Question

A student creates a model of a closed ecosystem by filling a glass tank half full with water, then adding 10 snails and two small aquatic plants. The next day, all the snails are dead. What is the most likely cause of their death?

Answer 1

1. Snails carry out respiration only
2. Aquatic plants carry out both respiration and photosynthesis

Although the aquatic plants can absorb carbon dioxide and release oxygen through photosynthesis, the amount of snail is much more than that of the aquatic plants. During night time,the absence of light prevent the plants from carrying out photosynthesis. No oxygen is released at this time. There is a net release of carbon dioxide in the closed system and hence the snail died of suffocation.