Gr 11 passive transport

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Video Summarizing Passive Transport

Diffusion

Diffusion is the net movement of molecules from a region of high concentration to a region of low concentration

This directional movement along a gradient is passive and will continue until molecules become evenly dispersed (equilibrium)
Small and non-polar (lipophilic) molecules will be able to freely diffuse across cell membranes (e.g. O₂, CO₂, glycerol)

The rate of diffusion can be influenced by a number of factors, including:

Temperature (affects kinetic energy of particles in solution)
Molecular size (larger particles are subjected to greater resistance within a fluid medium)
Steepness of gradient (rate of diffusion will be greater with a higher concentration gradient)

Osmosis

Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)

Water is considered the universal solvent – it will associate with, and dissolve, polar or charged molecules (solutes)
Because solutes cannot cross a cell membrane unaided, water will move to equalise the two solutions
At a higher solute concentration there are less free water molecules in solution as water is associated with the solute
Osmosis is essentially the diffusion of free water molecules and hence occurs from regions of low solute concentration

Facilitated Diffusion

Facilitated diffusion is the passive movement of molecules across the cell membrane via the aid of a membrane protein

It is utilised by molecules that are unable to freely cross the phospholipid bilayer (e.g. large, polar molecules and ions)
This process is mediated by two distinct types of transport proteins – channel proteins and carrier proteins

Osmolarity Experiment

What are the materials?

What are the variables?

What is the purpose?

What solute concentration would give no change in mass?

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