potato osmosis experiment analysis

Understanding Osmosis Using Potato Osmometer

To study by demonstrating the osmosis process by potato osmometer.

What is Osmosis?

Osmosis is the phenomena in which solvent molecules pass through a semi-permeable membrane from an area of higher concentration to an area of lower concentration. The process continues until the quantity of fluid is balanced or equalized in both regions, the region of higher concentration and the region of lower concentration of the semipermeable membrane. In other words, osmosis is the diffusion or movement of water from a region of higher water potential to a region of lower water potential.

In osmosis, what are solvent and solute?

The fluid that permeates through the semipermeable membrane is called the solvent, whereas the solute is the dissolved particles in the fluid.

What is the solution?

The mixture of solute and solvent form the solution.

List the different types of solutions.

The following are the types of solutions:

• Hypertonic solution – It is a solution with a high solute level. If living cells are placed in a hypertonic solution, because of lower concentration water moves out of the cell causing it to shrink and becomes plasmolyzed.
• Hypotonic solution – It is a solution with low concentration levels of solute. If living cells are placed in this solution, water passes into the cells because of higher water concentration in comparison to the cell causing the cells to swell and turn turgid.
• Isotonic solution – A solution is said to be isotonic if both solutions have an equal concentration of solute. If living cells are placed in an isotonic solution, no change is shown as there is the equal concentration on both the regions hence the cell retains its original shape.

Material Required

• A fresh large-sized potato tuber
• 20% sucrose solution
• Scalpel/blade
• A Bell pin needle that is labelled with a waterproof ink

• Slice the potato tuber into two equal halves with the help of a scalpel or a blade. The outer skin is to be peeled off. Since the tuber shape is irregular, slice the halves into squares
• From the mid-region of the tuber, scoop from the soft parenchyma, so as to form a tiny cavity of a square or a circular shape. At the base, the cavity prepared should have a minimum thickness.
• Fill up half the cavity with the freshly prepared 20% sugar solution. Into the cavity, fix a pin in a way that the mark is in the same line with the layer of the sucrose solution.
• Set up the osmometer in a Petri dish/beaker that is filled with water in a way such that 75% of the potato osmometer is immersed in water
• The set up should remain uninterrupted for close to 1 hour.
• Notice the sugar solution in the osmometer towards the end of the experiment
• Carry out the experiment with the help of water in the cavity and the sucrose solution in the petri dish/beaker.

Observation

After a period of time, within the osmoscope, the sugar solution rises and is seen coloured.

• An increase in the level of sucrose solution is observed in the osmometer. It is because of the entrance of water due to endosmosis from the beaker.
• Also, a water potential gradient is built between the sucrose solution in the external water and the osmometer.
• Though both the liquids are divided by living cells of the potato tuber, they allow the entrance of water into the sugar solution.
• This demonstrates the entrance of water into the sugar solution through the tissues of potato serving as a selectively permeable membrane.

Viva Questions

Q.1. What is plasmolysis?

A.1. It is a process, wherein the protoplasm of the plant cell turns round as a result of contraction when placed in a hypertonic solution due to exosmosis resulting in the decline in the tension of the cell wall.

Q.2. What is the significance of osmosis?

A.2. Osmosis maintains cell turgidity. It causes the transportation of nutrients and discharge of metabolic waste products. It preserves the interior environment of a living entity to maintain an equilibrium between the intracellular fluid levels and water.

Q.3. What is diffusion?

A.3. The movement of molecules from a region of higher concentration to a region of lower concentration. Osmosis is a type of diffusion.

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Study of Osmosis by Potato Osmometer

A study of osmosis can be done using a potato osmometer. Osmosis is a phenomenon in which water moves from high solvent to low solvent concentration. The movement of water occurs between two compartments, separated by a semipermeable membrane .

The cell membrane of living organisms behaves as a semipermeable or selective membrane. The permeability of a selective membrane differs based on the size, charge and mass of different molecules.

Biological membranes are impermeable to large biomolecules and polar molecules like ions. But, non-polar molecules (lipids) and small molecules (oxygen, carbon dioxide etc.) can cross the selective barrier.

Water is the solvent that travels down or up the cell concentration gradient through osmosis. We can study water diffusion by creating two compartments and a semipermeable membrane in between.

