That’s an interesting and important question! Animals, like humans, need oxygen in order to build tissues and organs. For example, without oxygen we wouldn’t be able to develop our muscles, bones, and vital organs like the heart.

The opposite it true for plants. The majority of a plant’s biomass comes from carbon dioxide that is absorbed from the atmosphere. Carbon dioxide (CO₂) enters the plant through tiny pores in the leaves. These pores are called stomata. Inside the leaf, the plant uses energy obtained from sunlight to capture CO₂ and uses it to build a carbohydrate molecule called glucose. The glucose is then used to make other carbohydrates (like cellulose) that comprise the plant body. Plants harness the energy of the sun to capture CO₂ and build their tissues and organs (roots, leaves and stems); this process is called photosynthesis. Without CO₂ photosynthesis just wouldn’t happen and the plant would not be able to survive.

So when an oak grows from an acorn into a huge tree, the carbon that comprises the trunk, leaves, and roots all comes from CO₂ in the atmosphere, which is pretty amazing!

Plants use the carbon from carbon dioxide to build their bodies, just as you use the carbon from the food you eat. Unlike plants, you also gain your energy from the food you eat; plants get their energy from sunlight, but they still need the carbon.

Plants need carbon dioxide as a source of carbon that allows the plant to create sugars. These sugars are then used by the plant as an energy source to allow the plant to grow.