5D - Nutrient cycles

Question 1

what are saprobionts?

Answer 1

an organism that feeds on dead material

Question 2

x3

explain the role of saprobionts in recycling chemical elements / waste

Answer 2

1. Decompose organic compounds e.g. protein/ urea/ DNA in dead matter
2. Secretes enzymes for extracellular digestion
3. Absorb soluble needed nutrients and release mineral ions

Question 3

what is mycorrhizae?

Answer 3

symbiotic association between fungi and plant roots

Question 4

x3

explain the role of mycorrhizae

Answer 4

1. Fungi acts as an extension of plant root to increase SA
2. Acts as a sponge to increase rate of uptake/ absorption of water and inorganic ions (resist drought)
3. So fungi receive organic compounds e.g. carbohydrates

Question 5

nitrogen containing compounds

what products can be made from the nitrogen cycle ?

Answer 5

amino acids/proteins, nucleic acids (DNA, RNA) and ATP.

Question 6

what are the 4 main stages of the nitrogen cycle?

Answer 6

ammonification, nitrification, denitrification and nitrogen fixation

Question 7

what is ammonification?

Answer 7

production of NH3 from organic nitrogen containing compounds

Question 8

describe the role of bacteria in ammonification

Answer 8

• saprobionts feed on faeces and dead organisms that release NH3 -> ammonium ions produced in the soil
• NH3 released from decomposition of compounds such as proteins, nucleic acids and urea

Question 9

what is nitrification?

Answer 9

a process that breaks down ammonia into nitrites or nitrates

Question 10

what is the role of bacteria in nitrification

Answer 10

• nitrifying bacteria in aerobic conditions
• oxidation of ammonium ions to nitrite ions (NO2-)
• oxidation of nitrite ions to nitrate ions (NO3-)
• this is oxidation so releases energy
• ions are taken up by plant root hair cells via active transport

Question 11

how can farmers improve the productivity of nitrifying bacteria?

Answer 11

• keep soil structure light and well aerated by ploughing
• Good drainage also prevents the air spaces from being filled with water and so prevents air being forced out of the soil

Question 12

what is nitrogen fixation?

Answer 12

nitrogen is converted into nitrogen containing compounds (NH3)

• NH3 then can be converted into NH4+

Question 13

What two types of nitrogen fixing bacteria carry out nitrogen fixation ?

Answer 13

• free-living
• mutualistic

Question 14

what do free living nitrogen-fixing bacteria do?

Answer 14

• reduces N2 gas to NH3, so AA can be manufactured
• nitrogen rich compounds are released from them when they die and decay

Question 15

what do mutualistic nitrogen fixing bacteria do?

Answer 15

• live in nodules on the roots of (leguminous) plants such as peas and beans.
• They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.

Question 16

what occurs in denitrification ?

Answer 16

Nitrates in the soil are converted to nitrogen gas

• When soils become waterlogged and have a low oxygen concentration, the type of microorganism present changes.
• Fewer aerobic nitrifying and nitrogen-fixing bacteria are found, and there is an increase in anaerobic denitrifying bacteria.
• These denitrifying bacteria anaerobically respire
• These convert soil nitrates into gaseous nitrogen.

Question 17

what biological molecules contain phosphorous

Answer 17

Phosphorus is required for the production of nucleic acids (DNA and RNA), ATP and phospholipids.

Question 18

x5

describe the phosphorous cycle

Answer 18

1. Phosphate ions in rocks are released into the soil or into sea/rivers by weathering / erosion
2. Plants and aquatic plants take in phosphate ions through roots and incorporate them into their biomass.
   This is enhanced by mycorrhizae which increase the rate of assimilation.
3. Phosphate ions are transferred through the food chain as animals eat plants and are then eaten by other animals.
4. Excess phosphate ions are lost from animals in their waste products to the soil. (Excretion)
5. When plants and animals die / release waste products (urine,faeces), saprobionts break down the organic compounds by extracellular digestion.

