Class 11 Biology Cell : The Unit of Life An overview of cell

An overview of cell

  • Cells are surrounded by a cell membrane and in plants cell membrane is surrounded by a cell wall.
  • Inside each cell is a dense membrane bound structure called nucleus, which contains the chromosome and in turn DNA.
  • Cells that have membrane bound nuclei are called eukaryotic whereas cells that lack a membrane bound nucleus are prokaryotic.
  • In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm occupies the volume of the cell.
  • Besides the nucleus, the eukaryotic cells have other membrane bound distinct structures called organelles like
  • Endoplasmic reticulum (ER)
  • Golgi complex
  • Lysosomes
  • Mitochondria
  • Microbodies and
  • Vacuoles
  • Mycoplasmas, the smallest cells, are only 0.3 μm in length while bacteria could be 3 to 5 μm.
  • The largest isolated single cell is the egg of an ostrich.
  • Human red blood cells are about 7.0 μm in diameter.
  • Nerve cells are some of the longest cells.


Fig. Egg of ostrich


Fig. Red blood cells


Fig. Nerve cell

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