Explain the purpose of cell division in living organisms.

Cell division is to help create a surplus of cells and establish growth

Explanation:

It is to grow, create, and repair the living organism

The other considerations would be:

She should increase her sample size to 50 plants and place them all in the same area.  She should be sure to give all the flowers the same amount of water.  She should make observations twice a day for four weeks for better results.  She should place one flower in a similar container, but not pump carbon dioxide into it.  

For reliability of any experiment:

There should be a considerable number of observations. For example, 50 plants would be better as compared to 5 plants.

There must be a control specimen with one can compare results. For example, one plant must be kept in a similar container but no carbon dioxide should be pumped into it.

In addition, all variables other than carbon dioxide must be kept the same or constant. For example, each flower should get an equal amount of water.

Lastly, for better results, she can record observation twice a day and for four years instead of two weeks.