Chloroplasts and mitochondria work together in plants to control environmental factors and create genetic material. They work independently to generate usable energy for biological activity, with chloroplasts performing photosynthesis and mitochondria executing the last three phases of cellular respiration.
Photosynthesis captures energy from sunlight on water and carbon dioxide to synthesize carbohydrates and release oxygen, using molecules such as ATP to transport chemical energy in intermediate steps. Cellular respiration uses chemical energy from carbohydrates in the presence of oxygen to create ATP, releasing carbon dioxide and water.
Photosynthesis and cellular respiration involve reverse inputs and products, but do not interact directly. Mitochondria and chloroplasts do not exchange ATP, carbohydrates, and carbon dioxide. The interactions have more in common with a warehousing system than an on-demand inventory. Corticular photosynthesis salvages carbon dioxide from cellular respiration as it escapes through the stems and bark of woody plants.
Photosynthesis creates signals based on whether a molecule is reduced or oxidated. These redox signals act on networks of receptors that trigger or inhibit photosynthesis. Inhibition is necessary because photosynthesis can generate dangerous levels of oxygen. Redox signals affect receptor systems in other parts of the cell, including those in mitochondria. In this way, chloroplasts affect processes within mitochondria.
Chloroplasts and mitochondria exhibit a more direct relationship during the creation of pyrimidines, the building blocks of DNA. Conversions one through three occur in the chloroplast, conversion four in the mitochondrion, and conversion five back in the chloroplast. Plants use this separation of duties, but other eukaryotes perform pyrimidine synthesis without chloroplasts.