Free Biology NEET Video Lectures for Cell: The Unit Of Life

00:00:33 [Music] [Applause] Hello friends, welcome to today's session cell the unit of life. Myself Dala Saji PGT bio from KB Keshub. First we are going to an introductory session who discovered cell. You have covered this aspect even in your ninth and eighth class also. Robert Hook in 1665 discovered a cell. Robert Hook an English botonist. You know the first cell discovered was bacteria and it was discovered by and one lean hog who discovered protoplasm. Perking in 1839 discovered protoplasm the physical basis

00:01:51 of life. Now regarding the discovery of a cell the basic unit of life you know cell is the structural and functional unit of of life of an organism. And as I have already told you, Robert Hook in 1665 discovered a cell. Regarding his discovery, he took thin sections of cork. The scientific name of the plant is caucus yuber. Ultra thin sections were taken and observed under his rudimentary microscope. He found honeycomb like structures which he named it as cellul in Latin word which means compartments. Later they were named as

00:02:59 cells. You know why the cell is known as the functional unit of life? All the vital functions of life that can be carried out in a cell and the cell contains different organals for doing different functions. Thus within a single cell itself there is division of labor. Each organal is doing a specific function vital function. For example, respiration is carried out by mitochondri. Digestion is carried out by s u by lysosomes and the reproduction is carried out by nucleus of the cell. That's within a

00:03:53 single cell itself. Even in the case of a unicellular organism also there is division of liver but it is within the cell itself because of the different organals. Now coming to the aspect of tissue. What constitute a tissue? As we have already learned this concept in your uh earlier classes. A group of cell having same origin and a common function. A group of cells that have a same origin and which will perform a common function that constitutes a tissue. Study of cells. The branch of biology that deals with the study of

00:04:49 cell it is known as cytology. And the branch of biology that deals with the study of tissues that is known as hisytologology. Now regarding cell theory, MJ Shielden a botonist and T. Shan the zoolologist put forward a cell theory in 1838. It consists of the following facts. All the living organisms are made up of cells. And cell is the basic structural and functional unit of an organism. A cell originates from a preexisting cell. The function of an organism as a whole is the sum total of all the

00:05:58 functions of the constituent cells. Now the cell theory that was modified by Rudolfph virtue he stated that omnis cellular cellular it means a cell is originates it a cell originates from a pre-existing cell. Now coming to the advantages of multisellularity in an organism. The first point here comes division of labor. It helps in division of a labor. Each cell is doing a specific function in order to avoid the duplication of a labor. Death of a few cells do not kill the organism. For example, RBC cells as well

00:07:07 as epithelial cells are replaced by new cells regularly but the organism is not much affected. Some of the surface cells are dead but they help in support as well as protection. Now regarding the size and shape of the cells it varies according to the functional status of a cell. They may be spherical for example RBC then spindle-shaped for example nonstriated muscles as well as platelets irregular in shape amieba and luccoyides elongated in shape nervous cells neurons so thus the shape and size of

00:08:11 the cell depends upon the functional status of the cell. Now regarding the size, size also varies in various organisms depending upon its function. Bacterium it is 3 m to 5 mm. And in ostrich the egg cell it is 170 into 135 mm in diameter. and microlopplasma the size varies from.1 mu m to.3 mm. Now coming to the differences between a proariotic cell and a ukareotic cell. A very important question. We have to distinguish these two different types of cells based on some of the specific characters. Here you can see the

00:09:17 differences. Proariotic cell comparatively smaller in size and ukareotic cell is larger in size. Now coming to the presence or absence of nucleus in proarotic cell. Nucleus is absent. Well defined and true nucleus is totally absent in ukareotic cell nucleus is present. Now coming to the organals membrane bound organals are totally absent in the case of a proaryotic cell. It is present in membrane bound organals are present in ukareotic cells. For example, membrane bound organals, mitochondrig bodies, endopplasmic

00:10:09 reticulum, lysosomes, all these comes under the category of membrane bound organals. So these membrane bound organals are totally absent in proarotic cell and it is present in ukareotic cell. Now coming to the nuclear membrane, we have already seen nucleus. The well-developed defined nucleus is totally absent. It means the nuclear membrane is also absent. But in ukareotic cell you can see welldeveloped nuclear membrane a double layered nuclear membrane with the nuclear pores and all seen here. Now coming to the ribosome

