Osmosis and Tonicity

What is osmosis

The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to high solute concentration, until equilibrium is reached

What does “semi-permeable” mean in osmosis

It means the membrane allows water to pass but blocks most solutes

Why does water move toward higher solute concentrations

In a hypertonic solution, fewer free water molecules cause water to move from a hypotonic area down its concentration gradient

Is osmosis an active or passive process

Passive, because water moves along the water concentration gradient and does not require energy (ATP).

What are aquaporins

Integral membrane proteins that act as water channels within the phospholipid bilayer

What is the function of aquaporins

They increase the rate of water transport across the membrane in response to solute concentration changes

How do aquaporins help maintain cell balance

Their number and activity can be regulated, allowing the cell to control osmotic conditions and prevent too much water gain or loss

What are the three types of osmotic solutions

Hypertonic, hypotonic, and isotonic

What is a hypertonic solution

A solution with a higher solute concentration than the cell

What happens to a cell in a hypertonic solution

Water moves out of the cell, causing it to shrink (animal cells shrink; plant cells become plasmolysed)

What is a hypotonic solution

A solution with a lower solute concentration than the cell

What happens to a cell in a hypotonic solution

Water enters the cell, causing it to swell (animal cells may burst, plant cells become turgid)

What is an isotonic solution

A solution with the same solute concentration as the cell

What happens to a cell in an isotonic solution

here is no net water movement the cell stays the same size