Cell basics

• Cell


  Structural and functional unit of organisms
• Totipotency


  • Every cell is capable of forming the whole individual
  • Potential of forming the whole individual
• Cell shape


  • Varies from organism to organism
  • Varies within the same organism
• Average cell size is 10 to 100 micron
• Smallest cell is Mycoplasma (0.15 micron)
• Largest cell in human is egg cell
• Smallest cell in human is sperm cell
• Longest cell is nerve cell
• Functions of different cell types

  • Nerve cell: Conduction of nerve impulses
  • Gland cell: Secretion
  • Squamous epithelium: Protective, give shape
  • Columnar epithelium: Absorption + secretion
  • Egg cell: Reproduction
  • Red blood cell: Carry oxygen
  • Fibrous muscle cell: Contractile
• Approximate number of cells in human body is 3.7 x 10^13
• Father of Biology


  Aristotle (384-322 BC)
• First recognized structural units

  Robert Hooke (1665)
• Coined the term "cell"


  Robert Hooke (1665)
• Father of Microbiology


  Antonie Van Leeuwenhoek (1611)
• Observed and named unicellular particles as "animalcules"


  Antonie Van Leeuwenhoek (1611)
• Discovered nucleus in plant cells


  Robert Brown (1831-39)
• Discovered Brownian movement


  Robert Brown (1831-39)
• Cell Theory


  All organisms are made up of cells, new cells are formed by the division of existing cells, and cells contain genetic material
• All metabolic reactions take place inside cells
• Viruses and viroids are exceptions to the Cell Theory
• Prokaryotes


  Organisms with primitive, nuclear material not enclosed within a nuclear membrane, DNA without histone proteins
• Eukaryotes


  Organisms with true nucleus enclosed within a nuclear membrane, DNA with histone proteins
• Merokaryotes


  Organisms that share characteristics of both prokaryotes and eukaryotes, have a nuclear membrane but DNA without histone proteins
• Types of organisms


  • Unicellular
  • Multicellular
• Unicellular organisms lack differentiation, include prokaryotes and some eukaryotes like protists, bacteria, and yeast
• Multicellular organisms have differentiation, are eukaryotes like animals and plants
• Endosymbiotic theory explains the origin of eukaryotes from the incorporation of prokaryotes like mitochondria and chloroplasts
• Types of cells


  • Muscle cells
  • Blood cells
  • Nerve cells
  • Cardiac cells
• Nerve cells are the longest cells
• Cell organelles in plant cells

  • Cell wall
  • Plasma membrane
  • Cytoplasm
  • Mitochondria
  • Golgi bodies
  • Endoplasmic reticulum
  • Ribosomes
  • Plastids
  • Nucleus
• Cell organelles in animal cells

  • Plasma membrane
  • Cytoplasm
  • Mitochondria
  • Golgi bodies
  • Endoplasmic reticulum
  • Ribosomes
  • Lysosomes
  • Centrosome
  • Nucleus
• Protoplasm


  Colourless, jelly-like substance surrounded by the plasma membrane, containing water, ions, nucleic acids, proteins, lipids
• Cell wall


  Outermost protective layer present in bacteria, fungi, and plants, but absent in animal cells
• Cell wall


  • Provides definite shape and rigidity to the cell
  • Made of different materials in different organisms (peptidoglycan in bacteria, chitin in fungi, cellulose in plants)
• Plasma membrane


  Extremely thin structure that holds the cytoplasmic contents, selects substances required by the cell, transports nutrients and water, prevents unwanted substances from entering
• Cytoplasm


  Semifluid, gelatinous substance between the plasma membrane and the nucleus, made up of 80% water and carbohydrates, proteins, etc., good conductor of electricity, contains organelles
• Cell organelles


  • Endoplasmic reticulum
  • Golgi bodies
  • Mitochondria
  • Plastids
  • Ribosomes
  • Lysosomes
  • Centrosome
  • Vacuoles
  • Nucleus
• Endoplasmic reticulum


  Network of tubes and sacs that helps in transportation within the cell, protein synthesis, and lipid gathering
• Golgi bodies


  Disc-shaped groups of flattened sacs that store, modify, and secrete proteins and carbohydrates
• Mitochondria


  Organelles that provide energy to the cell by generating ATP, have their own DNA and ribosomes