Cell

• Cell


  Smallest part of the body of an organism
• Cell


  • Able to carry out all the basic functions of life such as growth, metabolism and reproduction
  • Every organ is made of hundreds of thousands of cells
  • Every function performed by an organism is ultimately the outcome of the activity of cells only
  • Cells are the basic structural and functional unit of all living beings
• Characteristics of cells


  • Capable of independent existence
  • Independent existence
  • Building blocks of all living beings
  • Performs the basic functions of life
  • Replacement of old cells by new ones
• Life starts with the formation of a single cell
• Formation of tissue


  1. Cells of similar nature form a tissue

  2. Many tissues together form an organ

  3. Many organs form a system
• Every organism starts its life as a single cell, each cell has its own lifespan
• Cytology


  Branch of biology under which we study cell and its structure
• Biology


  Study of various aspects of cells including their structure, chemistry and physiology
• Salien gave the phrase "all cells arise from pre-existing cells"


  1885
• Cell


  The basic unit of structure and function of all plants and animals
• Discovery of cell


  • Discovered by Robert Hooke in 1665
  • Examined a thin slice of cork under a microscope and observed that the cork was made up of a large number of compartments joined together
  • These compartments were named cells
• Cell theory


  • Formulated by botanist Matthias Schleiden (1838) and zoologist Theodor Schwann (1839)
  • Cells are the basic unit of structure and function of all living organisms
  • All cells arise from pre-existing cells
• Exceptions to cell theory are viruses, which do not have cells
• Unicellular organisms


  Made up of only one cell, e.g. bacteria, yeast, Paramecium, Amoeba
• Multicellular organisms


  Made up of several cells, e.g. colonial algae like Volvox
• Newly born human baby has approximately 2 trillion cells
• An average size adult human has 30 million white blood cells, 25,000-30,000 million red blood cells, and 10,000 million nerve cells in the brain cortex, totalling 37.2 trillion cells in the whole body
• Cell size


  • Measured in microns or micrometres
  • Cells lie in the range of one-tenth to one-thousandth of a millimetre
• Smallest cells


  • Mycoplasma, 0.15 micron in diameter
• Largest cells


  • Nerve cells, 1 metre in length
  • Ostrich eggs, 170 x 135 mm in diameter
• Advantages of small cell size


  • Greater efficiency in diffusion of nutrients and metabolic wastes
  • Easier repair of any damage
  • Better communication between different regions of the cell
• Cell shapes


  • Amoeboid
  • Rounded
  • Elongated
  • Cuboidal
  • Cylindrical
  • Tubular
  • Irregular
  • Disc-shaped
• Cell structure


  • Cell membrane or plasma membrane
  • Cytoplasm with cell organelles
  • Nucleus
• Cell membrane


  • Extremely thin, double and selectively permeable
  • Formed of lipids and proteins
  • Binds the contents of the cell and gives it a definite shape
  • Permits only certain substances to pass through
• Cell wall


  • Found in plant cells only
  • Formed of cellulose
  • Provides rigidity, definite shape, and mechanical strength to the cell
  • Highly permeable, allowing free movement of substances in and out of the cell
• Nucleus


  • Small, spherical structure
  • Discovered by Robert Brown in 1831
  • Composed of nuclear membrane, nucleoplasm, nucleolus, and chromatin network
  • Nuclear membrane is a delicate, double-membrane structure with pores that allow exchange of materials between nucleus and cytoplasm
  • Contains hereditary material (DNA) and regulates all life processes of the cell
• Nucleoplasm


  Jelly-like substance inside the nucleus
• Nucleolus


  Participates in protein synthesis
• Chromatin network


  Tangled mass of thread-like structures that condense to form chromosomes during cell division
• Protoplasm


  Jelly-like living substance of the cell bounded by the plasma membrane, containing all the components and contents of the cell except the cell wall
• Cytoplasm


  The space between the plasma membrane and the nucleus, containing many chemical reactions and cell organelles
• Types of cell organelles

  • Double membrane bound organelles
  • Single membrane bound organelles
  • Non-membrane organelles
• Double membrane bound organelles

  • Endoplasmic reticulum
• Single membrane bound organelles

  • Lysosomes
• Cytoplasm


  The space between the plasma membrane and the nucleus
• Nucleoplasm


  The part of the cytoplasm within the nucleus
• Cytoplasm


  • Apprais colourless
  • Partly transparent
  • Somewhat viscous substance
  • Always in a state of movement
  • Many chemical reactions take place in it
• Endoplasmic reticulum (ER)


  A complex network of bound channels throughout the cytoplasm
• Types of ER


  • Rough ER
  • Smooth ER
• Rough ER


  Associated with the synthesis and storage of materials