Nutrient Cycle

Question 1

Nitrification

Answer 1

• Nitrifying bacteria oxidise ammonium ion to a nitrate
• NH₄⁺ ⇒ NO₂^- ⇒ NO₃^-

Question 2

Nitrogen fixation

Answer 2

• When nitrogen gas is reduced, converted into ammonia.
• The ammonia then dissolves in water, forming NH₄+.
• This is done by free-living bacteria and mutualistic bacteria

Question 3

Denitrification

Answer 3

• When anaerobic denitrifying bacteria covert soil nitrates into gaseous nitrogen

Question 4

Leeching and Eutrophication.

This is the same if fertilisers are nitrate of phoshpates

Answer 4

• Farmers apply fertilisers in large quantities
• Nutrients build up in bodies of water due to them being washed from the soil, making algae grow faster.
• This blocks light so submerged plants can’t photosynthesise. They die
• Saprobiotic microorganisms breakdown dead plants
• These use up O2 due to respiration so less in the water
• Aerobic organisms therefore die (e.g fish)

Question 5

Ammonification

Answer 5

• Saprobiotic microorganisms break down protein into ammonia

Question 6

🔴️ Dead leaves contain starch. How do microorganism make Carbon in starch available to plants?

Answer 6

• Saprobiotic microorganisms release enzyme (extra cellular digestion).
• This converts starch into monosaccharides.
• The microorganisms absorbs then respires the glucose made, releasing CO2
• In photosynthesis the plants absorb CO2 through the stomata of the leaf
• Useful organic products e.g Glucose is made in calvin cycle

Question 7

🔴️Advantages of using natural fertilisers

Answer 7

• Making artificial fertilisers uses energy so cheaper
• Less leeching and eutrophication as there is a slow release of nutrients
• Contains wider range of elements
• Aerates soil

Question 8

🔴️Why do plants have a higher carbon:nitrogen ratio than animal

Answer 8

• Plants have cellulose in cell walls
• They contain starch in plant tissue
• More protein in animal cells (muscle)

Question 9

🔴️How is the nitrogen in dead plants made available for other plants?

Answer 9

• Proteins are decomposed by Saprobiotic microorganisms
• Ammonia is formed
• NH₄+ ⇒ NO₂- ⇒ NO₃- by nitrifying bacteria
• Nitrate can be absorbed by roots

Question 10

🔴️Why does adding fertilisers increase the mass of crop?

Answer 10

• Replaces nitrates removed from the soil
• Fertilisers contain nitrate needed for protein production
• This leads to more growth as Nitrogen is in DNA

Question 11

🔴️Advantages of artificial fertilisers

Answer 11

• Easy to apply and store
• Can supply to specific needs
• Easy to control mass
• Faster releases of ions and minerals

Question 12

🔴️Why does a plant die if the leaves drastically diminish in size

Answer 12

• Less SA for light to be absrobed ]
• so less photosynthesis occurs
• Less glucose is made
• respiration rate > photosynthesis

Question 13

Explain why there would be an increase in the diversity of birds as the woodland developed from a farmland

Answer 13

• Greater variety diversity of plants and insects
• Greater varieties of food;
• More habitats and niches available

Question 14

Explain how human activities have contributed to global warming.

Answer 14

• Carbon dioxide is a greenhouse gas;
• Deforestation leads to less carbon dioxide removed by photosynthesis;
• Microorganisms decompose them respiring
• Combustion releases carbon dioxide;
• Methane is a greenhouse gas too
• This is released from livestock e.g rice fields and cattle;

Question 15

How does ploughing increase soil fetility

Answer 15

• Since there is more oxygen, fewer denitrifying bacteria convert NO₃ to N_2.
• More nitrates are formed as more nitrifying bacteria can oxidise NH₄⁺ to NO₂
• There is also less competition among bacteria

Question 16

How can application of high concentration of fertilisers affect plant growth?

Answer 16

• will lower water potential of soil
• so more water moves out by osmosis
• the plant will wilt as water is still lost via transpiration

Question 17

Explain how including leguminous plants in a crop rotation reduces the need to use artificial fertilisers.

Answer 17

1. contains nitrogen-fixing bacteria in nodules so don’t need fertiliser
2. nitrogen containing compounds added to the soil when plant dies

Question 18

Crop rotation involves growing different crops each year in the same field. How does this leads to high crop yields?

Answer 18

• Different crops have different pests
• Different crops use different nutrients and ions from the soil
• Lugiminous plants (Nitrogen fixing bacteria) can be grown, which increases the soil nitrate

Question 19

If there is an increase in the total biomass of a forest, why does the gross productivity decrease?

Answer 19

• More competition for light
• Reduced rate of photosynthesis so less glucose made

Question 20

Advantages of having leguminous plants

Answer 20

• Nitrogen fixing bacteria in root nodules
• N₂⇒ NH₄+
• NH4+ ⇒ NO2- ⇒ NO3- by nitrifying bacteria
• Less need for fertiliser;
• When they die nitrogen-containing compounds are released into the soil

Question 21

Explain how the decay of dead plants results in reduced oxygen concentration and increased nitrate production

Answer 21

1. saprobiotic micro decompose plants via extracellular digestion
2. they converts proteins into ammonia
3. microrganisms divide and respire;
4. respiration uses up oxygen;
5. nitrifying bacteria convert ammonium compounds to nitrates;
6. nitrification uses oxygen;

Question 22

How will reduced oxygen concentration of water change the composition of the communities in the river.

Answer 22

• lower species diversity
• species tolerant to low oxygen thrive
• species requiring high oxygen die out;

Question 23

why does the application of very high concentrations of fertiliser to the soil causes plants to wilt.

Answer 23

• lowers water potential in soil
• plants lose water to soil by osmosis;
• plants still lose water by transpiration;

Question 24

describe farming practices that results in more nitrogen-containing compounds in soil

Answer 24

1. growing legumes
2. ploughing
3. adding cattle manure
4. adding fertilisers

Question 25

describe the factors that results in less nitrogen-containing compounds in soil

Answer 25

• soil erosion
• leaching of nitrates into lakes
• having too many crop as more nitrates absorbed

Question 26

Define monoculture

Answer 26

• cultivation of single species of crop over a large area;

Question 27

Benefits to farmer of removing hedges when trying to grow monoculture.

Answer 27

• more space for crop
• easier to use machines
• removes habitat for pests;
• lower labour costs in maintenance;

Question 28

Use of phosphate in cells

Answer 28

• Found in DNA nucleotides;
• phospholipid bilayer;
• ATP formation from ADP

Question 29

How can an increase in the rate of photosynthesis increase the rate of respiration in roots

Answer 29

• Photosynthesis produces sugars;
• Sugars moved to roots;
• Sugars are used in respiration;