The difference in the concentration of solutes or solvents between two compartments is the driving force responsible for water movement. Here, we need to note that only solvents can pass the selective barrier, not solutes.

Thus, the diffusion or distribution of water is related to osmosis . This post describes the meaning, requirements, procedure and results of the potato osmometer experiment.

Content: Study of Osmosis by Potato Osmometer

Potato osmometer, materials required, precautions.

It is a common experiment to demonstrate both endosmosis and exosmosis using a potato. Using a potato Osmoscope, we can study osmosis in a living system.

Here, a potato is used because the porous outer surface of the potato acts as a selective membrane .

• The contents within the cell form one compartment.
• The solution surrounding the cell forms another compartment.

Thus, a selective membrane separates two compartments and allows the process of osmosis .

• High solvent concentration in the cell surrounding.
• Low solvent concentration in the cavity of potato tuber.

Following the rule of osmosis, water in the cell surrounding enters the tuber cavity via the cell membrane.

• High solvent concentration in the cavity of potato tuber.
• Low solvent concentration in the cell surrounding.

Following the rule of osmosis, water in the potato cavity enters the surrounding solution via the cell membrane.

• Peeled off potato
• Concentrated sugar solution
• Petri plate

Video: Study of Osmosis

To perform the potato osmometer experiment, we need to follow the given procedure:

• First, peel off the large-sized potato using a peeler or knife.
• Then cut the upper and lower portions of the peeled potato using a knife. Through this step, we can easily place the potato on the Petri plate.
• Using a knife, make a cavity from the centre of the potato deep into the bottom, leaving some space. Here, the bottom of the potato will function as a selective membrane.
• Then, keep the potato on the Petri plate.
• To study endosmosis , pour water into half of the Petri plate. Next, pour the concentrated sugar solution into half of the cavity created in the potato.
• To study exosmosis , add concentrated sugar solution on the Petri plate and water into the cavity of the potato tuber.
• Then, fix a pin into the potato tuber-A and B to mark the level of sugar solution and water added into the cavity.
• Leave the plate undisturbed for some time until you notice any change.

Observation

• Observe the level of sugar solution in the cavity of potato tuber-A.
• Notice the level of water in the cavity of the potato tuber-B.

Potato Osmosis Experiment Results

• The level of sugar solution in the cavity of potato tuber-A increases . It occurs because the water in the Petri plate will move towards the cell with a high solute or low solvent concentration. This experiment shows endosmosis , as water goes into the cell or potato tuber.
• In contrast, the level of water in the cavity of potato tuber-B decreases . Here, water in the cavity moves toward the solution in the Petri plate due to the high solute concentration in the surrounding. This experiment shows exosmosis as water leaves the cell or potato tuber.
• The cavity should be deep enough by leaving a minimum thickness at the bottom.
• The sugar solution should have a high osmotic concentration.

The water movement from the Petri plate to the potato cavity or vice versa is due to the difference in the solvent or solute concentration between the two compartments.

Related Topics:

• Germination of Plant
• Difference Between Root and Stem
• Nerve Impulse
• Ozone Formation
• Examples of Adsorption in Daily Life

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Required Practical: Osmosis ( AQA GCSE Biology )

Revision note.

Biology Lead

Osmosis required practical

• To investigate the range of concentrations of salt or sugar solutions on the mass of plant tissue
• Prepare samples of potatoes (or other plant tissue) and place in different concentrations of sugar or sodium chloride (salt) solution
• Make measurements of mass and length of your samples before and after soaking them in solutions
• Calculate the percentage change in mass of plant tissue
• Plot, draw and interpret appropriate graphs
• In this practical, you should take care to prepare your samples of potato carefully and record your measurements accurately
• This practical can be carried out with either salt or sucrose solutions of at least five different concentrations
• E.g. This experiment can be carried out in a water bath at 30 °C in 30 minutes 

Use these image

Measure out the volumes of solutions and potato lengths carefully using appropriate equipment; all measurements should be recorded

• Concentration of salt or sucrose solution in mol dm 3
• Mass and the length of each potato cylinder before and after it has been submerged in solution should be measured
• Percentage change in mass and length will be calculated using these measurements
• type and volume of solute in solution
• temperature

Analysing osmosis required practical

Use these images

A positive percentage change in mass indicates that the potato has gained water by osmosis (net movement of water from the solution into the potato) meaning the solution is more dilute, a negative percentage change suggests the opposite

Analysing osmosis graph results

• Where results lie above 0 on the X-axis, this means the potato has increased in mass and taken water in from the surrounding solution, via osmosis
• Where results lie below 0 on the X-axis, this means the potato has decreased in mass and water has been lost from the potato, via osmosis
• Where the line crosses the X-axis, this is the concentration of sugar/salt inside the potato and no water has been lost or gained at this point

This is an extremely common exam question – you should be able to calculate the percentage change in mass and length and be able to plot a graph of the results.

