Nitrogen cycle

Question 1

Give biological molecules that contain nitrogen.

Answer 1

• Proteins.
• Nucleic acids.
• ATP.
• Urea.

Question 2

Give key processes in nitrogen cycle.

Answer 2

• Saprobiotic nutrition.
• Nitrogen fixation.
• Ammonification.
• Nitrification.
• Denitrification.

Question 3

Role of microorganisms?

Answer 3

• Play vital role in recycling chemical elements ie. phosphorous/ nitrogen.

Question 4

True or False

Organisms can directly absorb the N2 in atmosphere/ convert it into nitrogen-containing compounds.

Answer 4

• False.
• Microorganisms needed to convert nitrogen gas into nitrogen-containing substances that plants/ animals absorb.

Question 5

What are saprobionts/ what do they do?

Answer 5

• Bacteria/ fungi that obtain their nutrients by secreting extracellular enzymes onto dead, organic matter.
• Digest externally and absorb breakdown products.

Question 6

Different micro-organisms in nitrogen cycle. Brief description of their role?

Answer 6

• Saprobionts: fungi/ bacteria that decompose dead, organic matter.
• Nitrogen fixing bacteria: nitrogen –> ammonium ions.
• Nitrifying bacteria: ammonium ions –> nitrite –> nitrate.
• Denitrifying baceria: nitrates –> nitrogen.

Question 7

What is a “mutalistic relationship?”

Answer 7

• A mutalistic relationship is interaction between two species in which both organisms benefit.

Question 8

What is 1st stage of nitrogen cycle?

Answer 8

• Nitrogen fixation.
• Nitrogen fixing bacteria found in root nodules of legumes.
• Converts nitrogen into ammonium ions: NH₄⁺.
• Nitrogen-fixing bacteria also in soil (not just root nodules!)

() - extra info for clarification.

Question 9

What is 2nd stage of nitrogen cycle?

Answer 9

• Ammonification.
• Conversion of nitrogen-containing compounds (ie. urea/ proteins/ nucleic acid) into ammonia.
• Saprobionts (bacteria/ fungi) convert these molecules to ammonia.
• Ammonia converted to ammonium ions in the soil.

Question 10

True or False

All nitrogen-fixing bacteria are found in root nodules of legumes.

Answer 10

• False.
• Nitrogen-fixing bacteria also found in the soil.

Question 11

Describe the relationship between nitrogen fixing bacteria in root nodules and legumes plants.

Answer 11

• Mutalistic relationship.
• Bacteria –> plant: convert nitrogen into ammonium ions that can be used by plants.
• Plant –> bacteria: supplies bacteria with organic compounds from photosynthesis.

Question 12

What is 3rd stage of nitrogen cycle?

Answer 12

• Nitrification.
• Nitrifying bacteria oxidise ammonium ions into nitrite ions: NO₂⁻
• Then, oxidise nitrite ions into nitrate ions: NO₃⁻
• NO₃⁻ ions assimilated into plant by active transport/ make nitrogen-containing compounds (cycle repeats itself)
• Nitrifying bacteria = aerobic, require well-aerated soil.

() - extra info for clarification.

Question 13

True or False

Saprobitioic nutrition and ammonification are the same process.

Answer 13

• False.
• Saprobitioic nutrition: how decomposers feed VS ammonification: conversion of nitrogen-containing compounds –> ammonium ions.

Question 14

What is 4th stage in nitrogen cycle?

Answer 14

• Denitrification.
• Conversion of nitrates to nitrogen gas.
• Denitrying bacteria require anaerobic conditions (ie. water-logged/ poorly-aerated soil.)
• Reduces availability of nitrates for plants.

Question 15

Is denitrification useful for agriculture?

Answer 15

• No.
• Reduces availability of nitrates in soil, denitrying bacteria converts nitrates to nitrogen gas.

Question 16

What type of reaction is nitrification?

Answer 16

• Oxidation (from ammonium –> nitrITE –> nitrate.)

Question 17

Give chemical formula for:
- Ammonium
- Nitrite ions.
- Nitrate ions.

Answer 17

• NH₄⁺
• NO₂⁻
• NO₃⁻

Question 18

What is assimilation?

Answer 18

• Movement of substances into cells where they can be used to make other molecules.