Question 19

x4

explain why fertilisers are used

Answer 19

• plants take minerals from the soil to grow
• if they are harvested, they are removed rather than allowed to die and decompose there, so nutrients aren’t returned to the soil
• even the removal of animals means the nutrients they have taken are not returned
• this improves efficiency of energy transfer + yield!

Question 20

describe the difference between artificial and natural fertilisers

Answer 20

1. • natural = organic
     - artificial = inorganic
2. natural = ions released during decomposition by saprobionts
   - artificial = contains inorganic compounds of N, P and K (potassium) -> may cause eutrophication

Question 21

how do fertilisers increase productivity?

Answer 21

• more nitrogen for AA, nucleotides in DNA and ATP
• Where nitrate ions are readily available, plants are likely to develop earlier, grow taller and have a greater leaf area.
  This increases the rate of photosynthesis and improves crop productivity.

Question 22

what are the disadvantages of using nitrogen containing fertilisers?

Answer 22

1. biodiversity loss
2. leaching - pollution into watercourses
3. eutrophication - caused by leaching of fertliser

Question 23

why do nitrogen containing fertilisers result in biodiversity loss?

Answer 23

• species are outcompeted and die
• as nitrogen rich soils favour the growth of grass, nettles and other fast growing species

Question 24

advantages of ORGANIC fertilisers

Answer 24

• Less soluble than artificial fertilisers, so the minerals are released more slowly as they are decomposed which this prevents leaching & means they last longer.
• Cheap as organic wastes need to be disposed of.
• Improves soil structure by binding soil particles together & provides food for soil organisms such as earthworms which this improves drainage & aeration.

Question 25

disadvantages of ORGANIC fertilisers

Answer 25

- offensive smells - may be difficult to spread - slow mineral release

Question 26

advantages of INORGANIC fertilisers

Answer 26

- Can control concentrations of each nutrient - Increase crop yield

Question 27

disadvantages of INORGANIC fertiliser

Answer 27

- readily leached from the soil - increased risk of eutrophication - expensive to manufacture/buy - risk of fertliser spray spreading to other areas

Question 28

define leaching

Answer 28

Leaching is the process by which nutrients (water-soluble compounds) are removed from the soil and washed away by rain or irrigation systems.

Question 29

what is the process of leaching

Answer 29

Rainwater will dissolve any soluble nutrients, such as nitrate ions, and carry them deep into the soil, eventually beyond the reach of plant roots. The leached nitrate ions find their way into watercourses, such as streams and rivers. This can affect drinking water. - nitrates are more soluble in water than phosphates

Question 30

what is eutrophication?

Answer 30

Eutrophication is a natural process by which nutrient concentrations increase in bodies of water which stimulates the growth of algae.

Question 31

# 9 lengthy points LMFAO how does eutrophication occur?

Answer 31

1. **Mineral (nitrate ion) concentrations** increase as a result of **leaching** from fertilised fields, which stimulates the growth of plants and **algae** whose populations rise. 2. As algae mostly grow at the surface, the upper layers of water become **densely populated (algal bloom).** 3. This dense surface layer of algae **absorbs light** and prevents it from **penetrating** to lower depths. 4. **Light becomes the limiting factor** for the growth of plants and algae at lower depths which cannot photosynthesise and so they eventually die. 5. **Saprobiontic bacteria populations rise**, as they feed on the dead organisms. 6. The saprobiontic bacteria require oxygen for their respiration, so the **concentration of oxygen in the water is reduced** and **nitrates are released** from the decaying organisms. 7. **Oxygen then becomes the limiting factor** for the population of **aerobic organisms**, such as fish. These organisms ultimately die as the oxygen is used up and they **cannot respire**. 8. Without the aerobic organisms, there is **less competition** for the **anaerobic** organisms, whose populations now rise. 9. The anaerobic organisms **further decompose dead material, releasing more nitrates** and some toxic wastes, such as hydrogen sulphide, which make the water **putrid.**