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Osmosis is the movement of molecules of a solvent from a solution of low concentration to a solution of high concentration through a semi-permeable membrane. Osmosis plays a significant role in plants, animals, and also in humans.
- Study of Osmosis by Potato Osmometer is a demonstration of osmosis in living plant cells.
- Potato Osmometer, also known as Potato Osmoscope is used to demonstrate the process of osmosis.
- The water from the surroundings moves into the cells of the potato through the semi-permeable plasma membrane.
- The water is transported from a region of higher concentration to a lower concentration within the potato cells.
Osmosis helps the roots of plants to absorb water from the surroundings into the cell sap. It also helps in transporting water to higher parts of plants such as leaves, branches, fruits, flowers, etc.
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Key Terms: Osmosis, Potato Osmometer, Potato Osmoscope, Cells, Plasma Membrane, Solvent, Molecules, Exosomosis, Endosmosis
Study of Osmosis by Potato Osmometer
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Osmosis is defined as the movement of molecules from a region of higher concentration to a lower concentration until the concentrations become equal on either side of the membrane.
- Osmosis can easily be demonstrated with the help of a Potato Osmometer.
- It helps to study the phenomenon of osmosis in a living system.
- The experiment is used to demonstrate both endosmosis and exosmosis using a potato.
- Potato is used in the experiment due to its porous outer surface acting as a selective membrane.
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Aim of Experiment
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To study the process of Osmosis by a Potato Osmometer.
Osmosis and DiffusionOsmosis and Diffusion are two types of passive transport that play an important role in moving molecules in and out of the cell.
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Principle
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Osmosis is the movement of water (or solvent) molecules from the region of their higher concentration to the region of their lower concentration through a semipermeable membrane. The process of osmosis continues until the quantity of fluid is equal in both regions, i.e. the region of higher concentration and the region of lower concentration.
- Osmosis is a special type of passive diffusion of only solvent molecules through a semi-permeable membrane.
- Semi-permeable Membrane is a kind of membrane that helps in the movement of solvents but prevents the movement of solute particles.
- The cell membrane of a living cell is semi-permeable in nature.
Types of Osmosis
Osmosis can be categorized into two major types depending on the concentration of solvent inside the cell and outside the cell:
- Exosomosis: It is the movement of water molecules out of the cell sap through the plasma membrane. It occurs when the solution outside the cell is hypertonic.
- Endosmosis: It is the movement of water molecules into the cell sap when the solution outside the cell is hypotonic in nature.
Important Terms Related to Osmosis
- Solvent: It is the fluid that permeates through the semipermeable membrane and dissolves the solute.
- Solute: It is a substance that can be dissolved into a solution by a solvent.
- Solution: Solution is a homogeneous mixture of one or more solutes dissolved in a solvent.
Osmotic Solutions
There are three different types of solutions during Osmosis:
- Isotonic Solution: It is a solution that has the same concentration of solutes both inside and outside the cell. If living cells are placed in an isotonic solution, there is no change as there is an equal concentration in both regions. Thus, the cell retains its original shape.
- Hypertonic Solution: It is a solution that has a higher solute concentration outside the cell than inside. If living cells are placed in a hypertonic solution, water moves out of the cell because of lower concentration causing it to shrink and become plasmolyzed.
- Hypotonic Solution: It is a solution that has a higher solute concentration inside the cell than outside. If living cells are placed in a hypotonic solution, water moves into the cells due to higher water concentration in comparison to the cell. It causes the cells to swell and turn turgid.
Materials Required
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To study Osmosis by Potato Osmometer, the following material is required:
- Fresh Large Potato
- 20% Sucrose Solution
- Beaker
- Water
- Scalpel/Blade
- Petri Dish
- Bell Pin Needle labeled with a Waterproof Ink
Procedure
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Follow the given steps to study the phenomenon of Osmosis by Potato Osmometer:
- Take a large and fresh potato and slice the potato tuber into two equal halves with the help of a scalpel or a blade.
