Nitrogen is a nutrient that organisms need to produce (12). Plants and animals cannot use the nitrogen that makes up a large percentage of the (13). The nitrogen is captured and converted into a form that is usable by plants in a process called (14). Nitrogen enters the food web when (15) absorb nitrogen compounds from the soil and use them to make proteins. (16) get nitrogen by eating plants or animals that contain nitrogen. Nitrogen is returned to the soil when animals (17) or when organisms die and (18). (19) break down organic matter found in organisms into (20). This compound is changed by organisms in the soil into other nitrogen compounds that can be used by plants. Finally, some soil bacteria convert nitrogen compounds into nitrogen gas, which returns to the atmosphere in a process called (21).

12. Protein 13. Atmosphere 14. Nitrogen fixation 15. Plants 16. Consumers 17. Urinate 18. Decay 19. Decomposers 20. Ammonia 21. Denitrification

Explanation:

12. Protein

Nitrogen is essential to organisms. It is the main constituent of amino acids, which is the building blocks of protein in organisms.

13. Atmosphere

Nitrogen occurs naturally as gas in the earth's atmosphere, accounts for about 78% of gases found in the atmosphere. This gaseous Nitrogen which is inert cannot be accessed by plants and animals for use.

14. Nitrogen fixation

For plants to be able to use the gaseous Nitrogen in the atmosphere, Nitrogen fixation has to take place. It involves the turning of gaseous Nitrogen in the atmosphere into ammonia. Nitrogen atoms is combined with Hydrogen atoms by enzyme called "nitrogenase". This enzyme is present in nitrogen-fixing bacteria.

15. Plants

Nitrogen enters the food web when plants assimilate nitrogen compounds from the soil to form nucleotides, amino acids, and other important chemicals in life.

16. Consumers

Consumers are mainly animals that feed on plants in an ecological food web in other to be able to use the amino and nucleic acids formed from Nitrogen as a major component. Consumers can be categorized as primary, secondary, and tertiary consumers.

17. Urinate

Nitrogen is very much concentrated in the urine of animals and also in their faeces. As animals urinate, Nitrogen is being returned to the soil.

18. Decay

Decay starts, as organisms die. The organisms start decomposing.

19. Decomposers

Decomposers are the bacteria in the soil that break down the nucleic and amino acids in dead organisms into nitrates and ammonia through a process called ammonification

20. Ammonia

This is the end result of the decomposition of dead organisms by decomposers

21. Denitrification

Compounds of nitrogen are turned back into gaseous nitrogen by anaerobic bacteria. This prevents