TRANSPORT ACROSS THE
CELL MEMBRANE
SEC 4.2 & 4.3
P 72-73
What is the difference
between the requirements of
each type of transport
shown?
ENERGY!!!
2 Main Categories of Transport:
1. Passive transport:
• No ATP energy required
• relies on random kinetic energy of particles
• depends on a CONCENTRATION GRADIENT.
• Ex: O2, CO2
2. Active transport:
• requires ATP energy
• May use a carrier protein
• works against a concentration gradient.
• Ex: Macromolecules: Ions, amino acids, sugars
PERMEABILITY & DIFFUSION
• Read pg 72-73 & complete your notes…
DEFINE DIFFUSION
the movement of molecules from a region of
higher concentration to a region of lower
concentration until equilibrium is reached.
-
does not require ATP energy.
occurs down a concentration gradient.
Real life examples: dye in water, perfume in a room
Examples across the cell membrane:
lipid soluble molecules, gases (O2, CO2)
https://www.youtube.com/watch?v=JShwXBWGMyY
SOLUTION VOCAB REVIEW
• A solution is made up of two components:
Solute: a substance (ex. kool aid crystals)
dissolved in a solvent
Solvent: a fluid (ex. water) that dissolves a solute
FACTORS AFFECTING THE RATE OF DIFFUSION
1. Concentration gradient:
the LARGER the difference in
concentration between the
two areas,
the more rapid the rate of
diffusion.
This is due to more collisions
between molecules.
FACTORS AFFECTING THE RATE OF DIFFUSION
2. Temperature:
Higher temp. = faster rate of diffusion
• increasing temp. of a solution increases the kinetic energy
of the molecules thus,
• increasing the rate of diffusion.
• due to more collisions.
• Ex. food colouring in water
FACTORS AFFECTING THE RATE OF DIFFUSION
3. Size of molecules/ions:
• smaller substances will diffuse faster!
• Ex: proteins cannot pass through the cell
membrane, but amino acids can.
FACTORS AFFECTING THE RATE OF DIFFUSION
4. Shape of molecules/ions:
similar to size, a substance’s shape may slow its rate of diffusion.
5. Viscosity:
• Refers to the fluid density of the solution.
• The less viscous, the more rapid diffusion can occur.
• Ex. substances diffuse more rapidly in water than in syrup.
FACTORS AFFECTING THE RATE OF DIFFUSION
6. Movement of medium:
• currents aid diffusion.
• Ex: wind aids in the diffusion of scents
• cytoplasmic streaming in cells has a similar effect.
• http://www.microscopyuk.org.uk/mag/indexmag.html?http://www.microscopyuk.org.uk/mag/artnov00/dwelodea.html