Question

What happens when red blood cells and onion cell are kept in hypotonic solution

Answer 1

If  an  onion  peel  is  kept  in  a  hypotonic  solution,  water  will  enter  the  cells  of  that  onion  peel  through  osmosis.

ie,  as  the  medium  of  water  outside  the  cell  is  more,  it  enters  into  the  cell  through  osmosis.  In  this  case,  the  cell  is  likely  to  swell  up.

The  same  thing  happens  to  Red  Blood  Cells  also.

Answer 2

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When the cells are kept in a hypotonic solution, endosmosis occur, i.e., inward movement of water. ... The RBCs burst easily because they are animal cells and do not have cell wall. The onion peel possess cell wall which makes it resistant to bursting due to swelling caused by endosmosis.