chapter 1

• Differences between prokaryotic and eukaryotic cells

  • Prokaryotic cell: Size generally small (1-10 μm), Nuclear region not well defined and known as nucleoid, Single chromosome
  • Eukaryotic cell: Size generally large (5-100 μm), Nuclear region well defined and surrounded by a nuclear membrane, More than one chromosome, Membrane-bound cell organelles present
• Viruses lack any membranes and hence do not show characteristics of life until they enter a living body and use its cell machinery to multiply
• Cytoplasm

  Fluid content inside the plasma membrane, contains many specialised cell organelles
• In prokaryotes, the membrane-bound cell organelles are absent
• In eukaryotic cells, the nuclear membrane as well as membrane-enclosed organelles are present
• Endoplasmic reticulum (ER)


  Large network of membrane-bound tubes and sheets, has two types - rough ER (with ribosomes attached) and smooth ER (helps in lipid manufacture)
• The ER serves as channels for the transport of materials (especially proteins) between various regions of the cytoplasm or between the cytoplasm and the nucleus
• The ER also functions as a cytoplasmic framework providing a surface for some enzymes
• Membrane biogenesis


  The process where proteins and lipids help in building the cell membrane
• Endoplasmic reticulum (ER)


  • Forms a network system
  • Serves as channels for the transport of materials (especially proteins) between various regions of the cytoplasm or between the cytoplasm and the nucleus
  • Functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell
• Smooth ER


  Plays a crucial role in detoxifying many poisons and drugs in liver cells of vertebrates
• Golgi apparatus


  A system of membrane-bound vesicles (flattened sacs) arranged approximately parallel to each other in stacks called cisterns<|>Functions include the storage, modification and packaging of products in vesicles<|>Involved in the formation of lysosomes
• Lysosomes


  Membrane-bound sacs filled with digestive enzymes<|>A kind of waste disposal system of the cell<|>Digest foreign material as well as worn-out cell organelles<|>Known as the 'suicide bags' of a cell
• Mitochondria


  • Have two membrane coverings (outer membrane is porous, inner membrane is deeply folded)
  • Release energy in the form of ATP (Adenosine triphosphate)
  • Have their own DNA and ribosomes
• Plastids


  Present only in plant cells<|>Two types: chromoplasts (coloured plastids) and leucoplasts (white or colourless plastids)<|>Chromoplasts containing chlorophyll are known as chloroplasts and are important for photosynthesis<|>Leucoplasts are organelles that store materials like starch, oils and protein granules
• Vacuoles

  Storage sacs for solid or liquid contents<|>Small in animal cells, very large in plant cells (may occupy 50-90% of the cell volume)<|>Provide turgidity and rigidity to plant cells<|>Store important substances like amino acids, sugars, organic acids and proteins<|>In single-celled organisms like Amoeba, the food vacuole contains the food items that the Amoeba has consumed
• Mitochondria and plastids have their own genetic material
• If the organisation of a cell is destroyed due to some physical or chemical influence, the cell will die
• Lysosomes are known as 'suicide bags' because during disturbance in cellular metabolism, they may burst and the enzymes digest their own cell
• Proteins are synthesised in the ribosomes
• The cell is the fundamental structural and functional unit of living organisms
• Mitosis


  Mother cell divides to form two identical daughter cells with the same number of chromosomes
• Meiosis


  Specific cells of reproductive organs or tissues divide to form gametes with half the number of chromosomes of the mother cell