Hypotonic, isotonic, and hypertonic solutions (tonicity) | Khan Academy
Khan Academy・6 minutes read
The cellular membrane's selective permeability allows water to enter or exit the cell based on the solute concentration of the surrounding solution, which can lead to different outcomes such as swelling, maintaining shape, or shrinking of the cell. In real-life scenarios, red blood cells demonstrate these effects in hypotonic, isotonic, and hypertonic solutions, showcasing how water movement impacts cell structure and pressure.
Insights
- The cellular membrane's selective permeability is crucial for maintaining homeostasis, as it allows water molecules to enter or exit while preventing solute particles from crossing, which directly influences cell behavior in various solutions.
- The behavior of cells in different solutions—hypotonic, isotonic, and hypertonic—demonstrates the importance of solute concentration in determining cell shape and function, with red blood cells serving as a practical example of how these changes can lead to swelling, stability, or shrinking depending on the surrounding environment.
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Recent questions
What is a semipermeable membrane?
A semipermeable membrane is a type of barrier that selectively allows certain substances to pass through while blocking others. This property is crucial in biological systems, particularly in cells, where the membrane regulates the movement of water and solutes. For instance, in the context of cellular membranes, they are primarily composed of a phospholipid bilayer that permits the passage of water molecules but restricts larger solute particles. This selective permeability is essential for maintaining homeostasis within the cell, as it ensures that necessary nutrients can enter while waste products can be expelled, thus supporting the overall function and health of the cell.
How do cells respond to different solutions?
Cells respond to different solutions based on the concentration of solutes in their environment, which can be classified as hypotonic, isotonic, or hypertonic. In a hypotonic solution, where the solute concentration outside the cell is lower than inside, water flows into the cell, potentially causing it to swell or burst due to increased internal pressure. Conversely, in an isotonic solution, the concentrations of solute are equal inside and outside the cell, resulting in no net movement of water, allowing the cell to maintain its shape and function normally. In a hypertonic solution, where the solute concentration is higher outside the cell, water moves out of the cell, leading to shrinkage and a wrinkled appearance. These responses are vital for cellular health and function, as they directly affect the cell's volume and pressure.
What happens in a hypotonic solution?
In a hypotonic solution, the concentration of solute outside the cell is lower than that inside the cell, which creates a gradient that drives water molecules to flow into the cell. This influx of water can lead to an increase in internal pressure, causing the cell to swell. If the pressure becomes too great, the cell may eventually burst, a process known as lysis. This phenomenon is particularly evident in red blood cells, which can swell and rupture when placed in a hypotonic environment. Understanding the behavior of cells in hypotonic solutions is crucial in fields such as medicine and biology, as it can inform treatments for conditions related to fluid balance and cell integrity.
What is an isotonic solution?
An isotonic solution is characterized by equal concentrations of solute both inside and outside the cell, resulting in no net movement of water across the cell membrane. This balance allows the cell to maintain its normal shape and function without experiencing pressure changes. In an isotonic environment, the rates of water entering and exiting the cell are equal, which is essential for cellular stability. For example, red blood cells in an isotonic solution retain their biconcave shape, enabling them to function effectively in transporting oxygen and carbon dioxide. Isotonic solutions are often used in medical settings, such as intravenous fluids, to ensure that cells remain healthy and do not undergo stress from osmotic pressure changes.
What occurs in a hypertonic solution?
In a hypertonic solution, the concentration of solute outside the cell is higher than that inside, leading to a net outflow of water from the cell. As water exits, the cell loses volume and can become shriveled or crenated. This process occurs because the cell attempts to balance the solute concentrations on both sides of the membrane, resulting in a decrease in internal pressure. For instance, red blood cells placed in a hypertonic solution will appear wrinkled due to the loss of water. Understanding the effects of hypertonic solutions is important in various biological and medical contexts, as it can influence cell viability and function, particularly in conditions where fluid balance is critical.
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Summary
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Cell Membrane Dynamics in Different Solutions
- The cellular membrane, depicted as a magenta circle, is a semipermeable phospholipid bilayer that allows water molecules (blue circles) to pass through but restricts solute particles (yellow circles) from crossing, leading to selective permeability.
- In a hypotonic solution, where the concentration of solute outside the cell is lower than inside, water molecules will predominantly flow into the cell, potentially causing it to expand or even burst due to increased internal pressure.
- An isotonic solution features equal concentrations of solute inside and outside the cell, resulting in no net inflow or outflow of water molecules, maintaining cell shape without pressure changes.
- A hypertonic solution has a higher concentration of solute outside the cell compared to the inside, leading to a net outflow of water molecules from the cell, which can cause the cell to shrivel due to loss of internal pressure.
- Real-life examples include red blood cells in different solutions: in a hypotonic solution, they swell and may burst; in an isotonic solution, they maintain their normal shape; and in a hypertonic solution, they shrink and appear wrinkled.
