Which of the following pathways represents the most probable flow of nitrogen through an ecosystem?

a.) animals → bacteria → air → plants → bacteria → animals
b.) air → bacteria → plants → animals → bacteria → air
c.) air → plants → bacteria → animals → bacteria → air
d.) animals → plants → bacteria → air → bacteria → animals

B

Explanation:

The reason that B is the correct answer, is as follows:

1. There is nitrogen in the air, in the form of N₂. Animals and plants cannot assimilate nitrogen in this form, so it is converted to ammonia, nitrates and nitrites by bacteria.

2. Once it is in the form of nitrogen containing compounds, plants then absorb the compounds and can use the nitrogen in them to build amino acids and other essential structures.

3. Animals will consume plants, and that way obtain the nitrogen stored in the plants. Once they have eaten the plants, they then absorb the nitrogen to use it in the formation of our own proteins and amino acids.

4. When there is too much nitrogen in our body, it is excreted as ammonia or urine, once in that form, bacteria then convert the nitrogen containing compounds back into atmospheric nitrogen in the form of N₂.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.

i think the answer is a.keratin is the pigment responsible for skin color.