THE CELL-SIZE, STRUCTURE,AND TYPES

    CELL-A cell is a structural and functional unit of all organisms. The cell was discovered by Robert hooke in 1665. In actually Hooke discover a non living cell. first living cell is discovered by Antony von Leeuwenhoek who described the algae Spirogyra.  MJ Schieiden and T Schwann give the cell theory in 1839.
Cell theory-
1.All life forms are made from one to more cells.
2.New cell formed by pre existing cells.
3.A cell is a smallest form of life.

CELL SIZE- There is a wide variation in the size of cells. The smallest cells are those of mycoplama. They have a size of 0.1-1.05µm. Viruses are still smaiier. They do not have cellular structure The smallest virus has a volume of 7.0×10^-7µm³.Cells of multicellular eukaryotes have a size of 5-100µm. Erythrocytes are 7-8µm in diameter. ‘small lymphocytes’ are still smaller.muscle and nerve cells are comparatively very large. Longest cells of human body are the nerve cells which may reach a length of 90cm.

Amongst plants,large cells occur in many algae.Inter-nodal cells of CHARA are 1-10cm in length. Acetabularia, a unicellular alga,is upto 10cm in length.In general,eggs are large sized cells because they store food for partial or complete development of the embryo.Human egg is slightly over 0.1mm or 100µm in diameter. Avian eggs are largest. The egg of Ostrich is 170×150mm with a  volume of 1.1×10¹⁵µm³

LAST YEAR QUESTION PAPER WITH SOLUTION

<sup>CELL STRUCTURE AND CELL TYPES-
A plant cell consists of cell wall and protoplast,But i animal cell the cell wall is absent.In the cytoplasmic matrix are embedded a large number of cell organelles having specific functions. They are plastid,mitochondria,golgibodies,Ribosome,Centrioles,lysosomes,micofilaments,etc.
Ergastic substances are chemical substances appear in the plant bodyas products of metabolism.They may occur in the cytoplasm or in the cell wall.The various such substance are carbohydrate,proteins,fats and oils,Tannins,resins,gums,etc.

CELL TYPES-Prokaryotic and Eukaryotic</sup>
There is a two types of cells-
(a)Prokaryotic-founds in becteria,blue green algae and the PPLO(Pleuronemonia like organisms)
(b)Eukaryotic-present in animal and plant body.

                      PROKARYOTIC CELL
These are one enveloped structure which has a central nuclear material surrounded by cytoplasm. A bacterial cell is the best modal of an prokaryotic cell structure,Its enclosed by three layers,the outermost covering of slime,the middle cell wall and the innermost plasma membrane. parts of prokaryotic cell-
(1)Slime Layer-Capsule,Glycocalyx -This layer is present on the outer surface of the cell wall,made of polysaccharides and a polypeptide chain of amino acid,When the constituents of this layer are only polysaccharides which form a viscous layer,it is termed as slime layer.

Specialization of plasma membrane

this article is on specialization of plasma membrane to read about membrane structure click on this link
CELL MEMBRANE STRUCTURE
Pores in plasma membrane-
In Plasma membrane's structure pores of 0.35 manometer are found. In size that pores are same as Na positive ion's size. only 0.1% surface has pores. there is many models for pore structure on membrane-
1.Structural pores
2.Dynamic pores
3.paving block pores
4.Protein channel pores
5. Ionophore

THE CELL COAT-
Every cell has cell coat which is made of polysaccharides this coat calls glycocalyx.The cell coat is outer layer which present on whole membrane but only absent on tight junctions.  
Structure- this is very mine layer which founds on cell membrane. this is made of mucous- polysaccharides.A fibre protein  FIBRONECTIN also take part in composition of this.
Function-
1.This gives stability to plasma membrane.
2.this works of selective barrier .
3.This controls cells outer micro environment.
4.In intestine it works like a protective layer.
5.Around kidney glomerulai it work life filter and control transfer of molecules.
6. in connective tissue cell coat has HYALURONATE.
7.plasma membrane of erythrocytes has special antigens of different blood groups.
8.A single cell has many types of glaycoprotiens in its cell membrane.

