Osmosis with an Egg Activity

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Questions and Answers

What is the net movement of water across a selectively permeable membrane called?

Diffusion

Osmosis (correct)

Endocytosis

Exocytosis

What happens to a de-shelled egg when placed in a concentrated salt solution?

It remains the same size

It swells

It shrinks (correct)

It dissolves

Why do uncooked de-shelled eggs swell in pure water?

Salt concentration decreases

Calcium carbonate is absorbed

Water molecules pass into the egg by osmosis (correct)

Water molecules are larger

Which of the following organisms acquires its food through endocytosis?

Amoeba Signup and view all the answers

What happens to dried raisins or apricots when placed in a concentrated sugar or salt solution?

They shrink Signup and view all the answers

What types of molecules make up the plasma membrane?

Lipids and proteins Signup and view all the answers

What is an example of osmosis in unicellular freshwater organisms?

Absorption of water Signup and view all the answers

Which process involves the cell engulfing food and other material from its external environment?

Endocytosis Signup and view all the answers

What is the primary component of the plant cell wall?

Cellulose Signup and view all the answers

What is the phenomenon called when the contents of a plant cell shrink away from the cell wall due to water loss?

Plasmolysis Signup and view all the answers

What happens to plant cells when placed in hypotonic external media?

They swell and build up pressure against the cell wall. Signup and view all the answers

Why are only living cells able to absorb water by osmosis?

Only living cells can maintain a semipermeable membrane. Signup and view all the answers

What is the main function of cellulose in the cell wall?

Structural strength Signup and view all the answers

Which staining solution can be used to observe different regions of cells more clearly?

Methylene blue Signup and view all the answers

Why did we use iodine solution on the temporary mount of onion peel?

To stain the cells and make them visible Signup and view all the answers

What is observed when dead Rhoeo cells are placed in a strong sugar solution?

Plasmolysis does not occur Signup and view all the answers

What characteristic allows plant, fungi, and bacteria cells to withstand hypotonic external media?

Presence of a rigid cell wall Signup and view all the answers

What is the function of chloroplasts observed in the Rhoeo leaf activity?

Photosynthesis Signup and view all the answers

Study Notes

Osmosis

Osmosis is the net movement of water across a selectively permeable membrane toward a higher solute concentration.
Water passes into a cell or solution with a lower solute concentration and out of a cell or solution with a higher solute concentration.

Activity 5.3: Osmosis with an Egg

The egg shell is mostly calcium carbonate and can be dissolved in dilute hydrochloric acid.
When an egg is placed in pure water, it swells due to water passing into it by osmosis.
When an egg is placed in a concentrated salt solution, it shrinks due to water passing out of the egg solution into the salt solution.

Activity 5.4: Observing Osmosis with Raisins and Apricots

Dried raisins or apricots swell when placed in water due to gaining water through osmosis.
Dried raisins or apricots shrink when placed in a concentrated solution of sugar or salt due to losing water.

Osmosis in Unicellular Organisms

Unicellular freshwater organisms and most plant cells tend to gain water through osmosis.
Absorption of water by plant roots is an example of osmosis.
Osmosis plays a crucial role in the exchange of gases and water in the life of a cell.

The Plasma Membrane

The plasma membrane is flexible and composed of organic molecules called lipids and proteins.
The structure of the plasma membrane can only be observed through an electron microscope.
The flexibility of the cell membrane enables the cell to engulf food and other material from its external environment through endocytosis.
Amoeba acquires its food through endocytosis.

Cellular Transport

Substances like CO2 and water move in and out of the cell through the plasma membrane, which is selectively permeable.
The plasma membrane is selectively permeable, allowing certain substances to pass through while restricting others.

Cell Wall

Plant cells have a cell wall, a rigid outer covering that lies outside the plasma membrane.
The cell wall is mainly composed of cellulose, a complex substance that provides structural strength to plants.
When a living plant cell loses water through osmosis, it undergoes plasmolysis, causing the contents of the cell to shrink away from the cell wall.

Osmosis and Plasmolysis

Osmosis is the movement of water molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane.
Plasmolysis occurs when a living plant cell loses water through osmosis, causing the cell contents to shrink away from the cell wall.
Only living cells, and not dead cells, are able to absorb water by osmosis.

Cell Walls and Osmoregulation

Cell walls permit cells of plants, fungi, and bacteria to withstand very dilute external media without bursting.
The cell wall exerts an equal pressure against the swollen cell, allowing it to withstand changes in the surrounding medium.

Nucleus

Iodine solution is used to stain cells and make the nucleus visible.
The nucleus is not evenly colored when stained with iodine solution, with different regions appearing darker than others due to their chemical composition.

Observing Human Cheek Cells

Human cheek cells can be observed by gently scraping the inside surface of the cheek and spreading the material onto a glass slide.
The material is then stained with methylene blue solution and observed under a microscope.
The shape of the cells observed is typically irregular or irregularly shaped.

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Description

Experiment with osmosis using an egg to understand the net movement of water across a selectively permeable membrane. Observe how the egg swells or shrinks in different solutions.