You may also be presented with a graph to analyse so make sure you understand what this type of graph is showing. 

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Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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Science Experiments on the Osmosis of a Potato

Osmosis Experiments With Potatoes for Kids

Osmosis, the process in which solvent molecules move from an area of lower solute concentration to an area of higher solute concentration, can easily be demonstrated with potato experiments. Potatoes are full of both water and starch, and will gain water when immersed in watery solutions. Conversely, they will lose water when in concentrated solutions, such as those containing a great deal of starch. You can use potatoes to set up osmosis experiments for students of all ages and levels.

Potatoes in Saltwater

Cut a potato in two, and immerse one of the halves in a very salty solution of water — one containing a quarter cup of salt in a cup of water. Immerse the other piece in tap water containing no added salt. Leave both in their respective solutions for half an hour, then remove the potato halves from their solutions and observe their differences. The one in the salty solution will have shrunk, indicating that water is diffusing from a less concentrated solution to a more concentrated solution. The one in the tap water solution, in contrast, will actually swell slightly, indicating that it is taking in water.

Salt, Sugar and Pure Water

This experiment helps students to differentiate between different degrees of concentration gradients. Make one salt water solution, one sugar water solution, and for the third solution, simply use tap water. Make three thin potato slices — 1/2 cm thick. Place each potato slice into each of the solutions, and leave the slices in the solutions for a half hour.

Observe that the slice placed in salt is very flexible, while the slice placed in sugar is flexible, but less so. Since potatoes already contain sugar, less water will diffuse out of the potato placed in sugar water. The slice placed in water will be rigid, since it will absorb water.

Potato Lengths in Saline Solutions

Give your students potato "cylinders" that are uniform in length and size: for instance, you could cut them to be 70 mm in length and 7 mm in diameter. Make solutions of saline in three different concentrations, 20 percent, 0.9 percent and 0.1 percent. Have the students measure the lengths and diameters of the potato cylinders before and after soaking them in the saline solutions for half an hour. Then, have them calculate the changes in the lengths and diameters of the cylinders, and plot the saline concentrations versus the changes.

Potato Cube Weights

Cut potatoes into four groups of small, uniform cubes measuring 1/2 cm by 1/2 cm. Make four different solutions of sucrose: 10 percent, 5 percent, 1 percent and 0.01 percent. Weigh each group, on a mass balance, before immersing it in the appropriate sucrose solution for half an hour. After immersion, weigh each group again and have your students calculate the changes in the potato masses. Ask them to comment on why a group gained mass, lost mass or retained the same mass.

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Osmosis Potato Experiment: DIY Science Project Ideas for Kids

Finished with your lesson on Osmosis but still confused? Then you need to perform this simple Osmosis experiment. All you need are some potato slices and water. Learn about osmosis with potato slices in this simple osmosis potato experiment. Performing science experiments for kids will enable them to understand challenging scientific concept they are learning in a much better way.

Step-by-Step Instructions on How to Perform Osmosis Potato Experiment

Osmosis is the process by which water or any other solvent moves towards a solution with a higher concentration through a semipermeable membrane. The molecules in the solution with a lower concentration move towards the solution with a higher concentration to equalize the concentration on both sides. Osmosis is how plants absorb water and nutrients from the soil.

A simple science experiment for kids like the Osmosis Potato Experiment helps kids understand the concept easily.

What You’ll Need?

If you leave cut slices of potatoes or apples or pears outside for a while, you’ll notice that they turn brown. Why do you think this discoloration occurs? When you cut these fruits or vegetables, it leaves the cells open. An enzyme present in the cells, polyphenol oxidase, reacts with the oxygen in the air and turns the fruit brown. But can you prevent the slices from turning brown and keep them fresher for longer? Let’s learn through this osmosis potato experiment.

