Cellular respiration takes place in the every living organisms, as it is the simple process of converting oxygen and glucose into carbon dioxide and water and ultimately producing energy for the cells of the body. On the contrary, photosynthesis occurs in green plants, which contain chlorophyll and uses sunlight and water to convert it into energy.
These are the two reciprocal process, with the same aim of obtaining energy but by using different methods, different sources and thus giving out different products. Even both are necessary for the exchange of energy which is required by the living things. Though cellular respiration is performed by all types of the living cell whether a plant or an animal, prokaryotes or eukaryotes but photosynthesis is executed in green plants only and in few bacteria.
One cant imagines the work to be performed without the requirement of energy, whether internally or externally, directly or indirectly. Therefore we can say that these two processes are one of the essential elements of maintaining life on the Earth. At this moment we will consider the difference between the two essential and energy providing reactions to the living cells, where one is cellular respiration and another is photosynthesis.
Content: Cellular Respiration Vs Photosynthesis
|Basis for Comparison||Cellular Respiration||Photosynthesis|
|Meaning||Cellular respiration is the process of converting energy and providing it to the different cells of the body. Here the glucose and oxygen are converted to carbon dioxide and water, and thus energy (ATP) is released.||The process of using the sunlight and water to convert it into energy is called as photosynthesis, which is specially performed by the green plants and few bacteria. The green pigment called chlorophyll is responsible for this conversion process.
|Occurs in||The living cell, as well in green and non-green plants.||Photosynthesis occurs only in plants containing chlorophyll.|
|Cellular respiration occurs in light (day) as well as in the dark (night).||Photosynthesis takes place in light (day) only.|
|Reaction involved||1. Glycolysis which occur in the cell cytoplasm.|
2. Krebs or Citric acid cycle occurs in the mitochondrial matrix of the cell.
3. Electron Transport Chain or oxidative phosphorylation which occurs in the mitochondrial membrane.
|1. The light reaction which occurs in grana of the chloroplast.
2. Dark reaction or Calvin cycle taking place in the stroma of the chloroplast.
3. Photolysis or Water-spitting complex which takes place in thylakoid lumen.
|Energy||It is an exothermic reaction, as energy is released during this process.||It is an endothermic process, as energy is stored or utilised.|
|The energy which is released is in the form of ATP is used in various metabolic activities.||The energy is in the form of glucose or chemical energy, which is used during the dark reaction.
|The potential energy is converted into the kinetic energy.||Light energy is converted into potential energy.|
|Oxidative phosphorylation||In the cellular respiration oxidative phosphorylation occurs.||Here photophosphorylation occurs.
|Other activities||It is a catabolic process.||It is an anabolic process.|
|Oxygen and carbohydrates are absorbed in the process.||Oxygen and carbohydrates released.|
|Carbon dioxide and water are released.||Carbon dioxide and water are absorbed.|
Definition of Cellular Respiration
In this process, the carbohydrate in the form of glucose is broken down and along with oxygen, is converted into carbon dioxide and water and thereby releasing energy as ATP or adenosine triphosphate. This energy is used for various metabolic activities and other cellular work.
Cellular respiration occurs in mitochondria and cytoplasm of the cell. Unlike photosynthesis, it works day and night. Though it is not as simple reaction as we say, it is a long process which undergoes four major steps.
- Glycolysis (splitting or breaking of the sugar) – It occurs in the cytoplasm of the cell, where one molecule of glucose C6H12O6 is broken into two molecules pyruvic acid. So here two ATP molecules are generated from the one molecule of glucose.
- Transition Reaction – Pyruvic acid is sent to the mitochondria, where it get converted into Acetyl CoA and get further broken down.
- Citric acid cycle or the Krebs Cycle – It occurs in the matrix of the mitochondria, where Acetyl CoA is broken, in the presence of the oxygen and four ATP are generated along with many NADH. Even the carbon dioxide and water are released as a waste product from this reaction.
- The Electron Transport Chain (ETC) – This is also known as Chemiosmotic Theory, which was proposed by Peter Mitchell. In this reaction, thirty-two (32) ATP are generated for every glucose.
So overall reaction is written as:
However, above we discussed was about only aerobic cellular respiration, which occurs in the presence of oxygen and thus resulting in the production of thirty-eight (38) molecules of ATP from one glucose molecule. But what about in the case when there is the shortage of oxygen like when we run or while performing any exercise. This is called anaerobic condition, where they produce only two (2) ATP molecules from one molecule of glucose from the glycolysis pathway only.
