Nutrient Cycles

Question 1

Explain what is meant by the term carbon sink.

Answer 1

• Takes up/stores 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.

Answer 2

• Increase in temperature of earth’s surface/mean global temperature
• Carbon dioxide is a greenhouse gas/due to an increase in greenhouse gases
• (Which) trap/reflect back heat/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
• Ammonification/ release of ammonium compounds
• By saprobionts/decomposers
• Conversion to nitrates via nitrites
• By nitrifying bacteria/named bacterium
• Nitrates absorbed into roots via active transport

Question 6

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 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
• (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
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 plants unable to photosynthesise and die
• Increase in saprobionts so increases rate of aerobic respiration
• Saprobionts / aerobically repsiring organisms die as lack of oxygen (anoxic)
• Increase in anaerobic microorganisms
• Production of toxins