Title Notes_Fundamental Unit of Life_Fundamental Unit of Life.pdf ✅

www.thinkiit.in Page 1 thinkIIT THE FUNDAMENTAL UNIT OF LIFE 1. INTRODUCTION :: Study of cell is called Cytology. Cells are the structural and functional units of life. 2. HISTORICAL ACCOUNT ::  Robert Hooke (1665) observing a slice of cork in which he saw honey comb like structure which he called cell.  Rudolf Virchow (1855) stated that all cell arise from the division of pre-existing cells.  Cell theory was proposed by Schleiden and Schwann (1839). (A) Postulates of Cell Theory :  Living things made of minute units, the cells, which are the small entities, Thus cells the structural unit of life.  Cells are normally alike in metabolic activities & structures.  A cell bounded by a cell membrane & some times cell wall also. It contains protoplasm & nucleus.  The function of an organism is the result of the activities & interactions of the constituent cell. (B) Modern Cell Theory :  It is also referred as cell principle.  Life exists only in cell.  Living beings are multinucleate mass of protoplast, containing nuclear material & some cell organelles, limited by a cell membrane.  Cell have basic similarity in chemical composition & physical structure.  Cell arise from pre-existing living cells by division.  Cell working & structure is controlled by DNA.  Cells have genetic information, stored in their DNA.  A cell can act (grow, divide & die) Independently.  A cell is made of living substance called protoplasm. Term ‘Protoplasm’ was coined by Purkinje (1839).  Protoplasm with cell organelles comprises cytoplasm.  Cytoplasm is a part of cell between plasma membrane & nuclear envelope.  Single celled organisms (unicellular organisms) are Bacteria, Amoeba and Chlamydomonas.  Many celled organisms (multicellular organisms) are Fungi, Plants and Animals.  Protoplasm is a aggregate of molecules of organic. (as protein, carbohydrates, fats or lipids), nucleic acid (DNA & RNA) and Inorganic (water, ions, salt etc.) compounds.  All kinds of true cells share the following three basic characteristic.  They contain a set of genes.  They contain a limiting plasma membrane.  They contain a metabolic machinery.  Organisms are again divided into following two main types :
www.thinkiit.in Page 2 thinkIIT (a) Prokaryotes (b) Eukaryotes  Differences between prokaryotic cells and eukaryotic cells are Prokaryotic Eukaryotic Cells Cells a Size of cell is generally Large (5-100 m) small (1-10m) b Nucleus Absent Nucleus Present c Contain single Contain many chromosome chromosome d Nucleolus is absent Present e Membrane bound cell Present organelles are absent (Ribosomes are present) f Cell division take place Cell division occurs fission or budding by mitosis or meiosis (No mitosis) g Ex. BGA, PPLO etc. Ex. Amoeba, Paramecium etc. 3. DIFFERENCE BETWEEN ANIMAL AND PLANT CELL :: Animal Cell Plant Cell 1 Animal cells are Plants cells generally small in size are larger 2 Cell wall is absent. Cell wall is present 3 Except the protozoan Plastids are present Euglena no animal cell possesses plastids. 4 Animals cell have a Plants cell have single highly complex many simpler units and prominent Golgi of Golgi apparatus apparatus. called dictyosomes 5 Animal cells have Plant cells lack centrosome and centrosome and centrioles centrioles. 4. STRUCTURE & FUNCTION OF CELL AND CELL ORGANELLES (A) Structure of Cell : The size, shape number and volume of cell vary greatly among unicellular and multicellular organisms.  Cell shape :  The shape of cell may be variable or fixed.  Variable shape occur in Amoeba, WBC etc.  Fixed shape occur in most plant and animals.
www.thinkiit.in Page 3 thinkIIT  Cells may be diverse shapes such as polyhedral (8, 12 or 14 sides) spherical (e.g. eggs of mainly animals), spindle shaped (Smooth muscle fibres), elongated (e.g. Nerves cells) so on.  Cell Size :  The size of different cells ranges between broad limits.  Some plants and animals cells are visible to the naked eye.  Most cells are visible only with microscope.  The prokaryotic cells usually range between 1 to 10 m.  The eukaryotic cells usually range between 10 to 100 m.  Amoeba proteus may reach a diameter of 0.5 mm.  The smallest cells are those of Mycoplasma laidlawiil (0.1μ in diameter) or PPLO (pleura pneumonia like organism).  The largest cell is egg of an Ostrich.  Cell Number :  The number of cell in living organisms also varies greatly.  In unicellular organisms, a single cell occur its body eg. Chlamydomonas, Chlorella, Amoeba.  In human body, the estimated number of cell is 100 trillion (1014) (B) Component of cell :  Major components are - A living part of cell Non living part of cell a. Plasma membrane a. Cell wall b. Cytoplasm b. Vacuoles (i) E.R. c. Cell inclusions (ii) Mitochondria (iii) Golgi apparatus (iv) Ribosomes (v) Lysosomes Centrioles Cell membrance Ribosomes E. R. Nucleus Mitochondrion Nucleolus Small vacuole Golgi complex Plant vacuole Starch grain Cell wall Chloroplast Animal Cell Plant Cell STRUCTURE OF CELL Tonoplast
www.thinkiit.in Page 4 thinkIIT (vi) Centrioles (animals only) (vii) Plastids (plants only) 4.1 Plasma Membrane and Cell Wall : (A) Plasma Membrane : Introduction :  Cell surface in all the cells is enclosed by a living membrane which is called cell membrane by C. Nageli and C. Kramer (1855). Historical Account :  J.Q. Plower (1931) coined the term Plasmalemma for cell membrane. Ultrastructure :  Plasma membrane forms outer covering of each cell.  It is present in both plant and animal cells.  Plasma membrane is a living, thin, delicate elastic, selectively permeable membrane.  It separates contents of a cell from the surrounding medium.  Fluid Mosaic Model :  In 1972, Singer Nicolson proposed this model. According to this, cell membrane consists-two layers of phospholipid molecules, phospholipid & protein molecules are arranged as a mosaic.  Phospholipid molecules have their polar heads directed outward non polar tail pointing inward.  The proteins are of two types –  Peripheral or integral. Peripheral proteins are located superficially while integral proteins are embeded in the phospholipid matrix. The protein monolayers have elasticity & mechanical support to the lipid matrix. Lipid bilayer Integral (trans membrane) proteins Peripheral protein Glycoprotein Extracellular fluid Peripheral protein Phospholipids : Polar head (hydrophilic) Fatty acid tails (hydrophobic) Polar head (hypdrophilic) Integral protein FLUID MOSAIC MODEL OF PLASMA MEMRANE