Osmosis And Tonicity Worksheet Answer Key

Osmosis and Tonicity Worksheet: A Comprehensive Guide with Answers

Understanding osmosis and tonicity is crucial for grasping fundamental biological processes. This comprehensive guide provides a detailed explanation of these concepts, along with answers to common worksheet questions. We'll explore the principles behind osmosis, the different types of tonicity (hypertonic, hypotonic, and isotonic), and how these concepts affect cells. By the end, you'll have a solid understanding and be able to confidently answer questions on osmosis and tonicity.

What is Osmosis?

Osmosis is a special type of passive transport – meaning it doesn't require energy – where water moves across a selectively permeable membrane. This membrane allows some substances to pass through while blocking others. The driving force behind osmosis is the difference in water potential between two solutions separated by the membrane. Water always moves from an area of higher water potential (lower solute concentration) to an area of lower water potential (higher solute concentration). Think of it as water trying to dilute the more concentrated solution.

Key Terms to Understand:

• Solute: The substance dissolved in a solution (e.g., salt, sugar).
• Solvent: The liquid that dissolves the solute (e.g., water).
• Solution: A homogeneous mixture of solute and solvent.
• Selectively Permeable Membrane: A membrane that allows certain molecules to pass through but blocks others. Cell membranes are excellent examples.
• Water Potential: The tendency of water to move from one area to another. It's influenced by solute concentration and pressure.

Tonicity: The Relationship Between Solutions and Cells

Tonicity describes the relative concentration of solutes in two solutions separated by a selectively permeable membrane, typically a cell membrane. It compares the solute concentration of the solution outside the cell (the extracellular fluid) to the solute concentration inside the cell (the intracellular fluid). There are three main types of tonicity:

1. Hypotonic Solution

A hypotonic solution has a lower solute concentration than the solution it's compared to (e.g., inside the cell). In other words, it has a higher water potential. When a cell is placed in a hypotonic solution, water moves into the cell by osmosis. This causes the cell to swell and potentially lyse (burst) if the influx of water is excessive. Animal cells are particularly susceptible to lysis in hypotonic solutions. Plant cells, however, have a cell wall that provides structural support, preventing lysis and resulting in turgor pressure.

2. Hypertonic Solution

A hypertonic solution has a higher solute concentration than the solution it's compared to. This means it has a lower water potential. When a cell is placed in a hypertonic solution, water moves out of the cell by osmosis. This causes the cell to shrink or crenate. In plant cells, this leads to plasmolysis, where the cell membrane pulls away from the cell wall.

3. Isotonic Solution

An isotonic solution has the same solute concentration as the solution it's compared to. Therefore, it has the same water potential. When a cell is placed in an isotonic solution, there is no net movement of water across the cell membrane. The cell maintains its shape and size.

Osmosis and Tonicity Worksheet Answers: Example Questions and Solutions

Let's tackle some common osmosis and tonicity worksheet questions to solidify your understanding. Remember, the key is to carefully consider the relative solute concentrations inside and outside the cell.

Question 1: A red blood cell is placed in a solution. After some time, the cell swells and bursts. What type of solution was the red blood cell placed in?

Answer: The red blood cell was placed in a hypotonic solution. The solution had a lower solute concentration than the inside of the cell, causing water to move into the cell, leading to swelling and lysis.

Question 2: A plant cell is placed in a solution. After some time, the cell membrane pulls away from the cell wall. What type of solution was the plant cell placed in?

Answer: The plant cell was placed in a hypertonic solution. The solution had a higher solute concentration than the inside of the cell, causing water to move out of the cell, leading to plasmolysis (separation of the cell membrane from the cell wall).

Question 3: Describe what would happen to a paramecium (a single-celled organism) if it were placed in distilled water.

Answer: Distilled water is essentially pure water and therefore hypotonic to the paramecium's cytoplasm. Water would rush into the paramecium via osmosis, causing it to swell and potentially burst. Paramecia have contractile vacuoles to pump out excess water, mitigating this effect, but in a very hypotonic solution, this mechanism may be overwhelmed.

Question 4: Explain the importance of osmosis and tonicity in maintaining cell homeostasis.

Answer: Osmosis and tonicity are crucial for maintaining cell homeostasis, which is the stable internal environment necessary for cell survival and function. By regulating water movement across cell membranes, cells can maintain appropriate internal pressure, volume, and concentration of solutes. Disruptions in tonicity can lead to cell damage or death. For instance, maintaining isotonic conditions within the body is vital for preventing red blood cell damage.

Question 5: A cell is placed in a 10% saline solution. The cell's cytoplasm has a 5% saline concentration. Describe the movement of water and the resulting effect on the cell.

Answer: The 10% saline solution is hypertonic to the cell's cytoplasm. Water will move out of the cell (from an area of higher water potential to an area of lower water potential) by osmosis. The cell will shrink or crenate as water leaves.

Question 6: Explain how the cell wall affects the response of a plant cell to different tonicities compared to an animal cell.

Answer: The rigid cell wall of plant cells prevents excessive swelling and lysis in hypotonic solutions. The cell wall provides structural support, resulting in turgor pressure, which helps maintain the plant cell's shape. In hypertonic solutions, the plant cell undergoes plasmolysis (the plasma membrane pulls away from the cell wall) but doesn't necessarily burst. Animal cells lack a cell wall, making them much more susceptible to both lysis in hypotonic solutions and crenation in hypertonic solutions.

Question 7: A researcher is studying the effects of different solutions on plant cells. They place one plant cell in a 0.9% NaCl solution, another in distilled water, and another in a 5% NaCl solution. Describe the expected outcome for each cell.

Answer:

• 0.9% NaCl solution (Isotonic): The cell will likely remain unchanged. There is no significant net movement of water.
• Distilled water (Hypotonic): The cell will absorb water, causing it to swell. The cell wall will prevent lysis, resulting in turgor pressure.
• 5% NaCl solution (Hypertonic): The cell will lose water, causing plasmolysis. The cell membrane will pull away from the cell wall.

Question 8: Why is maintaining isotonic conditions crucial for intravenous fluids administered to patients?

Answer: Maintaining isotonic conditions is crucial for intravenous (IV) fluids because administering a hypotonic solution can cause red blood cells to lyse, while a hypertonic solution can cause crenation. Both lead to damage to red blood cells and disruption of normal physiological function. Isotonic solutions prevent such damage and ensure that fluids are properly absorbed into the bloodstream without harming cells.

Question 9: How does osmosis contribute to water uptake by plant roots?

Answer: Osmosis plays a critical role in water uptake by plant roots. The soil solution generally has a higher water potential than the cells in the plant roots. Water, therefore, moves from the soil into the root cells by osmosis. This process facilitates the transport of water throughout the plant.

Question 10: Explain how the principles of osmosis and tonicity are used in food preservation techniques like salting or sugaring.

Answer: Salting and sugaring food are preservation techniques that utilize hypertonic solutions. High concentrations of salt or sugar create a hypertonic environment around microorganisms (bacteria, fungi). Water moves out of these microorganisms by osmosis, causing them to dehydrate and die or become unable to reproduce, thus preventing spoilage.

This detailed explanation and the example answers provide a strong foundation for understanding osmosis and tonicity. Remember to practice applying these principles to various scenarios to master the concepts and excel in your studies. By understanding the relationship between solute concentration, water potential, and cell behavior, you'll be able to effectively answer a wide range of questions on osmosis and tonicity.