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.

The Carbon Cycle

Thecarbon atomsthat make up

DNA, proteins,and other

molecules of life

Commonly cycle between earth’s rocks, atmosphere, and the bodies and cells of living things

The Carbon Cycle

and endlessly move between one location and the others

In the atmosphere

carbon atomsare found in

CO2

Some of these carbon atoms are taken in by plantsand used to synthesize molecules like sugar and starch

The Carbon Cycle

6 CO2 + 6 H2O + Sunlight C6H12O6 + 6 O2

Notice that 6 carbon atomswere removed from the atmosphere

The Carbon Cycle involves Photosynthesis

and end up in this molecule of glucose in a plant

Thus, we canthink of

photosynthesisas a first step in

the cycling of carbon

Photosynthesis is the major means by which carbon atomsleave 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 CO2 + 6 H2O + energyC6H12O6 + 6 O2

and the carbon atoms return to the atmosphere as CO2

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 CO2 + 6 H2O + energyC6H12O6 + 6 O2

the carbon atoms return to the atmosphere as CO2

When molecules that containcarbon react with oxygen

All three processes can be summarized by the same equation

6 CO2 + 6 H2O + energyC6H12O6 + 6 O2

But it also releases tons of CO2 to the atmosphere

When we burn wood or fossil fuels

…combustion…the carbon atoms in their

moleculesare oxidized rapidly

All three processes can be summarized by the same equation

This releases a lot of energythat we can use

3. Combustion of wood and fossil fuels

SUMMARY

During photosynthesis, carbon atoms leave the atmosphere and enter the biosphere

6 CO2 + 6 H2O + Sunlight C6H12O6 + 6 O2

During cellular respiration, carbon atoms return to the atmosphere

6 CO2 + 6 H2O + energyC6H12O6 + 6 O2

How do the summary equations for photosynthesisand cellular respiration differ from one another?

Compare and Contrast

6 CO2 + 6 H2O + Sunlight C6H12O6 + 6 O2

6 CO2 + 6 H2O + energyC6H12O6 + 6 O2

Answer - They are the reverse of each other

CO2 levels in earth’s

atmosphere are increasing

steadily today

What is the source of all this extra CO2?

Answers

Deforestation and Combustion of wood and fossil fuels

Name three importantfossil fuels

Oil Coal Natural gas

When plants of the past removed CO2 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 CO2

that photosynthesis removed from earth’s atmosphere in that same distant past

Atmospheric

CO2

Sugars andorganic molecules

in living things

Photosynthesis

Summary Drawing of the Carbon Cycle

Key Components:

Cellular Respiration

Atmospheric

CO2

Sugars andorganic molecules

in living things

Photosynthesis? ? ? ? ? ? ? ? ? ? ?

What processes can return CO2 to the atmosphere?

Cellular respiration Deforestation Combustion of wood and fossil fuels Oxidation of organic molecules