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What are Photosynthesis and Respiration?

Updated on March 26, 2013

Photosynthesis vs. Respiration

Photosynthesis and Respiration are the two most important chemical reactions on our planet. Between them they are responsible for all of the oxygen in our atmosphere and all of the biomass on the planet. The net result of the two processes is the conversion of light energy to heat energy.

Photosynthesis and respiration are essentially the reverse of each other. Photosynthesis uses up energy and involves building up complicated molecules - this is an anabolic reaction. Respiration releases energy and involves breaking down complicated molecules - this is a catabolic reaction. Both processes occur in special organelles in the cell:

  • Photosynthesis occurs in the chloroplasts
  • Respiration occurs in the mitochondria

Photosynthesis takes Carbon Dioxide from the atmosphere, water from the soil and energy from the Sun to create sugars for use in Respiration.
Photosynthesis takes Carbon Dioxide from the atmosphere, water from the soil and energy from the Sun to create sugars for use in Respiration. | Source

What is Photosynthesis?

The most common misconception held by my students regarding plant biology is where plants get their food from. Many pupils believe that plants get their food from the soil; if plants really ate the soil, then there would be no soil left! Plants actually grow by making their own food in a process called 'Photosynthesis.'

The Process of Photosynthesis

The raw materials for photosynthesis are:

  • Carbon Dioxide (from the air)
  • Water (from the soil)

The energy to drive this reaction comes from the Sun in the form of Light energy. In this chemical reaction, a green molecule called chlorophyll absorbs light energy to change carbon dioxide and water into glucose and oxygen (a waste product). This site of this reaction is the green leaves of the plant, which are packed with chlorophyll.

Photosynthesis is actually a many staged process broken into two sections: the light-dependent reactions and the light-independent reactions.

Equation for Photosynthesis

6CO2 + 6 H2O → C6H12O6 + 6O2

What is the Glucose made in Photosynthesis used for?

The glucose made in Photosynthesis is used for one of several things:

  1. Repiration: That's right - plants respire. Some of the glucose is used immediately to release energy needed for life processes.
  2. Storage: Some of the glucose is converted into insoluble starch for storage (rather like animals do with fat) These stores of energy can be used later when needed
  3. Biosynthesis: Some of the glucose is used to make new chemicals such as proteins, sugars and fats.

The oxygen we take for granted is a by-product of photosynthesis - the process of creating sugars using energy from the sun used by all plants.
The oxygen we take for granted is a by-product of photosynthesis - the process of creating sugars using energy from the sun used by all plants. | Source

General Equation for Respiration

C6H12O6 + 6O2 → 6CO2 + 6 H2O (+ energy)

What is Respiration?

The different life processes all require a steady flow of energy. Animals get this energy from the food they digest. Glucose is a store of chemical energy that is a product of digestion. Glucose can react with oxygen to release large amounts of energy in a process called respiration.

Looking at the word equation for respiration, it is similar to the equation for complete combustion of a fuel. Namely:

Fuel + oxygen → Carbon Dioxide + Water + Energy

Unlike combustion, respiration is a controlled reaction - it would be inconvenient if your cells caught fire every time they tried to release energy.

The Process of Respiration

Respiration comes in two forms: Aerobic (with air) and Anaerobic (without air). Just like photosynthesis, respiration is actually a complicated series of reactions comprising at least 30 separate steps.

Respiration converts glucose into a molecule called Adenosine Triphosphate, or ATP. This is the energy currency of the cell. If all the energy stored in glucose was released in a single step, the cell would be destroyed. ATP is a small, convenient package of energy that the cell can use safely and quickly.

Respiration Flow Charts

Click thumbnail to view full-size
A flowchart showing the steps involved in aerobic (right) and anaerobic (left) respirationA closer, colour co-ordinated look at aerobic respiration, including the use of ADP
A flowchart showing the steps involved in aerobic (right) and anaerobic (left) respiration
A flowchart showing the steps involved in aerobic (right) and anaerobic (left) respiration | Source
A closer, colour co-ordinated look at aerobic respiration, including the use of ADP
A closer, colour co-ordinated look at aerobic respiration, including the use of ADP | Source

Comments

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    • Lovely 7 profile image

      Lovely 7 5 years ago

      Hi TF Scientist,

      Actually I am not trying to convince you that I am right. I just wanted to tell you that Photosynthesis can be represented in this way also. In a comment, it is not possible to convey my view completely. That's why I posted a hub. All these information that I shared is meant to share information for better understanding and not for promoting my hub or arguing with you. As a college level teacher, I just conveyed my knowledge on this matter. It is up to you to delete my comment or keep it as such. Thank you for expressing your views and I think we will end this discussion here.

      Thank you very much and keep posting great hubs.

    • TFScientist profile image
      Author

      Rhys Baker 5 years ago from Peterborough, UK

      We shall agree to disagree. I have already said that if you are calling that equation the 'overall' then that is also wrong, as it too is merely a simplification of the summation of light dependent and independent reactions.

