Photosynthesis and respiration are reactions that complement each other in the environment. They are in reality the same reactions but occurring in reverse. While in photosynthesis carbon dioxide and water yield glucose and oxygen, through the respiration process glucose and oxygen yield carbon dioxide and water.

They work well since living organisms supply plants with carbon dioxide which undergoes photosynthesis and produces glucose and these plants and bacteria give out oxygen which all living organisms need for respiration.

Comparison chart

Cellular Respiration versus Photosynthesis comparison chart
Cellular RespirationPhotosynthesis
Production of ATP Yes; theoretical yield is 38 ATP molecules per glucose but actual yield is only about 30-32. Yes
Reactants C6H12O6 and 6O2 6CO2 and 12H2O and light energy
Requirement of sunlight Sunlight not required; cellular respiration occurs at all times. Can occur only in presence of sunlight
Chemical Equation (formula) 6O2 + C6H12O6 --> 6CO2 +6H2O + ATP (energy) 6CO2 + 12H2O + light --> C6H12O6 + 6O2 + 6H20
Process Production of ATP via oxidation of organic sugar compounds. [1] glycolosis: breaking down of sugars; occurs in cytoplasm [2] Krebs Cycle: occurs in mitochondria; requires energy [3] Electron Transport Chain-- in mitochondria; converts O2 to water. The production of organic carbon (glucose and starch) from inorganic carbon (carbon dioxide) with the use of ATP and NADPH produced in the light dependent reaction
Fate of oxygen and carbon dioxide Oxygen is absorbed and carbon dioxide is released. Carbon dioxide is absorbed and oxygen is released.
Energy required or released? Releases energy in a step wise manner as ATP molecules Requires energy
Main function Breakdown of food. Energy release. Production of food. Energy Capture.
Chemical reaction Glucose is broken down into water and carbon dioxide (and energy). Carbon dioxide and water combine in presence of sunlight to produce glucose and oxygen.
Stages 4 stages: Glycolysis, Linking Reaction (pyruvate oxidation), Krebs cycle, Electron Transport Chain (oxidative phosphorylation). 2 stages: The light dependent reaction, light independent reaction. (AKA light cycle & calvin cycle)
What powers ATP synthase H+ proton gradient across the inner mitochondria membrane into matrix. High H+ concentration in the intermembrane space. H+ gradient across thylakoid membrane into stroma. High H+ concentration in the thylakoid lumen
Products 6CO2 and 6H2O and energy(ATP) C6 H12 O6 (or G3P) and 6O2 and 6H20
What pumps protons across the membrane Electron transport chain. Electrochemical gradient creates energy that the protons use to flow passively synthesizing ATP. Electron transport chain
Occurs in which organelle? Mitochondria Glycolysis (cytoplasm) Chloroplasts
Final electron receptor O2 (Oxygen gas) NADP+ (forms NADPH )
Occurs in which organisms? Occurs in all living organisms (plants and animals). Occurs in plants, protista (algae), and some bacteria.
Electron source Glucose, NADH + , FADH2 Oxidation H2O at PSII
Catalyst - A substance that increases the rate of a chemical reaction No catalyst is required for respiration reaction. Reaction takes places in presence of chlorophyll.
High electron potential energy From breaking bonds From light photons.

Definitions of photosynthesis and respiration

Photosynthesis is a process in photoautotrophs that converts carbon dioxide into organic compounds in the presence of sunlight. Respiration is the set of metabolic reactions that take in cells of living organisms that convert nutrients like sugar into ATP (adenosine tri phosphate) and waste products.

Processes involved

Processes in photosynthesis are divided on basis of requirement of sunlight while respiration processes are divided on basis of requirement of oxygen. Hence in photosynthesis you have the light dependent reactions and the dark reactions while in respiration there is aerobic respiration and anaerobic respiration.

In photosynthesis light dependent reactions, ultra violet light strikes chlorophyll pigments which excites electrons leading to separation of oxygen molecules from carbon dioxide. In the dark reactions, carbon molecules now independent of oxygen are converted into carbohydrates and stored in plant cells as energy and food source. In aerobic cellular respiration oxygen is utilized to convert organic compounds into energy and in anaerobic respiration converts organic compounds into energy without using oxygen.

Site of Reactions

Photosynthesis takes place in the chloroplasts and organelles of a plant cell. Respiration takes place in the cytoplasm and mitochondria in the cell of a living organism.

Reaction kinetics

The electron acceptor in photosynthesis is NAD+ while in respiration the electron acceptor is NADH. In cellular respiration reaction 36 molecules of ATP are produced in complete oxidation of one molecule of glucose.

Video comparing Photosynthesis and Respiration


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