It does not undergo for further break down of the molecules, as the body demands immediate energy at that moment. Secondly, other reactions occur in the presence of oxygen, and this is the reason they are skipped. The anaerobic reaction is also called fermentation.
Therefore, it is called as the catabolic process as energy is released in any form by breaking the large molecules into the smaller ones.
Definition of Photosynthesis
In general, terms, if we define the process of photosynthesis, we will say ‘ the process of converting sunlight and water into energy or food, and it is performed by the green plants. But chemically it is an oxidation-reduction process (oxidation is the removal of electrons and reduction is gaining of electrons by a molecule). This process occurs in light (sunlight) only and so-called as light-energized oxidation process.
The photosynthesis occurs in leaves of the green plants, especially in the chloroplast which is the tiny structure present in cells of the leaves. The chloroplast contains chlorophyll (a green chemical) is responsible for the green colour of the leaves.
Chlorophyll absorbs sun’s energy and is used to separate water molecules into oxygen and hydrogen. Further oxygen is released into the atmosphere from the leaves, and the carbon dioxide and hydrogen are used to generate food or glucose for plants.
It can be elaborated by the following equation:
So we can say that the in the above reaction, there is oxidation of water H2O in the presence of sunlight and oxygen (O2) and hydrogen ions (H+) are released. The removed hydrogen ions and electrons moved to the carbon dioxide (CO2) and are reduced as the organic product. So overall reaction where carbohydrates (C6H12O6) are formed during photosynthesis is defined in the equation.
Though the above equation is a summary of the whole process, there is the involvement of many enzymes and other reactions too. The process is divided into two stages: Light reaction and Dark reaction.
- Light reaction – The light energy is absorbed and is used for the transfers of electrons and thus producing adenosine triphosphate (ATP) and reduction of nicotine adenine dinucleotide phosphate (NADPH).
- Dark reaction – In this, the carbon dioxide is reduced to organic carbon compounds, with the help of ATP and NADPH formed during the light reaction.
Key Differences Between Cellular Respiration and Photosynthesis
Upcoming points will present the substantial differences between cellular respiration and photosynthesis:
- The process where energy is produced for the cell to do work is known as cellular respiration. It occurs in mitochondria of the cell, where the oxygen and carbohydrates are converted into water and carbon dioxide and thus releasing energy. Meanwhile, another process of gaining energy with the help of sunlight and water is known as photosynthesis. Although this process is restricted to green plants and few bacteria only. However, in plants, the photosynthesis is performed by the pigment called as chlorophyll, which presents in the leaves.
- Cellular respiration takes place in all living cell (in mitochondria) while photosynthesis occurs only in plants containing chlorophyll. Photosynthesis occurs in daytime only whereas there is no such condition in case of cellular respiration as it occurs in the day as well as in night also.
- The reaction involved in cellular respiration are Glycolysis, Krebs or Citric acid cycle, Electron Transport Chain or oxidative phosphorylation. Though in photosynthesis the involving reactions are the Light reaction, Dark reaction or Calvin cycle, Photolysis or Water spitting complex.
- Cellular respiration is an exothermic reaction, as energy is released in the form of ATP and is used in various metabolic activities. On the other hand, photosynthesis is an endothermic process, as energy is stored or utilised and is in the form of glucose or chemical energy, used during the dark reaction.
- In the cellular respiration process, the potential energy is converted into the kinetic energy, meanwhile in photosynthesis light energy is converted into potential energy.
- Even the oxidative phosphorylation takes place in cellular respiration, while phosphorylation activity occurs in photosynthesis.
- Other important features of the cellular respiration are that it is a catabolic process. Secondly, oxygen and carbohydrates (glucose) are absorbed in the process, and carbon dioxide and water are released. But photosynthesis is an anabolic process where oxygen and carbohydrates released, and carbon dioxide and water are absorbed.
From the above article, we can say that both the biological process are in mutually beneficial relationship, where from one process (photosynthesis) oxygen is liberated, which is used in another process (cellular respiration) and in return the carbon dioxide is released from the cellular respiration process, which is used up in the photosynthesis.
We also noticed that the chemical reactions of both the methods are opposite of each other, we can say that these are the interdependent process, though one of them takes place in plants only.