1. A2 Biology NITROGEN CYCLE Unit 4
Populations
and
Environment
A2 Biology
Year 13
NITROGEN CYCLE
Explain how ammonification, nitrification, nitrogen fixation and denitrification contribute to the nitrogen cycle
Identify the microbes involved in ammonification, nitrification, denitrification, and nitrogen fixation
Describe how nitrogen gas can be converted into useful organic forms
Explain why it is important for plants in low nitrate conditions to have symbiotic relationships with bacteria
Learning Objectives (from spec):
The role of microorganisms in the carbon and nitrogen cycles in sufficient detail to
illustrate the processes of saprobiotic nutrition, ammonification, nitrification, nitrogen
fixation and denitrification.
(The names of individual species are not required.)

2. So why do plants struggle
78% of the Earth’s
atmosphere is N2 N2 N2
So why do plants struggle
to get enough nitrogen?
Students discuss in pairs why nitrogen gas although abundant cannot be used by plants

3. There’s lots of Nitrogen around!
It is an inert gas (the triple bond makes it very stable) so not easy to break apart in chemical reactions
Plants and Animals cannot use N2
Plants must secure their nitrogen in "fixed" form, i.e., incorporated in compounds such as:
nitrate ions (NO3-)
ammonia (NH3)/ammonium (NH+4)

4. The Nitrogen Cycle
Look at each of the information cards Each one talks about one part of the nitrogen cycle (the numbers on the cards indicate which part of the diagram they refer to) Use the cards to complete the diagram to explain what is happening at each arrow Words in purple are keywords you should use on your diagram. You must also add extra detail for some steps (eg. Enzymes involved)
Students look at the nitrogen cycle information cards and use them to complete the diagram of the nitrogen cycle (slide 5)
Terms legume and mycorrhizae not used on the info cards so make sure you mention these

5. This slide must be printed for students to complete using info cards

6. Found in roots of legumes
Nitrogenase enzyme needed
Protease and deaminase enzymes needed
Many plants have a symbiotic relationship with fungi called mycorrhizae that increases the surface area of the root system. Active transport used

7. Nitrogen-fixation video clip -http://www. youtube. com/watch
Use this to explain how one aspect of the nitrogen cycle occurs and to stress the importance of plant relationships with microbes. Through Q and A try to draw out ideas about what conditions most microbes will need to survive for nitrogen fixing or nitrification. Students should be aware that aerobic respiration is needed and therefore oxygen supply
Then pose question-How do plants survive where there are few microbes to convert nitrogen?
Again through Q and A try to draw out ideas about what other things may contain nitrogen so that students hopefully come up with the idea that other living things contain nitrogen

8. How do plants survive where there are few microbes
to convert nitrogen?
Video clip venus fly trap -

9. Why are carnivorous plants found in waterlogged soil?
Bacteria on the roots of legumes fix N2 into ammonia, which is absorbed by plant roots. Explain why nitrogen fixing bacteria in the root nodules of leguminous plants are an example of mutualism
Atmospheric
Nitrogen
The soil is waterlogged. Denitrification by bacteria returns nitrogen to the atmosphere.
Why are carnivorous plants found in waterlogged soil?
Ammonium
Compounds
Nitrites
Nitrogen Compounds
in Plants
Nitrates
Nitrogen Compounds
in Animals
Give students a copy of slide 9-questions based around SOLO taxonomy. They must attempt a few of the questions, or maybe 1 if they think they can do the extended abstract example
Ammonia created by saprobionts is made into nitrates by nitrifiying bacteria during nitrification. What are the 2 steps in nitrification?
An animal dies and ammonification is carried out by decomposers, turning the nitrogen compounds in their cells into an ammonium compound. What is the benefit of this to plants?

10. Example question and answer
Explain why nitrogen fixing bacteria in the root nodules of leguminous plants are an example of mutualism
Answer:
Nitrogen fixing bacteria convert nitrogen gas, which is inaccessible to plants directly, into nitrates. This can be taken up directly by the roots of the plant. The bacteria themselves get glucose that the plant makes. This is useful because it can be used in respiration by the bacteria. Nitrogen fixing bacteria need lots of glucose.
A=Add something they have missed
B= Build on an idea * that could be more detailed
C= Challenge/Correct anything you disagree with
students use green pens to Add, build on, and challenge the answers written
If doing the mutualism question students should pick up on things missing like: photosynthesis not mentioned directly, detail on glucose being important because nitrogen fixing uses a lot of energy, incorrect use of nitrate where it should be ammonia etc.

11. Example question and answer
Explain why nitrogen fixing bacteria in the root nodules of leguminous plants are an example of mutualism
Answer:
Nitrogen fixing bacteria convert nitrogen gas, which is inaccessible to plants directly, into nitrate. This can be taken up directly by the roots of the plant. The bacteria themselves get glucose that the plant makes. This is useful because it can be used in respiration by the bacteria. Nitrogen fixing bacteria need lots of glucose.
A=Add something they have missed
B= Build on an idea * that could be more detailed
C= Challenge/Correct anything you disagree with

12. Example question and answer
Describe how waterlogged soil can cause nitrate to be removed from the soil
Answer: Flooded wetlands give an opportunity for nitrogen fixation process to take place. In this process, nitrate is converted into nitrogen gas, which is released into the atmosphere. Denitrification requires aerobic conditions. Useful nitrogen fixing bacteria are not able to survive in these conditions.
A=Add something they have missed
B= Build on an idea * that could be more detailed
C= Challenge/Correct anything you disagree with
students use green pens to Add, build on, and challenge the answers written
If doing the flooding question they should pick up key terms that are missing e.g. denitrifying bacteria etc.

13. Example question and answer
Describe how waterlogged soil can cause nitrate to be removed from the soil
Answer:
Flooded wetlands give an opportunity for nitrogen fixation process to take place. In this process, nitrate is converted into nitrogen gas, which is released into the atmosphere. Denitrification requires aerobic conditions. Useful nitrogen fixing bacteria are not able to survive in these conditions.
A=Add something they have missed
B= Build on an idea * that could be more detailed
C= Challenge/Correct anything you disagree with