The relationship between photosynthesis and cellular respiration is such that the products of one system are the reactants of the other. Photosynthesis involves the use of energy from sunlight, water and carbon dioxide to produce glucose and oxygen. Cellular respiration uses glucose and oxygen to produce carbon dioxide and water. To emphasize this point even more, the equation for photosynthesis is the opposite of cellular respiration.
Humans, animals and plants depend on the cycle of cellular respiration and photosynthesis for survival. The oxygen produced by plants during photosynthesis is what humans and animals inhale for the blood to transport to the cells for respiration. The carbon dioxide produced during respiration is released from the body and absorbed by plants to help provide the energy they need for growth and development. This is the never ending cycle that sustains life on earth.
The process of photosynthesis is used by plants and other photosynthetic organisms to produce energy, whereas the process of cellular respiration breaks down the energy for use. Despite the differences between these two processes, there are some similarities. For example, both processes synthesize and use ATP, the energy currency.
Below are some of the similarities and differences between these two systems.
Similarities between Photosynthesis and Cellular Respiration
| Reduction-Oxidation Reaction | ||
| Electron Transport Chain (ETC) | ||
| Synthesize ATP | ||
| Utilize ATP | ||
| Phosphorylation | ||
| Electron Carriers |
Differences between Photosynthesis and Cellular Respiration
| Occurs in… | Plants, Algae and Photosynthetic Bacteria | All living organisms |
| Function/Purpose | Capture, convert and store energy – light energy from the sun is converted into chemical energy and stored in the bonds of glucose | Release energy – chemical energy stored in glucose is released to produce ATP for the cell |
| Reactants/Inputs | Carbon dioxide, Water and Light energy | Glucose and Oxygen |
| Metabolic Process | Anabolic - CO2 and energy from ATP and NADPH are used to build glucose molecules | Catabolic - glucose is broken down to produce CO2 and energy in the form of ATP, NADH and FADH2 |
| Location | Chloroplast of the plant cell | Glycolysis occurs in the Cytoplasm while the Mitochondria is the site of the Kreb’s Cycle and Electron Transport Chain (ETC) |
| Source of Energy | Sunlight | Glucose (sunlight is not required) |
| Electron Carriers | NADPH | NADH and FADH2 |
| Stages | Light dependent Reactions – Light energy and water are used to produce ATP and NADPH Calvin Cycle – Carbon dioxide and the energy from ATP and NADPH are used to produce glucose | Glycolysis – Glucose is combined with ATP to produce pyruvate molecules, NADH and more ATP Pyruvate Oxidation - Pyruvate molecules are broken down into Acetyl-CoA (2-carbon compound) and CO2 is produced Kreb’s Cycle – Acetyl-CoA is combined with 4-carbon molecules to form the 6-carbon citrate molecules used to generate NADH, CO2, FADH2 and ATP Electron Transport Chain – Energy stored in NADH and FADH2 during the Krebs cycle is used to generate ATP, Water, NAD+ and FAD |
| Products/Outputs | Glucose and Oxygen | Carbon dioxide and Water |
| Equation | 6CO2 + 6H2O –––> C6H12O6 + 6O2 | C6H12O6 + 6O2 –––> 6CO2 + 6H2O |
The cycle of photosynthesis and respiration maintains the balance of oxygen and carbon dioxide. Photosynthesis produces the oxygen to replenish oxygen that is used up by living organisms during respiration. Carbon dioxide produced during respiration is one of the reactants plants need to perform photosynthesis.
Photosynthesis and cellular respiration are both part of a mutually beneficial relationship. Cellular respiration cannot occur without photosynthesis, and photosynthesis certainly cannot occur without the help of its partner.