The Nitrogen Cycle - Stages

Question 1

What do living things need the element nitrogen to make?

4

Answer 1

Proteins

DNA

RNA

Other biomolecules

Question 2

What is the chemical formula for nitrogen gas?

Answer 2

N2

Question 3

What percentage of the air is made up of nitrogen gas?

Answer 3

79%

Question 4

Why can’t the nitrogen gas in air be used by organisms?

Answer 4

Because it is inert or unreactive and cannot be used by plants and animals

Question 5

Define nitrogen fixation.

Answer 5

Nitrogen fixation is the conversion of nitrogen gas into ammonia (NH3), ammonium (NH4+) or nitrate (NO3-)

Question 6

What is the formula for ammonia?

Answer 6

NH3

Question 7

What is the formula for ammonium?

Answer 7

NH4+

Question 8

What is the formula for nitrate?

Answer 8

NO3-

Question 9

What is nitrogen fixation carried out by?

4

Answer 9

Volcanic action

Lightning

Industrial processes

By nitrogen-fixing bacteria

Question 10

Where can nitrogen-fixing bacteria be found?

2

Answer 10

They can be found free in the soil

They may be associated with the roots of certain plants

Question 11

Some nitrogen-fixing bacteria may be associated with the roots of certain plants, where exactly are they found.

Answer 11

They live in nodules (swellings) on the roots of a group of plants called legumes,

Question 12

Some nitrogen-fixing bacteria live in nodules on the roots of what group of plants?

Answer 12

Legumes

Question 13

Where do nitrogen-fixing bacteria live in legumes?

Answer 13

In nodules on the roots

Question 14

Give four examples of legumes which have nitrogen-fixing bacteria living in nodules on their roots.

Answer 14

Clover

Soya beans

Peas

Beans

Question 15

Is nitrogen-fixation an aerobic or anaerobic process?

Answer 15

Nitrogen fixation is an anaerobic process

Question 16

Nitrogen fixation is an anaerobic process, what does this mean?

Answer 16

This means it does not require oxygen

Question 17

Nitrogen-fixation is an anaerobic process, how is it adapted for this process.

Answer 17

The nodules on roots allow the nitrogen-fixing bacteria to escape from oxygen

Question 18

How can the relationship between the nitrogen-fixing bacteria and the legume be described?

Answer 18

It can be described as a form of symbiosis

Question 19

Describe the symbiotic relationship between the nitrogen-fixing bacteria and the legume.

Answer 19

The bacteria get food and the plant gets nitrates (this is technically mutualism)

Question 20

What are nitrates converted into?

Answer 20

They are converted into plant and animal protein, DNA and RNA

Question 21

What organisms bring about decomposition?

Answer 21

Bacteria and fungi of decay

Question 22

What do bacteria and fungi of decay cause the decomposition of?

Answer 22

The decomposition of dead organisms

Question 23

Where are bacteria and fungi of decay mostly found?

Answer 23

They are mostly found in the soil

Question 24

What is released when bacteria and fungi of decay decompose dead organisms?

Answer 24

These organisms release nitrogenous compounds such as ammonia (NH3) into the soil

Question 25

Define nitrification.

Answer 25

Nitrification is the conversion of ammonia and ammonium (NH4+) compounds to nitrite and then to nitrate

Question 26

What carries out nitrification?

Answer 26

Nitrifying bacteria

Question 27

Where are nitrifying bacteria found?

Answer 27

They are found in the soil

Question 28

How do nitrifying bacteria get their food?

Answer 28

They are chemosynthetic, i.e. they make their own food (normally in darkness in the soil) using energy from chemical reactions

Question 29

What happens to some of the nitrate made by nitrifying bacteria?

Answer 29

Some of the nitrate formed in the soil is absorbed and used by plants

Question 30

Define denitrification.

Answer 30

Denitrification is the conversion of nitrates to nitrogen gas

Question 31

What carried out denitrification?

Answer 31

Denitrifying bacteria

Question 32

Where are denitrifying bacteria found?

Answer 32

In the soil

Question 33

Are denitrifying bacteria aerobic or anaerobic?

Answer 33

They are anaerobic

Question 34

Where is the preferred place for denitrifying bacteria to live?

Answer 34

Swampy soil or deep down in the soil where water collects to produce anaerobic conditions

Question 35

Why do denitrifying bacteria like living deep down in the soil?

Answer 35

As water collects here to produce anaerobic conditions

Question 36

List the stages of the nitrogen cycle. | 6

Answer 36

1. Describe the need for the nitrogen cycle 2. Nitrogen fixation 3. Decomposition 4. Nitrification 5. Plants absorb nitrate 6. Denitrification