Assignment for 5-8-14

Watch the video at the following link and use it to answer the questions that follow.  Be prepared to discuss your answers with the class.

Cell Transport

Explain why saltwater fish cannot live in fresh water and why freshwater fish can't live in saltwater.  In your answer, use terms such as hypertonic, hypotonic, isotonic, diffusion, and osmosis.




Dikscuss two situations in which facilitated diffusion would be used instead of simple diffusion.





If passive transport does not require energy expediture by the cell, where does the energy come from that moves the molecules?






Answers

1.  Saltwater fish cannot live in freshwater because the freshwater would be hypotonic to the fish.  Since there is more salt in the fish water would move in by osmosis causing the fish to swell.  Salt would diffuse out in an effort to reach equilibrium.

Freshwater fish cannot live in saltwater because the saltwater would be hypertonic to the fish.  There is a higher concentration of salt in the water than in the fish.   Therefore, the water would leave the fish by osmosis resulting in the cells of the fish becoming dehydrated.

2.  If molecules are too big to pass between the phospholipids but small enough to fit through a protein channel, they could use facilitated diffusion.  Molecules the size of sugar or amino acids would have to do this.  Also, molecules that are polar or have a charge would have to use a protein channel because they cannot get past the lipid tails of the phospholipids.  Water and ions would have to use this method for this reason.

3.  The molecules have their own energy.  They are constantly in motion, and when they collide, they transfer energy to one another.  Therefore, this motion is due to the energy the molecules themselves contain and requires no energy expenditure of the cell.