Osmosis

Question 1

What Is Osmosis

Answer 1

Osmosis is the net movement of water molecules from an area of high water potential to an area of low water potential, through a partially permeable membrane.

Question 2

Key Features:

Answer 2

Passive process (does not require energy)

Always involves the movement of water

Occurs through a partially permeable membrane

Continues until equilibrium is reached (no net movement of water)

Question 3

If two aqueous solutions are separated by a partially permeable membrane, water molecules will move from the solution with the ——- water potential to the ..

Answer 3

Highest, solution with the lowest water potential

Question 4

What is water potential ?l

Answer 4

Water potential (represented by the symbol Ψ) is a measure of the potential energy of water molecules to move.

Question 5

Understanding Water Potential

Answer 5

Pure water has the highest water potential: Ψ = 0

Adding a solute (a dissolved solid e.g salt or sugar) lowers the water potential (Ψ becomes more negative)

The more negative the value, the lower the water potential

Water always moves from high Ψ to low Ψ

Question 6

pure water has the ——– water potential of ————.
Adding solute to the solvent —————- the water potential of the solution

Answer 6

Highest
0 KPA
decreases

Question 7

Osmosis in Different Solutions

1️⃣ Dilute Solution (High Water Potential)

Answer 7

e.g. Pure water

Solution has a higher Ψ than the cell

Water moves into the cell by osmosis

In animal cells, this causes swelling and possible bursting (lysis) as the membrane can’t withstand pressure

Question 8

Isotonic Solution (Equal Water Potential)
example saline

Answer 8

Solution has the same Ψ as the cell cytoplasm

No net movement of water

Water moves equally in and out – equilibrium is reached

Cell remains the same size and shape

Question 9

Concentrated Solution (Low Water Potential)

Answer 9

e.g. sugar solution

Solution has a lower Ψ than the cell

Water moves out of the cell by osmosis

In animal cells, this causes them to shrink and shrivel (crenation), due to water loss from the cytoplasm

Question 10

Factors Affecting the Rate of Osmosis

Answer 10

📉 1. Water Potential Gradient

A greater difference in water potential = faster osmosis

As Ψ levels out (equilibrium), osmosis slows down

📐 2. Surface Area

Larger surface area = increased osmosis rate

More membrane area for water molecules to cross

🧮 3. Number of Aquaporins

Aquaporins = channel proteins that specifically allow water through

More aquaporins = faster osmosis (common in cells adapted for water transport)

Question 11

Hypertonic – define

Answer 11

Lower Ψ outside the cell (water moves out)

Question 12

Hypotonic – define

Answer 12

Higher Ψ outside the cell (water moves in)