00:10:52 the universal organal present in uh this proarotic cell. It is the 70S ribosome. But in ukareotic cell it is 70s and 80s ribosomes are present. Both the ribosome 70s and 80s are present. Now comes to this at another important point is misosomes present. Misosomes are the infoldings of the plasma membrane that is present in the proarotic cell and these misosomes are present here in proaryotic cell and it is absent in ukareotic cell. Spindle fibers are spindle fibers are not formed during cell division and here welldeveloped spindle

00:11:50 fibers are formed during cell division. Now regarding the nucleololis small spherical structure seen inside the nucleus so that is totally absent here in proaryotic cell and in ukareotic cell welldeveloped nucleololis is also present. Now coming to yet another point that is regarding the transcription and translation. Transcription you know already the copying of messenger RNA from one strand of the DNA and translation is synthesis of protein from the copied mRNA based on the codons sequence of codons and

00:12:38 alignment of specific amino acids. So these two process transcription and the translation both will takes place simultaneously in the cytoplasm. Since there is no developed uh membrane nuclear membrane this whole process that takes place in the cytoplasm. So this will takes place simultaneously in the cytoplasm itself. But here in ukareotic cell first there occurs transcription. Then after that transcription there will be the processing of mRNA and after that processing the functional mRNA will be

00:13:18 transferred into the cytoplasm where there occurs the synthesis of protein that means translation. So first there occurs transcription inside the nucleus which is then followed by translation in the cytoplasm. Both can occur simultaneously. Now regarding the classification of bacteria based on shape there are spherical bacteria. spherical in shape we will call them it as caucus. Now there are different types of spherical bacteria. If it is seen singly then we will call it as microcus and if it is seen in a group of

00:14:10 two then we will call it as diplocus. Diplo means two. And if it is seen in the form of a chain then we will call it as stptocus. And if it is seen in a group just like the bunch of grapes then it is known as tapiloccus. So there are four different types of caucus the spherical bacteria. Microcous diplocus streptococcus and stafylocus. Example of a diplocus bacteria that is diplocus pneumonia. Now if it is a road shaped then we will call it as baselus. They may not have any flag they are of again different

00:15:06 types. Streptobasilus that means they are in the form of filaments or chain. for example is baselus subtile. Vibrio that is commaped bacteria they are flagagillated and capable of movement. So it is flagillated and motile. Example is vibrio causing the disease colera. Now coming to the next one that is spiralum spring shaped with a fleellula at one end or both the ends. Example is spiralum. So here you can see the different types of bacteria caucus type. This is stptocus. This one you can see here a

00:15:59 group of two that is diplocus one. It's seen in groups stafylocus rotorshaped bacteria baselus roershaped bacteria baselus then a spring- shaped spiralum you can see here and commaped one that is vibrio. So these are the different types of bacteria based on their shape of the cell. Now we can classify this bacteria based on staining also. The staining that is gram staining. Based on gram staining based on the color retained we can divide the bacteria into two different groups. One is gram positive bacteria and the other

00:16:52 is gram negative bacteria. Gram positive bacteria will retain the blue color when it is stained with a crystal violet dye. And when they are treated with after uh treating with this gram stain we will treat with the iodine as well as decolorized with alcohol. And even after decolorization with alcohol also it will retain the purple color. Then that bacteria will be gram positive and the gram negative bacteria they will take the color of the counter stain either it may be basic fishin. So that will be the color will

00:17:43 be pink in color rather than purple in color. So pink colored bacteria they are gram negative and purple colored bacteria they will be gram positive based on gram staining. Now coming to the steps in gram staining as I have already told you here we are using the stain that is crystal violet. So the the primary stain application of the primary stain that is crystal violet later we will be dealing here as CV crystal violet heat uh and uh fix the smear the bacterial smear that will be heated and fixed after that it is stained with a

00:18:35 crystal violet dye. The crystal violated eye will dissociate into CV+ and Cl minus ions. These two ions then penetrate through the cell wall and cell membrane of both gram positive as well as gram negative bacteria. CV plus ions later interacts with the negatively charged bacterial components and stains the bacterial cells into purple in color. The second step is addition of grams iodine. Iodine is acting as a moderant in trapping the uh and act as a trapping agent. A moderant that is a substance that will

