Question

The following organisms can incorporate nitrogen directly from the atmosphere into their bodies:

	Animals
	Cyanobacteria
	Bacteria
	Plants
	Phytoplankton

Plants acquire nitrogen from:

	A) Ammonium (NH4+) from bacteria
	B) Nitrogen gas in the atmosphere (N2)
	C) Ammonium (NH4+) from fertilizers
	D) A and C
	E) A, B, and C

The washing of fertilizer into bodies of water can lead to all of the following EXCEPT:

	Decreased oxygen levels in the water
	Higher concentrations of nitrogen in the atmosphere
	Increased growth of aquatic microorganisms
	Decreased numbers of aquatic animals
	Higher concentrations of nitrogen in the water

In nitrogen-limited ecosystems, legumes often dominate over other plants because they:

	obtain supplemental nitrogen by trapping insects and other prey.
	inhibit the growth of denitrifying bacteria around their roots, keeping more nitrate in the soil.
	can use symbiotic bacteria to fix atmospheric nitrogen.
	do not need nitrogen at all.
	have long taproots that can extract nitrogen from deeper down in the soil.

Answer 1

1.) B.) Cyanobacteria can incorporate nitrogen directly from atmosphere into there bodies. And the process is biological nitrogen fixation. Cyanobacteria possess nif Genes which encodes for the enzymes responsible for fixing the atmospheric nitrogen with the use of ATP , energy currency.

2.) D.) Plants acquire nitrogen from bacteria in the form of nitrates, ammonium ions. Mostly the nitrogen is taken up as nitrates or nitrites as ammonia or ammonium are quite toxic to the cells.

Plants can acquire nitrogen from fertilizers in the form of ammonium ions. Nitrogen deficienct soils are usually added with urea as a source of nitrogen.

3.) B.) Higher concentration of nitrogen in the atmosphere. Washing  of fertilizers into water bodies , enrichment of water bodies with nitrogen and phosphorous, leads to excessive growth of algae and in turn more excessive growth of microbes feeding the algae thus depleting the dissolved oxygen content which will cause the death of aquatic animals. This process is known as Eutrophication.

4.) C.) In nitrogen limited ecosystems , legumes often dominates over other plants because they can use symbiotic bacteria to fix atmospheric nitrogen. Legumes harbors these bacteria either in there root nodules or in leaf nodules.This is known as symbiotic nitrogen fixation.  Example : Rhizobium - Pea family , Frankia - Alnus ,etc.

Hope this will help you.