A2 BiologyYear 13

Unit 4Populations

and Environment

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

Explain how ammonification, nitrification, nitrogen fixation and denitrification contribute to the nitrogen cycle

So why do plants struggle to get enough nitrogen?

N2

N2

78% of the Earth’satmosphere is N2

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 reactionsPlants 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)

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)

The Nitrogen Cycle

Found in

roots

of

legumes

Man

y plan

ts ha

ve a

sym

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relati

onsh

ip with

fung

i call

ed

myc

orrh

izae t

hat i

ncre

ases

the s

urfa

ce ar

ea of

the r

oot

syste

m. A

ctive

tran

spor

t use

d

Nitroge

nase e

nzyme

needed

Protease and

deaminase enzymes

needed

How do plants survive where there

are few microbes to convert nitrogen?

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

The soil is waterlogged. Denitrification by bacteria

returns nitrogen to the atmosphere.

Why are carnivorous plants found in waterlogged soil?

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?

Ammonia created by saprobionts is made into nitrates by nitrifiying

bacteria during nitrification. What are the 2 steps in nitrification?

Example question and answerExplain why nitrogen fixing bacteria in the root nodules of leguminous plants are an example of mutualismAnswer: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 missedB= Build on an idea * that could be more

detailedC= Challenge/Correct anything you disagree

with

Example question and answerExplain why nitrogen fixing bacteria in the root nodules of leguminous plants are an example of mutualismAnswer: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 missedB= Build on an idea * that could be more

detailedC= Challenge/Correct anything you disagree

with

Example question and answerDescribe how waterlogged soil can cause nitrate to be removed from the soilAnswer: 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 missedB= Build on an idea * that could be more

detailedC= Challenge/Correct anything you disagree

with

Example question and answerDescribe how waterlogged soil can cause nitrate to be removed from the soilAnswer: 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 missedB= Build on an idea * that could be more

detailedC= Challenge/Correct anything you disagree

with