00:19:31 increases the affinity of a cell wall to a particular stain. It will bind to the primary stain thus forming an insoluble complex which gets trapped in the cell wall. All the cells will then turn into purple in color. The third step here is decolorization with 95%age ethile alcohol alcohol or acetone that will dissolve the lipid outer membrane of the gram negative bacteria. So the pepidoglyen layer that get exposed and increases the porosity of the cell wall. The CV iodine complex is then washed away from the thin pepidoglycen

00:20:26 layer leaving gram negative bacteria a colorless one. On the other hand, alcohol has a dehydrating effect on the cell walls of gram positive bacteria. As a result, the pores of the cell wall shrinks. The CV iodine complex gets tightly bound into the multi-layered and highly cross-lin gram positive cell wall. So the cells get stained as purple in color. Now the last step here is counter staining with saffroninine. The decolorized gram negative cells are then counter stained with saffroninine or basic fushin can

00:21:27 also be used instead of saffroninine which will stain them pink in color. Now coming to the structure of a bacterial cell or a proarotic cell in detail. The first part that we can see here is the cell wall which is made up of murine or pepidoglycen. It is a polysaccharide crosslin with short amino acid chains. Second layer that is slimy gelatinous capsule. It is seen on the bacterial cell which protects them from desiccation under the conditions of drought. The third layer that is known as cell

00:22:22 membrane. It will surrounds the protoplasm. Fourth layer. Fourth one the major part that is the nucleus. A well organized and true well- definfined nucleus is totally absent in proaryotic cell noar membrane and no nucleus. So we can call this particular structure as nucleid oid means like nucleid means nucleus like structure but not the true nucleus. It has a long DNA molecule which get attached with the misosomes with the help of nucleoid proteins. Here you can see the structure of bacterial cell with the different

00:23:15 layers protective layers the nucleid structure cytoplasm py or even sex py flulum all structures plasmid an extra circular chromosomeal an extra chromosomeal and circular DNA A that is present in the cytoplasm of the cell. It can be used as a vector for transferring foreign DNA into the host organism in recombinant DNA technology. It contains antibiotic resistant genes that can be used as markers for identifying the reocombinants from nonrecombinants. Now coming to cytoplasm granular in nature and it is colorless containing

00:24:13 ribosome the 70s ribosome granules of a glycogen fat and other food reserves other cell membrane bound organals like mitochondri chloroplast endopplasmic reticulum gg bodies etc totally absent in the procarot cell pile. Some of these bacteria contains a small hairlike or rod-shaped structures called as piley which help in the attraction of the opposite sex. So it is known as sex pile. Flagulum originates from the basal granule seen in the cell membrane. In proarotic cells, the cell envelope contains three different layers such as

00:25:15 first one that is glycoalics. It is the outermost layer and it may be loose or it may be thick and tough layer. If it is a a loose sheath then it is known as slime layer. If it is thick and tough layer then we will call it as a capsule. Both are made up of polyaccharides. Second layer that is known as cell wall. Cell wall is the second layer of the cell envelope seen in bacteria or proaryotic cell which is seen just below the glycoalics. It is a rigid due to special macroolelecule that is called as

00:26:08 pepidoglyen. It is composed of a repeating framework of long glyon strands that is n acetile muramic acid and n acetile glucose amine which are cross-lin with short peptide chains. Plasma membrane made up of lipoproteins and oligosaccharides not the steroids. Plasma membrane fold inwards in the form of vesicles tubules and lame which are called as misosomes in proarotic cells. Now coming to the functions of misosomes. It increases the surface area of a transport. Helps in replication of a DNA during cell division. Helps in the

00:27:11 formation of a cell wall during binary fision. Helps in respiration and it also helps in secretion. A proarotic cell contains many inclusions like phosphate granules, glycogen granules, cyanopician granules. They contain gas vacules which help in positioning the proarotic cell in the water medium by giving buoyancy. Now coming to the structure of cell membrane. Cell membrane or plasma membrane or plasma lema. The well accepted model suggested by yes Jonathan Singer and G Nicholson that is the fluid mosaic model

00:28:19 of plasma membrane. It is the most accepted model of plasma membrane. There are other models also unit membrane model proposed by Robertson. So here it is the most accepted one that is the fluid mosaic model proposed by Jonathan Singer and G Nicholson. It is said that plasma membrane is formed of protein iceberg in a sea of lipids. Plasma membrane is trilaminar. It contains three layers and it is made up of lipoprotein. Lipid molecules are the phospholipids which form blayer. Phospholipids itself will form

