Photosynthesis and cellular respiration

This article will give you information on the processes of photosynthesis and cellular respiration. It will discuss how these processes are linked to each other, and also describe the points of differences between them.


Photosynthesis and cellular respiration are the two main processes performed by most living organisms to obtain usable energy from nature. While photosynthesis is performed by most plants who can prepare their own food, most animals fulfill their energy requirements through cellular respiration.

Photosynthesis is the process used by plant cells to convert light energy from the sun into chemical energy, so as to create energy-rich carbohydrate molecules like glucose. Cellular respiration is the process of breaking down food molecules to obtain energy and store it in the form of adenosine triphosphate (ATP) molecules.


Plant cells, after creating sugar molecules through photosynthesis, undergo cellular respiration to create ATP molecules. Animals obtain food molecules from plants and other organisms, and then undergo cellular respiration to obtain ATP molecules. All living organisms utilize these stored ATP molecules to carry out their metabolic processes.




Photosynthesis takes place in the cells of plant leaves in structures called chloroplasts, which contain chlorophyll. The plant cells absorb light from the sun through the chlorophyll pigment, and using water and carbon dioxide obtained from the environment, undergo a series of chemical reactions to produce carbohydrate molecules.


The chemical reaction in photosynthesis is:


Carbon Dioxide + Water + Sunlight → Glucose + Oxygen


6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2


The process of photosynthesis involves two stages of chemical reactions:


Light-dependent Reactions

This is the first stage of the photosynthetic process. These reactions take place in the presence of sunlight, and use light energy from the sun to produce ATP molecules and other molecules known as NADPH. These molecules are used as the energy source to carry out the reactions in the next stage of photosynthesis.


Light-independent Reactions (Calvin Cycle)

In this stage, energy-containing sugar molecules are synthesized. The ATP and NADPH produced in stage I are used to fuel the reactions in this stage. Here, CO2 molecules are broken down and converted into sugars and other compounds. The Calvin Cycle is repeated twice in order to yield one molecule of glucose.


Cellular Respiration


Cellular respiration takes place in the same way in both plants and animals. Living cells obtain the products of photosynthesis (sugar molecules) and undergo cellular respiration to produce ATP molecules. Some cells respire aerobically, using oxygen, while others undergo anaerobic respiration, without using oxygen. The process involves a set of chemical reactions to convert chemical energy from the glucose molecules into ATP molecules.


The process of breakdown of glucose molecules involves two major stages – glycolysis (anaerobic respiration) and aerobic respiration.



Cellular respiration begins at this stage in the cytoplasm of the cells, and yields 2 carbon-based molecules called pyruvate, and 2 molecules of ATP. Oxygen plays no part during this stage, so it is called anaerobic respiration.


Aerobic Respiration

This process takes place in specialized structures within the cell called mitochondria, and uses the products of glycolysis, the pyruvate molecules, to release energy, along with CO2 and water as the by-products of the reaction. The energy released is stored in the form of ATP molecules. Usually, a total of 38 ATP molecules are produced.


Here is the chemical equation of the reaction that takes place:


Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP)


C6H12O6 + 6O2 → 6CO2 + 6H2O + 2900 KJ




☛ Photosynthesis utilizes sunlight to produce food molecules.☞ Cellular respiration utilizes glucose molecules to obtain energy-storing ATP molecules.


☛ Photosynthesis takes place in plant leaves containing the chlorophyll pigment.☞ Cellular respiration takes place in the cytoplasm and mitochondria of the cell.


☛ Photosynthesis uses water, sunlight, and CO2 from the atmosphere to create glucose molecules, and releases oxygen as a by-product.☞ Cellular respiration uses glucose molecules and oxygen to produce ATP molecules and CO2 as the by-product.


☛ Photosynthesis takes place only when there is sunlight.☞ Cellular respiration occurs at all times.


☛ Photosynthesis involves conversion of one type of energy into another: light energy into chemical energy.☞ Cellular respiration involves using that chemical energy and breaking it down to release energy.


☛ Photosynthesis takes place in two stages of light reactions and dark reactions.☞ Cellular respiration involves aerobic (glycolysis) and anaerobic respiration.


☛ Photosynthesis occurs only in plants and some bacteria.☞ Cellular respiration takes place in all types of living organisms.


Muhammad Ramzan Rafique
Muhammad Ramzan Rafique

I am from a small town Chichawatni, Sahiwal, Punjab , Pakistan, studied from University of Agriculture Faisalabad, on my mission to explore world I am in Denmark these days..

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