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Cell - Demonstrate and explain osmosis, diffusion, and membrane permeability in cells

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Diffusion is the spontaneous movement of substances (like O2O_{2} and CO2CO_{2}) from a region of high concentration to a region of low concentration.

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Osmosis is a specific type of diffusion involving the movement of water molecules through a selectively permeable membrane from a region of high water concentration to a region of low water concentration.

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A Hypotonic solution is one where the external medium has a higher water concentration than the cell ([H2O]outside>[H2O]inside[H_{2}O]_{outside} > [H_{2}O]_{inside}), causing the cell to swell due to endosmosis.

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An Isotonic solution is one where the concentration of water is the same inside and outside the cell, resulting in no net movement of water.

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A Hypertonic solution is one where the external medium has a lower water concentration than the cell ([H2O]outside<[H2O]inside[H_{2}O]_{outside} < [H_{2}O]_{inside}), causing the cell to shrink due to exosmosis.

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Plasmolysis occurs when a living plant cell loses water through osmosis, leading to the shrinkage or contraction of the protoplast away from the cell wall.

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The Plasma Membrane is called a selectively permeable membrane because it allows the entry and exit of some materials while preventing the movement of others.

📐Formulae

Net Water Movement=(Water Inflow)−(Water Outflow)Net\ Water\ Movement = (Water\ Inflow) - (Water\ Outflow) sentiments

Concentration Gradient (ΔC)=Chigh−Clow\text{Concentration Gradient } (\Delta C) = C_{high} - C_{low}

Condition for Endosmosis: [H2O]ext>[H2O]int\text{Condition for Endosmosis: } [H_{2}O]_{ext} > [H_{2}O]_{int}

Condition for Exosmosis: [H2O]ext<[H2O]int\text{Condition for Exosmosis: } [H_{2}O]_{ext} < [H_{2}O]_{int}

💡Examples

Problem 1:

A dry raisin (dried grape) is placed in a beaker containing pure water for 4 hours. What will happen to the raisin and why?

Solution:

The raisin will swell and increase in size. This happens because the concentration of water inside the raisin is lower than the concentration of pure water in the beaker ([H2O]beaker>[H2O]raisin[H_{2}O]_{beaker} > [H_{2}O]_{raisin}).

Explanation:

This is an example of endosmosis where water moves across the selectively permeable skin of the raisin into the cells.

Problem 2:

What happens to a Red Blood Cell (RBC) if it is placed in a concentrated salt solution?

Solution:

The RBC will shrink in size. The concentrated salt solution is hypertonic to the cell sap ([H2O]cell>[H2O]solution[H_{2}O]_{cell} > [H_{2}O]_{solution}), leading to the movement of water out of the cell.

Explanation:

This process is called exosmosis. Unlike plant cells, animal cells like RBCs do not have a cell wall, so they can shrink significantly or even shrivel up.

Problem 3:

If a plant cell is placed in a sugar solution and the cell contents shrink away from the cell wall, identify the phenomenon.

Solution:

The phenomenon is called Plasmolysis.

Explanation:

When a plant cell is placed in a hypertonic solution, it loses water through osmosis. Since the cell wall is rigid, it maintains its shape while the inner contents (plasma membrane and cytoplasm) contract toward the center.