Environmental Chemistry - Biogeochemical cycles

Welcome to the COMPETITIVE EXAM MCQs SERIES of ENVIRONMENTAL SCIENCE for UGC-NET/JRF, SLETGATE, and other entrance tests: Environmental Chemistry – Biogeochemical cycles.

Syllabus outline

  1. Definition and significance of biogeochemical cycles.
  2. Types of biogeochemical cycles (e.g. 1. Carbon cycle – photosynthesis, respiration and combustion. 2. Nitrogen cycle – Nitrogen fixation, nitrification, and denitrification. 3. Phosphorus cycle – Weathering, absorption, and assimilation. and 4. Sulphur cycle – Sulphur sources and sinks).
  3. Role of Microorganisms in Biogeochemical Cycles
  4. Deforestation and its effects on the carbon cycle.
  5. Fertilizer use and its effects on nitrogen/phosphorus cycles.
  6. Industrial activities and their impact on the sulfur cycle.
  7. Climate change and its impact on biogeochemical cycles

This quiz contains the concept-based most frequently asked 25 MCQs of “Environmental Chemistry – Biogeochemical cycles“. Each question has a single correct/most appropriate answer.

1. Which of the following is not a way in which sulfur dioxide emissions affect the environment?

a) Smog formation

b) Global warming

c) Respiratory problems

d) Acid rain

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2. What is the possible path of nitrogen movement?

a) Air-animals-soil-plants-air

b) Air-soil-plants-animals-soil-air

c) Soil-air-plants-air-animals-soil

d) Soil-animals-plants-air-soil

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3. In which environmental compartment are metals most likely to undergo redox reactions?

a) Soil

b) Aquatic sediments

c) Oceans

d) Atmosphere

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4. Which of the following is not a way in which phosphorus is lost from ecosystems?

a) Erosion

b) Harvesting of crops

c) Uptake by plants

d) Leaching

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5. Which of the following is a major source of phosphorus in aquatic ecosystems?

a) Phosphorus fixation by bacteria

b) Human sewage and agricultural runoff

c) Weathering of rocks and minerals

d) Atmospheric deposition

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6. Which of the following is an example of sulfate-reducing bacteria?

a) Thiobacillus

b) Desulfovibrio

c) Nitrobacter

d) Pseudomonas

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7. Which of the following is not a way in which nutrient cycling affects ecosystem productivity?

a) Nutrient cycling regulates the pH and salinity of soils and water.

b) Nutrient cycling increases the availability of essential elements for plant growth.

c) Nutrient cycling reduces the competition for resources among different species

d) Nutrient cycling promotes the decomposition of organic matter.

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8. Which metal is often associated with acid mine drainage pollution?

a) Copper

b) Arsenic

c) Selenium

d) Zinc

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9. Which of the following forms of nitrogen can be used by microorganisms in place of molecular oxygen?

a) Nitrate

b) Organic Nitrogen

c) Ammonium ion

d) Nitrogen

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10. Which of the following organisms can transform nitrite to nitrate?

a) Nitrobacter

b) Rhizobium

c) Pseudomonas

d) Nitrosomonas

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11. The legume root releases ______________ that is absorbed by the rhizobial symbionts, initiating the expression of plasmid-encoded nod (nodulation) genes.

a) Glycolipids

b) Leghemoglobin

c) Flavonoids

d) Chitolipooligosaccharides

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12. In the root nodules of leguminous plants, the level of __________ is controlled by Leghemoglobin.

a) Water

b) Cellular respiration

c) Nitrogen

d) Oxygen

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13. Which of the following nutrient cycles is a sedimentary cycle?

a) Sulphur

b) Hydrogen

c) Phosphorus

d) Nitrogen

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14. ________ is a glycoprotein found in milk that binds to iron and is known to exhibit antimicrobial activity against a broad spectrum of bacteria and viruses.

a) Ovotransferrin

b) Lactoferrin

c) Serotransferrin

d) Melanotransferrin

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15. Which of the following organisms can transform ammonium ion to nitrite?

a) Pseudomonas

b) Nitrobacter

c) Nitrosomonas

d) Rhizobium

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16. Which of the following is not a step in the sulfur cycle?

a) Sulfur oxidation by bacteria

b) Sulfur assimilation by plants

c) Sulfur deposition in soils and sediments

d) Sulfur release from volcanic eruptions

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17. Which of the following is not a way in which climate change is affecting biogeochemical cycles?

a) Decreasing soil erosion

b) Changing ocean currents

c) Increasing atmospheric carbon dioxide concentrations

d) Altering precipitation patterns

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18. Assertion (A): Metal hyperaccumulating plants are adapted to grow in soils with high metal concentrations.

Reasoning (R): These plants use metal hyperaccumulation as a defence mechanism against herbivores.

a) Both A and R are true, and R is the correct explanation of the A.

b) A is true, but R is false.

c) Both A and R are true, but R is an incorrect explanation of A.

d) Both A and R are false.

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19. The phosphorous cycle differs from the water, carbon, and nitrogen cycles in that

a) Phosphorus is primarily found in a mineralized state within rocks

b) Phosphorous is far more abundant than water, carbon, or nitrogen.

c) Phosphorous is less important to biological systems than water, carbon, or nitrogen.

d) Phosphorous once used by an organism, does not cycle back to the environment.

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20. The wood roaches died when they were placed in a bell jar containing wood chips and a high concentration of oxygen because

a) Oxygen is toxic to flagellates present in the guts of wood roaches

b) Lack of food availability

c) Oxygen is toxic to wood roaches

d) Oxygen has an inhibitory effect on cellulose oxidation

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21. What is the primary mechanism of bioaccumulation of metals in aquatic ecosystems?

a) Sedimentation

b) Bacterial activity

c) Decomposition

d) Trophic levels

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22. The phenomenon of metal hyperaccumulation in plants is most closely associated with:

a) Chromium

b) Nickel

c) Cadmium

d) Lead

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23. What role do ligands play in transporting trace metals in aquatic environments?

a) Precipitation

b) Oxidation

c) Chelation

d) Inhibition

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24. Some bacteria can fix nitrogen. This means

a) They convert ammonia into nitrites and nitrates.

b) They convert nitrate into nitrogen gas.

c) They convert atmospheric nitrogen gas into biologically useful forms of nitrogen.

d) They break down nitrogen-rich compounds and release ammonium ions.

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25. In enhanced biological phosphate removal, Acinetobacter, Pseudomonas or Nocardia utilize the stored organics and take up phosphorus to produce ___________ to store energy under aerobic conditions.

a) High-energy carbon compound

b) Inorganic Phosphorus (Pi)

c) ATP

d) Polyphosphate

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Next: Toxic chemicals


  1. Manahan, Stanley E. (2019) Environmental Chemistry, CRC Press, 10th edition.
  2. Tyagi, Anil K. (2018) Environmental Science and Engineering, Khanna Publishers, 3rd edition.
  3. Reddy, M. Anji (2016) Principles of Environmental Chemistry, BS Publications, 4th edition.
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