The Carbon Cycle

The carbon atoms that make up DNA, proteins, and other molecules of life Commonly cycle between earth’s rocks, atmosphere, and the bodies and cells of living things and endlessly move between one location and the others

In the atmosphere carbon atoms are found in CO 2 Some of these carbon atoms are taken in by plants and used to synthesize molecules like sugar and starch

6 CO H 2 O + SunlightC 6 H 12 O O 2 Notice that 6 carbon atoms were removed from the atmosphere The Carbon Cycle involves Photosynthesis and end up in this molecule of glucose in a plant

Thus, we can think of photosynthesis as a first step in the cycling of carbon Photosynthesis is the major means by which carbon atoms leave the atmosphere and become part of the molecules making up living things The Carbon Cycle involves Photosynthesis

At any given time, many tons of carbon atoms are temporarily locked up in the bodies and molecules of living things

How do carbon atoms return to the atmosphere? Cellular respiration Oxidation Combustion of wood and fossil fuels There are several ways

1. Summary of Cellular Respiration 6 CO H 2 O + energyC 6 H 12 O O 2 and the carbon atoms return to the atmosphere as CO 2 When plants and animals carry out cellular respiration, they break down sugars and similar molecules to extract their energy All three processes can be summarized by the same equation

2. Summary of Oxidation 6 CO H 2 O + energyC 6 H 12 O O 2 the carbon atoms return to the atmosphere as CO 2 When molecules that contain carbon react with oxygen All three processes can be summarized by the same equation

6 CO H 2 O + energyC 6 H 12 O O 2 But it also releases tons of CO 2 to the atmosphere When we burn wood or fossil fuels … combustion … the carbon atoms in their molecules are oxidized rapidly All three processes can be summarized by the same equation This releases a lot of energy that we can use 3. Combustion of wood and fossil fuels

SUMMARY During photosynthesis, carbon atoms leave the atmosphere and enter the biosphere 6 CO H 2 O + SunlightC 6 H 12 O O 2 During cellular respiration, carbon atoms return to the atmosphere 6 CO H 2 O + energyC 6 H 12 O O 2

How do the summary equations for photosynthesis and cellular respiration differ from one another? Compare and Contrast 6 CO H 2 O + SunlightC 6 H 12 O O 2 6 CO H 2 O + energyC 6 H 12 O O 2 Answer - They are the reverse of each other

CO 2 levels in earth’s atmosphere are increasing steadily today What is the source of all this extra CO 2 ? Answers  D eforestation and  C ombustion of wood and fossil fuels

Name three important fossil fuels  Oil  Coal  Natural gas When plants of the past removed CO 2 from the atmosphere, sometimes they did not burn or decay, but were covered with sediments to become fossil fuels

Today we burn fossil fuels to release the energy captured by photosynthesis in the distant past The trouble is, we are also releasing all that CO 2 that photosynthesis removed from earth’s atmosphere in that same distant past

Atmospheric CO 2 Sugars and organic molecules in living things Photosynthesis Summary Drawing of the Carbon Cycle Key Components: Cellular Respiration

Atmospheric CO 2 Sugars and organic molecules in living things Photosynthesis ? ? ? ? ? ? ? ? ? ? ? What processes can return CO 2 to the atmosphere?  Cellular respiration  Deforestation  Combustion of wood and fossil fuels  Oxidation of organic molecules