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Homework Help: Biology Cell Question

  1. Nov 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A protozoa that normally lives in the ocean is placed in a freshwater fish tank. What would happen to the water balance in the cell? Use the terms osmosis, turgor, cell membrane, hypertonic or hypotonic. Describe what could happen to this cell (remember to include any cellular organelles that could help the cell out.)

    2. Relevant equations

    3. The attempt at a solution
    I know that because the protozoa was in ocean water, there would be salt solute in the cell. Through osmosis, the diffusion of water molecules (solvent) would occur through the differentially permeable cell membrane. The cell membrane would allow the fresh water to rush into the cell, and some of the salt molecules to flow it, creating a balance both inside and outside the cell. Due to the salt solute going out of the cell, and the fresh water molecules going in, I believe that it would be a hypotonic solution with a lower concentration of solute (higher concentration of water) outside the cell than inside, because the net flow of water is into the cell. The cell would be turgid, because the fresh water would make the cell more full, and rectify any shrinkage that occurred because of the salt. The contractile vacuole is the cell organelle that could help it out, because it could expel water if the cell becomes too bloated and pops.
  2. jcsd
  3. Nov 16, 2008 #2
    I've worked on this question a little more and have come up with this...

    Because the protozoan is used to living in salt water and having large quantities salt water in its environment, it will retain a large quantity of salt water within itself. When the protozoan is placed in the freshwater fish tank, the high concentration of salt on the inside will result in osmosis. The water molecules (solvent) will diffuse through the differentially permeable cell membrane. The cell membrane allows substances in and out of the cell, in an attempt to maintain homeostasis both inside the cell and in its surrounding environment. Fresh water will move in to the cell, because it is in a hypotonic solution. There is a lower concentration of solute (higher concentration of water) outside the cell than inside. Moving from ocean water (which contains salt) to fresh water will result in a change in water balance. Therefore, the flow of water is into the cell, in an attempt to equalize the amount of salt water and fresh water within the cell. All animals that live in water are equipped with a contractile vacuole. This cellular organelle could definitely help the protozoa, as it pumps excess water out of the cell. The contractile vacuole can save the cell from popping. Turgor is a force exerted outward based on the amount of water contained in the cell.
  4. Nov 20, 2008 #3
    the cell would eventually burst, though, because it was used to living in salt water.
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