 Now, we talk about the cell wall. All the plant cells, the algae, fungi and prokaryotic cells do have a cell wall. Cell wall is a layer, consists of different types of material, which is present outside the cell membrane. The plant cell wall consists of a specific fiber, long fiber called cellulose. It also have certain other fibers included in it, which attach different cellulose fibers to each other. These are called hemicellulose and pectin. The fungal cell walls consist of another type of polymer called chitin. In comparison, in contrast, the cell walls of the prokaryotes, they consist of another fiber, which consists of, which is a polymer of the amino acids, different types of amino acids and sugars. This is called peptidoglycane. Now, again, look at the diagram. This diagram shows structure of cell wall. Now, the plant cell wall. Plant cell wall is of two types, primary cell wall and a secondary cell wall. The primary cell wall is present in most of those cells, which have to perform like various functions and sometimes the cells, which are not yet mature. Some cells, which have to be a retention or for example, the cells, which have to allow the transport of water from roots to the stem or other parts of the plant, those cells have another cell wall, secret actually, another type of cell wall towards inside, which is called a secondary cell wall. So, it means that primary cell wall remains the external most layer, then comes the secondary cell wall if it is present, then comes the cell membrane, then cytoplasm and then the nucleus. Here in the diagram, you can see a structure of a plant cell wall, which is the primary cell wall. You can see the middle lamella, which is a layer present between the cells. Then you can see long, long structures in blue big fibers. These fibers are called the cellulose, cellulose micro fibrils. You can see that they are arranged differently. There is one layer, which is going horizontally at a straight angle. There is second layer, which is going in comparison to the lower layer. And there is a third layer, which is again in the same arrangement. Then you can see different cross linkings in between these cells, these micro fibrils. These micro fibrils are attached to each other with the help of certain fibers, which are cross linkings. We call them cross linkings, because these are linking, crossing layers of the cellulose molecules, cellulose micro fibrils. Then you can see there is a third molecule called pectin. Pectin is also attached at a different angle to the cellulose micro fibrils. Pectin is a material that is present in the jams and jellies and it is used to solidify those or make, convert them into a gel. What actually pectin do? It attracts water molecules and calcium molecules and some other and convert this interior of the cell wall, the primary cell wall, into a gel like matrix. Down there, you can see the plasma membrane. So it means that plasma membrane, then there is a thick layer of cell wall, the primary cell wall. Then comes the contact between the cells, the middle lamella. What are the functions of the cell wall? Functions of the cell wall is protection, strength and support. Large cells have these two types of cell walls. Primary cell wall, give them support. Secondary cell wall, give them even more support. The primary cell wall and secondary cell wall are different in their structure. We look at next diagram. Here you can see in that diagram that the lower layer, the layer which is external most is the primary cell wall. Then comes different layers of the secondary cell wall. Secondary cell wall, you can see the outer layer, the middle layer and the inner layer. These makes the whole of secondary cell wall. It means that secondary cell wall is secreted in layers. When a cell matures, initially it have a primary cell wall. When it matures, it secretes outer layer of the wall. Then if it needs more, it secretes more layer, more layer and that is it. These layers, the difference between the primary cell wall and the secondary cell wall is this. That particularly primary cell wall have cellulose fibrils in comparatively a lesser quantity. The secondary cell wall have cellulose fibrils in a more quantity. They have more cellulose micro fibrils present in them. The primary cell wall have more number of pactin and hemicellulose molecules in comparison. Secondary cell wall have less hemicellulose and pactin molecules. Secondary cell wall also have another characteristic that is its cellulose micro fibrils, micro plummets are more arranged. They are in comparison to the primary cell, they are more arranged. That is they are more ordered and as you know that if in a particular structure it is less ordered, it will have less strength. If it is more ordered, it have more strength. So in primary cell wall, cellulose fibrils, micro fibrils which give it more strength. They are less orderly arranged, they are less organized. In a secondary cell wall, they are more orderly arranged and they are more organized. With the result, they give the cell more strength and secondly as you can observe in the diagram that these cellulose micro filaments, these are present in different directions. In the first one, you can see these are horizontally arranged. In the second one, these are vertically arranged. In the third one, they are arranged at another angle. This difference in arrangement gives more and more strength to the structure of the cell. So we finished talking with the cell wall and the cell membrane, the layers, the coverings. Now we talk about the cytoplasm, cytoplasm, cyto of cell, plasm, plasma or the fluid. Cytoplasm is the living matter part of the protoplast. This is a semi-transparent substance that have different types of materials, proteins, various carbohydrates, enzymes and other materials present inside it in dissolved form or a semi-dissolved form. It means that these materials are present inside the cytoplasm either in dissolved form or a semi-dissolved form. We can say it have organic material inside, it have inorganic material inside which are dissolved in a watery fluid, the major fluid is water and it have dissolved particulate matter that consist of organic molecules, proteins, lipids, carbohydrates, etc., and it have inorganic molecules like different types of, like magnesium, calcium, potassium or so. What are the functions of cytoplasm? Functions of cytoplasm are there are two major functions. One is that cytoplasm provide space for different types of organelles, all the organelles, mitochondria, ribosomes, vanduplasmic reticulum, oligopods, they are all present inside the cytoplasm. A cytoplasm also provide a watery fluid which is required for different metabolic processes. It means that cytoplasm support and help in different types of metabolic processes. For example, the glycolysis which is the breakdown of glucose, it occur in the cytoplasm and enzymes which are required to break down glucose into smaller parts, different small parts and to release energy, they are present inside the cytoplasm, they are dissolved in the cytoplasm. So cytoplasm give a space for organelles, it gives a space for metabolic reactions to occur and it gives space to nucleus inside as well.