Nutrient Cycles 5.4

Question 1

why is nitrogen needed in organisms?

Answer 1

To make nitrogen containing biological molecules such as DNA RNA ATP and Amino acids

Question 2

Describe the process of ammonification?

Answer 2

-SAPROBIOTIC BACTERIA AND FUNGI scerete extracelluar enzymes on to dead organisms faeces and urine
-enzymes hydrolyse nitrogen containing compounds eg proteins and absorb the products eg amino acids
-Ammonium ions are released into the soil

Question 3

Describe the process of nitrification?

Answer 3

Nitrifying bacteria oxidise ammonium ions in 2 stages:
1. ammonium ions to nitride ions NO2-
2. nitride ions to nitrate ions NO3-
-Plants absorb nitrate ions by active transport and use them to make proteins
-Requires aerobic conditions

Question 4

Describe the process of denitrification

Answer 4

-Denitriying bacteria reduce nitrate ions to nitrogen gas
-Occurs in anaerobic conditions

Question 5

Describe the process of nitrogen fixtation

Answer 5

-Nitrogen has is reduced to ammonium ions
-by nitrogen fixing bacteria in soil or root nodules of legumes

Question 6

Why does mycorrhizal fungus benefit plants and the fungus?

Answer 6

Fungi increase surface area of plants roots to increase absorption of water and nitrates/phosphates
Fungus recieves carbohydrates from photosynthesis from the plant

Question 7

How do animals obtain nitrogen and what do they use it for?

Answer 7

• Consumers eat other organisms
• Hydrolyses nitrogen containing compounds into monomers eg proteins to amino acids/nucleotides
• Absorb them
• Monomers assimilted to make new nitrogen containing compounds eg proteins DNA RNA

Question 8

Why do farmers keep their field drained and regularly ploughed?

Answer 8

-Maintain aerobic conditions
-More nitrifying bacteria less denitryfying bacteria
-More nitrification more nitrate ions to be absorbed by plants
-Less denitrification

Question 9

When writing about the nitrogen cycle in an exam what are 3 things you need to include?

Answer 9

1. The stage
2. What form of nitrogen is being converted into what form of nitrogen
3. Name the bacteria involved

Question 10

What enzymes is involved in each stage of the nitrogen cycle?

Answer 10

Nitrification- Nitrifying bacteria
Denitrification- Denitrifying bacteria
Ammonification- Saprobiotic bacteria
Nitrogen fixation- Nitrogen fixing bacteria

Question 11

What molecule is converted to what molecule in each stage of the nitrogen cycle

Answer 11

Nitrification- Ammonia ->nitride -> nitrate
Denitrification- Nitrate -> nitrogen
Ammonification- Nitrogen containing compounds eg DNA -> ammonia
Nitrogen fixation- Nitrogen -> ammonia

Question 12

Phosphorus cycle part 1. How are phosphate ions released from sedimentary rocks where do they go?

Answer 12

-Weathering and erosion of rocks
-Phosphate ions dissolve
-Into soils oceans and lakes

Question 13

Phosphorus cycle part 2. How do plants absorb and use phosphate ions?

Answer 13

-Phosphate ions absorbed into roots by active transport
-Mycorrhizae increase SA for max absorption
-Used to make Molecules such as DNA ATP and phospholipid
-Incorporated into biomass

Question 14

Phosphorus cycle part 3. How are Phosphates transferred to animals?

Answer 14

-Consumers eat plants
-Hydrolyse biological molecules via digestion and absorb them
-Assimilate ions into new tissue eg phospholipid

Question 15

Phosphorus cycle part 4. How do phosphates reenter soil when animals die?

Answer 15

-Animals decomposed by saprobiotic bacteria
-Secrete extracelluar enzymes which hydrolyse phosphorus containing molecules eg DNA to phosphate ions

Question 16

Phosphorus cycle part 5. How do phosphate ions reenter soil through excretion?

Answer 16

-Exess phosphate ions are excreted in urine and guano (birds) hydrolysed by saprobiotic bacteria

Question 17

Phosphorus cycle part 6. How do phosphate ions reform rocks?

Answer 17

Sedimentary rock reformed by deposition

Question 18

What biological molecules contain phosphorus?

Answer 18

Phospholipid ATP DNA RNA

Question 19

Why are fertilisers neccecary for agricultural ecosystems but not natural ecosystems?

Answer 19

-Fertaliser adds nitrates and phosphates to soil
-Agricultural land- Crops are removed do not decompose, livestock removed no longer replacing nitrates and phosphates eaten - nitrates and phosphates do not reenter soil need replacing
-Natural ecosystems - plants decompose, animals excrete egest and decompose nitrates and phosphate reenter soil

Question 20

What are types of natural fertiliser? What is an advantage and disadvantage of this type?

Answer 20

Compost and manure
+ no environmental issues
- take longer to provide absorbable form of nitrogen need saprobiotic bacteria

Question 21

What is artificial fertiliser? What is an advantage and disadvantage of this type?

Answer 21

Chemical compounds nitrates/ammonium and phosphates straight to soil
+provide plants with nitrate and phosphate ions faster
-environmental issues: leeching, eutrophication, less growth of plants in high concentrations

Question 22

Why does the addition of fertiliser in high concentrations decrease productivity of crop?

Answer 22

-Lowers water potential of soil
-Plants have a higher water potential than soil
-Moves out of plants cells by osmosis
-Plants have less water for metabollic reactions eg photosynthesis

Question 23

What is leaching?

Answer 23

• Removal of nitrates and phosphates into soil by rainwater into rivers and lakes
• Can cause eutrophication

Question 24

What is eutrophication?

Answer 24

• leaching occurs
• Nitrates and phosphates increase cause an algal bloom on water surface
• Reduces sunlight available to plants in water, stop photosynthesising and die
  -Saprobiotic bacteria reproduce rapidly an docompose death plant matter using oxygen for aerobic respiration
  -decreases oxygen concetration in water, other organisms eg fish can no longer aerobically respire and die