 movements across cell membranes osmosis first the contents definition of osmosis osmotic pressure hyper osmotic environment isosmotic environment hypo osmotic environment and role of osmosis in the cells so first the definition of osmosis osmosis is basically the movement of water molecules through semipermeable membrane from high concentration to the low concentration. If I simply want to define it, then I will say that there are two compartments between this semipermeable membrane. So where the water molecule concentration is more, from there it will move towards low concentration, so from high concentration towards low concentration the movement of water molecules and when the semipermeable membrane is in between, then what we will say? It is the osmosis. Osmotic pressure. Osmotic pressure is actually the pressure which resists the inflow of water molecules. Usually the osmotic pressure is basically the minimum pressure required to prevent the inward flow of its solvent. Solvent means water molecules. Diagrammatically, I will explain to you a little bit. Osmotic pressure has two compartments. In compartment number one, the water molecules are more, the solute particles are less. In compartment number two, the solute particles are more than the water molecules. So it means simply water moves from high concentration to low concentration. As you can see from the arrow, the compartment has a specific dimension. When water moves here, what will happen? Will the level of water increase here? Because of which, when the water column increases, it will exert pressure. So what will happen is that the pressure increases here. So what we will say about that pressure is that it is high osmotic pressure. If I say this again, when a specific dimension of a compartment where the water molecules enter, then in that compartment, when the volume of the water increases, then the pressure of the water increases because of the excess volume. That is, the pressure of the molecules increases here. Now the new molecules have to face the pressure of the water from before. So the pressure exerted by the water from before, so that the new molecules can be stopped, what will we say? It is the osmotic pressure. In simple words, where the solute concentration is excess, the water molecules go excess and the osmotic pressure increases. So students, if we talk about osmosis, then in some places, one of the three osmotic conditions will exist. The first one is the hyper osmotic condition. Hyper osmotic condition is a type in which a special container or special environment has a lot of solute concentration. The second compartment is the outer compartment, so solute concentration is less. So where the solute concentration is excess, the water molecules will have more inflows. And a hyper osmotic condition will be generated there. So in simple words, the hyper osmotic condition is produced. When there is concentrated material in a cell, when it is diluted outside the cell, then where the concentrated material is present, the solute concentration is excess, there the hyper osmotic condition exists. For example, if you take a cell like red blood cells or any other cells, they are kept in pure water. Now, solute concentration is excess in the cell, whereas solute concentration is very less in the pure water. So the internal environment of the cell is hyper osmotic. What is this? It is hyper osmotic. Iso osmotic conditions. Iso means the same. Iso osmotic condition is the condition in which the outside of the cell and inside of the cell has the same osmotic condition. Solute concentration is the same. The best example of this is marine animals, especially marine invertebrates. Marine water, ocean water, the salt concentration is very high. It is salt water. It is more than 3-5% salt. The simple organisms in the oceans, what they do is that they collect salt in the same concentrations in the cells. The ocean water, the marine water, the salt concentration is also the same. And the salt concentration in the cells of the animals is also the same. What are these two conditions called? They are the isosmotic. In the isosmotic condition, the animal that has the biggest benefit is that there is no water loss. Neither water will enter in them nor will it exit there. So the animals that are to be saved from the water loss, especially marine animals, they produce isosmotic conditions. The third type of osmotic environment that is the hypoosmotic condition. Hypoosmotic means that the specific cells in it have the solute concentration. What is the solute concentration outside? It is more. For example, we have red blood cells. We keep the cells in a very salty water. The internal environment of the cells has less solute concentration. The salt water outside is very salty. So the solute concentration in the cells is less and the external concentration is more. Now the internal environment of the cells is the hypoosmotic environment. So the internal environment of the cells is also the hypoosmotic environment. So what is the role of osmosis in living organisms? In living organisms, osmosis is having a very important role. All the materials that are to be entered in the cells play a vital role. For example, there are nutrients. The food materials are absorbed by those nutrients that are absorbed through osmosis. In addition, our blood also has a special osmotic pressure. If I talk about our blood, the osmotic pressure of the blood is maintained. That is the important role of the albumin protein. In albumin, what is the special amount of water in our blood? It is controlled. Thirdly, the nutrients you take or the salt you take. The salt and the nutrients they are also taken up by the with the help of osmosis process or through osmosis, they are basically taken up.