A Comparison of Photosynthesis and Cellular Respiration: How are They Connected? How are They Different?

A Comparison of Photosynthesis and Cellular Respiration: How are They Connected? How are They Different?
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All of Earth’s living things are comprised of cells. There is a variety of different cells, each of which perform a variety of functions necessary for the life of living things. Find a comparison of photosynthesis and cellular respiration to help you better understand how this vital life process works. 

Understanding the Photosynthesis Process

Photosynthesis, a chemical process, is part of a larger process known as plant metabolism. This process occurs in sunlight, at which point plants create stores of energy and their own food. This takes place in the plant cells that contain chlorophyll, the pigment within plant leaves that give them their green color. The chlorophyll absorbs light energy and uses it to create sugars (carbohydrates) from water (H2O) and carbon dioxide (CO2). Oxygen is created by this chemical reaction and is then released into the atmosphere.

This chemical reaction is often described as: Water + Carbon Dioxide + Sunlight = Oxygen + Glucose

6H2O + 6CO2 + Sunlight —–> 6O2 + C6H12O6

The carbohydrates that photosynthesis produces are utilized by the plant as immediate energy for things such as, reproduction, growth, and nutrient absorption. They also take on the role of energy reserves stored as starch to help the plant survive severe conditions, such as droughts or extreme winters. Carbohydrates are also utilized to help the formation of the plants components such as, plant tissues that are necessary to grow leaves, flowers, roots, wood, roots, and other components.

Several different factors influence the process of photosynthesis including:

  • Carbon Dioxide: The process of photosynthesis is stimulated by high concentrations of carbon dioxide in the atmosphere.
  • Water Availability: Photosynthesis is slowed down when transpiration is reduced. In order to absorb carbon dioxide, plants must transpire. When water is scarce, transpiration is reduced, resulting in photosynthesis being slowed down.
  • Temperature: Photosynthesis' optimum temperature is between about 20 degrees Celsius and 35 degrees Celsius. The plants physiology will slow down when the temperature dips below zero degrees Celsius, resulting in photosynthesis stopping.
  • Sunlight: Chlorophyll is more effective as light’s intensity increases, which in turn enhances the photosynthesis process.

Understanding Cellular Respiration

cellular respiration and photosynthesis

Cellular respiration is a process in which water and carbon dioxide are produced through the break down of chemical bonds of glucose or the oxidizing of food molecules. Energy is released during cellular respiration and is captured as Adenosine Triphosphate (ATP) and then utilized by different cell activities that consume energy. Aerobic respiration and glycolysis are the two main steps responsible for completely breaking down glucose into water and carbon dioxide.

  • Aerobic Respiration: This process, at which point the pyruvate molecules created during glycolyis, breaks down further when there is oxygen and creates 34 ATP molecules.
  • Glycolysis: This anaerobic catabolism of glucose produces two ATP molecules and two pyruvate molecules, and happens in all cells.

What are the Differences Between The Two Processes?

There are a few key differences between cellular respiration and photosynthesis.


  • This process involves plants making food by using sunlight.
  • In order to produce glucose, this process requires energy.
  • This process occurs in some bacteria and in all plants.
  • This process occurs within the chloroplasts, the chlorophyll-containing organelles inside a plant.
  • In order to release oxygen back into the atmosphere and create sugar, this process requires water, sunlight, and carbon dioxide from the atmosphere.

Cellular Respiration:

  • This process converts the food created by photosynthesis into energy which is then utilized by living organisms and plants.
  • This process creates energy (ATP) by using glucose.
  • All living organisms experience cellular respiration.
  • This process occurs within the mitochondria, organelles with the ability to break down glucose.
  • When combined with oxygen and sugars, energy in the form of ATP, water, and carbon dioxide are released as byproducts.


Palomar College. (2001). Photosynthesis and Cellular Respiration. Retrieved on June 18, 2010 from Palomar College: https://waynesword.palomar.edu/photsyn1.htm

BioChemWeb. (2010). Metabolism, Cellular Respiration and Photosynthesis. Retrieved on June 18, 2010 from BioChemWeb: https://www.biochemweb.org/metabolism.shtml

Image Credits

Photosynthesis Diagram: Daniel Mayer - Wikimedia Commons

Cellular Respiration Diagram: Sean William - Wikimedia Commons