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MEMBRANE STRUCTURE AND TRANSPORT – Week 5
Plasma Membrane
 A ________________________ membrane that surrounds the cytoplasm of a cell
and
 Separates the contents of the cell from the outside environment and
 Regulates what ____________________________ the cell.
Fluid Mosaic Model
 A model that describes the cell membrane as a flexible mosaic composed of
embedded __________________ dispersed in a fluid
______________________________.
Membrane Structure
 The membrane structure is composed of:
o A Phospholipid bi-layer
 Made of amphiphatic molecules, meaning the molecules have both a
_____________________ and ______________________ portion.
o Steroid Cholesterol
 Helps _____________________ phospholipids and affects
_____________________.
o Carbohydrates
 Used for ___________________________.
Membrane Function
To ___________________________ transport IN and OUT of the cell:
 Simple Diffusion, Osmosis, Active Transport, Endocytosis/Exocytosis
 Adhesion
 Cell Communication
Simple Diffusion – “Down the CONCENTRATION GRADIENT”
 The movement of molecules from an area of their ______________________
concentration to an area of their __________________________ concentration.
 Passive Transport
o Diffusion across a biological membrane with NO expenditure of energy.
 At Equilibrium
o Particles are in _______________________ motion.
Osmosis*
 A special kind of passive transport.
 Diffusion of water through a semi-permeable membrane from an area of the
highest H2O concentration to an area of the lowest H2O concentration.
Tonicity:
The relative solute concentration of one solution compared to another solution.
 H20 moves from the HYPOTONIC --> HYPERTONIC solution.
o Hypotonic:
 ____________________ solute concentration.
o Hypertonic:
 ____________________ solute concentration.
o Isotonic:
 Solutions with _____________________ solute concentrations.
Osmosis & Tonicity
In osmosis, the solvent, typically H2O, moves from the
 ______________________ solution to the ______________________
solution.
Cell Physiology & Tonicity
Plant cells are surrounded by a rigid cell well, Animal cells are not.
 Lysed (blood cell):
o When placed in a hypotonic solution, the blood cell will ________________
due to intake of water.
 Shriveled (blood cell):
o When placed in a hypertonic solution, the blood cell will ________________
due to loss of water.
 Turgid (plant cell):
o Hypotonic solution fills vacuoles with water and develops a turgid pressure.
 Flaccid (plant cell):
o Isotonic solution, cell with neither gain nor lose water.
 Plasmolyzed (plant cell):
o Hypertonic solution, vacuoles will lose water and the cytoplasm with shrink
(plasmolysis).
Facilitated Diffusion
 Passive Transport: ___________________ expenditure of energy
 Movement of particles (ions and polar molecules) down a concentration gradient
via a _____________________________ that is embedded in a plasma membrane.
Active Transport
 Requires expenditure of energy in the form of _________________________.
 Movement of solutes _______________________ the concentration gradient.
 Requires a transport protein.
Selective Permeability
 Simple Diffusion
 Facilitated Diffusion
 Active Transport
Endocytosis
 The movement of materials _________________ a cell via membranous vesicles.
o Phagocytosis  Cell “Eating”
o Pinocytosis  Cell “__________________________”
Exocytosis
 The movement of materials ________________ of a cell via membranous vesicles