Answer: A cell placed in solution swells up. The solution is a hypotonic solution. In the hypotonic solution, the cell will gain water by osmosis and will swell up. Hypertonic solution is the one that contains more concentration of solutes relative to the solute concentration in the cytoplasm of the cell. Articles to Explore:
In order to continue enjoying our site, we ask that you confirm your identity as a human. Thank you very much for your cooperation.
Large quantities of water molecules constantly move across cell membranes by simple diffusion, often facilitated by movement through membrane proteins, including aquaporins. In general, net movement of water into or out of cells is negligible. For example, it has been estimated that an amount of water equivalent to roughly 100 times the volume of the cell diffuses across the red blood cell membrane every second; the cell doesn't lose or gain water because equal amounts go in and out. There are, however, many cases in which net flow of water occurs across cell membranes and sheets of cells. An example of great importance to you is the secretion of and absorption of water in your small intestine. In such situations, water still moves across membranes by simple diffusion, but the process is important enough to warrant a distinct name - osmosis. Osmosis and Net Movement of WaterOsmosis is the net movement of water across a selectively permeable membrane driven by a difference in solute concentrations on the two sides of the membrane. A selectively permiable membrane is one that allows unrestricted passage of water, but not solute molecules or ions. Different concentrations of solute molecules leads to different concentrations of free water molecules on either side of the membrane. On the side of the membrane with higher free water concentration (i.e. a lower concentration of solute), more water molecules will strike the pores in the membrane in a give interval of time. More strikes equates to more molecules passing through the pores, which in turn results in net diffusion of water from the compartment with high concentration of free water to that with low concentration of free water. The key to remember about osmosis is that water flows from the solution with the lower solute concentration into the solution with higher solute concentration. This means that water flows in response to differences in molarity across a membrane. The size of the solute particles does not influence osmosis. Equilibrium is reached once sufficient water has moved to equalize the solute concentration on both sides of the membrane, and at that point, net flow of water ceases. Here is a simple example to illustrate these principles:
Additional examples are provided on how to determine which direction water will flow in different circumstances. TonicityWhen thinking about osmosis, we are always comparing solute concentrations between two solutions, and some standard terminology is commonly used to describe these differences:
 In the examples above, Solutions A and B are isotonic (with each other), Solutions A and B are both hypertonic compared to Solution C, and Solution C is hypotonic relative to Solutions A and B. Diffusion of water across a membrane generates a pressure called osmotic pressure. If the pressure in the compartment into which water is flowing is raised to the equivalent of the osmotic pressure, movement of water will stop. This pressure is often called hydrostatic ('water-stopping') pressure. The term osmolarity is used to describe the number of solute particles in a volume of fluid. Osmoles are used to describe the concentration in terms of number of particles - a 1 osmolar solution contains 1 mole of osmotically-active particles (molecules and ions) per liter. The classic demonstration of osmosis and osmotic pressure is to immerse red blood cells in solutions of varying osmolarity and watch what happens. Blood serum is isotonic with respect to the cytoplasm, and red cells in that solution assume the shape of a biconcave disk. To prepare the images shown below, red cells from your intrepid author were suspended in three types of solutions:
Predict what would happen if you mixed sufficient water with the 500 mOs sample shown above to reduce its osmolarity to about 300 mOs. Calculating Osmotic and Hydrostatic PressureThe flow of water across a membrane in response to differing concentrations of solutes on either side - osmosis - generates a pressure across the membrane called osmotic pressure. Osmotic pressure is defined as the hydrostatic pressure required to stop the flow of water, and thus, osmotic and hydrostatic pressures are, for all intents and purposes, equivalent. The membrane being referred to here can be an artifical lipid bilayer, a plasma membrane or a layer of cells. The osmotic pressure P of a dilute solution is approximated by the following: P = RT (C1 + C2 + .. + Cn)where R is the gas constant (0.082 liter-atmosphere/degree-mole), T is the absolute temperature, and C1 ... Cn are the molar concentrations of all solutes (ions and molecules). Similarly, the osmotic pressure across of membrane separating two solutions is: P = RT (ΔC)where ΔC is the difference in solute concentration between the two solutions. Thus, if the membrane is permeable to water and not solutes, osmotic pressure is proportional to the difference in solute concentration across the membrane (the proportionality factor is RT). Advanced and Supplemental TopicsSend comments to 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 outside solution has higher solute concentration than the cell cytoplasm called?
Pos Terkait
Copyright © 2024 membukakan Inc.
