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NEET BIOLOGY Unit 3 Biology CELL : THE UNIT OF LIFE

CELL : THE UNIT OF LIFE

What is Cytology? 
 Cytology : Structural study of cell

 What is Cell Biology? 
 Cell Biology : Structural & Functional study of cell.

 HISTORY 

Discovery of cell – In 1665 Robert Hooke examined thin slices of cork under his self made microscope (Magnification = 42 times). 

The cork seen was dead bark of spanish oak (Quercus suber).

 Robert Hook coined the term "Cellula" for Honey comb like structure of bottle cork (Greek cellulae = Hollow space) which later modified to cell. 

Actually he saw only the dead cell walls of plant cells. He published his findings in his book 'Micrographia'. Karl Nageli showed that cells in plants arises by the division of pre existing cell.  Discovery of living cell by  Leeuwenhoek– Leeuwenhoek examined mud, semen, saliva, blood, Insects etc. Under his self made microscope and observe protozoans, sperm, bacteria, RBC, muscle cells etc. 
 He called these tiny creatures as "Animalcules" and published his finding in "Secrets of nature”.  
He is known as father of microbiology, father of bacteriology, father of protozoology. R.Virchow stated "Omnis cellula e cellula" which means all cells arises from pre existing cell. This is known as "Law of Lineage".  Father of cytology is Hertwig & R. Hooke.  Father of Indian cytology is Dr. A.K. Sharma.  Father of modern cytology is C.P. Swannson. General facts Related With cells

 Longest cell is nerve cell of Giraffe. (more than 1m) (90 cm in man).  Largest cell is egg of ostrich (17cm x 13.5 cm dimension).  Smallest cell is PPLO (Pleuro Pneumonia Like Organism).  
Smallest plant cell mycoplasma Laidlawii 0.1 .  Largest plant cell – Acetabularia (10cm)  
Longest plant cell – Remie fibre (Boehmeria nevia)  Centre for cellular and molecular biology is at Hyderabad. 

Cell Theory Cell theory 

 Schleiden (Botanist) (1838) Schwann (Zoologist) (1839) 

 Cell theory was proposed by Schleiden and Schwann. 

According to cell theory, all livings things are made up of cells. 

Cell is structural and functional unit of living being. 

They have power of Reproduction.

Apposition
Intussusception 
When the particles are deposited between the substance which are already present then this types of growth is called Intussusception Growth 

 This type of growth takes place in primary, secondary and tertiary cell wall. Apposition (Accretion) When the layers are desposited on to the layers which are present already , then this types of growth is called apposition growth 
 This types of growth takes place in secondary cell wall. Functions 
 Cell wall protects the protoplasm. 
 Cell wall gives a particular size & shape to cell & functions in form of exoskeleton of cell. 
 It gives a mechanical support to cell. 
 Cell wall is permeable so it helps in transport of water & mineral substances 
 Cell wall plays an important role in absorption, transpiration, transport and secretion etc.

Cell Coat
 (Glycocalyx) Position – It is found outside the plasma membrane in many protistants and animals cell. Made by sialic acid mucin & Hyluronic acid Function.
 It protects the underlying plasma membrane. 
 It provides definite shape to the cell.
 It helps in recognition of microbes for defence.

Term plasma lemma was given by J.Q. Plower (1885). 
 Term cell membrane or plasma membrane was given by Nagelli. 
 Term unit membrane was given by Robertson.
 At first, structure of cell membrane was studied by Overton and postulated that cell membrane is composed of a continous layer of lipid material. 
 It is outermost boundary of animal cell.

Model of cell membrane 
To describe structure of plasma membrane numerous models have been proposed but the important model are as follow :– Fluid mosaic model (1973) 
 This model was proposed by Singer and Nicholson.
 It described protein as ice bergs in a sea of lipids. 
It is the most accepted model.
 There is a central bilipid layer (2 layer) composed of phospholipids arranged in a specific manner. 
 Hydrophilic polar head constitute top and bottom surfaces.
 Hydrophobic non polar tail end-are buried in the membrane. 
 Within phospholipid, bilayer, proteins are arranged in (2) forms 
1. Intrinsic proteins 2. Extrinsic proteins

TIPS

1. The middle lamella can be dissolved by strong acid only. 
2. Bacterial cell without cell wall is called Lister-Form.(L-form) 
3. Mucopeptide is a polymer of two amino-sugar, N-acetyl Glucosamine (NAG) and N-acetyl muramic acid (NAM).
 4. In cellulose, a polymer of unbranched chain of glucose molecule linked by 1-4 glycosidic bond. 
5. The cellulose formation is takes place in presence of celulose synthetase enzymes which is present in membrane
6. Plasma membrane is a thin selective permeable & living membrane. 
7. It is flexible and porous membrane. 
8. Plasmalemma of animal cells is elastic due to the presence of lipids.

 The cell is the basic structural, functional and biological unit of all known living organisms,  Robert Hooke (1665) observedd honey-comb like dead cells in a thin slice of cork and named them ‘cell’. Anton van  Leeuwenhoek (1667) was the first to describe a living cell. 
 The properties of a living organism depend on those of its individual and RNA found in the cell nucleus and cytoplasm. 
 All cells are basically the same in chemical composition in organisms of similar species. Energy flow (metabolism and biochemistry) occurs within cells.) CELL THEORY (Magna Carta of Cell Study)  MJ Schleiden ; 1838 and Theodor Schwann; 1839.
 The postulates are: (a) All living beings are made up of cells (cell is the basic unit of life). (b) All cells arise from pre-existing cells (Omnis cellula e cellula - Rudolf Virchow). (c) Cell is the smallest independent unit of life.
 Size of biological cell is generally too small to be seen without a microsscope. There are exceptions as well as considerable range in the sizes of various cell types. 
 Growth of Cell Wall The growth and formation of cell wall occurs by two ways: (i) By intussusception : It is the deposition of wall material in the form of fine grains. (ii) By apposition : In this method, the new cell wall material secreted by protoplasm is deposited by definite thin plates one after other.  Function of the cell wall : (i) It maintains the shape of plant cell and protects it from mechanical injury. (ii) It wards off the effect of pathogens. 
 Plasma Membrane Plasmalemma contains about 58 - 59 % proteins, 40 % lipids and 1-2 % carbohydrates. 
 Autosomes: These are the somatic chromosomes which do not take part in fertilisation process. These are also called allosomes and they are 44 in number in human body. MITOCHONDRIA  Visible under the microscope only after specific staining. 
 Number per cell is variable, depending on the physiological activity of the cells

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