Nutrient cycles

Question 1

Explain what is meant by the term carbon sink (2)

Answer 1

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

Question 2

Explain what is meant by the term global warming (5)

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 (2)

Answer 3

• decompose proteins / DNA / RNA / urea;
• Producing / releasing ammonia / ammonium ions;

Question 4

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

Describe the role of microorganisms in this process (6)

Answer 4

1. Proteins/amino acids broken down;
2. Deamination/ammonification/ release of ammonium compounds;
3. By saprophytes/saprobionts/decomposers;
4. conversion to nitrates via nitrites;
5. by nitrifying bacteria/named bacterium;
6. nitrates absorbed into roots via active transport

Question 5

The scientists used units of μg g−1 for the concentration of soil.
Suggest why, in this investigation, the scientists used these units (2)

Answer 5

• 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 6

Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested (8)

Answer 6

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 7

Plants absorb a number of other nutrients from the soil including phosphates. Describe why phosphates are needed by a growing plant (6)

Answer 7

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

Question 8

Outline the advantages of having Mycorrhizae
growth near plants (2)

Answer 8

• 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);