Biosphere: (Nitrogen Cycle)

Question 1

Reservoirs of nitrogen:

Answer 1

-soil.
-atmosphere.

Question 2

Use of element:

Answer 2

•78.1% of earths atmosphere is nitrogen.
-N2(g) is not useable for most organisms.
•proteins (amino acids).
•genetic material (DNA).
•fertilizers.

Question 3

Processes involved:

Answer 3

-1. Nitrogen fixation.
-2. Ammonification.
-3. Denitrification.
•bacteria and lightning play an important role in converging N2(g) into NO3- (nitrate) which can then be used by plants.
•non-photosynthetic organisms are then dependent on plants for sources of nitrogen.

Question 4

1. Nitrogen fixation:

Answer 4

-bacteria, found either in the soil or in the roots of legumes convert atmospheric nitrogen (N2) into ammonium (NH4+).

Question 5

Nitrification:

Answer 5

•other bacteria in the soil convert ammonium (NH4+) to nitrates (NO3-).
•lightning can also convert atmospheric nitrogen (N2) to nitrates (NO3-).
•plants can use ammonium (NH4+) or nitrates (NO3-).

Question 6

2. Ammonification:

Answer 6

•detritus (waste or dead) is decomposed and NH4+ is released back into the soil.
•most NH4+ is used by bacteria and is converted into NO2- and then to NO3-.
•plants then use this NO3-.

Question 7

3. Denitrification:

Answer 7

•some bacteria use the oxygen from NO3-, the N2(g) is returned back to atmosphere.
•works best (only) in anaerobic conditions.

Question 8

Human impacts:

Answer 8

•agriculture removes nitrogen from the soil.
•deforestation removes nitrogen from soil.
•fertilizers return nitrogen and phosphorus to soil.
-may create acidic soil and can limit types of bacteria that can grow (therefore less decomposition).
-fertilizer can run-off into H2O and cause algal blooms—> cause decreased O2 levels—> fish die—> and increases the number of decomposers (bacteria).
•overpopulation: too much excretion (nitrogen found in urine).

Question 9

Fertilizer and farming:

Answer 9

•adding fertilizer to the soil is expensive. Crop rotation is a common farming method, which involves growing legumes (such as alfalfa and clover) one season and crops (such as corn) the next. This helps maintain a high nitrogen content in the soil!
•nitrogen-fixing bacteria live in the round nodules on the roots of legume plants.

Question 10

Denitrification environments:

Answer 10

•denitrifying bacteria function best in anaerobic conditions.
•aerating a lawn increases the oxygen which reduces the activity of these bacteria, increasing the access to nitrogen for plants.
•acidic soils and waterlogged areas enhance denitrification.
•in bogs, where there is a lot of standing water, denitrification is so efficient many plants have to acquire nitrogen by digesting insects.
-ex) Venus flytrap.