chapter 7.3: moving materials into and out of cells
DESCRIPTION
Traffic Across Membranes Selectively Permeable Membranes – some substances can move through and others cannot Also called, semipermeable membranes Can move through - Hydrophobic, non-polar molecules - Small molecules Can’t move through -Large molecules -hydrophilic, polar molecules - Ions (Na +, Ca +, Cl - )TRANSCRIPT
Chapter 7.3:Moving Materials Into and Out of Cells
Homeostasis = keeping a constant internal environment
The cell membrane does this by allowing only certain molecules to go in and out
Traffic Across MembranesSelectively Permeable Membranes – some substances can move through and others cannot Also called, semipermeable membranes
Can move through-Hydrophobic, non-polar molecules- Small molecules
Can’t move through-Large molecules-hydrophilic, polar molecules- Ions (Na+, Ca+, Cl-)
Concentration:The amount of a substance in a given area.
[substance] = mass of substance (g)
volume (l)
Q: Which side has a higher concentration of red dots?
A BA: Side A
Passive Transport
Transport of molecules without the use of extra energy.Three types:
DiffusionFacilitated diffusionOsmosis
Goes from high concentration to low concentration.
Diffusion The movement of molecules from an area
of high concentration to an area of low concentration
Down(with) the concentration gradient (slope) – energy is not needed to go downhill!
High Low
Factors that influence the rate of diffusion include:
1. Temperature: Heat increases kinetic energy and thus diffusion
2. Steepness of concentration gradient: 50:1 > 2:1
3. Particle Size: Small molecules diffuse at a quicker rate than larger molecules.
The net movement of molecules will continue until an equilibrium is reached between the two areas
net movement Once equilibrium is reached, molecules
continue to diffuse across the membrane in both directions but at equal rates.
Equilibrium
Facilitated Diffusion Molecules are too big to squeeze through
the membrane. Channel proteins act like tunnels to let the
molecules through. Goes with (down) the concentration gradient.
Q: Is extra energy needed for facilitated diffusion? Why or why not?
Osmosis is an Example of Facilitated Diffusion
The diffusion of water. Water always flows from high water
concentration to low water concentration.
Requires the use of aquaporins (special channel proteins for the movement of water)
Tonicity: The Effects of Osmosis on Cells
Solvent: the liquid you dissolve a substance into. ie: waterSolute: the substance dissolved in the solvent. ie: salt
Water will tend to go from an area of low solute concentration to an area of high solute concentration
Isotonic: when the concentration of solutes on either side of the membrane are equal
- cells do not change
Hypotonic: when the solution outside the cell has a lower solute concentration in relation to inside the cell
- cells tend to swell and burst
Hypertonic: when the solution outside the cell has a higher solute concentration in relation to inside the cell
- cells tend to shrink
2M
NaCl
a) b)
c)
1M NaCl
2M NaCl2M
NaCl2M NaCl
1M NaCl
Hypotonic Isotonic
Hypertonic
Active Transport
Movement across a membrane that DOES require energy
Different types of Active Transport include:Sodium-Potassium pumpEndocytosisExocytosis
Q: From which molecule does the cell get this energy? How?
Molecules move from an area of low concentration to an area of high concentration
Go against (up) the concentration gradient
High Low
Sodium-Potasium Pump Protein Pumps: sodium (Na+) in and
potassium (K+) out.
Potassium
Sodium
Q: Why does this pump require energy to work?
Bulk Transport Endocytosis: transport of larger molecules
into the cell• Phagocytosis: “cell eating” solid materials are
taken into the cell• Pinocytosis: “cell drinking” liquid materials are
taken into the cell
Exocytosis: transport of larger molecules out of the cell.