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You put an uncooked chicken egg in vinegar and leave it in your fridge for an entire week. When you examine the egg after one week, you discover that the hard outer shell of the egg has completely dissolved. However, the egg is still held together by a thin, yet resilient membrane, which is semi-permeable.

You put the shell-free egg in a solution that contains 5% salt and 5% sucrose, but no other dissolved compounds. The interior of the egg contains 25% sucrose and 15% salt with no other dissolved substances. If the egg membrane is permeable to water and salt, but NOT sucrose, in which direction (if any) would you expect the following molecules to begin diffusing when the egg is first placed into the salt/sucrose solution?

WATER movement:
[ Select ]

SALT movement:
[ Select ]

SUCROSE movement:
[ Select ]

1 answer

When the shell-free egg is placed in a solution containing 5% salt and 5% sucrose, let's analyze the movement of each of the different molecules based on their concentration gradients and the permeability of the egg membrane.

  1. WATER movement:
    Water will move out of the egg into the surrounding solution. The interior of the egg has a higher concentration of solutes (25% sucrose and 15% salt) compared to the surrounding 5% salt and 5% sucrose solution. As water moves toward the area of higher solute concentration (inside the egg), it will diffuse out, leading to a net movement of water out of the egg.

  2. SALT movement:
    Salt can move through the membrane. Since the concentration of salt inside the egg is 15%, which is higher than the 5% salt concentration in the surrounding solution, salt will diffuse out of the egg into the solution until equilibrium is reached.

  3. SUCROSE movement:
    Sucrose cannot move through the egg membrane as it is not permeable to sucrose. Therefore, there will be no movement of sucrose in either direction; the sucrose concentration inside the egg will remain higher than that in the surrounding solution.

To summarize:

  • WATER movement: Out of the egg
  • SALT movement: Out of the egg
  • SUCROSE movement: No movement