Biology: Do plants need oxygen?

Yes they do. Plants take in water and carbon dioxide, and with the energy from sunlight to make carbohydrates for food, and give of oxygen as by-product. This is called Photosynthesis. But Photosynthesis alone would be like preparing food and it never being eaten. Plants need to use the food they make. They do this in a process called Respiration, and like animal plants do this all day.

Respiration is like the opposite of Photosynthesis. Respiration uses oxygen to and carbohydrates to make carbon dioxide and water, releasing energy in the process. This energy powers the plant.

Sources: Yahoo Answers
Wikipedia

Image: plantcare.com