learning outcomes describe the cycle of carbon through the ecosystem describe how humans have...
TRANSCRIPT
Learning outcomes
• Describe the cycle of carbon through the ecosystem
• Describe how humans have affected the carbon cycle
How humans affect the cycle
• Human activity has affected the balance of the carbon cycle by
• Think, pair share
Burning down forests – reduces CO2 absorption by photosynthesis, increases CO2 formation by combustion
Burning fossil fuels
Nitrogen
• Essential element
• Used in proteins, enzymes, antibodies, hormones, cell membranes
• Often in short supply in biological system
• Very stable in its molecular form (N2 )
Sources of Nitrogen
1. 78% of the atmosphere is made up of nitrogen2. Ammonia (NH3) from excretion and decay of
organic matter (mineralization)
• Only a few organisms can use it in these forms
• All others must have it converted to a nitrate ion (NO3
-)
Nitrogen fixation
• Requires a large amount of energy• Can be done by– Lightening strikes– Nitrogen fixing bacteria - Rhizobium– Free living soil bacteria– Blue-green algae (Cyanobacteria)– Industrial processes
Atmosphere to Plants – Ammonification
Nitrogen fixing bacteria living freely in the soil change atmospheric nitrogen (N2) to ammonia (NH3)
• E.g. Azotobacter
Atmosphere to plants – Nitrification I
• The ammonia that is free in the soil is then turned into a nitrite ion (NO2
- ) by nitrifying bacteria such as Nitrosomonas
• This is an aerobic reaction requiring oxygen
Atmosphere to plants – Nitrification II
• The nirtite ion (NO2-) is then changed into the nitrate ion (NO3-) by a different nitrifying bacteria (Nitrobacter)
• This is an aerobic reaction requiring oxygen
• The nitrate ion is now available for plants to absorb
Atmosphere to plants – Symbiotic relationship
• Rhizobium is a bacteria living in a mutualistic relationship in the nodules of legumes.
• Converts atmospheric nitrogen (N2) into ammonia (NH3)
• This is then used by the plants to make its own organic compounds
• In exchange the Rhizobium gets carbohydrates, proteins and environment with the right amount of O2 for the nitrogen fixing reaction
Denitrification
• The reduction of nitrates (NO3-) to nitrogen gas
(N2)• Replenishes the atmosphere with nitrogen• Done by bacteria in anaerobic conditions