Resources for teachers: BIOLOGY

Problems with survival in different types of water

Discipline: BIOLOGY

Key Stage: 4

Key idea: CELLS


Problems with survival in different types of water


You should understand the need for osmoregulation in aquatic animals


Different types of aquatic animals survive in different types of water; pond water, river water, estuaries and the sea. Even the seas are different, some are warmer others are saltier. Osmoregulation is the process by which organisms regulate their cells concentration of dissolved materials within the environment in which they live.
It is important to regulate the concentration of solutes within the cell so that the chemicals needed for the reactions that support life are present in the correct quantities and dangerous chemicals are disposed of .
Too salty an environment can be fatal to organisms adapted to survive in fresh water and vice versa. In animals, whose cells are bounded by a flexible membrane, the cells can be made to rupture under certain circumstances.


  • Using a knife and a cutting tile, make five slices of potato about 3mm wide. Cut them so that they are the same size and make them into a fish shape. Ensure that they can fit into the containers that you have available, for example 100ml beakers.
  • Use distilled water in one beaker and make up four other concentrations by adding one spatula of table salt to 100ml of water. Increase by one each time.
  • Find the mass of each ‘fish’, record it - don’t muddle them up!
  • Estimate a floppy factor on a scale of 1-5, 1 being firmest.
  • Immerse each ‘fish’ into a separate solution and leave them for 15minutes.
  • Carefully remove each fish’, dab it dry and then re-mass it and record the new floppy factor.


1. Describe what happens to the fish that have been placed in; [a] the most concentrated solution and [b] the distilled water.
2. What has caused the fish to [a] gain mass, [b] lose mass?
3. Use the idea of osmosis to explain how water moves into and out of cells.
4. What would happen to a freshwater minnow if it were placed in seawater?
5. What could happen if a sea bass was placed in a fish pond?
6. What special problems do organisms living in estuaries face in order to survive?

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February 2007