Nitrogen Cycle

Question 1

What is the nitrogen cycle

Answer 1

The nitrogen cycle shows how nitrogen gas is converted into nitrogen containing compounds in plants and animals and then how the nitrogen these compounds contain is recycled either back into the air or made available to other organisms.

Question 2

Why is it important

Answer 2

It is important as it shows how organisms obtain their amino acids and proteins which are required for growth.

Question 3

Define nitrification

Answer 3

The build up of nitrogen into amino acids and protein in plants and animals and the eventual breakdown of these compounds into nitrates that can be readily absorbed by plant roots

Question 4

Define denitrification

Answer 4

Denitrification is the process that converts nitrates back into nitrogen gas.

Question 5

Why is denitrification undesirable?

Answer 5

This is an undesirable process as it results in less nitrate being available in the soil and therefore reduced plant growth.

Question 6

What conditions does denitrification favour?

Answer 6

The process is favoured by anaerobic conditions in waterlogged soils.

Question 7

How does flooding decrease the concentration of nitrogen compounds in the soil?

Answer 7

Flooded soil results in anaerobic conditions therefore nitrification will be prevented and denitrification will be favoured. Nitrates could also be dissolved

Question 8

What are nitrogen fixing bacteria? What does it provide for the plant ?

Answer 8

Nitrogen fixing bacteria can be found living in the soil as well as in the root nodules in leguminous plants. The bacteria gain carbohydrates from the legumes and the legumes in turn provide a ready source of nitrates for the benefit of the plants

Question 9

Why is nitrate content of the soil important to plants?

Answer 9

It is important because nitrate content is how organisms obtain their amino acids and proteins required for growth

Question 10

Why do farmers apply fertilisers to their fields?

Answer 10

The nutrients in the soil after the crops are harvested is decreased and therefore adding artificial fertiliser will increase plant growth

Question 11

Why do farmers use artificial fertiliser instead of natural fertiliser?

Answer 11

The nutrients the plants need are available immediately and they are highly analysed to produce the exact amount of nutrients required

Question 12

Name the type of water pollution caused by fertilisers in river water

Answer 12

Eutrophication

Question 13

Describe the process of the nitrogen cycle

Answer 13

• nitrogen in the air
• nitrogen fixing bacteria in root modules provide the plant with nitrates for amino acids and proteins
• plants absorb nitrates and use them in building proteins
• animals feed on plant protein
• death and excretion of animal
• animals decompose through fungi and bacteria breaking down dead living material and releasing ammonia into the soil
• nitrifying bacteria convert ammonia to nitrates
• denitrifying bacteria convert nitrates into nitrogen gas

Question 14

Describe the types of bacteria and their preferred conditions in the nitrogen cycle

Answer 14

Decay - Aerobic, warm, moisture
Nitrifying - Aerobic, warm
Denitrifying - Anaerobic (e.g. waterlogged soils)
Nitrogen Fixing - Aerobic, warm

Question 15

Name the types of bacteria in the nitrogen cycle (4)

Answer 15

Decay
Nitrifying
Denitrifying
Nitrogen fixing

Question 16

What does decay do

Answer 16

Feeds on dead materials and releases ammonia

Question 17

What does nitrifying bacteria do ?

Answer 17

Convert ammonia to nitrates

Question 18

What do denitrifying bacteria do?

Answer 18

Converts nitrates info atmospheric nitrogen gas. This is a wasteful and undesirable process

Question 19

What does nitrogen fixing bacteria do?

Answer 19

Converts nitrogen gas to nitrates

Question 20

Name three examples of legumes

Answer 20

Peas
Beans
Clover

Question 21

What is the process of converting nitrogen from the atmosphere into nitrates called ?

Answer 21

Nitrogen fixation

Question 22

Describe how root hair cells uptake nitrogen (2)

Answer 22

• nitrate ions are taken into the root hair cell by the process of active transport (uptake)
• There is a steeper concentration gradient between the nitrate ions inside the root hair cell than outside and therefore oxygen is required to produce energy needed to move the nitrates against the concentration gradient

Question 23

How are root hair cells adapted to their function ?

Answer 23

They have a large surface area (due to their finger like shape)

Question 24

Apart from fertilisers, what else do farmers add to agricultural lands (2)

Answer 24

They add calcium (needed for plant cell walls) and magnesium (needed to make chlorophyll)

Question 25

What is the type of draining used for sewage or fertiliser that kills fish?

Answer 25

Runoff

Question 26

How does a high nitrate concentration in the water kill the fish? (5)

Answer 26

• High nitrate concentration causes aquatic plants in the water to grow much faster by providing the nitrates needed for growth
• The extra nitrates make the algae grow so quickly that the water surface becomes green in colour (algal bloom)
• This may block the light from Plants lower in the water (resulting in death) and the excessive growth of the surface plants uses up the nitrates and so they also die
• Dead plants are then decomposed by Aerobic bacteria which use up the oxygen dissolved in the water and the fish and other animals die due to lack of oxygen
• This process is called eutrophication