- Peel off the outer skin and slice the halves into squares.
- Scoop off the potato from the mid-region of the tuber to form a tiny cavity of a square or a circular shape.
- The cavity prepared should have a minimum thickness at the base.
- Now, fill up the cavity with the freshly prepared 20% sugar solution halfway.
- Fix a pin in the cavity in a way that the mark is in the same line as the layer of the sucrose solution.
- Set up the prepared osmometer in a Petri Dish/Beaker filled with water such that 75% of the potato osmometer is immersed in water.
- The setup should be kept uninterrupted for up to 1 hour.
- Keep a note of the sugar solution in the osmometer towards the end of the experiment
- Lastly, carry out the same experiment with water in the cavity and the sucrose solution in the petri dish/beaker.
Study of Osmosis by Potato Osmometer
Observation
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On observing the Potato Osmometer under the given setup, the following observations can be made:
- The sugar solution rises and is seen colored within the osmoscope after an interval of time.
- The rise in the level of sugar solution in the cavity of the potato tuber indicates that the sugar solution has absorbed water from the petri dish.
- The two regions are separated from each other by a large number of cells.
- Cell membranes of different cells serve as one unit of a selectively semipermeable membrane.
Conclusion
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Through the given experiment, the following conclusion is derived:
- The level of sucrose solution is increased in the osmometer due to the entrance of water through endosmosis from the beaker.
- Cytoplasm of the cells of the tuber that lie between the sugar solution and the water of the petri dish act as a single semipermeable membrane.
- Water enters the sugar solution through the tissues of the potato serving as a selectively permeable membrane.
Precautions
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The following precautions need to be taken care of during the experiment:
- The cavity should be vertical and deep so as to leave only a thin layer of tissue at the base.
- Peel off the skin of the tuber from the base and sides.
- Make a flat base so as to keep the potato tuber intact in water in the petri dish.
- The sugar solution should have a higher osmotic concentration as compared to the cell sap of the tuber cells.
- Marking of level with pin should be done carefully.
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Things to Remember
- Osmosis is the movement of water molecules from a region of high concentration to a region of low concentration.
- Osmosis is of two types namely Exosmosis and Endosmosis.
- The solvent molecules move inside the cell in Endosmosis while the molecules move outside the cell in Exosmosis.
- Isotonic Solution, Hypertonic Solution, and Hypotonic Solution are the three types of Osmotic Solutions.
- In the potato osmometer experiment, the cells of the potato allow the entry of water molecules, i.e. the cells exhibit endosmosis.
- The water molecules reach the sugar solution kept inside the potato osmometer, causing a rise in the level of the sugar solution.
- Potato acts as a selectively permeable membrane due to its porous outer surface.
Viva Questions
Here are some important viva questions related to the experiment on ‘Study of Osmosis by Potato Osmometer’:
Ques. What is Osmosis?
Ans. Osmosis is defined as the movement of molecules of a solvent from a solution of low concentration to a solution of high concentration through a semi-permeable membrane.
Ques. What is Plasmolysis?
Ans. Plasmolysis is a process in which the protoplasm of the plant cell turns round due to the contraction when placed in a hypertonic solution due to exosmosis leading to a decline in the tension of the cell wall.
Ques. Name the different types of Osmotic Solutions.
Ans. There are three types of Osmotic Solutions:
- Isotonic Solution
- Hypertonic Solution
- Hypotonic Solution
Ques. State the Significance of Osmosis.
Ans. Osmosis is an integral process in plant cells as it helps to maintain cell turgidity. It helps in the transportation of nutrients and the discharge of metabolic waste products. Osmosis also maintains the internal environment of a living entity to maintain an equilibrium between intracellular fluid levels and water.
Ques. What is Diffusion? Is Osmosis diffusion only?
Ans. Diffusion is defined as the movement of molecules from a region of higher concentration to a region of lower concentration. Yes, Osmosis is a special type of diffusion.
