 First the contents, definition of tonicity, hypotonic solution, isotonic solution and hypotonic solutions. First the definition, so, tonicity is the relative concentration of solute particle dissolved in the solution with reference to the outer environment or the other compartment. Students, if we look at the tonicity and osmosis, if I compare it a little bit, in the tonicity, we basically talk about the solutes, we talk about solute concentration, whereas in osmosis, we usually take water concentration as a principle, where the water is more, the water will come from there, where it is present in a low amount. So the definition of tonicity is that where the tonicity is basically solute, it is a matter which deals the concentration of solute between two compartments. In two compartments, when we will discuss solute concentration, then this will be the tonicity. Where the tonicity is more, it means that there is more solute concentration there, and where the tonicity is less, it means that there will be less solute concentration there. Now, there are three types of tonic conditions that exist in this tonicity. The first one is the hypotonic solutions, the second is the isotonic solutions, and the third one are the hypotonic solutions. Hypotonic. The word hyper means to increase, to increase. So hypotonic solutions are such solutions where solute concentration is more than a special level. If we suppose that a cell is in a hypotonic environment, then its simple means that the solution in a cell is more than a solute concentration, and there is less solute concentration in a cell. Now, where the solute concentration is more, the water molecules will move in the same way. If a cell is in a hypotonic environment, then since it is in a hypotonic environment, the solute concentration is more, then the water molecules will come out of the cell. So the water molecules will come out from the cell. Now, when the water molecules will come out of the cell, the cell will shrink. The specific condition we are talking about is the crenation. The word crenation means that the shrinkage of cells. Because here we have to keep it clear, we have to keep it in mind that we are talking about the environment. The environment is hypotonic. What is the solute concentration in the environment? We are not talking about the inside of the cell. There is more solute concentration outside, and then what will definitely be in the cell? It will be less. Isotonic solution. Isotonic means the same solute concentration. If there is such an environment where the solute concentration is as much as in the cell, then what will be its overall impact? If the water molecules are coming out of the cell, then they are going in from the outside. Ten molecules are coming out of the cell, and ten molecules are going out of the cell. So there will be no difference on the overall cell. Neither will the cell shrink, nor will there be crenation. Neither will the cell burst, nor will it be a target. Hypotonic solutions. Hypotonic solutions are such solutions, or there is an environment where solute concentration is less. Hypotonic means low concentration of solute, such an environment where solute concentration is less. What will be its scenario? Environment is hypotonic, which means solute concentration is less. There is more solute concentration in the cell, and the water has to always move from low solute to high solute. The result is that when you keep a solute in a low concentration cell in a hypotonic environment, then the water molecule will move into the cell. The cell that moves inside the molecule will be first translated, flattened, and then ultimately burst. This will shrink the cell in a hypotonic environment. The cell volume will remain the same in an isotonic environment. The cell will swell in a hypotonic environment, and there will be chances of burst. If we look at the diagram, in the isotonic environment, this cell is the proper shape of the red blood cell. Now we know that the shape of the biconcave is the shape of the red blood cell. So this is the proper shape of the biconcave. The amount of water molecules are entering the cell, and the amount of molecules are going out. This is what you have to keep in mind, but we cannot say that there will be no molecules entering the cell. Molecules always cross the membrane. But in isotonic, the amount of molecules that cross the membrane, they cross out as much as possible. This is how the ratio is equal. So no one will have to worry about the volume of the cell. In the hypotonic environment, hypotonic means that there is a lot of outside salt concentration. There are high salts. Salt concentration. There is a lot of outside salt concentration in the cell. The environment is hypotonic, hypotonic. If I simplify this, I will write it as hypotonic environment. So in the hypotonic environment, molecules will come out of the cell, because there is a lot of salt and solute concentration in the cell. So molecules will come out of the cell, because of which the cell will shrink. In the hypotonic environment, hypotonic means low. There is less solute concentration in the environment. What is outside the cell? Low solute concentration. What is the impact of this? Outside the solute concentration is low. The cell has a high solute concentration in the cell. So the water always goes there, because there is a lot of solute concentration. So in the hypotonic environment, water molecules will move from the outside to the inside. Now when the water molecules go inside the cell, then what will happen? The cell has a special volume. Before coming inside the water molecule, the cell will swell. If you look at isotonic and hypotonic, there is a proper shape in the isotonic. There is a proper shape in the cell, where the cell has already swelled. When the water molecule enters the cell, it will burst. So the cell will burst. We have to see this experimentally. So let's put the cells in the hypotonic environment. If the cells are bursting in the hypotonic environment, which means there is less solute concentration.