The process of photosynthesis occurs in the chloroplasts of the cell. It the process in which, carbohydrates are synthesized in the presence of sunlight, carbon dioxide and water, releasing oxygen.
Respiration is a process in which the oxidation of organic compounds like the carbohydrates takes place in the presence of oxygen, producing carbon dioxide, water and energy in the form of ATP. Mitochondria is the site of respiration. The process of photosynthesis and respiration form a continuous cycle as the product of one process serves as a precursor for the other process.
In the image given, the box 2 represents oxygen which is a requirement for the process of respiration. Similarly the box 4 represents carbon dioxide which is a requirement for the process of photosynthesis. Mitochondria is called the power house of a cell as it is the source of energy for all the life processes of the cell. The box 3 represents the energy currency of the cell called the adenosine triphosphate or the ATP.