Living organisms use osmoregulation to balance solute and water concentrations in their cells, tissues and organs. many marine organisms have internal solute concentrations that are similar to their environment. however, this is not typically true of freshwater and terrestrial organisms. what is likely to happen to the cells of a marine plant if placed in a freshwater environment?

If the marine plant is placed in a freshwater environment, then the cells will undergo plasmolysis.  

The plants found in the freshwater surroundings are adjusted for osmoregulation in hypotonic environments. If one place this type of plant in a marine environment, that is, one with a greater concentration of dissolved salts, then the environment is considered as hypertonic environment. The cells of the plant will lose water and will go through the process of plasmolysis.  

The Cell will burst or swell due to the large amount of water enters in plan call.

the answer is:

carbon dioxide