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Plasma Membrane unit Vocabulary
Diffusion - the movement of molecules in a fluid from regions of high concentration to
regions of low concentration, (driven by a concentration gradient.) Example: If you put a
drop of food coloring in pure water, with out siring or shaking the dye will eventually
become distributed even throughout the water.
Concentration gradient – the difference in concentration of a substance between two parts
of a fluid or across a membrane
Active transport – the movement of materials across a membrane through the use of
cellular energy. Usually across a concentration gradient.
Osmosis- the diffusion of water across a semi permeable membrane. Water will move to
the side of the membrane that has a lower concentration of water or a higher
concentration of solutes (stuff dissolved in the water.)
Hypotonic –refers to a solution having a lower concentration of dissolved particles than
the cytoplasm of a cell. (Usually causes the free water to move into the cell.)
Isotonic –refers to a solution that has the same concentration as the cytoplasm of a cell.
Hypertonic –refers to a solution having a higher concentration of dissolved particles than
the cytoplasm of a cell. (Usually causes water to move out of a cell into the solution)
Permeable – a substance that allows liquids and gasses to pass through.
Semipermeable membrane -a membrane which will allow certain molecules or ions to
pass through it by diffusion.
phospholipid –a lipid consisting of a glycerol with to which two fatty acids and one
phosphate are bonded. Molecules that make up cell membranes. The phosphate “head” is
hydrophilic and the lipid “tail” is hydrophobic.
phospholipid bilayer – a double layer of phospholipids that make up all cellular
membranes. The hyrophillic phosphate heads face the outside, contacting the extracellular fluid and the cytoplasm. The hydrophobic lipid tails face each other on the inside
of the membrane.
Hydrophilic –literally meaning “water-loving”. Refers to a substance that dissolves
readily in water, or to parts of a large molecule which forms weak hydrogen bonds with
water.
Hydrophobic –literally means “water-fearing”. Refers to a substance that does not
dissolve in water, such as oil and other lipids.
Glycoprotien – a protein to which a sugar or carbohydrate is attached.
Glycolipid – a protein to which a lipid is attached.
Transport proteins – a protein that regulates the movement of water-soluble molecules
through the cell membrane.
Channel proteins –a protein that forms a channel or pore completely through the
membrane. And that is usually permeable to one or more water-soluble molecules such
as ions.
Carrier proteins – a membrane protein that facilitates (helps) diffusion of specific
substances across the membrane. The molecule to be transported binds to the outer
surface of the carrier protein, the protein then changes shape allowing the molecule to
move across the membrane through the protein.
Receptor proteins –protein in the cell membrane that recognizes and binds to specific
molecules. Often trigger some response by the cell such as endocytosis or cell division.
recognition proteins – a protein or glycoprotein that identifies the cell as belonging to a
specific species or organ. Helps immune system tell invading cells from cells belonging
to the organism.
Passive transport –Movement of materials across a membrane without the use of energy.
Usually moves from an area of high concentration to an area of lower concentration.
Endocytosis – the movement of material into the cell in which the plasma membrane
engulfs extracellular material (material from outside of the cell), forming a membrane
bound sac that enters the cytoplasm.
Exocytosis –The movement of material out of a cell in which the material within the cell
is enclosed in a membrane-bound sac that moves to the plasma membrane and unites with
it. Releasing the material outside of the cell.