Why do plants need air?

Plants need water, nutrients, heat, light and air for normal growth and development. Air is a mixture of different gases. It contains oxygen and carbon dioxide. Plants use oxygen for respiration, and carbon dioxide for food – the formation of sugar and starch.
In the light, photosynthesis takes place in a plant – the process of generating energy from carbon dioxide. Oxygen is a byproduct of photosynthesis.
At night in the dark, the plant breathes in the same way as a person, absorbing oxygen and emitting carbon dioxide.