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Materials enter or leave the cells in the following ways:

  1. Diffusion: It is the movement of substances from the region of the higher concentration to the region of their lower concentration.
  2. Osmosis: Movement of water molecules from their higher concentration to lower concentration through a semi-permeable membrane.
  3. Active transport:
    (a)
    Movement of ions and molecules across a membrane against the concentration gradient, i.e. from lower to higher concentration.
    (b) It requires energy (ATP).
  4. Bulk transport:
    (a)
    Transport of large quantities of micro-molecules, macro-molecules and food particles through the membrane.
    (b) They are of two types:
    • Pinocytosis: Bulk intake of fluid, ions and molecules across the cell membrane by forming small endocytic vesicles of 100-200 nm in diameter. Also called ‘Cell drinking’.
    • Phagocytosis: Ingestion of large particles by living cells. Also called ‘Cell eating’.
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