Dark reactions occur in the stroma of a plant cell's chloroplasts. The stroma is the space surrounding the thylakoid membranes, which are the structures responsible for the light reactions of photosynthesis. Both light and dark reactions are necessary for photosynthesis to produce glucose.
Dark reactions can occur in the presence or absence of light. These reactions use the energy created in the light reactions to process carbon dioxide in the Calvin cycle. Light reactions take the energy from sunlight and convert it into the chemical energy that is necessary for the Calvin cycle to occur. Chlorophyll and other pigments in the thylakoid membranes capture light from the red and blue spectrum of the sun's rays during the light reactions. The light from the green spectrum is reflected, giving the plant its green color.
Some of the glucose produced by the dark reactions of photosynthesis is used by the plant. The glucose the plant doesn't use is stored in the plant's tissues. Animals eat the plants and take in the extra glucose that is stored. The glucose is used by both plants and animals to produce energy for cellular processes during cellular respiration. Besides energy, cellular respiration also produces carbon dioxide and water, which are necessary ingredients for the process of photosynthesis.