Osmosis with an Egg Activity

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.