Photosynthesis and cellular respiration have a tightly linked, cyclical relationship, where the products of one process serve as the reactants for the other, making them interdependent.

Relationship Between Photosynthesis and Cellular Respiration

• Photosynthesis converts carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂), using energy from sunlight. Glucose serves as food for the plant, and oxygen is released as a by-product

• Cellular respiration uses glucose and oxygen to produce energy in the form of ATP, releasing carbon dioxide and water as by-products. This energy fuels cellular activities in plants, animals, and other organisms

• The chemical equations for the two processes are essentially opposites:
  • Photosynthesis: 6CO2+6H2O+light energy→C6H12O6+6O26CO_2+6H_2O+\text{light energy}\rightarrow C_6H_{12}O_6+6O_26CO2​+6H2​O+light energy→C6​H12​O6​+6O2​
  • Cellular respiration: C6H12O6+6O2→6CO2+6H2O+ATP energyC_6H_{12}O_6+6O_2\rightarrow 6CO_2+6H_2O+\text{ATP energy}C6​H12​O6​+6O2​→6CO2​+6H2​O+ATP energy

How They Depend on Each Other

• The oxygen produced by photosynthesis is essential for cellular respiration in most organisms, including plants themselves, which need oxygen to efficiently produce ATP

• The carbon dioxide released by cellular respiration is used by plants during photosynthesis to make glucose

• This exchange maintains stable levels of oxygen and carbon dioxide in the atmosphere, supporting life on Earth and driving the carbon cycle

• In autotrophs (like plants and algae), both processes occur within the same cells, balancing energy production and consumption according to environmental conditions

Summary

Photosynthesis and cellular respiration form a biological cycle where:

• Photosynthesis stores energy from sunlight in glucose and releases oxygen.
• Cellular respiration releases energy from glucose using oxygen, producing carbon dioxide and water.
• The products of one process are the reactants of the other, making them interdependent and essential for sustaining life and atmospheric balance