That looks like a Tomato Worm, they are caterpillars that turn into a Five Spotted Hawk Moth.
Answer:
If there are no plants in the tank, they will run out of oxygen because there is nothing producing oxygen.
Explanation:
When fixed carbon leaves the Calvin cycle or light dependent reactions, it will become the molecule G3P, which is then combined to make glucose. The rest of the carbon is recycled to replace RUBP.
Glucose and oxygen..................... :D
Fungi, they are decomposers of nature and are food for creatures. Like worms they are needed to decompose dead plants. For soil/nutrients.