🐣 Cell Basics

Cell

• The word cell is derived from the Latin word “Cellula” which means a little room. An English scientist, Robert Hooke, discovered the cell in 1665 while examining thin section of cork under his simple microscope. (Term Cell → Robert Hooke)
• He observed a mass of empty hexagonal chambers like a honeycomb and called the compartment cells (dead).
• Robert Hooke wrote the book Micrographia.
• A cell is the structural and functional unit of life and is defined as a mass of protoplasm bounded by a plasma membrane.
• In 1838, a German botanist, Schleiden and in 1839, a German zoologist, Schwann proved that the plants and animals are cellular in character and founded the cell theory. They postulated that the cell is the basic unit of all life.
• In 1861, De Bary and Schultze put forward ‘Protoplasm theory’ means the cells (units of plants and animals) are tiny masses of protoplasm, each containing a nucleus.
• In 1884, Strasburger concluded that the nucleus is related to inheritance of characters.
• In 1885, Virchow proposed the idea that all cells arise from pre-existing cells.
• The size of majority of cells is 3-30 µ.
• Smallest cell: PPLO : size : 0.1-0.5 µ; PPLO means pleuro-pneumonia like organism.
• Largest cell: Ostrich egg : size: 170mm x 135mm
• Largest cell in human body: Nerve cell : Size: 90 µ in length.
• Resolving power of human eye: 100 µ.
• Resolving power of Light Microscope: 3000 A° or (0.3 µ)
• Resolving power of Electron microscope: 0.25 A° (1 µ = 10-6 m; 1 A° = 10-10 m).
• Structurally the cell is formed of three parts viz.
  • Cell boundaries
  • Cytoplasm
  • Nucleus

    

• Hyaloplasm under electron microscope:
• The hyaloplasm, which refers to the clear, fluid portion of the cytoplasm, contains water, minerals, ions, amino acids, sugars, etc.
  • Plasma membrane
  • Endoplasmic Reticulum
    • Smooth
    • Rough (with Ribosome)
  • Dictyosomes (Golgi apparatus of plants)
  • Lysosomes
  • Tonoplast (Vacuole)
  • Spherosomes
  • Plasmodesmata

Differences between prokaryotic and eukaryotic cells

Plasma membrane/Cell membrane/Plasma lemma

• It is the extremely delicate, thin, elastic and living membrane which surrounds a cell.
• In plant cell, it is present on the inner side of the cell wall. It is made up of two layers of lipid (fat) molecules (size 35 A°) with protein molecules (each 20 A°) sandwiching it and embedded in it.
• It is a lipo-protein membrane.
  • Protein (20 A° thickness)
  • Lipid, bilayer (35 A°)
  • Protein (20 A°) monolayer
• Total thickness of the membrane is 75 A° - 100 A°
• Plasma membrane is a selectively permeable (semi-permeable) membrane and its function is osmoregulation of molecules. It protects the internal structures and gives shape and rigidity to cell.
• In animal it is the outermost structure of the cell and hence called `ectoplast’.
• Plasma membrane is absent in virus.
• Sialic acid is a constituent of the cell membrane. It acts as a cell receptor. It is a monosaccharide with a nine-carbon atom.
• Membrane less Cell Organelles: Ribosome, Centriole, Centrosome, Microtubules.
• Single Membrane bound Cell Organelles: Peroxisomes, Lysosomes, Sphaerosome, Glyoxysomes
• Double Membrane bound Cell Organelles: Nucleus, Mitochondria, Chloroplast

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