Module 3/ Osmosis

Question 1

Non penetrating molecules

Answer 1

They interact with water molecules, preventing them to cross the membrane.

Question 2

Osmolarity

Answer 2

Concentration of all solutes in a solution both penetrating and non-penetrating (osmole/L).

Question 3

Tonicity

Answer 3

The ability of a solution to create a net movement of water inside or outside of a cell. Tonicity is therefore the effective osmolarity with regards to the osmotic pressure and us expressed as “effective osmole/L”.

Question 4

Osmosis

Answer 4

-Diffusion of free water across a selectively permeable membrane. Osmosis depends on the concentration of non-penetrating molecules.

-Water moves through a semipermeable membrane from the compartment of low to the compartment of high concentration of non-penetrating solutes.

-From hypotonic to the hypertonic compartment.

Question 5

Osmotic pressure

Answer 5

Osmosis can create an osmotic pressure and change the volume of a cell.

-Osmotic pressure is the minimum pressure required to stop the net movement of water across a semipermeable membrane.

-The osmotic pressure is a function of the difference in the concentration on non-penetrating molecules. Higher tonicity inside the cell increases the osmotic pressure inside the cell.

Question 6

Osmosis in life

Answer 6

In plants, the maintenance of osmotic pressure facilitates the transport of water. Freshwater protists are hypertonic compared to their environment, creating a movement of water inside the cell by osmosis.