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SNC1D
Date: _________________
The Nitrogen Cycle
Read Nelson Science 10, pages 66-68.
1. What two materials is nitrogen required for?
_____proteins_____________
_______DNA_________________
2. Although nitrogen gas (N2) makes up 79% of the atmosphere, it cannot be used by plants and
animals. Why not?
The nitrogen gas in the atmosphere is too stable for them to break it down.
3. From what form of nitrogen do plants and animals obtain
their nitrogen requirements?
_____nitrates__________
4. Explain the term “nitrogen fixation” and state the two ways it is carried out:
Nitrogen fixation: The conversion of nitrogen into nitrates
Method 1:
The energy from lightning combines oxygen and nitrogen in the air
Method 2:
Nitrogen-fixing bacteria convert nitrogen into nitrates
5. Plants and nitrogen-fixing bacteria:
a) Name 3 plants (legumes) that are the host to nitrogen-fixing bacteria:
____clover_____________
_______peas_________
______alfalfa_________
b) How do the nitrogen-fixing bacteria benefit from the plants?
The plant produces sugar which the bacteria need.
c) How do the legume plants benefit from the nitrogen-fixing bacteria?
The bacteria provide the plant with a supply of nitrates.
d) How do other plants benefit from the nitrogen-fixing bacteria?
Any extra nitrates produced move into the soil, which nearby plants can use.
6. How do animals get their nitrogen?
They eat the plants, or eat the animals that eat the plants.
7. Denitrification
a) Explain the term denitrification.
Breaking down nitrates into nitrites, which then break down into nitrogen gas.
b) Why is this process not beneficial to living organisms?
It depletes the soil of nitrates, so the plants cannot grow as well as before.
SNC1D
The Nitrogen Cycle
Date: _________________
8. Older lawns often have bacteria in them that carry out denitrification (called denitrifying
bacteria). Why is it good practice to aerate lawns?
Oxygen can kill the denitrifying bacteria, so aerating the lawn will expose them to
fresh air, killing them.
9. Why are bogs and swamps low in nitrogen?
There are many decomposers, turning nitrates into nitrites into nitrogen.
The nitrates are constantly leached away by too much water – this is one of the problems
that over-watering plants can cause in the city as well.
10. How can you tell if a plant is growing in nitrogen-poor soil?
Its colour will be a dull, yellowish-green instead of a dark-green.
The Nitrogen Cycle:
SNC1D
Date: _________________
The Nitrogen Cycle
Read Nelson Science 10, pages 66-68.
1. What two materials is nitrogen required for?
__________________________
___________________________
2. Although nitrogen gas (N2) makes up 79% of the atmosphere, it cannot be used by plants and
animals. Why not?
3. From what form of nitrogen do plants and animals obtain
their nitrogen requirements?
_______________________
4. Explain the term “nitrogen fixation” and state the two ways it is carried out:
Nitrogen fixation:
Method 1:
Method 2:
5. Plants and nitrogen-fixing bacteria:
a) Name 3 plants (legumes) that are the host to nitrogen-fixing bacteria:
_______________________
________________________
______________________
b) How do the nitrogen-fixing bacteria benefit from the plants?
c) How do the legume plants benefit from the nitrogen-fixing bacteria?
d) How do other plants benefit from the nitrogen-fixing bacteria?
6. How do animals get their nitrogen?
7. Denitrification
a) Explain the term denitrification.
b) Why is this process not beneficial to living organisms?
SNC1D
The Nitrogen Cycle
Date: _________________
8. Older lawns often have bacteria in them that carry out denitrification (called denitrifying
bacteria). Why is it good practice to aerate lawns?
9. Why are bogs and swamps low in nitrogen?
10. How can you tell if a plant is growing in nitrogen-poor soil?
The Nitrogen Cycle: