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 Cycle

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

Rhizobium

Denitrification

• The reduction of nitrates (NO3-) to nitrogen gas

(N2)• Replenishes the atmosphere with nitrogen• Done by bacteria in anaerobic conditions

Human effect on Nitrogen cycle

Nitrogen cycle

Biozone pages

109 and 110