OSMOSIS
Your first mission: find a water molecule.
2. Make a prediction
Which way do you think the water will move?
More available water
More solute
The vertical strip is a partially permeable membrane.
3. Watch osmosis happen
HIGHER WATER POTENTIAL → LOWER WATER POTENTIAL
Water moves through the partially permeable membrane. That net movement is osmosis.
4. The core idea — tap to explore
OSMOSIS
The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.
Same idea, deeper language
🌱 Beginner:
Water moves from where there is more available water to where there is less.
📘 GCSE:
Water moves from higher to lower water potential through a partially permeable membrane.
🎓 A-Level:
Osmosis is the net movement of water molecules down a water-potential gradient across a partially permeable membrane.
5. Explore a rotatable plant cell
Tap a structure
I'll explain it here — and it'll glow on the cell too.
6. Put the plant cell into a solution
Choose the surrounding solution:
Watch what happens to the water, vacuole and cell.
7. Plant cell vs animal cell
🌱 Plant cell
A cell wall helps the cell resist bursting.
🔵 Animal cell
No cell wall — too much water can cause lysis.
8. A-Level extension: water potential
Tap for detail
Tap for detail
9. Control the water-potential gradient
Solution A
Solution B
More solute → lower water potential.
10. Osmosis in real life
🌱 Plants
Water enters root hair cells by osmosis. Turgor helps keep plant tissues firm.
🥒 Pickles
High salt concentration outside cells lowers water potential, drawing water out by osmosis.
🍇 Raisins
In water, water enters the raisin cells by osmosis, making them swell.
🩺 IV fluids
Solutions must be carefully balanced so cells do not gain or lose excessive water.
🐟 Fish
Freshwater and marine animals face different water-potential gradients and must regulate water balance.
🧠 Body cells
Cells need their surrounding fluid to stay within a suitable concentration range.
11. Ready to test yourself?
You've predicted, watched, explored a rotatable cell, run experiments, and applied osmosis to real life.
Your quiz for this lesson is right where it already lives — close this interactive lesson and tap 🎯 Take the Quiz on the lesson page. Same questions, same scoring, same progress tracking you already trust — nothing new to duplicate here.
OSMOSIS
The movement of water across a partially permeable membrane ♡
1. What is Osmosis?
Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane. 💙
2. Key Terms
- Water Potential (Ψ) — the tendency of water to move from one place to another.
- Partially Permeable Membrane — lets water through but not solutes.
- Solute — substance dissolved in water.
- Solvent — the liquid (usually water) doing the dissolving.
Pure water has the highest water potential (Ψ = 0).
3. How Osmosis Works
🔵 Water molecules 🟣 Solute molecules
4. Effect of Osmosis in Animal & Plant Cells
Animal Cell
Plant Cell
5. Importance of Osmosis
- Absorption of water by root hair cells.
- Water balance in plants — turgidity provides support.
- Opening and closing of stomata.
- Maintenance of cell shape and size in animals.
- Kidney tubule reabsorption of water.
- Preservation of food (salting/sugaring). 💚
6. Factors Affecting Osmosis
- Concentration gradient — bigger difference, faster osmosis.
- Temperature — higher temp, faster osmosis.
- Surface area of membrane — larger area, faster.
- Thickness of membrane — thinner, faster.
- Nature of membrane — more permeable, faster.
7. Water Potential (Ψ)
(always −ve)Pressure potential
(may be +, − or 0)
Pure water → Ψ = 0. Water moves from higher Ψ to lower Ψ.
8. Examples
- Raisins in water swell — water enters by osmosis.
- Salted cucumber softens — water leaves by osmosis.
- Fish in freshwater take in water and excrete excess.
- Wilted plants become firm again when watered.
9. Summary Table
| Solution | Definition | Water Movement | Animal Cell | Plant Cell |
|---|---|---|---|---|
| Hypotonic | Lower solute conc. (higher Ψ) | Enters the cell | Swells, may burst (lysis) | Turgid (firm) |
| Isotonic | Same solute concentration | No net movement | Normal | Flaccid (limp) |
| Hypertonic | Higher solute conc. (lower Ψ) | Leaves the cell | Shrinks (crenation) | Plasmolysed (shrunken) |
You explored, predicted, experimented and applied the concept.