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THE NITROGEN CYCLE
3133
Most of the nitrogen on Earth is found in the atmosphere. Bacteria in the soil
change the nitrogen found in the atmosphere into a form usable by plants.
In this unit you should learn how to do the following:
1.
2.
3.
4.
Draw and explain the nitrogen cycle.
Explain the role of bacteria in the nitrogen cycle.
Distinguish between usable and non-usable nitrogen.
Identify organic compounds made with nitrogen that are needed by all living
organisms.
5. Use the following words correctly:
Nitrogen
nitrogen cycle
bacteria
atmosphere
The Nitrogen Cycle
3133
Nitrogen is needed by all living things to create proteins and DNA. The process
where nitrogen flows from the environment into living organisms and then is
recycled back into the environment is called the Nitrogen Cycle. This cycle allows
nitrogen to be available to all living things so they may grow and reproduce.
How the Nitrogen Cycle Works:
Most of the nitrogen is found as a gas in the atmosphere. In fact, most of
what you breathe in is nitrogen, not oxygen. Unfortunately living things, including
humans, cannot use the nitrogen that is found in the air. So, we simply breathe it
out again.
There are certain bacteria found in soil that can turn the unusable form of
nitrogen into a form of nitrogen, called ammonia that is useful to plants. When
these bacteria act on the unusable form of nitrogen they convert into a usable
form of nitrogen. Plants absorb this useful source of nitrogen, ammonia, into their
roots and use it as a part of the plant. When animals that feed on plants can then
consume the nitrogen and use it for their body. So nitrogen changed from a gas in
the atmosphere to become a part of a plant or animal.
When a plant or animal dies, the nitrogen is once again released by the
action of decomposers into the atmosphere. So the nitrogen changed from being
a part of a plant or animal back into nitrogen gas in the atmosphere. The cycle
begins again.
REMEMBER THIS !!!
Certain bacteria found in the soil are responsible for changing nitrogen into
a form that can be use by plants.
Question 1. How would you explain the nitrogen cycle?
Question 2. What would happen if all of the bacteria in the ground stopped
working?
Question 3. What is nitrogen used for in living organisms?
Interesting Scientific Fact: 78% of the air we breathe is nitrogen. None of it is
useful to plants or other animals.
Summary
The Nitrogen Cycle (3133)
Nitrogen is a very important element to living things. Nitrogen atoms are
found in DNA, RNA, proteins and ATP. Nitrogen atoms must be used over and over
again so that new molecules can be made and used by all living things.
In the atmosphere, nitrogen gas is the most abundant gas. Plants and
animals cannot use nitrogen gas, but certain bacteria can change it into a usable
form. Certain bacteria are able to change nitrogen gas into a different
molecule that is usable by plants. These bacteria live in the soil. So the useful
nitrogen molecules they make are found in the soil. Because of this, plants can
take these useful nitrogen molecules into their roots and use them to make DNA,
RNA, proteins, and ATP.
Once a plant is consumed by an animal, the nitrogen is transferred to
the animal. Animals also need to make DNA, RNA, protein, ATP. Animals must eat
plants or other animals to get the nitrogen they need.
Plants and animals have nitrogen in the molecules of their bodies. When a
plant or animal dies, the decomposition of their body returns molecules
containing nitrogen to the atmosphere. When they come into contact with
certain soil bacteria they are changed into a useful form. Then plants use these
molecules to make new molecules which can be consumed by animals. The plants
and animals eventually die and are decomposed. Their nitrogen is then released
into the atmosphere. This is the nitrogen cycle.
Nitrogen Cycle
Test Yourself
Fill in the Blank
DNA
proteins
- Two words will be used twice.
RNA
atmosphere
ATP
bacteria
producers
consumers
waste
1. Nitrogen is very important to _____________, _______________ and
__________________.
2. Bacteria convert nitrogen in the _______________ to a molecule that plants
can take into their roots.
3. Once nitrogen containing molecules are in their roots, plants can make molecules
like _________, __________, _____________, and _____________.
4. __________________ must also make these molecules so they eat plants to
get nitrogen containing molecules.
5. Animals return nitrogen to the soil in their _____________.
6. _________________ can convert nitrogen containing molecules back to
gaseous nitrogen.
True or False
_____ 1.
_____ 2.
_____ 3.
_____ 4.
Nitrogen atoms are found in DNA and RNA.
Nitrogen atoms are found in proteins and carbohydrates.
Nitrogen is the most abundant gas in Earth’s atmosphere.
Nitrogen gas in the atmosphere is taken in by plants and used for
photosynthesis.
_____ 5. Nitrogen gas in the atmosphere cannot be used by plants.
_____ 6. Nitrogen gas in the atmosphere cannot be used by animals.
_____ 7. Nitrogen gas in the atmosphere cannot be used by bacteria.
_____ 8. Some bacteria are able to change nitrogen gas into a different molecule
that plants can use.
_____ 9. Plants take molecules containing nitrogen into through their roots.
_____ 10. Animals eat plants or other animals to get the nitrogen they need.
_____ 11. Animals return nitrogen to the atmosphere when they decompose.
_____ 12. Animals return nitrogen to bacteria.
_____ 13. The decomposition of dead plants and animals returns nitrogen
containing molecules to the air.
_____ 14. . The decomposition of dead plants and animals returns nitrogen
containing molecules to the soil.
_____ 15. Bacteria are able to change nitrogen contain molecules into atmospheric
nitrogen.
Answer the Following
1. What molecules in living things contain nitrogen?
2. How does nitrogen in the atmosphere get into nitrogen containing molecules in
the soil?
3. How do plants get nitrogen?
4. How do animals get nitrogen?
5. How is nitrogen gas returned to the atmosphere?
6. Draw and explain the nitrogen cycle.
The Nitrogen Cycle (3133)
Answer Sheet
Question 1. How would you explain the nitrogen cycle?
Question 2. What would happen if all of the bacteria in the ground stopped
working?
Question 3. What is nitrogen used for in living organisms?