      If you are going to use a simplified equation, then simplify it right down to the most basic form - basic rules of algebra.

      The net equation is a perfectly acceptable representation of photosynthesis. I have stated this is not the place to go into the complexities of photosynthesis - something you also shied away from in your own look at photosynthesis.

      If my pupils were to write down your slightly less simplified version of the equation in their exams they would not get the mark. As this hub is aimed at my students, I will not be changing it.

      Lastly, it is not good form to promote your own hubs in another's feed.

      It says immediately below the comment box "Comments are not for promoting your Hubs." As such, I will be deleting your comment shortly. If you would like to send it again without the link, I would be happy to keep it in the feed.

    • Lovely 7 profile image

      Lovely 7 5 years ago

      Once again Hai,

      I think, what I have given is the right equation as far as overall reaction of photosynthesis is concerned. I agree that the equation you have given is commonly cited while explaining photosynthesis. But factually, that equation represented photosynthesis earlier (1930), but was later corrected by C. B. Van Niel. For more go through this link

      https://hubpages.com/education/an-overview-of-phot...

      Thank you very much and Happy Hubbing

    • TFScientist profile image
      Author

      Rhys Baker 5 years ago from Peterborough, UK

      If you want to get technical then that is also wrong. The equation I have given is the net equation - Photosynthesis is a series of reactions summarised with the equation I have given in the text. In fact, it says this in one of the sources you have provided.

      My own degree level textbooks summarise it as written. I teach my students as I have written. This is not the place to go into light dependent and light independent reactions, the photosystems or the complex biochemistry behind the reactions.

      Every source I have looked at ultimately gives the equation I stated above. It is a simplification. After all, the equation you have given is merely a simplification of:

      2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light ? 2 NADPH + 2 H+ + 3 ATP + O2

      and

      3 CO2 + 9 ATP + 6 NADPH + 6 H+ ? C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O

    • Lovely 7 profile image

      Lovely 7 5 years ago

      Hai TF Scientist,

      I think, the overall equation for photosynthesis is:

      6CO2+12 H2O=C6H12O6+6H2O+6O2.

      Here water molecules appear on both sides of the equation because the molecules that enter the reaction are not same molecules that emerge from the reaction; water molecules do not move intact through the process. The six water molecules formed during photosynthesis have carbon dioxide as their source of oxygen and water as their source of hydrogen atoms.

      Please go through this link

      http://www.life.illinois.edu/govindjee/paper/gov.h...

      http://www.course-notes.org/Biology/Outlines/Chapt...

      or refer

      any of the advanced Cell and Molecular Biology books

      (Gerald Karp: 5th edition), page:218.

    • TFScientist profile image
      Author

      Rhys Baker 5 years ago from Peterborough, UK

      @Lovely 7: I'm afraid that is incorrect. Water is a reactant in this equation, not a product. My equation is also balanced - count the atoms :) May I ask where you have got this idea from?

    • Lovely 7 profile image

      Lovely 7 5 years ago

      Hai TF Scientist,

      please check the equation for Photosynthesis. I think this is not balanced equation for photosynthesis.

      The by products of photosynthesis are glucose, oxygen and water.

      The correct equation for photosynthesis:

      6CO2+12 H2O=C6H12O6+6H2O+6O2.

    • TFScientist profile image
      Author

      Rhys Baker 5 years ago from Peterborough, UK

      @Marcy: Wow! Thanks for the share :D I'm glad you are still finding my science hubs interesting - I feel I need to broaden my horizons soon!

    • TFScientist profile image
      Author

      Rhys Baker 5 years ago from Peterborough, UK

      @Cre8tor: :) We all take liberties from time to time. There are still a number I have taken in this hub! I am really happy that your son could easiliy understand it - this topic is often explained really badly!

      Thanks for the useful vote

    • Cre8tor profile image

      Dan Robbins 5 years ago from Ohio

      Thanks TF! This one was fun because my son read with me and told his version of the topic from school...we did some reviewing with your hub to help clarify some 'liberties' he took with his version. Very nice hub and was easy enough for an 8 year old to draw from. (with a little help) Voted up! and Useful!

    • whonunuwho profile image

      whonunuwho 5 years ago from United States

      A wonderful and concise explanation of the two vital processes needed in all life on this planet. It would be truly miraculous if all of those individuals responsible for chemical wastes in waters and air, that we all share with plants and other animals, understood this need for mutual sharing of life processes that will have detrimental effects if we don't do something radical about practices carried on in fishing, deforestation, and dumping activities around the world.Thanks for you great hub!

    • Marcy Goodfleisch profile image

      Marcy Goodfleisch 5 years ago from Planet Earth

      Another amazing hub! I love all the things you share here about science; I've learned a ton of things just by reading your hubs. Voted up and up, and shared with followers and on FB!