BPK 105 Chapter Notes - Chapter 3.4: Active Transport, Facilitated Diffusion, Membrane Transport
27 Apr 2018
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Module 2: Cell Structures and their Functions - 3.4
3.4 - Movement through the Cell Membrane
- Cell membranes = selectively permeable
- Enzymes, glycogen, potassium ions found at higher concentrations intracellularly
- Na+, Ca2+, Cl- found in greater concentrations extracellularly
- Rupture of membrane, alteration of permeability characteristics, inhibition of transport
processes ----> disrupt normal intracellular concentration of molecules ----> cell death
- Movement thru cell membrane = passive/active
- Passive = no energy expended
- Passive membrane transport mechanisms: diffusion, osmosis, facilitated diffusion
- Active mechanisms: active transport, secondary active transport, endocytosis,
exocytosis
- Diffusion:
- Solution generally composed of 1 or more substances (solutes) dissolved in the
predominant liquid or gas (solvent)
- Solutes (ie. ions/molecules) tend to move from area of higher concentration of solute to
area of lower concentration of that same solute in solution.
- Ex of diffusion: distribution of smoke throughout a room w/ no air currents
- Gradual spread of salt throughout beaker of still water
- Diffusion results from natural, constant random motion of all solutes in a solution
- Equilibrium: net movement of solute stops (random motion continues)
- Concentration gradient: difference in concentration
of a solute in a solvent b/w 2 points
divided
by distance b/w 2 points
- Concentration gradient = steeper when concentration difference is larger/distance is
small
- Substance moves down (with) concentration gradient. Means that solutes = diffusing
from higher to lower concentration of solutes.
- Substance moves up (against) concentration gradient. Requires energy.
- Nutrients, waste products can diffuse into + out of cell
- Normal intracellular concentrations of many substances ----> depend on diffusion.
- Ex. if extracellular [O2] is reduced, not enough O2 diffuses into cell. Cell cannot function
properly.
- Phospholipid bilayer = barrier to most water-soluble substances
- Certain small, water-soluble (lipid soluble) substances can diffuse b/w phospholipid
molecules of cell membranes. Ex. O2, CO2, steriods.
- Other water-soluble substances can diffuse across cell membrane only by passing
through cell membrane channels
- Cell membrane channels incl. large protein molecules that extend from one surface of
cell membranes to other
Document Summary
Module 2: cell structures and their functions - 3. 4. Enzymes, glycogen, potassium ions found at higher concentrations intracellularly. Na+, ca2+, cl- found in greater concentrations extracellularly. Rupture of membrane, alteration of permeability characteristics, inhibition of transport processes ----> disrupt normal intracellular concentration of molecules ----> cell death. Passive membrane transport mechanisms: diffusion, osmosis, facilitated diffusion. Active mechanisms: active transport, secondary active transport, endocytosis, exocytosis. Solution generally composed of 1 or more substances (solutes) dissolved in the predominant liquid or gas (solvent) Solutes (ie. ions/molecules) tend to move from area of higher concentration of solute to area of lower concentration of that same solute in solution. Ex of diffusion: distribution of smoke throughout a room w/ no air currents. Gradual spread of salt throughout beaker of still water. Diffusion results from natural, constant random motion of all solutes in a solution. Equilibrium: net movement of solute stops (random motion continues)