Here is a list of things you’ll need to perform the experiment:

• 1 medium sized potato
• 2 – 4 tablespoons of salt
• Distilled water
• 2 medium sized mason jars or drinking glasses

How to Perform Osmosis Potato Experiment?

Follow these instructions to perform the experiment:

• Step 1: Peel and cut the potatoes so you have wedges that are neither too thick nor too thin. Ensure that the potato wedges are roughly the same size. Note down the color of the freshly cut potato wedges and how they feel when you touch them.
• Step 2: Pour 200ml of distilled water into one glass or jar. 
• Step 3: Into the second glass, pour 200ml of distilled water and add 2-4 tablespoons of salt. Stir it well until the salt is completely dissolved.
• Step 4: Add two potato wedges into each of the glasses and let them sit overnight.
• Step 5: The next day, you’ll notice a difference in both the glasses. The potato wedges in the glass with the unsalted water have become bigger, while the wedges in the salted water have shrunk slightly.
• Step 6: Take the potato wedges out of the unsalted water and try bending them. You’ll notice that it is firm and breaks but doesn’t bend. Additionally, it still has a white color like a freshly cut piece of potato.
• Step 7: Now take the potato wedges out of the salted solution and try to bend them. You’ll notice the wedges have turned brown and bend easily without breaking.

What You’ll See?

Once you’ve performed the experiment, help your child understand the science behind the osmosis experiment. Here are a few questions and answers that will help children understand the behavior of the potato wedges in the two different solutions.

• Why did the potato wedges in the glass with plain distilled water become bigger?

The potato wedges expand and become bigger because of osmosis. Potatoes are made of millions of cells and the cell walls act as a semipermeable membrane. The water molecules move into the potato through this membrane to balance the concentration levels. The water moving inside the potato cells causes it to expand and become bigger. 

• Why did the potato wedges in the glass with salt water shrink?

Again it’s because of osmosis. The salt solution has a higher concentration and the water inside the potato moves through the cell walls to balance the concentration in the saltwater. Since the water moves out of the potato wedge, it shrinks and becomes smaller. This is also the reason why the potato wedge in the salt solution becomes less rigid and bends easily.

• Why did the potato wedges in the salt solution change color?

The water moving out of the potato damages it’s cells, which causes them to release an enzyme called catechol oxidase. The enzyme in the potato cells reacts with the oxygen in the air and turns the wedges brown.

Other Way to Perform Osmosis Potato Experiment for Kids

Another cool way to see osmosis in action is to perform this experiment using grapes and raisins.

• 2 – 3 raisins
• 2 – 3 fresh grapes
• 3 – 4 tablespoons of sugar

Step-by-Step Guide on How to Perform Osmosis Potato Experiment

Follow these instructions to perform this experiment:

• Step 1: Add the 3 – 4 tablespoons of sugar into one glass of water and stir it until all the sugar is dissolved. Then add 2 -3 fresh grapes into the sugar solution.
• Step 2: Add 2 – 3 raisins to the second glass of water. Allow both glasses to sit for a few hours.
• Step 3: After a few hours, you’ll notice that the raisins in the plain water have plumped up almost as if they are grapes. The raisins have a higher concentration of sugar, so the water moves into the raisins to balance the amount of sugar. This causes the raisins to expand and plump up.
• Step 4: Meanwhile the grapes in the sugar solution have shrunk and almost look like raisins. The water surrounding the grapes has a higher concentration of sugar than water in the grape cells. So the water in the grape cells moves out to balance the level of sugar. This causes the grapes to shrink in size.

Can you use other vegetables or fruits to perform this experiment? Will sliced bananas or pineapples work the same way? The only way to know is to try. Looking for more cool science experiments to try with your kids? Check our kids learning section for more fun and informative science experiments.

Frequently Asked Questions on Osmosis Potato Experiment

What is osmosis.

Osmosis is the process by which a solution with a lower concentration moves towards a solution with a higher concentration through a semipermeable membrane to balance the levels of concentration.

Why does the potato in the salt solution shrink?

Potato cells also have water in them. The water in the potato tries to equalize the concentration by moving towards the saltwater. The loss of water causes the potato to shrink and also makes it bendy and less firm.

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