Respuesta :
They may have ran out of oxygen, or they may not have been water dwelling snails, as not all are, lack of food, no flow of water into and out of the tank would cause them to run out of oxygen.
Explanation:
Since the student created a closed ecosystem, therefore, the system will have lack of oxygen for any living organism.
Therefore, when snails are placed into it then due to non-availability of sufficient amount of oxygen the snails died.
Whereas effect of closed system on plants cannot be observed as plants do not move from their place.
Thus, we can conclude that due to lack of oxygen snails die in the closed ecosystem.