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Organisms Show Variety in Cell Number, Shape and Size

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Topics

  • Definition: Unicellular Organisms
  • Definition: Multicellular Organisms
  • Key Points: Number, Size, and Shape of Cells
CISCE: Class 10

Definition: Unicellular Organisms

Living organisms made up of only a single cell are called unicellular organisms.
Examples: Amoeba, Paramecium, bacteria, Chlamydomonas, etc.

CISCE: Class 10

Definition: Multicellular Organisms

Majority of living organisms are made up of millions or billions of cells and are called multicellular organisms.
Examples: Volvox, rose, mosquito, mango, humans, etc.

CISCE: Class 10

Key Points: Number, Size, and Shape of Cells

  1. The number of cells in an organism increases with its size—from single-celled organisms like Amoeba to humans with approximately 37.2 trillion cells.
  2. Humans have about 200 different cell types, including 100 billion nerve cells in the brain and 25 trillion red blood cells.
  3. Cells are microscopic in size; the smallest include bacteria and red blood cells, while the largest is the ostrich egg (a single cell).
  4. Cell shapes vary according to function—e.g., biconcave red blood cells for oxygen transport, amoeboid white blood cells for mobility.
  5. Specialized cell shapes support specific roles—nerve cells are long for impulse conduction; guard cells are bean-shaped to regulate stomatal openings.
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