The nitrogen cycle is one of the most important and complex of the biogeochemical cycles. It is important because nitrogen: A. is a greenhouse gas B. is an essential part of biological molecules such as proteins and nucleic acids (DNA) C. is the most toxic element to living organisms D. dilutes the oxygen in the atmosphere causing respiratory problems E. is a crucial part of the process of photosynthesis

B

Explanation:

Nitrogen is an inorganic nutrient needed by virtually all organisms including plants and animals. Its production and consumption in the biogeochemical cycle is of utmost importance as it is a major component of the structures of biomolecules in living organisms. It is a structural component of amino acids (in the NH2 group) that forms proteins.

Nitrogen is also involved in the structural build up of the genetic material (DNA, RNA) of living organisms. It is an element of one of the major components (nitrogenous bases) of nucleotides that assemble to form RNA and DNA.

Hence, a deficiency of Nitrogen can lead to serious structural problems for such organism.

the major parts of the digestive system:

salivary glands.

pharynx.

esophagus.

stomach.

small intestine.

large intestine.

rectum.

accessory digestive organs: liver, gallbladder, pancreas.

the second type of galaxy is called a barred spiral, which has a thing called a bar straddling the nucleus