex: salt water) HYPOTONIC = solution is low (hypo = below) in solute (ex: fresh water) ISOTONIC = solution is a equilibrium with outside environment 1 2 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) ex) molecular : small molecules and ions - moved through special protein channels - nerve cells use the Na/K pump (33% of all our energy!) ex) bulk: for very large items - 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 system organism
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