Hypertonic refers to a solution with higher osmotic pressure than another solution. In other words, a hypertonic solution is one in which there is a greater concentration or number of solute particles outside a membrane than there are inside it.
Red blood cells are the classic example used to explain tonicity. When the concentration of salts (ions) is the same inside the blood cell as outside of it, the solution is isotonic with respect to the cells, and they assume their normal shape and size. If there are fewer solutes outside the cell than inside it, such as would happen if you placed red blood cells in fresh water, the solution (water) is hypotonic with respect to the interior of the red blood cells. The cells swell and may burst as water rushes into the cell to attempt to make the concentration of the interior and exterior solutions the same. Incidentally, since hypotonic solutions can cause cells to burst, this is one reason why a person is more likely to drown in fresh water than in salt water. It's also a problem if you drink too much water. If there is a higher concentration of solutes outside of the cell than inside it, such as would happen if you placed red blood cells in a concentrated salt solution, then the salt solution is hypertonic with respect to the inside of the cells. The red blood cells undergo crenation, which means they shrink and shrivel as water leaves the cells until the concentration of solutes is the same both inside and outside the red blood cells. Manipulating the tonicity of a solution has practical applications. For example, reverse osmosis may be used to purify solutions and desalinate seawater. Hypertonic solutions help to preserve food. For example, packing food in salt or pickling it in a hypertonic solution of sugar or salt creates a hypertonic environment that either kills microbes or at least limits their ability to reproduce. Hypertonic solutions also dehydrate food and other substances, as water leaves cells or passes through a membrane to try to establish equilibrium. The terms "hypertonic" and "hypotonic" often confuse students because they neglect to account for the frame of reference. For example, if you place a cell in a salt solution, the salt solution is more hypertonic (more concentrated) than the cell plasma. But, if you view the situation from the inside of the cell, you could consider the plasma to be hypotonic with respect to the saltwater. Also, sometimes there are multiple types of solutes to consider. If you have a semipermeable membrane with 2 moles of Na+ ions and 2 moles of Cl- ions on one side and 2 moles of K+ ions and 2 moles of Cl- ions on the other side, determining tonicity can be confusing. Each side of the partition is isotonic with respect to the other if you consider there are 4 moles of ions on each side. However, the side with sodium ions is hypertonic with respect to that type of ions (another side is hypotonic for sodium ions). The side with the potassium ions is hypertonic with respect to potassium (and the sodium chloride solution is hypotonic with respect to potassium). How do you think the ions will move across the membrane? Will there be any movement? What you would expect to happen is that sodium and potassium ions would cross the membrane until equilibrium is reached, with both sides of the partition containing 1 mole of sodium ions, 1 mole of potassium ions, and 2 moles of chlorine ions. Got it? Water moves across a semipermeable membrane. Remember, water moves to equalize the concentration of solute particles. If the solutions on either side of the membrane are isotonic, water moves freely back and forth. Water moves from the hypotonic (less concentrated) side of a membrane to the hypertonic (less concentrated) side. The direction of the flow continues until the solutions are isotonic.
The effects of isotonic, hypotonic, and hypertonic extracellular environments on plant and animal cells is the same. However, due to the cell walls of plants, the visible effects differ. Although some effects can be seen, the rigid cell wall can hide the magnitude of what is going on inside. Osmosis has different meanings in biology and chemistry. For biologists, it refers to the movement of water across a semipermeable membrane. Chemists use the term to describe the movement of water, other solvents, and gases across a semipermeable membrane. Both biologists and chemists define diffusion as the movement of solute particles (dissolved materials) from an area of higher concentration to lower concentration until equilibrium is reached. Osmosis is a passive transport system, meaning it requires no energy. It causes water to move in and out of cells depending on the solute concentration of the surrounding environment. This movement is caused by a concentration gradient created when there are different solute concentrations inside and outside the cell. It doesn’t matter what dissolved materials make up the solute, only the overall concentration. It is important to note that cells do not regulate the movement of water molecules in and out of their intracellular fluid. They rely on other systems in the body (such as the kidneys) to provide an isotonic external environment (see below). A cell in an isotonic solution is in equilibrium with its surroundings, meaning the solute concentrations inside and outside are the same (iso means equal in Latin). In this state there is no concentration gradient and therefore, no large movement of water in or out. Water molecules do freely move in and out of the cell, however, and the rate of movement is the same in both directions. A hypotonic solution has a lower solute concentration than inside the cell (the prefix hypo is Latin for under or below). The difference in concentration between the compartments causes water to enter the cell. Plant cells can tolerate this situation better than animal cells. In plants, the large central vacuole fills with water and water also flows into the intercellular space. The combination of these two effects causes turgor pressure which presses against the cell wall causing it to bulge out. The cell wall helps keep the cell from bursting. However, if left in a highly hypertonic solution, an animal cell will swell until it bursts and dies. In Latin, the prefix hyper means over or above. Hypertonic solutions have a higher solute concentration than inside the cell. This causes water to rush out making the cell wrinkle or shrivel. This is clearly seen in red blood cells undergoing a process called crenation. Plant cells in a hypertonic solution can look like a pincushion because of what’s going on inside. The cell membrane pulls away from the cell wall but remains attached at points called plasmodesmata. Plasmodesmata are tiny channels between plant cells that are used for transport and communication. When the inner membrane shrinks, it constricts the plasmodesmata resulting in a condition called plasmolysis.
 The image above shows what happens to a cell in isotonic, hypertonic, and hypotonic solutions. References
|
When the concentration of solutes outside the cell is higher the solution is said to be relative to the inside of the cell?
Postagens relacionadas
direito autoral © 2024 comojogaruno Inc.