00:29:22 two layers. Proteins are globular and are of two types intrinsic and exttrinsic proteins. Here you can see the diagram of fluid mosaic model. Phospho lipid molecules are here. They are arranged in two different layers with a header region and tail regions. Then different other protein molecules they are seen scattered in the lipid billayer. Some other oligosaccharides, glyolippids, even cholesterol molecules are also here. Proteins which are seen completely inside the billayer, lipid billayer that

00:30:21 is known as intrinsic or integral protein. Proteins which are completely seen outside the lipid billayer they are known as exttrinsic protein or peripheral protein. Some of the proteins they are very large and project on both the surface of phospho lipid billayer which are called as transmembrane proteins. They act as charge channels for the passage of water and soluble materials. Now coming to the structure of a phospholipid molecule. A phospholipid molecule is an amphipathic molecule which posess a hydrophilic head

00:31:21 and a hydrophobic tail. Head is made up of glycerol and phosphate while tail is made up of fatty acid. Glyolippids or glyoproteins are the carbohydrates associated with the plasma membrane. cholesterol molecules present in between the phospho lipids which provide stability to the animal membranes. Regarding phosphoippids, more common types of phosphoippids are phosphhatidile choline known as lecithine and the other one is sephylin that is phosphatidile ethanol amamine and yet another one that is

00:32:22 phosphatidile serin. So these are the different types of phospholipids that are commonly seen in the plasma membrane. They allow the fast movement of fat soluble molecules. Cholesterol molecules stabilizes the plasma membrane. Plasma membrane helps in intracellular and extracellular transport of molecules. Now coming to cell wall. The outermost protective and rigid supportive layer that is seen in all the bacteria, cyanobacteria, protist and all the plant cells. It is absent in animal cell and it was discovered by Robert Hook.

00:33:22 Types of a cell wall there present primary cell wall and secondary cell wall. Coming to primary cell wall outer and thinner elastic and it is living present in the meristematic cells and parangimma cells. It is made up of cellulose, hemiselulose, pectin and protein. Second one is secondary cell wall. It is seen inner to the primary cell wall in a mature and non-ividing cells. It is made up of cellulose, hemiselulose and subberin. in the case of a cork cells or cutin in all the aerial parts of the plants or it may be lignen in the

00:34:23 case of woody plants and in grasses it is silica. Now regarding middle lamala a thin and binding layer that is seen between the cell walls of adjacent plant cells. It is made up of calcium and magnesium pectates plasma desma cytoplasmic connections between neighboring cells that takes place through the pits present in the cell wall. Now pits are the portions unthickened areas present in the cell wall and through these pits the cytoplasm of the neighboring cells can form connections and that cytoplasmic connection which is

00:35:17 known as plasmoda. It helps in exchange of materials between the cells. An aggregation of a cytoplasm of a neighboring cells that occurs through plasmod that unit is known as simpl. The components of the cell wall present in a plant cellulose, hemiselulose, water molecules, pectic substances, proteins and even lipids are present in the cell wall of plant cells. Now coming to the functions of a cell wall. Since it is rigid hard, it gives protection. It gives a definitive shape to the cell. It is involved in

00:36:13 mechanical support. It helps in the absorption of water and mineral elements. For example, the cell walls of root hair absorbs water from the soil by imbivision. Subarin and that will prevent evaporation of water or transpiration. Cytoplasm an amorphous and translucent homogeneous and colloidal ground substance that is seen between the plasma membrane and the nucleus. Cytoplasm can be differentiated into two parts. One is cytoplasmic matrix and the other is cytoplasmic structures. Cytoplasmic matrix is known as cytosol or

00:37:10 hyaloplasm which is again divided into ectoplasm and endopplasm. Cytoplasmic structures includes the different cell organals the living components and non-living components that is cell inclusions. Now regarding the different functions one it provide raw materials for cell organals it helps in exchange of materials. It helps in the biosynthesis of molecules. Now regarding the vacules, it is present in all the ukarotic cells. A single large vacule that is seen in plant cell at the center and in animal

00:38:03 cells. Small vacules are seen and they are scattered. A vacule has two different parts. The outer membrane just like that of plasma membrane made up of lipoprotein in composition that is known as tonoplast. The fluid content seen inside the vacule that is known as cell sap. Fluid content present inside the vacule and it contains different components like water, mineral elements, sugars, amino acids, proteins, alkoids and even pigments. Now coming to the functions of vacules, cell samps tar pressure.

