What is the difference between photosynthesis and respiration?

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mvball | College Teacher | (Level 1) Adjunct Educator

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This question deserves  several "answers" aimed at different levels.

For elementary-school students, it is important to know that photosynthesis is how green plant cells trap sunlight to make sugar, and respiration is how all plant cells (and most other cells) break sugar down to release and use that stored energy.

At the high school level, we can add the understanding that all cells break down fuel molecules but only certain cells can use sun energy to create fuel molecules.  Also, although the summary equations are sort of "the reverse of each other", the processes are not just "the same but completed in reverse", but involve enzymes and chemical reactions that are specific to the process of either photosynthesis or respiration. 

In terms of ecological implications of deforestation as they relate to photosynthesis, it is not the lack of oxygen production that concerns us, because marine algae release much more oxygen per year than trees do.  Our concern is that a lot of carbon, stored in wood, is released as carbon dioxide when wood is burned, adding to the impact of "greenhouse gases" on global average temperature.

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clane | High School Teacher | (Level 3) Educator

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The biggest difference between photosynthesis and respiration is that photosynthesis only occurs in plants and some bacteria while respiration occurs in all living organisms. They do share one big similarity and that is that the process of photosynthesis is actually the same process only it is completed in reverse.

Photosynthesis is Carbon Dioxide and Water that, through the process, yield Glucose and Oxygen.

Respiration is Glucose and Oxygen that, through the process of respiration, yield Carbon Dioxide and Water.

The two work well together because living organisms supply plants and some bacteria with the carbon dioxide needed to undergo photosynthesis, and plants and some bacteria give off oxygen which living organisms need to breathe or respire.

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sid-sarfraz | Student, Graduate | (Level 2) Salutatorian

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Respiration is the breakdown of glucose to make energy using oxygen.


Photosynthesis is the process through which plants make food for themselves in form of glucose.




Glucose + Oxygen = Carbon dioxide + water


Carbon dioxide + water = Glucose + Oxygen



It is a process that is not timely and is done in both day and night


Photosynthesis use energy from the sun to make glucose and oxygen in the day.



Animals and human use glucose and oxygen to carry out respiration


Plants produce glucose and oxygen to carry out respiration.



In respiration, carbon dioxide is exhaled where as oxygen is inhaled by living beings


In photosynthesis, carbon dioxide is inhaled during day and oxygen is exhaled where as in night plants inhale oxygen and exhale carbon dioxide.

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parama9000 | Student, Grade 11 | (Level 1) Valedictorian

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Photosynthesis is where the plant takes in carbon dioxide in the presence of light to produce glucose and water vapour and oxygen to the surroundings.

Respiration is where the plant takes in oxygen and releases carbon dioxide to the surroundings. This occurs all the time.

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cathyluv | Student, Grade 12 | (Level 1) eNoter

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Photosynthesis and respiration occur during different parts of the day. Photosynthesis mainly occurs during daytime as there would be light. The plant takes in the energy from the light and carbon dioxide to produce its 'food' and as a result oxygen is given out as a by product. The oxygen exits through the stomata on the leaves and into the air.

Respiration however occurs mainly at night when no light is present. It is very similar to human respiration as it takes in the oxygen in the air to break down its food supply and in turn gives out carbon dioxide. Some people advise not to keep plants in your room if you keep it closed for this very reason!

There is a specific time however (about sunset) when the rate of photosynthesis is equal to the rate of transpiration. This is known as compensation point. Basically what happens is that all the oxygen being created in photosynthesis is being used for respiration and all the carbon dioxide produced in respiration is being used up for photosynthesis. Therefore there would be no net product being produced.

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jess1999 | Student, Grade 9 | (Level 1) Valedictorian

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In photosynthesis, carbon dioxide and water yield glucose and oxygen. In respiration, process glucose and oxygen yield carbon dioxide and water. Photosynthesis takes place in the chloroplast while respiration takes place in the mitochondria.

The Equation

Photosynthesis : 6CO2 + 12H2O + light --> C6H12O6 + 6O2 + 6H20

Respiration : 6O2 + C6H12O6 --> 6CO2 +6H2O + ATP (energy)

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zumba96 | Student, Grade 11 | (Level 3) Valedictorian

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Photosynthesis is a process that converts carbon dioxide into organic compounds in 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 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 inrespiration there is aerobic respiration and anaerobic respiration.

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yukyukco | (Level 1) eNoter

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One difference of photosynthesis and respiration is that their process is being reversed. In photosynthesis, carbon dioxide and water is yielded to glucose or also known as sugar and oxygen while in respiration, it is the other way around. Sugar and oxygen is yielded to carbon dioxide and water. In other words, in photosynthesis, carbon dioxide is absorbed and oxygen is released while in respiration, oxygen is absorbed and carbon dioxide is released.

 Another difference of the two is that photosynthesis can occur only in presence of sunlight while respiration doesn't require sunlight for it to perform the process. The main function of photosynthesis is to produce food and it captures energy for it to perform the process while respiration breakdowns food and it releases energy in the process.

