Question

Topic 3: Osmosis, osmolarity, and tonicity.

Describe the process of osmosis, including answers of the following

• Define osmosis

• Is osmosis an active or passive process? What does this mean?

• What molecules are moving and in what direction? What factors influence this movement?

• What is the difference between osmolarity and tonicity? Give definitions of both

• For each of the following solutions, state the tonicity of the solution and describe what would happen to RBC if placed in a solution

  • O.15M NaCl solution

  • 0.2M urea solution

  • 0.5M glucose solution

• What type of solution is given in a typical IV? Why?

Answer 1

1. Osmosis = Movement of solvent particles along the concnetration/pressure gradient across a semi-permeable membrane.
It is mediated by pressure gradient or concentration gradient.

2. Osmosis is a passive process
i.e. It does not require ATP hydrolysis

3. Solvent moelcules are moving from high concentration/pressure to low concentration/pressure.

4. Osmolarity = Total solute concentration
Osmolarity takes into consideration of all solutes (Both penetarting and nonpenetrating solutes)
Tonicity = Concentration of impermeable solutes
Tonicity takes into consderation of non-freely penetrating solutes only