Guard cells are specialized cells in the epidermis of leaves, stems and other organs that are used to control gas exchange,
including water vapor via transpiration. Guard cells perceive and process environmental stimuli to trigger cellular responses
resulting in stomatal opening or closure. All but one environmental stimuli might trigger stomatal opening. That would be

it has to be understood that the sea water contains a huge amount of sodium and chlorine ions and if they enter the cell of the atlantic cod fish, the cell will shrivel and the fish will die. to avoid such a condition, the fish uses active transport for the purpose of removing the ions against the gradient.

explanation:

the atlantic cod is not a maritime osmoconformer. its native application of salts is less than that of the seawater it lives in. it is continually falling water from the gills to the ocean via osmosis.

countering that, the fish is going to be swallowing seawater. but since its internal collection of salts is lower than seawater, the fish will want to go free of excess salt, and since that's going upon a gradient, then active transport, requiring energy, must be used to pump out the salt. much marine fish use the organs to filter out the salt and these fish discharge very straight urine.

not: both offer magnification to the atomic level.

yes, because even though a theory has a  lot of evidence to support it, it is not always true

prothallium

explanation: