Difference Between Photosynthesis and Cellular Respiration

Edited by Diffzy | Updated on: May 28, 2023


Difference Between Photosynthesis and Cellular Respiration

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You must have heard about many life processes that take place from the single atomic level to the high molecular level. A process takes place in a single-celled organism when comprised multiple times forms a process in a multicellular organism. And this just goes on inside every living organism on this planet. Together comprising all these life processes form an ecosystem.

During this article, we are going to talk about two such fundamental processes, which depend on each other. These two processes are interdependent or interrelated to each other.

The two processes are Photosynthesis and Cellular Respiration. Photosynthesis and cellular respiration are complementary to each other, photosynthesis produces oxygen and glucose that are used in cellular respiration to produce energy.

Photosynthesis vs. Cellular Respiration

Both processes are dependent on each other, as mentioned above. But there are some differences. Photosynthesis is the process of producing glucose and oxygen using sunlight, water from roots, and carbon dioxide from the atmosphere. Whereas, in cellular respiration, the same products, i.e., glucose and oxygen are used as the reactants in this process to give energy, carbon dioxide and water.

Difference between photosynthesis and cellular respiration in tabular form

Parameters of comparisonPhotosynthesisCellular Respiration
DEFINITIONPhotosynthesis is a process, where a plant uses light, water, and carbon dioxide to convert oxygen and glucose.Cellular Respiration is a process, that living organisms use glucose and oxygen to release energy and carbon dioxide.
ENERGY CONVERSIONIn photosynthesis, there is a change in the light energy to chemical energy.In cellular respiration, there is a change in chemical energy to usable energy (Adenosine Triphosphate).
ORGANISMS THAT SHOW THESE PROCESSESOccurs in plants, algae, and some bacteria.Occurs in plants, animals and, bacteria.
LOCATIONIt takes place in the chloroplasts of plants cell.It takes place in the mitochondria of the eukaryotic cell, and the cytoplasm of the prokaryotic cell.
PROCESS NAMEIt is an Anabolic process. The anabolic process means building up.It is a Catabolic process. The catabolic process means breaking down.
CYCLE FOLLOWSIt follows Calvin’s cycle. It has two stages, i.e., light-dependent reactions and light-independent reactionsIt follows Krebs’s Cycle. It has three stages, i.e., glycolysis, the citric acid cycle and, oxidative phosphorylation.
COMPONENTS INVOLVEDIt requires carbon dioxide (CO2), water, and sunlight.It requires oxygen and glucose.
BY-PRODUCTSIt releases oxygen as a by-product.It releases carbon dioxide and water as by-products.
Role of carbon dioxide (CO2)It uses carbon dioxide as one of the organic products.Carbon dioxide is one of the by-products.
Role of oxygenIt releases oxygen as a by-product.It uses oxygen as one of the reactants.
Complementary ProcessesOne of the by-products of cellular respiration, i.e., carbon dioxide is used in this reaction.The products of photosynthesis are used as reactants in this process.
ATP generationIn photosynthesis, we generate ATP through a process called phosphorylation.In cellular respiration, we generate ATP through a process called oxidative phosphorylation.



Photosynthesis is the process which plants and some other living organisms follow. It is one of the most important processes in the ecosystem. We get many things associated with this process. Not only it creates food for themselves, but it also creates food for all planting-eating organisms and omnivorous creatures. It does not stop over here, during this process plants also release oxygen into the atmosphere, which is the backbone supplying oxygen to the atmosphere. It also purifies the air by using carbon dioxide as one of the reactants in the process. We will come to that in detail, later in the article.

The complete process

Photosynthesis is a process, where they use some components to produce glucose and water. The components which they use are water, carbon dioxide and sunlight. They put together all these components to complete the process. The equation of Photosynthesis, as stated:

6CO2+ 6H2O+SunlightC6H12O6+6O2

There, are also some chlorophylls involved in the process which cannot be shown in the reaction.

Photosynthesis occurs in the chloroplasts of plants through photosynthetic pigments. Some photosynthetic pigments are chlorophyll a, chlorophyll b, carotene, and xanthophyll.

Step-by-step processes in photosynthesis are:

  1. Light absorption- It is the first process of the photosynthetic reaction. The light gives the power to start photosynthesis. The pigments such as chlorophyll and other such pigments absorb the light in the chloroplasts present in the leaves of plants.
  2. Conversion of light energy into chemical energy- Light in form of the light energy is converted into chemical energy which exists in the form of ATP (Adenosine Triphosphate) and NADPH (Nicotinamide adenine Dinucleotide Phosphate) is used in the next process. These two molecules carry the whole chemical energy of the complete photosynthesis reaction.
  3. Carbon Fixation- The chemical energy is then used to fix the carbon into a molecule called RuBP (Ribulose 1,5-biphosphate) through a process of the Calvin cycle. A six-carbon molecule is formed, which then converts into PGA (Phosphoglycerate), i.e., two-three carbon molecules.
  4. Reduction of PGA- The PGA is then reduced to G3P (glyceraldehyde 3-phosphate) using ATP and NADPH. Some G3P is transferred to produce glucose and the remaining is transported back.
  5. Regeneration of RuBP- The reverted G3P is used to generate RuBP and the process goes on.

Factors Affecting Photosynthesis-

  1. Light Intensity- The more the light intensity, the more is the rate of photosynthesis.
  2. The concentration of CO2 – The rate of photosynthesis depends upon the amount of carbon dioxide supplied to the organism.
  3. Water- It is also an important factor, if the plant faces a deficiency of water, then the stomata do not happen, and eventually the photosynthesis process stops.
  4. Temperature- The atmosphere must have temperatures between 25° to 35° C.
  5. Pollution- Due to excessive pollution in the atmosphere, the dust might settle on the surface of leaves, which would block the stomata opening and stop the carbon dioxide intake.

Why photosynthesis' is Important?

It might sound like a very normal thing that photosynthesis is just another process, which is essential for nature. But photosynthesis is the backbone of Earth's ecosystem. If we ignore the importance of photosynthesis, then soon this planet will be devoid of oxygen. If there are better outcomes from the process, then obviously there must be bad outcomes too. As good things and bad things coexist. Though, let us come back to the original topic. If you ignore the importance, there will be a shortage of plants day by day, and it will later kill other organisms that are dependent on plants. The ecosystem is vast, and there are still some more conclusions to photosynthesis, which even science is searching for. The energy produced in the process carried out millions of years ago; is responsible for fossil fuels that power industries. The organisms that fed on green plants and other organisms increased as the years went by, and their remains from millions of years went through earthly processes and turned into fossil fuels. This energy so produced, is used in today's world. It is a slow process and takes millions of years. The importance of photosynthesis is unimaginable, as it existed before the arrival of many organisms on this planet.

Cellular respiration

Cellular Respiration is a process where chemical energy gets converted into ATP (Adenosine Triphosphate) or usable energy. This ATP is used to proceed further.

During this process, biological fuels are oxidised to drive the bulk production of ATP (Adenosine Triphosphate). The fuels gets oxidised due to an inorganic electron acceptor, i.e., oxygen. Cellular respiration is a series of metabolic reactions where reactions occur in organisms’ cells. The reactions that are carried out in this process are all catabolic reactions, which break large molecules into smaller ones to release large amounts of ATP. And, if a series of reactions take place, then some can be combustion reactions, redox reactions, and vice versa. Nutrients that are used in animals and plant cells are mainly sugar, amino acids and fatty acids.

As already mentioned above, the oxidising agent that is mainly used is oxygen. If you are carrying out processes then there must be the release of some waste products that are carbon dioxide and water.

ATP captures the whole chemical energy obtained from the breakdown of food molecules. Then the ATP formed is then released to carry out various other processes.

