DIFFUSION & OSMOSIS

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What is Diffusion?

The Movement of Particles Down the concentration gradient

When particles move down the concentration gradient they travel from a place of high concentration to low concentration
This process of diffusion DOES NOT REQUIRE ATP (ENERGY( and it's a method of passive transport.
In the cell particles can diffuse by moving between the loosely bound phospholipids in the cell membrane's bilayer
- However, only small non-polar (lipid soluble) molecules can pass through.
  - Examples of lipid soluble molecules are O2, CO2, H2O, glycerol, alcohol etc.
  - Only small non-polar molecules can slip through the membrane since they are not attracted to the hydrophilic (polar-loving) heads of the phospholipid bilayer.

Factors that Affect the Rate of Diffusion

TEMPERATURE:

The more kinetic energy the particles have the faster they are able to diffuse through any medium.
As the particles gain energy they are able to rapidly move around at high speeds which aids them as they attempt to cross the cell membrane or any other medium.
- The faster the particle the quicker it can diffuse and the easier it is for it to get through any medium like the cell membrane.

PARTICLE SIZE:

Smaller particles, especially ones that are non-polar, can move more rapidly through a medium like the cell membrane.
The smaller the particle the easier it is to slip through a medium.

CONCENTRATION GRADIENT:

The greater the concentration difference across a medium the faster the rate of diffusion will be.
Particles will ALWAYS want to move to the side of the medium that has the LOWEST CONCENTRATION. Therefore, particles on the side of high concentration will rapidly move to a place of low concentration if there is one.

DENSITY OF THE MEDIUM:

The medium is what the particles are moving across or through (it can be anything from the cell membrane to a simple paper)
The more tightly packed or denser the medium is the harder it is for particles to slip through it. If the medium is loosely packed or less dense than particles are more easily able to move across it with less effort and resistance and therefore, increases the diffusion rate.

Equal Concentration

High Concentration

What is Osmosis?

Osmosis is the movement of water particles across a membrane from a place of high concentration to a low concentration.
This process is also a part of passive transport as it DOES NOT REQUIRE ANY ATP (ENERGY).
A water particle is able to move across the phospholipid bilayer even through it is a polar molecule because it is a VERY SMALL PARTICLE that is able to slip through the loosely packed phospholipid bilayer without becoming attracted to the hydrophilic (polar-loving) heads.
Water can easily move across the membrane since it follows the law of diffusion.
- Law of Diffusion: water will move from where it is highly concentrated to a place of lower concentration.
- THE MORE SOLUTE (like salt) THAT IS DISSOLVED IN WATER THE SMALLER THE WATER CONCENTRATION ON THAT SIDE.

High Concentration of H2O

Low Concentration of H2O

Key Terms

Osmosis

The net movement of water from a place of high concentration to low concentration through a selectively permeable membrane.

Solute & Solvent

Solute are particles (like salt) that are dissolved in water (more solute dissolved in water the lower the water concentration). Solvent is a liquid (usually water) that dissolved the solute within it.

High Concentration of H2O

Solution

Combination of solute and solvent.