1. In many leaves, as fast as sugar is produced, it is turned into starch.
2. Carbon and oxygen can be supplied by carbon dioxide (CO2) from the air.
3. Is carbon dioxide needed for photosynthesis?
1. In many leaves, as fast as sugar is produced, it is turned into starch.
Here, "produced" is the correct form. The sentence is describing an ongoing process, and the passive voice is appropriate to emphasize the action of sugar production without specifying a particular agent.
2. Carbon and oxygen can be supplied by carbon dioxide (CO2) from the air.
In this sentence, the passive voice "can be supplied" is the correct form. It conveys the idea that carbon and oxygen are provided or made available through the process of carbon dioxide from the air.
3. Is carbon dioxide needed for photosynthesis?
In this question, the active voice "Is carbon dioxide needed" is appropriate. It's a direct and clear way to inquire about the requirement of carbon dioxide for photosynthesis.