4: Nutrient Cycles

Question 1

Under what conditions does nitrogen fixation occur?

Answer 1

Aerobic

Question 2

Under what conditions does denitrification occur?

Answer 2

Anaerobic

Question 3

How does the nitrogen in dead plants end up as proteins in a animal?

Answer 3

• organic matter in dead plant converted to ammonia by saprobiotic bacteria by extra-cellular digestion (ammonification)
• ammonia converted to nitrites and then nitrates by nitrifying bacteria (nitrification)
• nitrates absorbed by active transport into plant roots
• nitrates assimilated by plant into proteins
• plant eaten by animal
• animal assimilates the nitrogen containing compounds (usually amino acids) into proteins

Question 4

How does nitrogen gas in the air end up as proteins in a plant?

Answer 4

• nitrogen gas converted to ammonia by nitrogen fixing bacteria in aerobic conditions (nitrogen fixation)
• ammonia converted to nitrites and then nitrates by nitrifying bacteria (nitrification)
• nitrates absorbed by active transport into plants roots
• nitrates assimilated into proteins in the plant

Question 5

Is nitrification oxidation or reduction?

Answer 5

Oxidation

Question 6

What type of digestion is done by saprobiotic organisms?

Answer 6

Extracellular

Question 7

Explain why the carbon dioxide concentration of the atmosphere is often less on a summers day than a winters day

Answer 7

Light intensity is greater and the temperature is higher, more CO2 is fixed so less in atmosphere

Question 8

How does carbon in a dead mouse become available to a plant cell

Answer 8

Saprophytic bacteria use extra cellular digestion to decompose de dad organism, absorbs products
Respires product with O2
CO2 released in to atmosphere
Diffuses into leaf through stomata

Question 9

What is leaching?

Answer 9

the process by nutrients are removed from the soil. Rain water will dissolved any soluble nutrients, such as nitrates, and carry them deep into the soil, end up in water sources

Question 10

Describe nitrification

Answer 10

Nitrifying bacteria oxidise ammonia into nitrites and then nitrates

Question 11

Describe nitrogen fixation

Answer 11

Root nodule bacteria in leguminous plant convert atmospheric nitrogen to ammonia

Question 12

Describe ammonification

Answer 12

The production of ammonia from nitrogen containing compounds e.g. proteins, DNA, urea

Question 13

Describe denitrification

Answer 13

In anaerobic condition, denitrifying bacteria convert nitrates to nitrogen gas