 Today, we are going to talk about the diversity of cells and cell division. The topics we are going to cover today will include comparison of important cell types, cell division and its significance. We will cover the process of one of the cell divisions called mitosis. We will talk about the significance of mitosis, various errors of mitosis, why mitosis is required and what are the results, there are some errors in the process of mitosis. First of all, we will talk about the comparison between various cell types, important cell types. As we know that animals and plants are two important divisions of the living organisms. Animals in comparison to plants are more complex organisms. They have to perform more functions and more complex functions. Plants in comparison have simpler structures. This is the reason that the cells of animals and cells of plants, they have certain differences. But of course, they do have certain similarities. We talk about the differences and then we will talk about the similarities. In animal cells, the cell membrane or the plasma membrane is the outermost layer. But in plant cells, there is a cell wall that surrounds the cell membrane, which means that plant cells have their outermost layer, the cell wall. But in animal cells, the outermost layer is the cell membrane or the plasma membrane. In animal cells, there are many vacuoles, food vacuoles, vacuoles for storage or other functions. In plant cells, however, particularly mature plant cells, they do have a single very large vacuole that covers almost all volume of the cell. This large vacuole is generated or developed by merging of smaller vacuoles which were present in the immature cell. In animal cells, they are roughly round in shape or maybe they have diverse types of shapes. For example, a human body have about 200 types of different cells. Animal cells, they also have various different types. For example, a nerve cell have a particular structure. A muscle cell have another type of structure. The cells of stomach have a different types of structure. And the plant cell, due to presence of cell wall, have a roughly rectangular structure. The animal cells, they have their nucleus present almost inside the center. In the plant cells, in contrast, they have their nucleus in mature cells particularly, on side of the cell because of presence of a very large vacuole, the nucleus is put aside and this is not present in the center. This is another difference and that difference is due to the presence of large vacuole inside the plant. In animal cell, celia are usually present but in the plant cells, celia are rarely present. Animal cells do have centrioles which we know act in the cell division. Centrioles are not present in most of the plants, the plant cells but in fewer, lower plants, centrioles are present. Now we look at the diagram of an animal cell and the plant cell. We can find out so many similarities. As we know that animal and plant cells both are eukaryotes. As the diagram shows, you can see that both have a nucleus in the center, which is covered by nuclear membrane and which have nucleolus inside, chromosomes, the chromatin material inside and both of these have a cell membrane. Though in plants this cell membrane is covered by a cell wall, both of these cells, animal and the plant, have mitochondria, many mitochondria which we know are the powerhouse of the cell and they produce energy in the form of ATP for the cells. Both of these have ribosomes which actually produces the proteins for these cells. Both of these cells have endoplasmic reticulum which actually modifies the proteins, particularly in the three-dimensional structure of proteins, they play a good role. Both of these cells have Golgi bodies or the Golgi complex, which actually is the post office of the cell, which packages different materials inside the cells, for example, proteins. As we see both have cytoplasm, both of the cells have a fluid in which all the colloidal material, the organelles, the nucleus and everything is present. Both of these cells have cytoskeleton as well. So the plant and animal cells have so many similarities and some differences based upon the functions they have to carry out. Now we finish talking about the animal and plant cell and we are going to talk about the difference between prokaryotic and eukaryotic cells and then similarities. Prokaryotic, as the name says, pro, initial, ancient, old, old type of nuclear material, eukaryotic, true, true nucleus. The prokaryotic cells actually do not have a defined nucleus. Though they are nuclear material, their chromatin material is present in almost center of the cell and do not move from its place, but this is not covered by a nuclear membrane. So we cannot call it a nucleus. We say that prokaryotic cells do not have a defined nucleus. But the eukaryotic cells, they do have a defined nucleus covered by a membrane that is called the nuclear membrane, which separates the chromatin material from the cytoplasm. The second important difference is that prokaryotic cells do not have membrane-bound organelles, like endoplasmic reticulum. But the eukaryotic cells, they do have membrane-bound organelles. In prokaryotic cells, they are usually small in size. In comparison to the eukaryotic cells, their size usually ranges from 1 to 2 micrometers. But the size of most of the eukaryotic cell, on average, is fairly large in comparison to the prokaryotic cells. They are about 20 to 30 micron in size, but their sizes do vary. But on average, eukaryotic cells are larger than the prokaryotic cells. For example, we know that bacteria, the common most bacteria, their size is about 1 to 2 microns, that is 1 micrometer wide and about 2 micrometer long. But the animal cells, on average, for example, their diameters is roughly 20 micrometers. The next difference is this, that the prokaryotic cells have a cell wall. Eukaryotic cells, not all of them, animal cells don't have a cell wall, but the plant cells and the fungal cells, they do have cell walls. But there is a difference between the prokaryotic cell wall and the eukaryotic cell wall. The prokaryotic cell wall consists of a polymer of amino acids and sugars, which is called peptidoglycane. But the cell walls of the eukaryotic cells, the plant cell, consist of large fibres of cell lose molecules and the fungal cells, they do have a cell wall of chitin. So, cell wall is present in both, but it consists of different components. Different, its chemical composition is different from each other. Now, we look at the diagram for comparison of a bacterial cell with an animal cell. In the diagram, you can see, there is an animal cell on the left and there is a bacterial cell on the right. In the animal cell, you see that there is a clear cut nucleus which have a membrane surrounding it, which is separating the materials of the animal cell of the nucleus, the chromatin material with the cytoplasm. In the bacterial cell, you can see that there is a region in which the chromatin material is present, but there is no membrane. This region is called nucleoid region. The chromatin material is present in this region. Though bacteria, brokaryotic cells, do have another type of DNA which is present in the cytoplasm and this is in circular form and this is called plasmid. Plasmids are very important parts of DNA because these are used in biotechnology. These are used when we want to insert, for example, a human gene into a bacteria and then we want its mass production, production on large scale. We want to make multiple copies because bacteria, when they divide, plasmids also divide and we can get many plasmids and many copies of that human gene or an animal or a plant gene that we want. We can see that both have a cell membrane, so here they are like, they have a cell membrane, they have a nuclear material, chromatin material and both have ribosomes which are like.