Modifications of cell membrane-

1.Microvilli-the small finger like structure which founds on uutside the plasma membrane call microvilli .microvilli mostly founds in ALIMENTARY CANAL's absorption cells.for example- intestinal cells,hepatic cells,uriniferous tubules. the surface where microvillis are present call Brush border. some cells has very high number of microvilli like intestine's epithelium cells  has 3000 microvillis.When we cut the section of micrlvilli we see a central core in its structure.this canter core is completely covers by cell membrane.cores of microvillis are connected by on the base by many micro filaments web.
function-microvillis are increase the absorption power of cell by grow the surface.
2. Empty areas between microvillis works like sieve.
read about animal physiology on this link-
ANIMAL PHYSIOLOGY
                                           Cell junctions-
these are many types-
1.Tight junctions-oh this outer layer of plasma membrane of two cells connects and block the empty area very tightly so no empty area has left.it stop particles transfer to one to other cell completely.from cell.this stop  pancreas's digestive juice to dissolve in blood.this controls communication of protein and other elements to one to other cell.

2.Gap Junctions-Gap junctions are a means of communication. channel protein of two opposite cells joint together providing channels for sugar,ions,amino acids and other small molecules to pass .every gap junction is made up of specialized protein channels called connexins.

3.PLasmodesmata- They are protoplasmic bridges amongst plant cells which occur in the areas of cell wall pits or pores.

4. Desmosomes-Adjacent membranes possess disc shaped ticking of about 0.5 µm diameter, a number of tonofibrils and trans-membrane linkers embedded in dense intercelluler material. Desmosomes function as spot welds and are hence called spot desmosomes. They occur in epithelia subjected to disruption.

5.Terminal bars- Terminal bars are desmosomes without tonofibrils. Bands of thickening occur on the inner surface of membrane. The bands contain micro filaments and intermediate filaments.

Membrane structure and function

                               Membrane structure and function
ABOUT CELL-
                         A cell is a structural and functional unit of all organisms. The cell was discovered by Robert hooke in 1665. In actually Hooke discover a non living cell. first living cell is discovered by Antony von Leeuwenhoek who described the algae Spirogyra.  MJ Schieiden and T Schwann give the cell theory in 1839.
Cell theory-
1.All life forms are made from one to more cells.
2.New cell formed by pre existing cells.
3.A cell is a smallest form of life.
definition of cell membrane- the cell membrane is the outer layer of cell body which septate cell from outer environment. the membrane control molecules and ions who come and go out from cell.
Thickness- plasma membrane is very thin its thickness is nearly 75Å but it may be different in different types of cell. in RBC its thickness is 21.5Å.
ULTRASTRUCTURE-
the structure of plasma membrane is tree layered-
(a)20Å thine outer layer
(b)20Å thine inner layer
(c)middle layer between outer or inner layer of 35Å
the outer and inner layer is made of protein and middle layer is phosphpholipid layer. first modal of plasma membrane is presented by Daniel and Davison in 1935.

CHEMICAL COMPOSITION-plasma membrane is mostly made of protein and lipid and some quantity of carbohydrate is also founds.
read about DNA Molal-
DNA MODAL
Different models of plasma membrane- 
1. Lamellar theory-this theory is given by Annelida and Davison in 1935. according to this theory in plasma membrane structure there is one bimolecular layer of phospholipid is presents between two layers of protein. non-poler hydrophobic ends of both layer are arranged by facing. but poler hydrophilic ends are connected with protein molecules .one protein molecule connects with 75 to 90 molecules of lipid.each layer of phospholipid is separates by CHOLINE BASE. one cholesterol molecule is found between two molecules of phospholipid.

LEARN ABOUT PROTEIN ON THIS LINK-

STRUCTURE OF PROTEIN

2. Micellar theory- according to Hillier and Hoffman plasma membrane is made of pounded subunits or micellar. every subunit has central cord. protein particles are presents in molecular layer.         4Å gape between pounded micellar indicates water holes. micellar structure founds in intra cytoplasmic membranes not in cell membrane.

3.Fluid mosaic model- this theory is given by Singer and Nicholson. in this theory these are important points-
(a) lipid molecules made double layer which made skeleton of plasma membrane. intrinsic protein is presents inside of this and view like mosaic.
(b) intrinsic protein and lipid both are amphipathic. poler end is present on surface side.

(c)amphipathic protein made  liquid crystal pair. lipid molecules also built a layer and arranged between protein layer in this way that poler ends shows on outer surface. and by this structure active place for enzymes are presents outside cell membrane. 
   
       you can also read about-
BLOOD AND CIRCULATION

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