11 terms

CARBON AND NITROGEN CYCLE

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carbon cycle
all living things contain billions of carbon atoms in their cells
how carbon is stored
SHORT TERM STORES
-vegetation on land
-plants in the ocean
-in land-based and marine animals
-found in the atmosphere as carbon dioxide gas (CO2)
-stored in its dissolved form in top layers of the ocean

LONG TERM STORES
-middle and deep ocean waters as dissolved carbon dioxide
->in cold ocean waters the dissolved carbon will sink to the bottom and remain for 500 years, eventually it may be used by bacteria and released again
-coal, oil and gas deposits
->these are fossil fuels that are formed from dead plants and animals
-largest long term stores are found in marine sediments and sedimentary rock
how carbon is cycled
PHOTOSYNTHESIS
-chemical reaction that converts solar energy into chemical energy and produces carbohydrate energy and oxygen
energy (sunlight) + 6CO2 + 6H20 -> C6H1206 + 6O2

CELLULAR RESPIRATION
-both plants and animals release carbon dioxide back into the atmosphere by converting carbohydrates and oxygen into carbon dioxide and water
C6H1206 (carbohydrates) + 6O2 -> 6CO2 + 6H2O

DECOMPOSITION
-breaking down of dead organic material by decomposers
-bacteria and fungi convert organic molecules such a cellulose back into carbon dioxide and is then released into the atmosphere

OTHER WAYS CARBON IS CYCLED
-ocean mixing moves carbon throughout the worlds oceans.
-CO2 is released to tropical atmospheres as ocean currents carry the warmer water to polar areas
-some CO2 is released from volcanic eruptions, decomposing trees and forest fires
human activities in the carbon cycle
-land clearing
-agriculture
-urban expansion
-mining
-industry
-motorized transport
-so much carbon is released so quickly into the atmosphere from these activities that the natural carbon cycle can no longer move all of it to the other stores
-most carbon stored in the atmosphere is a greenhouse gas and greenhouse gases contribute to global climate change
nitrogen cycle
-nitrogen is an important component of DNA and proteins which are essential for life processes
-in animals proteins are essential for muscle function
-in plants nitrogen is important for growth
how nitrogen is stored
LARGEST STORE
-found in the atmosphere as nitrogen gas (N2)

OTHER MAJOR STORES
-oceans
-organic matter in soil

SMALLER STORES
-terrestrial ecosystems
-organisms
-lakes and marshes
how nitrogen is cycled
3 PROCESSES
-nitrogen fixation
-nitrification
-uptake

NITROGEN FIXATION
-nitrogen gas (N2) is converted into nitrate (NO3-) or ammonium (NH4+)
-occurs in 3 ways
1. atmosphere
2. soil
3.water bodies

1. atmosphere
-N2 is converted to NO3- by lightning

2. soil
-N2 is converted to NH4+ by decomposing bacteria
->nitrogen-fixing bacteria (Rhizobium)

3. water bodies
-cyanobacteria in aquatic ecosystems fix nitrogen into NH4+
-cyanobacteria is blue-green bacteria that manufacture their own food during photosynthesis
-nitrogen-fixing cyanobacteria make nitrogen compounds available to plants in the surface of the waters
nitrification and uptake
NITRIFICATION
-NH4+ is converted to NO3-
-takes place in 2 stages
-involves soil bacteria -(nitrifying bacteria)

1. first stage
-certain species of nitrifying bacteria converts NH4+ to NO2- (nitrite)

2. second stage
-different species of nitrifying bacteria converts NO2- into NO3-

-once nitrates are made available, the nitrates can enter plant roots and eventually be incorporated into plant proteins
-the uptake of nitrates is only important not only for the plants but also for other organisms
-when organisms eat plants they incorporate nitrogen into the proteins of their tissues
how nitrogen is returned to the atmosphere
DENITRIFICATION
-involves denitrifying bacteria
-denifitrying bacteria converts NO3- back into nitrogen gas (N2)
-it is also returned to the atmosphere as ammonia NH3 in volcanic ash etc
how nitrogen is removed from ecosystems
-excess NO3- and NH4+ that are not taken up by plants mix with rainwater and washed into groundwater and streams
-unused nitrogen may settle to ocean, lake or river bottoms in sediments and eventually it will form rock
human activities
-human activities doubled the available nitrogen in the biosphere
-millions of tonnes of nitrogen are added to the atmosphere in the form of nitrogen oxide (NO) and nitrogen dioxide (NO2)
-> this is due to fossil fuel combustion in power plants and sewage treatments
-clearing trees/grasslands by burning also releases trapped nitrogen into the atmosphere
-chemical fertilizers release excess nitrogen into the atmosphere
-> the increased amount of dissolved nitrogen causes eutrophication in which excess nutrients result in increased plant production and decay