13.3 nutrient cycles

Question 1

What is the importance of nitrogen?

Answer 1

Required in living organisms to manufacture proteins and nucleic acids.

Question 2

How is nitrogen maintained in an agricultural vs. natural ecosystem?

Answer 2

Agricultural - nitrogen concentration restored by fertilisers
Natural- nitrogen cycle (Recycling)

Question 3

What are the 4 main stages of the nitrogen cycle

Answer 3

Ammonification
Nitrification
Nitrogen fixation
Denitrification

Question 4

The nitrogen cycle

what takes place during ammonification?

Answer 4

(saprobionts-> ammonium ions)
Saprobionts feed on faeces and dead organisms
releasing ammonia
which then forms ammonium ions in the soil

Question 5

The nitrogen cycle

what takes place during nitrification?

Answer 5

(ammonium ions -> nitrite ions -> nitrate ions)
(NH4+) -> (NO2-) -> (NO3-)
Nitrifying bacteria oxidise ammonium ions to nitrite ions which are then oxidised to nitrate ions.

Question 6

The nitrogen cycle

what takes place during nitrogen fixation?

Answer 6

Nitrogen gas is converted into nitrogen containing compounds.

Question 7

The nitrogen cycle

what takes place during nitrogen fixation by free-living nitrogen-fixing bacteria?

Answer 7

Reduce gaseous nitrogen to ammonia
(use to manufacture amino acids)
Release nitrogen when they die and decay.

Question 8

The nitrogen cycle

what takes place during nitrogen fixation by mutualistic nitrogen-fixing bacteria?

Answer 8

Plant acquires amino acids from bacteria.

Question 9

The nitrogen cycle

what takes place during denitrification?

Answer 9

(nitrate ions-> nitrogen in the atmosphere)

Denitrifying bacteria convert soil nitrates into gaseous nitrogen.

Question 10

nitrogen cycle see book for cycle MUST MAKE PAPER FC ON THIS

Answer 10

N fixation by free living bacteria
__________________________________
| |
| |
| nitrification denitrification |
V V
(NH4+)->(NO2-)->(NO3-)—————–> N in atmosphere
^ | /
| | /———————–/ n fixation
| v v mutualistic
| producers->consumers bacteria
| | |
| v v
|—————————saprobionts
ammonification

Question 11

Common features of nutrient cycle

What is the 1st step?

Answer 11

Nutrients are taken up by producers (plants) as simple inorganic molecules

Question 12

Common features of nutrient cycle

what happens after nutrients are taken up by producers (plants) as simple inorganic molecules?

Answer 12

Producer incorporates nutrient into a complex organic molecule.

Question 13

Common features of nutrient cycle

what happens after producer incorporates nutrient into a complex organic molecule?

Answer 13

Producer eaten, nutrient is now in the consumer.

Question 14

Common features of nutrient cycle

what happens after producer eaten and nutrient is now in the consumer?

Answer 14

eventually producers and consumers die
complex molecules are broken down by saprobiontic microorganisms (decomposers)
that release the nutrient in its original simple inorganic form

Question 15

What is ammonia released from?

3 examples

Answer 15

Urea
Proteins
Nucleic acids

Question 16

What do nitrifying bacteria require?

Answer 16

Oxygen.

Question 17

What causes an increase in denitrification?

Answer 17

Soils water logged/low oxygen concentration

Few aerobic nitrifying and nitrogen fixing bacteria = increase in anaerobic denitrifying bacteria

Question 18

What are the negatives to denitrification?

Answer 18

Bad for crop production.

Question 19

How to over come negatives of denitrification?

Answer 19

Must keep soil aerated.

Question 20

What is the relationship between mutualistic nitrogen-fixing bacteria and plants?

Answer 20

Live in nodules on the roots of plants.

Use carbohydrates from plant. (e.g. symbiotic relationship)

Question 21

Why do nitrifying bacteria
oxidise ammonium ions into nitrite ions
then oxidise nitrite ions into nitrate ions?

Answer 21

The oxidation releases energy which is obtained by the bacteria.