1. Chapter 42 Ecosystems (Sections 42.7 - 42.10)

2. 42.8 The Carbon Cycle The carbon cycle is an atmospheric cycle
Most carbon is stored in rocks – it enters food webs as gaseous carbon dioxide or bicarbonate dissolved in water
carbon cycle
Movement of carbon, mainly between the oceans, atmosphere, and living organisms
atmospheric cycle
Biogeochemical cycle in which a gaseous form of an element plays a significant role

3. 6 Steps in the Carbon Cycle
Carbon in rocks is largely unavailable to living organisms
Carbon enters land food webs when plants use CO2 from the air in photosynthesis
CO2 released by aerobic respiration returns to the atmosphere
Carbon diffuses between atmosphere and ocean; bicarbonate forms when CO2 dissolves in seawater

4. 6 Steps in the Carbon Cycle
Marine producers take up bicarbonate for photosynthesis; marine organisms release CO2 from aerobic respiration
Many marine organisms incorporate carbon into shells
Shells become part of sediments
Sediments become limestone and chalk in Earth’s crust
Burning fossil fuels derived from ancient remains of plants puts additional CO2 into the atmosphere

5. 6 Steps in the Carbon Cycle
Atmospheric CO2 1
photosynthesis 2 6
burning fossil fuels
aerobic respiration
diffusion between atmosphere and ocean 3
Land food webs
Dissolved carbon
in ocean 4
Fossil fuels
death, burial, compaction over millions of years
Marine organisms
Earth’s crust
sedimentation 5
Figure The carbon cycle. Most carbon is in Earth’s crust, where it is largely unavailable to living organisms.
Carbon enters land food webs when plants take up carbon dioxide from the air for use in photosynthesis. 1 1
Marine producers take up bicarbonate for use in photosynthesis, and marine organisms release carbon dioxide from aerobic respiration. 4
Carbon returns to the atmosphere as carbon dioxide when plants and other land organisms carry out aerobic respiration. 2
Many marine organisms incorporate carbon into their shells. After they die, these shells become part of the sediments. Over time, the sediments become carbon-rich rocks such as limestone and chalk in Earth’s crust. 5
Carbon diffuses between the atmosphere and the ocean. Bicarbonate forms when carbon dioxide dissolves in seawater. 3
Burning of fossil fuels derived from the ancient remains of plants puts additional carbon dioxide into the atmosphere. 6
Fig , p. 716

6. Animation: Carbon Cycle
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7. Carbon, the Greenhouse Effect, and Global Warming
Atmospheric CO2 and other “greenhouse gases” help keep Earth warm enough for life through the greenhouse effect
greenhouse effect
Warming of Earth’s lower atmosphere and surface as a result of heat trapped by greenhouse gases

8. Three Steps in the Greenhouse Effect
Earth’s atmosphere reflects some sunlight energy back into space
Some light energy reaches and warms Earth’s surface
Earth’s warmed surface emits heat energy
Some escapes into space
Some is absorbed and emitted in all directions by greenhouse gases

9. Three Steps in the Greenhouse Effect

10. Three Steps in the Greenhouse Effect
light energy
heat energy 3 1
Figure Greenhouse effect. 2
Fig , p. 717

11. Animation: Greenhouse Effect

12. Global Warming
Human-induced increase in atmospheric greenhouse gases correlates with global climate change
Current atmospheric CO2 is the highest in 420,000 years –and climbing
global climate change
A rise in temperature and shifts in other climate patterns

13. Key Concepts The Carbon Cycle
Most of Earth’s carbon is tied up in rocks, but organisms take carbon up from water or the air
Carbon dioxide is one of the atmospheric greenhouse gases that help keep Earth’s surface warm
Increasing carbon dioxide in the air is the most likely cause of climate change

14. BBC Video: Carbon Dioxide’s Impact on Our Oceans

15. 42.9 The Nitrogen Cycle
Nitrogen moves in an atmospheric cycle (nitrogen cycle)
Atmospheric nitrogen (N2 or gaseous nitrogen) is Earth’s main nitrogen reservoir, but most organisms can’t use N2
nitrogen cycle
Movement of nitrogen among the atmosphere, soil, and water, and into and out of food webs

16. Bacteria and Nitrogen Conversions
Only certain bacteria can make nitrogen available to other organisms, or return N2 to the atmosphere
nitrogen fixation
Bacteria use nitrogen gas (N2) to form ammonia (NH3)
nitrification
Bacteria convert ammonium (NH4+) to nitrates (NO3-)
denitrification
Bacteria convert nitrates or nitrites (NO2-) to nitrogen gas

17. 6 Steps in the Nitrogen Cycle
Nitrogen fixing cyanobacteria in soil, water, or lichens break bonds in N2 and form ammonia, which is ionized in water as ammonium (NH4+) and taken up by plants
Another group of nitrogen-fixing bacteria forms nodules on roots of peas and other legumes
Consumers get nitrogen by eating plants or one another; bacterial and fungal decomposers break down wastes and remains and return ammonium to the soil

18. 6 Steps in the Nitrogen Cycle
Nitrification converts ammonium to nitrates:
Ammonia-oxidizing bacteria and archaeans convert ammonium to nitrite (NO2–),
Bacteria convert nitrites to nitrates (NO3–)
Nitrates are taken up and used by producers
Denitrifying bacteria use nitrate for energy and release nitrogen gas into the atmosphere

19. The Nitrogen Cycle