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gelsaied | Student, College Freshman | (Level 1) Honors

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Ultimately, the energy in organic molecules comes from the sun. Energy enters an ecosystem in the form of sunlight and exists as heat. Photosynthesis generates organic molecules and oxygen used by the mitochondria of eukaryotes for the process of cellular respiration. Respiration breaks this feul down, which generates ATP. The waste products of repsiration, carbon dioxide and water, are the raw materials needed for photosynthesis.

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senioreeto | Student, Undergraduate | (Level 1) Valedictorian

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  1. photosynthesis:the process in which carbon dioxide and water react in the presence of sunlight and chlorophyll(present in the leaves of plants) to form glucose is called the photosynthesis.oxygen and water are released in this process as bi_products.this process takes place in plants only in daytime as it needs sunlight.reaction is as follows:                                            6CO2 + 12H2O-----> C6H12O6 + 6O2 + 6H2O                             where C6H12O6 is the glucose.
  2. respiration:the process in which breakdown of organic material(GLUCOSE) takes place in the presence of oxygen to give carbon dioxide and water is called the respiration.energy is also released in this process.it takes place in plants both in day and at night because it doesnt need sunlight.reaction is as follows:                 C6H12O6 + 6O2 -----> 6CO2 + 6H2O + ENERGY .
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rock-star790 | Student, Grade 10 | (Level 1) Salutatorian

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In order for plants to perform their important functions, certain processes are required. Two of these are photosynthesis and cellular respiration. While the two have characteristics in common, there are many differences between them.

Photosynthesis is a process by which plants use light from the sun to make food. After the photosynthesis happens, then the cells in the plant use cellular respiration to turn this food into energy that the plant can actually use. Photosynthesis happens before respiration can.

Both involve a type of organelle inside the cells, but photosynthesis takes place inside the chloroplasts, which contain chlorophyll. Cellular respiration takes place inside the mitochondria, which are the organelles that are able to break down glucose.

In photosynthesis, the energy that is used comes from sunlight, which is converted into energy. In cellular respiration, the energy is taken from glucose and then transferred to ATP, also known as adenosine triphosphate or derived energy, for the organism to use. Determine what part energy plays in both processes. Photosynthesis needs energy from the light in order to start the whole process. But in cellular respiration, energy is produced from the glucose that results in photosynthesis. In other words, photosynthesis needs energy to make glucose, while cellular respiration uses this glucose to actually create energy. In scientific equations, photosynthesis takes carbon dioxide from the air, water and sunlight to create sugar. After this happens, oxygen is released back into the air. Cellular respiration takes these same sugars and combines them with oxygen to release the energy as ATP. Carbon dioxide and water are released due to this.
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chaslcoleman | High School Teacher | (Level 1) eNoter

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Cellular respiration is the careful enzymatic taking apart of glucose molecules. Some of the energy trapped in the bonds of this sugar molecule is captured and stored in the bonds of ATP molecules. The destruction of one glucose molecule results in the construction of 36 ATP molecules. The energy not captured in ATP is lost to the surroundings as heat. The ATP formed is used by cells for processes such as growth.

Photosynthesis is the plant process where light energy is used to generate the production of ATP. The ATP so formed is used to form the bonds between carbon dioxide molecules and hydrogen atoms released from water by the light energy. The process forms sugar (glucose) molecules and produces oxygen as a waste product. At a glance, the equations: sugar + oxygen --> carbon dioxide + water + ATP energy (cellular respiration) and carbon dioxide + water + sun's energy --> sugar + oxygen (photosynthesis) look to be the reverse of each other. In fact they are both very complex and dissimilar processes.

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swetank | Student, Grade 10 | (Level 1) Honors

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  1. Photosynthesis occurs only in plants while respiration in all living things.
  2. Photosynthesis occurs in presence of sun light whereas respiration always and require no light but air.
  3. In Photosynthesis solar energy is converted into chemical energy and in respiration chemical energy is converted into heat energy.


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matthew0109 | Student | (Level 1) Honors

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Photosynthesis uses light energy to convert carbon dioxide into glucose. Oxygen is produced as a by product during photosynthesis.

Sugar and other carbohydrates are used as fuel by cells. During the process of Cellular Respiration, glucose is broken down using oxygen. This reaction releases energy which is used to create ATP molecules.

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jaykaran | Student, Grade 10 | (Level 1) Honors

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The differences between photosynthesis and respiration are :  

Photosynthesis produces food Respiration breaks down food

In photosynthesis carbon dioxide In respiration glucose is broke down into
combines with water to produce glucose carbon dioxide and water

Photosynthesis absorbs sun’s energy Respiration releases energy trapped in food or

Photosynthesis takes place in the presence No catalyst is needed for respiration
of a catalyst chlorophyll

CO2 is absorbed in photosynthesis CO2 is released in respiration

Oxygen is released in photosynthesis Oxygen is absorbed in respiration

Photosynthesis has to take place in sunlight Respiration does not need sunlight

Photosynthesis occurs only during daytime Respiration occurs at all times during the lifetime 
of the living cell

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