In eukaryotic cells, respiration is carried out by enzymes. And these individual steps take place in a rod-shaped component known as mitochondria.

If a process supports plants and animals, then that process must have various steps to carry it, which are:

  1. Glycolysis (Glycolytic pathway)- It is a sequence of 10 chemical reactions that take place in almost all the cells that break many molecules like glucose and other organic fuel molecules from carbohydrates, fats, and proteins. When these molecules break it gives 2 pyruvate molecules. When these organic fuel molecules break, it gets stored down into ATP. These pyruvate molecules produced during glycolysis get stored in mitochondria, which then get converted to a compound named acetyl coenzyme A. And we move on, to the TCA cycle.
  2. Tricarboxylic acid cycle (also known as Krebs cycle)- It is the cycle where catabolism takes place. When we go on searching on the Internet, we read about this process in the definition of Cellular Respiration. The cycle is possessed of eight steps catalysed using eight different enzymes and the level of energy releases also differs. Most of the energy released during all eight processes is captured by compounds like NAD+and flavin adenine dinucleotide (FAD), which is then converted to ATP.  In The CA cycle, carbon dioxide is also released as a waste product. The product releases in one cycle consist of 3 NAD+ molecules and one FAD molecule. Both are reduced NADH molecules and a single FADH2 molecule.
  3. Oxidative Phosphorylation- From the above-reduced molecules, i.e., FADH2 and NADH molecules, pair of hydrogen atoms are taken and used as electrons. These hydrogen atoms reduce one atom of oxygen to form water. One pair of electrons transferred to oxygen results in the formation of 3 molecules of ATP. This ATP stores a large amount of energy, which provides the cell.

Main Differences Between Photosynthesis and Cellular Respiration (In points)

  • Photosynthesis is an anabolic process, whereas Cellular Respiration is a catabolic process.
  • Photosynthesis takes place in the chloroplasts of plants, whereas cellular respiration takes place in the mitochondria or cytoplasm of cells.
  • Photosynthesis releases products like glucose and oxygen, which are further used in the process of cellular respiration to give carbon dioxide and water as by-products.
  • Photosynthesis follows the Calvin cycle which takes two steps, whereas Cellular Respiration follows the Krebs cycle which takes three steps.
  • Photosynthesis converts light energy into chemical energy, whereas cellular respiration converts chemical energy into usable energy.
  • Photosynthesis uses sunlight, water, and carbon dioxide as reactants, whereas the products of photosynthesis. i.e., glucose and oxygen are used as reactants in the process of Cellular Respiration.
  • Both photosynthesis and cellular respiration helps in balancing the ecosystem.


In summary, both processes are essential for the survival of living organisms on Earth. Each of these is dependent on one other, which completely forms a cycle. If this cycle does not get completed then the survival of living beings would get tougher and soon there will be nothing left. Photosynthesis gives oxygen as a by-product, which is very essential to maintain the oxygen flow in the atmosphere. At the same time, the glucose released is used in the process of cellular respiration to generate energy to support the well-being of living organisms. The process is endless, molecules go on forming and breaking. As wildlife is spread across the Earth like wildfire. And humans need to understand the value of these processes, which are the reason we are alive. These processes increase the probability of our time on this planet. Understanding these processes and their interdependence is very helpful in fields like biology, ecology, and climate science. Therefore, these processes are vital for the existence of living organisms on this planet.


  • Cellular Respiration and Photosynthesis | Biology Dictionary
  • Difference between Photosynthesis and Cellular Respiration (vedantu.com)
  • Difference Between Photosynthesis And Respiration in Tabular Form (toppr.com)
  • Photosynthesis - Wikipedia
  • Cellular respiration - Wikipedia


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"Difference Between Photosynthesis and Cellular Respiration." Diffzy.com, 2024. Mon. 26 Feb. 2024. <https://www.diffzy.com/article/difference-between-photosynthesis-and-cellular-respiration>.

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