The atomic number for carbon is 6. Carbon exists in many different forms. They each have very different properties because the carbon atoms are arranged differently. Carbon-60 has a similar structure to a football. Clearly a molecule of carbon-60 is smaller.
Plants extract carbon from the atmosphere and convert it into food.
During photosynthesis, carbon dioxide reacts with water to form carbohydrates and oxygen. Transpiration is the process by which plants lose water, mainly from their leaves. Respiration is the process by which animals break down carbohydrates into carbon dioxide and water. So you could say, respiration is the reverse of photsynthesis. There are more than 10 million carbon compounds.