We eat 3 times a day and the food we eat provides all of the nutrients we need to live. The chemicals in food are used by our bodies to grow and maintain our body parts. The protein you eat helps build muscles. Carbohydrates provide energy that is used for all kinds of things such as moving, breathing, thinking and eating more food.
Most of the food we eat is in the form of large molecules such as protein, carbohydrates, DNA, and fats. Our digestive system takes these large molecules and breaks them down into smaller molecules like simple sugars and nitrates. Our bodies then use these small molecules as building blocks to build new large molecules. Our bodies are actually a very efficient recycling plant. We take food in, break it down into basic building blocks, and then use these building blocks to create complex body parts.
Plants differ from humans and other animals in that they do not have a digestive system. Therefore, they are not able to break down large molecules. Plants must start with small molecules like nitrate and phosphate and build the large molecules they need.