Podcast
Questions and Answers
What is the net movement of water across a selectively permeable membrane called?
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?
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?
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?
Which of the following organisms acquires its food through endocytosis?
What happens to dried raisins or apricots when placed in a concentrated sugar or salt solution?
What happens to dried raisins or apricots when placed in a concentrated sugar or salt solution?
What types of molecules make up the plasma membrane?
What types of molecules make up the plasma membrane?
What is an example of osmosis in unicellular freshwater organisms?
What is an example of osmosis in unicellular freshwater organisms?
Which process involves the cell engulfing food and other material from its external environment?
Which process involves the cell engulfing food and other material from its external environment?
What is the primary component of the plant cell wall?
What is the primary component of the plant cell wall?
What is the phenomenon called when the contents of a plant cell shrink away from the cell wall due to water loss?
What is the phenomenon called when the contents of a plant cell shrink away from the cell wall due to water loss?
What happens to plant cells when placed in hypotonic external media?
What happens to plant cells when placed in hypotonic external media?
Why are only living cells able to absorb water by osmosis?
Why are only living cells able to absorb water by osmosis?
What is the main function of cellulose in the cell wall?
What is the main function of cellulose in the cell wall?
Which staining solution can be used to observe different regions of cells more clearly?
Which staining solution can be used to observe different regions of cells more clearly?
Why did we use iodine solution on the temporary mount of onion peel?
Why did we use iodine solution on the temporary mount of onion peel?
What is observed when dead Rhoeo cells are placed in a strong sugar solution?
What is observed when dead Rhoeo cells are placed in a strong sugar solution?
What characteristic allows plant, fungi, and bacteria cells to withstand hypotonic external media?
What characteristic allows plant, fungi, and bacteria cells to withstand hypotonic external media?
What is the function of chloroplasts observed in the Rhoeo leaf activity?
What is the function of chloroplasts observed in the Rhoeo leaf activity?
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.