Energy Transfers in and Between Organisms: Nutrient Cycles - Nitrogen Cycle

Question 1

Why do organisms need nitrogen?

Answer 1

• Plants and animals need nitrogen to make proteins and nucleic acids (DNA and RNA)

Question 2

What are the four main processes in the nitrogen cycle?

Answer 2

• Nitrogen fixation
• Ammonification
• Nitrification
• Denitrification

Question 3

Draw the nitrogen cycle

Answer 3

Question 4

What is nitrogen fixation?

Answer 4

• When nitrogen gas in the atmosphere is turned into ammonium ions by bacteria called Rhizobium
• Rhizobium are found in the root nodules of leguminous plants (e.g peas, beans)
• Plants absorb the ammonium ions to make nitrogen compounds

Question 5

What type of relationship do Rhizobium and plants have?

Answer 5

• Mutualistic relationship

- Both species benefit

Question 6

Which bacteria is involved in nitrogen fixation?

Answer 6

• Rhizobium

Question 7

What is an ammonium ion?

Answer 7

• NH4^+

Question 8

What is ammonification?

Answer 8

• When nitrogen compounds from dead organisms and animal waste are turned into ammonia, then ammonium ions by saprobionts

Question 9

What is nitrification?

Answer 9

• When ammonium ions in soil are changed into nitrates, so they can be used by plants
• First, nitrifying bacteria called Nitrosomonas change ammonium ions into nitrites
• Then other nitrifying bacteria called Nitrobacter change nitrites into nitrates

Question 10

Name the bacteria involved in nitrification in order

Answer 10

• Nitrosomonas

- Nitrobacter

Question 11

Give the formula of nitrites

Answer 11

• NO2^-

Question 12

Give the formula of nitrates

Answer 12

• NO3^-

Question 13

Which are produced first in nitrification: nitrites or nitrates?

Answer 13

• First, nitrites (NO2^-)

- Second, nitrates (NO3^-)

Question 14

What is denitrification by bacteria?

Answer 14

• When denitrifying bacteria convert nitrates in soil into nitrogen gas
• They use nitrates to carry out anaerobic respiration and produce nitrogen gas

Question 15

Where may dentrification occur (anaerobic conditions)?

Answer 15

• Waterlogged soils

Question 16

How else can nitrogen enter an ecosystem?

Answer 16

• Lightning

- Haber process (artificial fertilisers)

Question 17

How does lightning release nitrogen compounds?

Answer 17

• Lightning fixes nitrogen gas into nitrogen oxides

Question 18

How does the Haber process release nitrogen compounds?

Answer 18

• N2(g) + 3H2(g) ⇌ 2NH3(g)

- Uses atmospheric nitrogen and produces ammonia