 Now we will proceed the chapter cell the fundamental unit of life and the next topic is the structure of a cell. The general structure of cell you can see it is circular in nature but different cell have different shape, size and volume. So, we will study the structure of a typical cell, typical means a general cell. So, there is one circular part inside the cell that is known as master of the cell and called as nucleus. This outer part is known as cell membrane. Another name of cell membrane is plasma membrane as well as plasma lemma. So, if it is given by the name of plasma lemma in some books to do not get confused it is the same as cell membrane. The area between the cell membrane and the nucleus is a jelly like fluid which contains different type of cell organelles and this jelly like fluid is known as cytoplasm. So, cytoplasm is the area that is present between the nucleus and the plasma membrane. This area is jelly like and it contains different cell organelles like mitochondria, Golgi body, endoplasmic reticulum, ribosomes. So, these organelles will perform the different function that will help in this whole cell to perform its basic metabolic activity. As we have studied this general structure of a cell, we will study each and every part of this cell individually. So, first part is plasma membrane. Plasma membrane is also known as cell membrane as well as plasma lemma as I told you. So, there was a scientist whose name was Singer and one scientist was Singer and another was Nikolson. These both scientists work together and in year 1972 they proposed a model whose name was Fluid-Ruzek model. Remember this is an important model for detailed study of structure of cell membrane or plasma membrane. So, according to this Fluid-Ruzek model, the plasma membrane is made up of two layer. If I make like this two layer and these two layer should be of phospholipid. You can also write bilayer. If I am talking about two, it should be bilayer phospholipid. So, one layer is this first layer and another is second layer. In order to understand this diagram clearly, I will make this diagram. It is circular structure of lipids. They are arranged in a straight way as it is bilayer to there are two layers of lipid and these lipids having a structure one head and one tail. Head is at the outer part and the tail is inside the inner part. If you have the notebook, you can copy this diagram. You will copy the diagram. If you will make the diagram of your own, then you will practice it also. So, this lipid it is in the form of bilayer means two layers are there. The outer layer is hydrophilic head. See this if this is a lipid this is known as head and this is known as tail. So, the head is hydrophilic means it is water loving. In bracket you can write down this is the nature of hydrophilic head that it is water loving. And the second this tail like structure this is hydrophobic, hydrophobic tail. Hydrophobic means water hating. So, the nature of head is hydrophilic and the nature of tail is hydrophobic. So, this is the lipid bilayer. Now, one more thing is there it contains two types of protein. The structure of plasma membrane contain two types of protein. First is intrinsic protein and second is expensive protein. As it is clear by the name intrinsic means it is present in the inner surface of the lipid and extrinsic means those proteins which is present at the outer surface of the lipids. So, let us draw this diagram. Let us arrange this protein in this structure according to the fluid mosaic model. These are intrinsic protein and those proteins which are present at the outer surface is known as extrinsic protein. Let us label it this is intrinsic protein. Now, another nature of plasma membrane or second membrane is that it is semi permeable. Semi permeable is an old word. Now, in new book you will get one more word that is now known as the most correct form selective permeable. Instead of semi permeable new word is selective permeable. The nature of plasma membrane or the plasma lemma is a thin, delicate structure that is a kind of covering over the cell. It is selectively permeable it means it will allow only selected molecules to cross this membrane. So, what we have studied today let us summarize this. Plasma membrane is also known as cell membrane as well as plasma lemma. Second point in order to understand the structure of plasma membrane there was two scientists who worked together in 1972. Singer and Nicholson both of them they proposed a model whose they was fluid mosaic model. According to this model there is a bilayer lipid that contains one hydrophilic head and hydrophobic tail. Inside this lipid bilayer there are protein that is known as intrinsic protein and outer surface of this lipid bilayer contains protein that is known as extrinsic protein. After this this is semi permeable, selective permeable it means selective permeable is more correct but if it is written in some books semi permeable they both have the same meaning but this is the most advanced form. So, selective permeable means that it will allow the membrane to cross only selected molecules. Now, next cell membrane if the question arises what is the cell membrane made up of? So, cell membrane is made up of lipids and protein and cell membrane is mainly found in animal cell. Cell membrane is mainly found in animal cell.