Autotrophs are organisms that can prepare food themselves. Plants are called autotrophs because they prepare food themselves through the process known as photosynthesis. Photosynthesis is the process by which plants prepare food (carbohydrates) from raw materials such as water, carbon dioxide, sunlight and chlorophyll. During the process of photosynthesis, the cells of leaves containing chlorophyll in the presence of sunlight, synthesise carbohydrate from carbon dioxide and water. Oxygen is also released as a byproduct in the process.