Chapter 42 Ecosystems (Sections 42.7 - 42.10)

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

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

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

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 42.10 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. 42.10, p. 716

Animation: Carbon Cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

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

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

Three Steps in the Greenhouse Effect

Three Steps in the Greenhouse Effect light energy heat energy 3 1 Figure 42.11 Greenhouse effect. 2 Fig. 42.11, p. 717

Animation: Greenhouse Effect

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

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

BBC Video: Carbon Dioxide’s Impact on Our Oceans

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

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

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

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

The Nitrogen Cycle