READ: How do Plants and Animals Work Together?

1. Photosynthesis and Respiration

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.

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:

                      Cellular Respiration:         C₆H₁₂O₆ + 6O₂ → ATP + 6CO₂ + 6H₂O

                      Photosynthesis:                   6CO₂ + 6H₂O + light  → C₆H₁₂O₆+ 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.

2. Photosynthesis vs. Respiration

Cellular respiration and photosynthesis are direct opposite reactions. Some of the ATP made in the mitochondria is used as energy for work, and some is lost to the environment as heat.

3. Summary and Vocabulary

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.

Vocabulary

• carbon cycle: Pathways through which carbon is recycled through the biosphere.
• cellular respiration: Process of breaking down glucose to obtain energy in the form of ATP.
• photosynthesis: Process by which specific organisms (including all plants) use the sun's energy to make their own food from carbon dioxide and water; process that converts the energy of the sun, or solar energy, into carbohydrates, a type of chemical energy.
• products: End results of a chemical reaction.
• reactants: Molecules that come together to start a chemical reaction.

CK-12 Foundation, Life Science. http://creativecommons.org/licenses/by-nc-sa/3.0/