Celery stalks that are immersed in fresh water for several hours become stiff and hard. similar stalks left in a salt solution become limp and soft. from this we can deduce that the cells of the celery stalks are

hypertonic to water and hypotonic to salt solution.

Explanation:

When two solutions of unequal solute concentrations are separated by a permeable membrane, water molecules move from the solution with lower solute concentration to the solution with higher solute concentration until an equilibrium is reached. The solution with higher solute concentration is referred to as being hypertonic while the other one is referred to as being hypotonic.

The cells of celery stalks have higher solute concentration in their cell saps compared to the surrounding fresh water. Hence, water keeps entering the cells, resulting in turgidity. The cells are therefore hypertonic to fresh water.

The salt solution however seemed to have more solute concentration compared to that of the cell sap of the celery stalks. This made the cells of the celery stalks to lose water to the surrounding solution, resulting in flaccidity. Hence, the cells are hypotonic to salt solution.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."