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Sample Questions
Ques. Define Osmosis. (3 Marks)
Ans. Osmosis is a special type of diffusion that involves the movement of molecules from a region of higher concentration to a lower concentration through a semi-permeable membrane.
- It continues until the quantity of fluid is balanced or equalized in both the regions, i.e. the region of higher concentration and the region of lower concentration.
- It is a passive process and occurs without any expenditure of energy.
- Osmosis plays a significant role in plants, animals, and humans.
Ques. What will happen if a plant cell is kept in a solution of higher Water Potential? (2 Marks)
Ans. If the solution has a higher water potential, then Endosmosis will occur. The solvent molecules move inside the cell and the cell becomes turgid or undergoes deplasmolysis. A solution that has a higher solute concentration inside the cell than outside is known as Hypotonic Solution. Endosmosis occurs in a Hypotonic Solution leading to the turgidity of cells.
Ques. What is a Semipermeable Membrane? (3 Marks)
Ans. Semi-Permeable membrane is defined as a membrane through which only smaller molecules like water can pass but not the bigger molecules like solutes.
- It allows only the entry of solvent or selective solute substances.
- They appear to be continuous sheets or films but contain a network of sub-microscopic holes or pores through which smaller solvent molecules can pass easily.
- Examples of semipermeable membranes include Cellulose acetate, potassium ferrocyanide, etc.
Ques. State the different types of Osmotic Solutions. (3 Marks)
Ans. Osmotic Solutions are of three types namely:
- Isotonic Solution: Isotonic Solution is a solution that has the same concentration of solutes both inside and outside the cell.
- Hypertonic Solution: Hypertonic Solution is a solution that has a higher solute concentration outside the cell than inside.
- Hypotonic Solution: Hypotonic Solution is a solution that has a higher solute concentration inside the cell than outside.
Ques. What are the types of Osmosis? (3 Marks)
Ans. Osmosis is classified into two types which are:
- Endosmosis: During endosmosis, the solvent moves into the cell. When a cell is placed in a hypotonic solution, the water moves inside the cell and swells as the solute concentration of the surrounding solution is less than that inside the cytoplasm.
- Exosmosis: During exosmosis, the solvent moves out of the cell. When a substance is placed in a hypertonic solution, the solvent molecules move outside the cell and it becomes flaccid as the solute concentration of the surrounding solution is higher than that inside the cytoplasm.
Ques. Define an Osmotically Active Solution. (1 Mark)
Ans. Osmotically Active Solution is a solution that can cause an osmotic entry of water into it.
Ques. What is Turgidity in Osmosis? (1 Mark)
Ans. Turgidity is a condition of the cell under which it cannot absorb more water by osmosis when placed in a hypotonic solution.
Ques. Explain the Significance of Osmosis. (3 Marks)
Ans. Osmosis is a very important phenomenon owing to the following reasons:
- It influences the transport of nutrients and the release of metabolic waste products in Plants.
- It helps in the absorption of water from the soil and conducts it to the upper parts of the plant through Xylem.
- It maintains the balance between water and intercellular fluid levels, thus, stabilizing the internal environment of a living organism
- Osmosis maintains the turgidity of plant cells.
- It is a process through which plants are able to maintain their water content despite the constant water loss due to transpiration.
Ques. What will be the rate of osmosis if a 5% sugar solution is used in the Osmometer? (1 Mark)
Ans. The rate of osmosis in a 5% sugar solution in an osmometer will be low as osmosis is dependent upon the degree of reduction of free energy of one solvent over the other.
Ques. How does water from outside enter the Osmometer? Does it pass through the cells of the Tuber? (2 Marks)
Ans. The water enters the osmometer through the semipermeable membrane of the cells of the potato, which allows the entry of solvent or selective solute substances. The water passes through the cells of the tuber into the cavity. The cell membrane of different cells of both regions serves as one unit of a selectively semipermeable membrane.
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