Connecting Cellular
Respiration and Photosynthesis
Jessica Harwood
Douglas Wilkin, Ph.D.
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AUTHORS
Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
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Printed: November 9, 2015
CONTRIBUTORS
Doris Kraus, Ph.D.
Niamh Gray-Wilson
Jean Brainard, Ph.D.
Sarah Johnson
Jane Willan
Corliss Karasov
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Chapter 1. Connecting Cellular Respiration and Photosynthesis
C HAPTER
1
Connecting Cellular
Respiration and Photosynthesis
• Name the products and reactants of photosynthesis and cellular respiration.
• Explain how cellular respiration and photosynthesis are connected.
How do trees help you breathe?
Recall that trees release oxygen as a byproduct of photosynthesis. And you need oxygen to breathe. Do you know
why? So your cells can perform cellular respiration and make ATP.
Connecting Cellular Respiration and Photosynthesis
Photosynthesis and cellular respiration are connected through an important relationship. This relationship enables
life to survive as we know it. The products of one process are the reactants of the other. Notice that the equation
for cellular respiration is the direct opposite of photosynthesis:
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• Cellular Respiration: C6 H12 O6 + 6O2 → 6CO2 + 6H2 O
• Photosynthesis: 6CO2 + 6H2 O → C6 H12 O6 + 6O2
Photosynthesis makes the glucose that is used in cellular respiration to make ATP. The glucose is then turned
back into carbon dioxide, which is used in photosynthesis. While water is broken down to form oxygen during
photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water. While photosynthesis
requires carbon dioxide and releases oxygen, cellular respiration requires oxygen and releases carbon dioxide. It is
the released oxygen that is used by us and most other organisms for cellular respiration. We breathe in that oxygen,
which is carried through our blood to all our cells. In our cells, oxygen allows cellular respiration to proceed.
Cellular respiration works best in the presence of oxygen. Without oxygen, much less ATP would be produced.
Cellular respiration and photosynthesis are important parts of the carbon cycle. The carbon cycle is the pathways
through which carbon is recycled in the biosphere. While cellular respiration releases carbon dioxide into the
environment, photosynthesis pulls carbon dioxide out of the atmosphere. The exchange of carbon dioxide and
oxygen during photosynthesis ( Figure 1.1) and cellular respiration worldwide helps to keep atmospheric oxygen
and carbon dioxide at stable levels.
FIGURE 1.1
Cellular respiration and photosynthesis
are direct opposite reactions.
Energy
from the sun enters a plant and is converted into glucose during photosynthesis. Some of the energy is used to make
ATP in the mitochondria during cellular
respiration, and some is lost to the environment as heat.
Summary
• The equation for cellular respiration is the direct opposite of photosynthesis.
• The exchange of carbon dioxide and oxygen thorough photosynthesis or cellular respiration worldwide helps
to keep atmospheric oxygen and carbon dioxide at stable levels.
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Chapter 1. Connecting Cellular Respiration and Photosynthesis
Explore More
Use the resource below to answer the questions that follow.
• Photosynthesis and Respiration at http://www.youtube.com/watch?v=JEnjph9miK4 (3:46)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57361
1.
2.
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4.
What is needed for photosynthesis to occur? Be specific.
What is needed for cellular respiration to occur?
What is ATP?
Do autotrophs need to carry out cellular respiration? Why or why not?
Review
1. How are the equations for photosynthesis and cellular respiration related?
2. What keeps atmospheric oxygen and carbon dioxide at stable levels?
References
1. LadyofHats. Cellular respiration and photosynthesis are direct opposite reactions .
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