Difference Between Cellular Respiration and Photosynthesis

Cellular respiration occurs in every living organism as it is a simple process of converting oxygen and glucose into carbon dioxide and water into energy for the cells of the body. On the contrary, photosynthesis takes place in green plants that contain chlorophyll and uses sunlight and water to convert it into energy.

Cellular respiration and photosynthesis are the two processes with the same aim of production of energy but by using different methods sources and thus giving out different products. Both are compulsory processes for the exchange of energy, which is the requirement of all living things. All types of the living cell perform cellular respiration whether a plant or an animal, prokaryotic cell, or eukaryotic cell, but photosynthesis happens only in green plants, a few algae, and bacteria.

All living things cannot imagine the work to be performed without the requirement of energy. So, both processes are vital in maintaining life on earth.

Comparison Chart

Basis for Comparison Cellular Respiration Photosynthesis
Definition Cellular respiration is a series of metabolic reactions that take place in the cells of organisms to convert chemical energy from oxygen molecules into ATP and then release waste products. Photosynthesis is the process by which plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water.
Discoverer Sir Hans Adolf Krebs Jan Ingenhousz
Occurs in cells In all living cells In plants’ cells only
Occurs in cell organelle In mitochondria In chloroplast
Time of occurrence Both day and night time In day time only
Reactions involved Glycolysis, Citric acid cycle and Electron Transport Chain Light reaction, Calvin cycle and photolysis
Process type Exothermic process Endothermic process
Oxidative phosphorylation Oxidative phosphorylation occurs Photophosphorylation occurs
Reaction Equation C6H12O6+ 6O2→6CO2+6H2O+38ATP 6CO2+6H2O+sunlight→C6H12O6+6O2

What is Cellular Respiration?

Cellular respiration is the breakdown of carbohydrates in the form of glucose by the use of oxygen for the production of carbon dioxide and water. Energy is produced in the form of ATP or adenosine triphosphate, which is used for various metabolic activities and other cellular work. Cellular respiration takes place in the mitochondria and cytoplasm of the cell. This energy-producing process occurs day and night.

Aerobic Respiration

Aerobic respiration occurs in the presence of oxygen and results in the production of 38 molecules of ATP from one molecule of glucose.


Cellular respiration is not a simple process. It is a complicated process with four steps.

  1. Glycolysis: It is the process of splitting the sugar and takes place in the cytoplasm of the cell. In this process, one molecule of the glucose is broken down into two molecules of the pyruvic acid. As a result, two ATP molecules are generated from the one molecule of the glucose.
  2. Transition Reaction: In this step, pyruvic acid is taken to the mitochondria where it is converted into acetyl CoA and broken down further.
  3. Krebs Cycle: This step is also known as the Citric acid cycle. This step occurs in the matrix of the mitochondria, where acetyl CoA is broken down in the presence of oxygen to generate four ATP with many NADH. In this step, water and carbon dioxide are also released as a waste product.
  4. The Electron Transport Chain: This step is also known as Chemiosmotic Theory proposed by Peter Mitchell. The electron transport chain generates 32 ATP from each glucose molecule.

Anaerobic Respiration

Anaerobic respiration happens in the absence of oxygen. When one does exercise or runs, then the anaerobic condition is produced. In this condition, respiration generates only two molecules of ATP from one molecule of glucose by the process of glycolysis.

In anaerobic respiration, the body needs immediate energy, so the process is not that much longer and glucose does not break down into any further molecules. Other processes of cellular respiration need oxygen to occur and due to lack of oxygen, they do not happen. Anaerobic respiration is also called fermentation. Anaerobic respiration is an catabolic process as energy is released in any form by breaking the large molecule into the smaller molecules.

What is Photosynthesis?

Photosynthesis is the process of converting solar energy into chemical energy in the chloroplasts of the green plants. Chemically it is an oxidation-reduction process. It happens in the presence of sunlight, so it is known as a light-energized oxidation process. This process gives energy to all living organisms, either directly or indirectly. Without this process, life on earth would cease to exist.

Photosynthesis occurs in the leaves of the green plants. Chloroplasts are the organelles that perform photosynthesis. These are the tiny structure present in the cells of the leaves. The chloroplast has chlorophyll, a green pigment, which is responsible for the green color of the leaves.

Chlorophyll absorbed solar energy and used this to separate water molecules into oxygen and hydrogen. Oxygen is released into the atmosphere from the leaves and carbon dioxide and hydrogen are used to form food in the form of glucose for the plants. In this reaction, there is the oxidation of the water in the presence of sunlight and oxygen and hydrogen ions H+ are released. The removal of hydrogen ions and electrons moved to the carbon dioxide and are reduced as the organic product.

Many enzymes and other reactions are involved in the process of photosynthesis. This process is further divided into two stages; light reaction and dark reaction.

In light reaction, the light energy is absorbed and is used for the transfers of electrons and thus producing adenosine triphosphate and reduction of nicotine adenosine dinucleotide phosphate.

In dark reaction, carbon dioxide undergoes reduction to form organic carbon compounds with the help of ATP and NADPH formed during the light reaction.

Key Differences

  1. Cellular respiration occurs in all types of cells, whereas photosynthesis occurs only in plant cells.
  2. Cellular respiration can occur at any time, whereas photosynthesis occurs only in daytime.
  3. Cellular respiration occurs in mitochondria, whereas photosynthesis occurs in chloroplasts.
  4. Cellular respiration is an exothermic process, whereas photosynthesis is an endothermic process.
  5. In cellular respiration, the potential energy is converted into the kinetic energy, whereas in photosynthesis, light energy is converted into the potential energy.
  6. In cellular respiration, oxidative phosphorylation occurs whereas, in photosynthesis, phosphorylation occurs.
  7. Reactions involved in cellular respiration are Glycolysis, Krebs cycle and electron transport chain, whereas in photosynthesis, light reaction, Calvin cycle, photolysis occurs.
  8. Cellular respiration is a catabolic process, whereas photosynthesis is an anabolic process.

Key Similarities

  1. Both processes provide energy to the cells.
  2. Both involved in the exchange of gases.
  3. Both processes take place in the organelles.


In conclusion, cellular respiration and photosynthesis are used to provide energy to the cell. But they differ from each other in many aspects. Both are opposite to each other.

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