Demonstration of Osmosis using Potato Osmoscope
What you will learn
Demonstrate endosmosis through living plant tissue using a potato tuber osmoscope containing concentrated sucrose solution placed in water.
Materials needed
- Large healthy Potato TuberWhat is it?Large healthy Potato Tuber₹50
Large firm unsprouted potato tuber (Solanum tuberosum).
Specifications- Freshness
- Fresh harvested turgid tuber
- Dimensions
- Approx 80 mm × 50 mm
- Condition
- Free of greening or mechanical damage
- Concentrated Sucrose / Sugar Solution (20% w/v) colored with eosin/food coloring mLWhat is it?Concentrated Sucrose / Sugar Solution (20% w/v) colored with eosin/food coloring mL₹95
20% (w/v) Analytical grade Sucrose solution with Eosin dye marker.
Specifications- Concentration
- 20.0 g sucrose per 100 mL distilled water
- Osmotic Pressure
- Approx 1.5 MPa hypertonic
- Color Marker
- 0.01% Eosin red dye for high visibility
- Petri Dish with distilled waterWhat is it?Petri Dish with distilled water₹140
Heavy glass Petri dish and stainless steel entomological marking pins.
Specifications- Petri Dish
- 100 mm diameter × 20 mm depth borosilicate glass
- Pins
- 30 mm rust-proof surgical steel indicator pins
- Scalpel / Kitchen Knife & Potato CorerWhat is it?Scalpel / Kitchen Knife & Potato Corer₹185
Standard laboratory apparatus used in Demonstration of Osmosis using Potato Osmoscope.
Specifications- Category
- Biology Apparatus
- Grade
- CBSE / NEP 2020 Laboratory Standard
- All-metal common pinsWhat is it?All-metal common pins₹230
Standard laboratory apparatus used in Demonstration of Osmosis using Potato Osmoscope.
Specifications- Category
- Biology Apparatus
- Grade
- CBSE / NEP 2020 Laboratory Standard
- Petri dish and rulerWhat is it?Petri dish and ruler₹275
Standard laboratory apparatus used in Demonstration of Osmosis using Potato Osmoscope.
Specifications- Category
- Biology Apparatus
- Grade
- CBSE / NEP 2020 Laboratory Standard
Tick items as you collect them. Tap + to see the product, specifications and buy options.
Stay safe
- The bottom wall of the potato cavity must be kept thin (3-5 mm) to facilitate measurable osmotic flux.
- Ensure the sucrose solution level inside the cavity is higher than the outside water level to prevent hydrostatic backpressure.
- Use living, fresh potato cells; boiled potatoes fail because boiling denatures plasma membranes.
- Color the sugar solution with a drop of dye to ensure clear visual tracking.
Steps
- 1Peel the skin from the base and sides of a large fresh potato tuber.Observation
Peel large fresh potato tuber; slice flat base so it stands upright; carve deep central rectangular cavity leaving 5 mm thin walls.
SafetyUse sharp scalpel with care; cut away from fingers on a cutting board.
- 2Slice the base flat so the potato stands upright steadily in the petri dish.Observation
Fill cavity half-full with 20% sucrose solution colored with a trace of eosin red dye.
SafetyDo not spill sugar solution onto outer potato walls.
- 3Scoop out a deep rectangular cavity from the top with a scalpel, leaving a thin base wall (~5 mm thick).Observation
Insert a fine stainless steel pin horizontally into inside cavity wall exactly marking initial meniscus level.
SafetyAlign pin tip precisely with lowest point of colored sucrose meniscus.
- 4Fill the cavity halfway with colored 20% sucrose solution.Observation
Place potato osmoscope in a petri dish filled with distilled water up to one-third of potato height.
SafetyEnsure water level in petri dish is strictly lower than cavity sugar level.
- 5Insert a common pin horizontally into the inner wall of the potato cavity to mark the initial liquid level.Observation
Leave undisturbed for 4 hours; observe marked rise in cavity fluid level above reference pin.
SafetyKeep apparatus covered with bell jar to minimize surface evaporation.
- 6Place the potato osmoscope upright into a petri dish containing clean distilled water (water level below cavity brim).Observation
Mark final level with second pin; measure 15.5 mm rise confirming endo-osmosis across living plant cell membranes.
SafetySet up boiled potato control in parallel to prove necessity of living cell membrane.
- 7Leave the setup undisturbed for 2 hours, then observe and mark the final sugar solution level with a second pin.
Tap + on a step to see what you will observe and any safety tips.
Record your observations
| Time Interval (Hours) | Osmoscope Initial Level (mm) | Current Liquid Level (mm) | Net Rise in Level Δh (mm) | State of Cavity Liquid |
|---|---|---|---|---|
| 0 Hours (Initial) | 10.0 mm (Pin mark) | 10.0 mm | 0.0 mm | Clear hypertonic 20% sucrose |
| 1 Hour | 10.0 mm | 14.5 mm | +4.5 mm | Gradual upward fluid rise |
| 2 Hours | 10.0 mm | 19.0 mm | +9.0 mm | Steady endo-osmotic inflow |
| 3 Hours | 10.0 mm | 23.0 mm | +13.0 mm | Level well above initial pin |
| 4 Hours (Equilibrium) | 10.0 mm | 25.5 mm | +15.5 mm | Steady osmotic hydrostatic equilibrium |
Tap a highlighted cell to write your own observation.
Result and conclusion
Liquid level in the potato cavity rises significantly above the initial pin mark due to water entering from the petri dish (hypotonic) into the sucrose solution (hypertonic) across selectively permeable potato membranes.
| Observation | What it means |
|---|---|
| Living Semi-Permeable Membrane | Living potato tuber cell protoplasm acts as a selectively permeable membrane permitting water molecules while blocking sucrose. |
| Direction of Endo-Osmosis | Water molecules move along water potential gradient from high potential (pure water petri dish) to low potential (sugar cavity). |
| Hydrostatic Turgor Head | Fluid rise in cavity (+15.5 mm) generates hydrostatic pressure head balancing osmotic draw at dynamic equilibrium. |
| Boiled Control Verification | A boiled potato tuber control shows zero rise in liquid level because heat denatures cell membranes, destroying semi-permeability. |
Sample readings. Replace with your own results.