B13 - Nutrient Cycles

Question 1

Define a saprobiont.

Answer 1

A microorganism which feeds on dead or decaying organic matter.

Question 2

What is the role of saprobionts in the decomposition and recycling of nutrients?

Answer 2

• Secrete enzymes into organic matter
• Break larger, insoluble molecules into smaller, soluble ones
• These can be either stored in the saprobiont, or they use them in respiration to provide energy

Question 3

What are the stages of the nitrogen cycle?

Answer 3

1. Nitrogen fixation
2. Ammonification
3. Nitrification
4. Denitrification

Question 4

Explain the significance of nitrogen to living organisms.

Answer 4

Plants take up nitrates via active transport and use them to make:
- Amino acids
- NAD/NADP
- Nucleic acids

Question 5

Why can’t organisms use nitrogen directly from the atmosphere?

Answer 5

N2 is very stable due a strong covalent triple bond.

Question 6

What happens in nitrogen fixation?

Answer 6

Atmospheric nitrogen is converted into ammonia by nitrogen-fixing bacteria in the soil.

Question 7

Where are mutualistic nitrogen-fixing bacteria found?

Answer 7

Live in nodules of roots of peas and beans (legumes)

Question 8

What happens in ammonification?

Answer 8

Production of ammonia from organic compounds
- By-product of saprobiont nutrition

Question 9

Outline the process of nitrification.

Answer 9

Oxidation of ammonium ions into nitrate ions which release energy for bacteria.
- Ammonium to nitrite
- Nitrite to nitrate

Question 10

What happens in denitrification?

Answer 10

Nitrates turn into atmospheric nitrogen - this happens in anaerobic conditions such as waterlogged soil.

Question 11

How does the nitrogen cycle benefit life on Earth?

Answer 11

Provides plants and other organisms with nitorgen, which helps them produce proteins and DNA.