The Nitrogen Cycle

ICS Book Pages 569-572

• The nitrogen cycle is the movement of nitrogen atoms through organisms in the food chain and the abiotic community.

• Nitrogen is an atom needed for life.– It is used in the bodies of plants and animals to

make proteins and DNA.

Questions 1 and 2

1) Why is nitrogen important to living things?2) Do living things need more carbon or

nitrogen? Explain.

• Most nitrogen is found in the atmosphere (sky) as a gas.– But it can’t be used by living things in this form.– Nitrogen gas is very stable and doesn’t react

• Most living things can only get nitrogen when it is found in a molecule called nitrate (NO3

-)– Nitrogen fixation is when nitrogen gas is changed

into nitrates, allowing living things to use it.

• Most nitrates are created by special microorganisms.– These Nitrogen fixing bacteria live in the soil and

create most of the nitrogen (nitrates) used by living things.

– They live on the roots of plants called legumes.– Examples: Clover, soybeans, peas, alfalfa

Question 3

3) How do plants get nitrogen into their bodies?

• Nitrogen fixing bacteria create nitrates the plant can use, and animals get the nitrogen in their food.– Herbivores get nitrates by eating the plant.– Carnivores get the nitrates by eating these

animals, etc.

Questions 4-6

4) How do animals get nitrogen into their bodies?

5) What would happen if there were no nitrogen in the soil?

6) EXTRA CREDIT: What kinds of plants should a vegetarian eat? Why?

• When organisms create urine, feces, or they die; nitrogen is released and used by decomposers.– Nitrogen fixing bacteria change it back to nitrates

that plants can use again.– This is why manure and fertilizers are used to

return nutrients like Nitrogen back to the soil.

Last Questions!

7) How does nitrogen get into the ground?8) When they were farming, Native Americans

used to put a dead fish in the ground with their seeds. Why did they do that?