the nitrogen cycle

sending nitrogen back to the atmosphere

Turning nitrate back into nitrogen gas, the process of denitrification, happens through the work of denitrifying bacteria. These bacteria often live in swamps and lakes. They take in the nitrate and release it back to the atmosphere as nitrogen gas. Just like the carbon cycle, human activities impact the nitrogen cycle. These human activities include the burning of fossil fuels, which release nitrogen oxide gasses into the atmosphere. Releasing nitrogen oxide back into the atmosphere leads to problems like acid rain.

the nitrogen cycle

Like water and carbon, nitrogen is also repeatedly recycled through the biosphere. This process is called the nitrogen cycle. Nitrogen is one of the most common elements in living organisms. It is important for creating both proteins and nucleic acids, like DNA. The air that we breathe is mostly nitrogen gas (N2 ), but, unfortunately, animals and plants cannot use the nitrogen when it is a gas. In fact, plants often die from a lack of nitrogen even through they are surrounded by plenty of nitrogen gas. Nitrogen gas (N2 ) has two nitrogen atoms connected by a very strong triple bond. Most plants and animals cannot use the nitrogen in nitrogen gas because they cannot break that triple bond. In order for plants to make use of nitrogen, it must be transformed into molecules they can use. This can be accomplished several different ways ( Figure 1.1). Lightning: When lightening strikes, nitrogen gas is transformed into nitrate (NO3 ) that plants can use. Nitrogen fixation: Special nitrogen-fixing bacteria can also transform nitrogen gas into useful forms. These bacteria live in the roots of plants in the pea family. They turn the nitrogen gas into ammonium (NH4 + ) (a process called ammonification). In water environments, bacteria in the water can also fix nitrogen gas into ammonium. Ammonium can be used by aquatic plants as a source of nitrogen. Nitrogen also is released to the environment by decaying organisms or decaying wastes. These wastes release nitrogen in the form of ammonium. Ammonium in the soil can be turned into nitrate by a two-step process completed by two different types of bacteria. In the form of nitrate, nitrogen can be used by plants through the process of assimilation. It is then passed along to animals when they eat the plants.

instructional diagrams

No diagram descriptions associated with this lesson


nitrogen is important for creating both proteins and carbohydrates.

a. true

-->  b. false

most plants and animals cannot use the nitrogen in nitrogen gas.

-->  a. true

b. false

the initial step of producing a nitrogen containing compound from nitrogen in the soil is

a) assimilation.

-->  b) ammonification.

c) nitrification.

d) denitrification.

the final step of releasing nitrogen gas back into the atmosphere is

a) assimilation.

b) ammonification.

-->  c) nitrification.

d) denitrification.

nitrogen gas is two nitrogen atoms held together by

a) a very strong single bond.

b) a very strong double bond.

-->  c) a very strong triple bond.

d) a nitrogen bond.

nitrogen enters the roots of plants in a process called

-->  a) assimilation.

b) ammonification.

c) nitrogen fixation.

d) nitrification.

what bacteria live in the root nodules of legumes?

a) denitrifying bacteria

b) nitrifying bacteria

-->  c) nitrogen-fixing bacteria

d) all of the above

diagram questions

No diagram questions associated with this lesson