Nutrient Cycles

Question 1

Which microorganism undergoes nitrification?

Answer 1

Nitrifying bacteria

Question 2

Which microorganism undergoes denitrification?

Answer 2

Denitrifying bacteria

Question 3

What is the reaction for nitrogen fixation

Answer 3

Nitrogen gas to ammonia (reduction)

Question 4

What is Nitrification

Answer 4

Conversion of ammonium ions to nitrite ions (NO2-) and then nitrate ions (NO3-) in the soil
NH4+ ions —> NO2 - ions —> NO3 - ions

Question 5

What is Rhizobia

Answer 5

A bacterium found in the root nodules of legumes (undergo nitrogen fixation)

Question 6

What is Ammonification

Answer 6

Decomposition of dead organisms which releases ammonia or ammonium ions into the soil
Organic nitrogen (e.g. DNA, RNA, proteins etc.) —> NH4+ ions

Question 7

What is Nitrogen fixation

Answer 7

The conversion of atmospheric nitrogen to nitrogen compounds such as ammonia
N2 gas —> NH3 / NH4+ ions

Question 8

What is Denitrifcation

Answer 8

The conversion of nitrates back to nitrogen gas. (Waterlogged soil, Anaerobic conditions - Pseudomonas denitrifying bacteria)
NO3 - ions —> N2 gas

Question 9

Explain what is meant by the term carbon sink.

Answer 9

• Takes up / locks up / stores carbon / carbon dioxide (for a long time) / eq ;
• Named example e.g. peat / coal / limestone / trees / fossil fuel / chalk / shells ;

Question 10

Explain what is meant by the term global warming.

Answer 10

• Increase in {temperature of earth’s surface / mean global temperature / eq};
• Carbon dioxide is a greenhouse gas / due to an increase in greenhouse gases ;
• (Which) {trap / reflect back} {heat / long wave / infra red} (in the atmosphere) ;
• Reference to an {increased / enhanced} greenhouse effect ;
• Reference to valid {effect / consequence} e.g. melting ice caps, flooding, climate
• change ;

Question 11

Describe the role of saprobionts in the nitrogen cycle.

Answer 11

• (use enzymes to) decompose proteins / DNA / RNA / urea;
• Producing / releasing ammonia / ammonium ions;

Question 12

Explain how carbon-containing compounds present in the pine leaves that fall from the trees are absorbed and used for growth by saprobionts/fungi that live in the soil.

Answer 12

• extracellular digestion;
• by secretion of enzymes;
• absorption of digested/soluble products;
• synthesis of structural compounds/named compound;.
• respiration provide energy for growth

Question 13

Nitrogen compounds in the plants are made available for the main crop after ploughing in spring.

Describe the role of microorganisms in this process.

Answer 13

• proteins/amino acids broken down;
• deamination/ammonification/ release of ammonium compounds;
• By saprophytes/saprobionts/decomposers;
• conversion to nitrates via nitrites;
• by nitrifying bacteria/named bacterium;
• nitrates absorbed into roots via active transport

Question 14

The scientists used units of μg g−1 for the concentration of ammonia in soil.
Suggest why, in this investigation, the scientists used these units.

Answer 14

• (μg because) very little ammonia (in soil);
• (μg because) avoids use of (lots of) decimal places (in their results) / avoids the use of powers of 10 / avoids the use of standard form /makes numbers more manageable / Accept makes easier to plot graph
• (g-1) to allow comparisons (between samples);

Question 15

Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested.

Answer 15

1. amino acid/protein/ polypeptide/peptide;
2. nucleic acid/nucleotide/base;
3. DNA;
4. RNA / pre-mRNA / mRNA / rRNA / tRNA
5. ATP/ADP;
6. NAD/NADP (reduced or not);
7. Cyclic AMP/cAMP;
8. Chlorophyll;

Question 16

Plants absorb a number of other nutrients from the soil including phosphates. Describe why phosphates are needed by a growing plant.

Answer 16

• production of phospholipids;
• in cell membranes;
• synthesis of ATP;
• production of DNA;
• production of RNA;
• production of NADP

Question 17

Describe how a lack of phosphates in the soil surrounding a plant can affect its growth

Answer 17

• (Required to) make ATP/glucose phosphate, so less respiration/less energy for growth;
• (Required to) make nucleotides, so less DNA/mRNA/tRNA for cell division/production of protein (for growth);
• (Required to) make RuBP/NADP, so less CO2 fixed/reduced into sugar;
• (Required to) make phospholipids for membranes;

Question 18

Outline the advantages of having Mycorrhizae
growth near plants

Answer 18

• Mycorrhizae help plants to defend themselves (causing an increase in crop yield);
• Mycorrhizae help plants to take up nitrates/phosphates (causing an increase in crop yield);

Question 19

Describe the process of eutrophication.

Answer 19

• Nitrates / Phosphates / Ammonium ions flushed into waterway
• Increased algal bloom
• Light blocked out
• Submerged aquatic plant unable to photosynthesise and die
• Increase in saprobionts so increases rate of aerobic respiration
• Saprobionts / aero.resp organism die as lack of oxygen (anoxic)
• Increase in anaerobic microorganisms
• Production of toxins