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Biology 1308 Chapter 5
Structure and Function of Plasma Membranes
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Biology
Undergraduate 3
09/22/2016

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Term
Cell Membrane or Plasma Membrane
Definition
is the outermost boundary of a living cell.
its function is to regulate the passage of materials into and out of the cell.
they exhibit Selective Permeability, allowing some substances to cross more easily than others.
acts as the site of cellular recognition or the ability of an organism to distinguish between "self" and "non-self" which plays an important role in immunity.
Term
Fluid Mosaic Model
Definition
is a structure of cell membranes that are composed of a bi layer of phospholipids with embedded and attached proteins.
Term
Hormones
Definition
chemical messengers
Term
Cell Membrane proteins
Definition
some proteins help maintain cell shape and coordinate changes inside and outside the cell through their attachment to the Cytoskeleton and Extracellular Matrix.
some proteins function as receptors for Hormones from other cells.
some membrane proteins function as Enzymes.
Term
Phospholipids
Definition
the key ingredient of biological membranes, spontaneously self-assemble into simple membranes.
Term
Phospholipid Bilayer
Definition
a two layer sheet formed by Phospholipids in which Hydrophilic are exposed to water and Hydrophobic are shielded from water.
Term
Transmembrane Proteins
Definition
are either Peripheral Proteins or integral Proteins.
some form channels or tunnels that shield ions another hydrophilic molecules as they pass through the hydrophobic center of the membrane.
others serve as pumps, using energy to actively transport molecules, into or out of the cell.
Term
Peripheral Proteins
Definition
attached to the membrane surface.
Term
Integral Proteins
Definition
embedded within the phospholipid bilayer.
Term
Passive Transport
Definition
is the movement of molecules from an area of high concentration to an area of low concentration without energy being expended. The molecules move down their CONCENTRATION GRADIENT (from high to low). two types are SIMPLE DIFFUSION and OSMOSIS.
Term
Simple Diffusion
Definition
is the tendency of molecules to spread out evenly in an available space.
three physical factors that affect the rate of Diffusion are temperature, molecular size, and state of matter.
Term
Equilibrium
Definition
when molecules move from an are of high concentration to an area of low concentration until they reach a point at which they are spread equally in all areas is call the point of EQUILIBRIUM.
where the concentration of molecules are the same throughout.
Term
Temperature
Definition
warm temperatures cause molecules to diffuse faster than colder temperatures.
Term
Molecular Size
Definition
large molecules diffuse more slowly than small molecules.
Term
State of Matter
Definition
matter exists in three basic states, Solids, Liquids, and Gasses. Solids diffuse more slowly than gasses. Liquids diffuse at a rate somewhere in between.
Term
Osmosis
Definition
is the diffusion of water molecules from an area of high concentration to an area of low concentration across a membrane until Equilibrium is reached.
also a type of Passive Transport.
Term
Tonicity
Definition
describes the ability of a solution to cause a cell to gain or lose water.
mostly depends on the concentration of a solute on both side of the membrane.
Term
Tonicity
Definition
the relative concentration of SOLUTES vs. SOLVENTS into two different environments, such as inside vs. outside of a cell.
Term
Solutes
Definition
are the substances which are dissolved into other substances called SOLVENTS.
Term
Solvents
Definition
the substance that SOLUTES are dissolved in.
Term
Solution
Definition
a combination of SOLUTES and SOLVENTS.

ex: dissolving salt (solute) into water (solvent) to make a solution of saltwater.
Term
Remember this:
Definition
water will always move in the direction of the greater concentration of Solutes.
Term
Hypertonic (low)
Definition
if a cell is placed into a HYPERTONIC solution, there is a higher concentration of solutes outside of the cell (than inside of the cell), and water molecules will move out of the cell causing it to shrink. In plant cells this is called PLASMOLYSIS and in animal cells it is called CRENATION.
Term
Hypotonic (low)
Definition
is a cell is place into a HYPOTONIC solution, there is a lower concentration of solutes outside of the cell and water molecules will move into the cell. In plant cells, the cell will expand and fill with water causing TURGOR PRESSURE but will not burst due to the presence of a strong Cell Wall. In animal cell, the cell may burst and this is called CYTOLYSIS.
Term
Isotonic (equal)
Definition
if a cell is places in an ISOTONIC solution, the concentration of solutes is the same on both sides of the membrane and the net movement of water will be zero.
Term
Osmo-regulation
Definition
the control of water balance.
in order for cells to survive in a hypotonic or hypertonic environment, they must engage in OSMO-REGULATION.
Term
Active Transport
Definition
cells move molecules from an area of low concentration to an area of high concentration using energy. These molecules move against the concentration gradient (low to high).
several different types.
Term
Bulk Transport
Definition
is the movement of large molecules across membranes and Is a type of ACTIVE TRANSPORT.
Term
Endocytosis
Definition
is used to import substances such as food and water.
Term
Phagocytosis (cell eating)
Definition
is the import of food molecules into the cell.
Term
Pinocytosis (cell drinking)
Definition
is the import of liquids into the cell.
Term
Exocytosis
Definition
is used to export bulky molecules, such as proteins or polysaccharides.
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