00:39:02 Now here comes the word tger pressure. The pressure exerted by the expanding cytoplasm in a charged cell against the cell wall. So that pressure that is known as tur pressure. The cell sap will exert tur pressure and it helps in the cell growth enlargement of the cell. It stores water and mineral elements as well as various types of nutrients. It stores even the waste materials of metabolism also. Now coming to the different types of vacules. There are food vacules meant for the storage of food

00:39:50 molecules. Contractil vacules are there mainly they are seen in the protozoans. It is meant for osmo regulation as well as excretion. There are gas vacules. They help in floating or maintaining buoyancy. Now here comes the organal century old. It was discovered by Van Bendon. It is seen in all the animal cells except in the case of mature mamalian RBCs. It is absent in plant cells. It is seen in protest as well as flagagillated plant cells. It is totally absent in procariots. Cendrosome. It is the portion that is

00:40:53 formed with the help of two stained darkly stained granules called as cendriolles and this since they are two in number they are known as diplosome. Here is the structure of a centriole with different filaments microtubules. We'll see the detailed structure here. Centrialsles are surrounded by an amorphous and cytoplasmic area that is known as centrosphere. Centrial do not have any outer membrane in order to give a definitive shape. So it is amorphous and it is surrounded by a clear area that is known as

00:41:50 centrosphere. Centrialsles and centrosphere together we will call it a centrosome. Now coming to the structure of a centriole they are hollow cylinders. They are perpendicular to each other. They are twin numbers arranged perpendicular to each other. And each centriole is microtubular structure made up of microtubules. They are arranged in 9 + 0 manner. Nine peripheral tubules and at the center there is no tuble at all. So it is written as 9 + 0 configuration. Each microtubule is a triplet. There are nine peripheral

00:42:44 microtubule and each microtubule is a triplet formed of three different subtubules that we can write or represent as A, B and C. A subtub is formed of 13 parallel protoilaments. The single A microtubule of the peripheral tubule that is made up of 13 parallel protoilaments B and C subtubules that is formed of 10 parallel protoilaments. So there are total nine peripheral tubules microtubules and each microtubule is a triplet represented as A B C and A subtle is made up of in turn protoilaments that is 13 in number and B

00:43:47 and C subtubules that is made up of 10 parallel protoilaments. C subtubule of each microtubule is linked to A subtubule of the adjacent microtubule by AC linger and hence all the microtubules are a little bit tilted at 40° at the center there is a proteinious hub at the center of the central there won't be any microtubule at all it is made up of a proteinious hub. The a microtubule that is connected with the central hub with the help of proteinious radial spokes. Now coming to the functions of a

00:44:47 centriole, they form a during cell division. In the case of an animal cell, they will form the basal body or blifaroplast of the fleellula which is seen in the plasma membrane. Distendriol of the sperm that give rise to axonym of the tail region of the sperm. Now, here are some of the questions for you to think and answer. Identify which among the following is not correct. Robert Brown discovered the cell. Scen and Schwan formulated the cell theory. Vir explained that cells are formed from the pre-existing cells.

00:46:08 A unisellular carriers carries out its life activity within itself. The second question for you to answer. New cells generate from A bacterial fermentation, B regeneration of older cells, C preexisting cells, D abiotic materials. Think from the lessons that you observed. Now here is your third question. Which of the following is correct? Cells of all living organisms have a nucleus. Both animal and plant cells have welldefined cell wall. In proariots there are no membrane bound cell organals. cells are formed denovo from abiotic

00:47:34 materials. So out of these four options which of the following is correct that you have it to think and respond. Now coming to the fourth question for you. It is a match the following question. Match the answers questions and answers or options correctly. Christ sister thyloids here in the part B options flat membranous sacks in stroma infoldings in mitochondria discshaped sacks in GG apparatus here are some more questions for you to answer. What is a misosome? Mention the functions of it. The sixth question for

00:48:47 you. How do neutral solutes move across plasma membrane? Can the polar molecules also move across it in the same way? If not then how are these transported across the membrane? Think it properly and respond. Now the next question for you. Name two cell organals that are double membrane bound. What are the characteristics of these two organals? State their functions and draw the label diagram of both. So all these questions you have to think it over and answer correctly. Thank you.