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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?
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?
Why do uncooked de-shelled eggs swell in pure water?
Why do uncooked de-shelled eggs swell in pure water?
Which of the following organisms acquires its food through endocytosis?
Which of the following organisms acquires its food through endocytosis?
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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?
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What types of molecules make up the plasma membrane?
What types of molecules make up the plasma membrane?
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What is an example of osmosis in unicellular freshwater organisms?
What is an example of osmosis in unicellular freshwater organisms?
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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?
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What is the primary component of the plant cell wall?
What is the primary component of the plant cell wall?
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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?
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What happens to plant cells when placed in hypotonic external media?
What happens to plant cells when placed in hypotonic external media?
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Why are only living cells able to absorb water by osmosis?
Why are only living cells able to absorb water by osmosis?
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What is the main function of cellulose in the cell wall?
What is the main function of cellulose in the cell wall?
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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?
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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?
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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?
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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?
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What is the function of chloroplasts observed in the Rhoeo leaf activity?
What is the function of chloroplasts observed in the Rhoeo leaf activity?
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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.
