nutrient cycle

Question 1

Explain what is meant by the term carbon sink.

Answer 1

• 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 2

Explain what is meant by the term global warming.

Answer 2

• 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 3

Describe the role of saprobionts in the nitrogen cycle.

Answer 3

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

Question 4

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 4

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

Question 5

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 5

• 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 trans

Question 6

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

Answer 6

• (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 7

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

Answer 7

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 8

Plants absorb a number of other nutrients from the soil including phosphates.

Describe why phosphates are needed by a growing plant.

Answer 8

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

Question 9

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

Answer 9

• (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 10

Outline the advantages of having Mycorrhizae
growth near plants

Answer 10

• 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 11

Describe the process of eutrophication.

Answer 11

• 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 organismsn die as lack of oxygen (anoxic)
• Increase in anaerobic microorganisms
• Production of toxins

Question 12

Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants (5)

Answer 12

1. Protein converted into ammonia
2. By saprobionts
3. Ammonia into nitrite
4. Nitrite into nitrate
5. By nitrifying bacteria
6. Nitrogen gas to ammonia
7. By nitrogen fixing bacteria

Question 13

Describe nitrification (2)

Answer 13

1. Ammonia to nitrites to
   nitrates
2. By nitrifying bacteria

Question 14

Describe denitrification (2)

Answer 14

1. Nitrates to nitrogen gas
2. By denitrifying bacteria

Question 15

Describe nitrogen fixation (2)

Answer 15

1. Nitrogen gas to ammonia
2. By nitrogen fixing bacteria

Question 16

Describe ammonification/ decomposition (2)

Answer 16

1. Nitrogen containing compounds to ammonia
2. By saprobiants

Question 17

Describe the phosphorus cycle (5)

Answer 17

1. Phospholipids, RNA and DNA from dead organisms into phosphate ions
2. Decomposed by saprobionts
3. Phosphate ions also found in waste and remains
4. Phosphate ions transported by lakes
5. Form sedimentary rock
6. Weathering and erosion of rocks helps phosphate ions dissolve in lakes
7. Phosphates become available for absorption by plants to incorporate into biomass

Question 18

You are given samples of water from three different rivers. Describe how you would obtain a quantitative measurement of their cloudiness (2)

Answer 18

1. Use of colorimeter
2. Measure absorbance of light
3. Standardise method e.g. same volume of water, zeroing calorimeter, same wavelength of light