Flexi Says: Cellular respiration and photosynthesis are direct opposite reactions. Photosynthesis occurs in the chloroplast, an organelle specific to plant cells. Energy from the sun enters a plant and is converted into glucose during photosynthesis. Cellular respiration is the process of extracting energy from glucose to form ATP, a usable form of energy to run cell processes. Cellular respiration occur in all organisms. Most of the reactions of cellular respiration are carried out in the mitochondria.