Biogeochemical cycles

Question 1

Are nutrients and energy lost up in an ecosystem

Answer 1

Energy: Lost as heat, cannot be reused, decreases system’s usefulness.

Nutrients: Recycled indefinitely, never used up, can be reused continuously.

Question 2

Biogeochemical cycles

Answer 2

Circular movement of nutrients between living and non-living components of the ecosystem (biogeochemical cycle).

Question 3

Types of Nutrient Cycles

Answer 3

Perfect Cycle: Nutrients replaced as fast as utilized (e.g., Gaseous cycles). Imperfect Cycle: Some nutrients lost or locked up (e.g., Sedimentary cycles).

Gaseous Cycle: Reservoir = atmosphere/hydrosphere (e.g., water, carbon, nitrogen, methane cycles). Sedimentary Cycle: Reservoir = Earth’s crust (e.g., phosphorus, sulfur, calcium, magnesium cycles).

Question 4

Carbon Cycle

Answer 4

Gaseous Cycle
Short-term: Carbon exchanged between atmosphere, organisms, Earth. CO₂ absorbed by plants, transferred to animals, and returned through respiration/decomposition.
Long-term: Carbon stored in soils/aquatic sediments for millions of years. Fossil fuels release carbon back to the atmosphere when burned.

Question 5

What does decomposition of organic matter produce?

Answer 5

The decomposition of decaying organic matter produces nitrogen and carbon dioxide.

Question 6

Photosynthesis

Answer 6

Sunlight (free energy) is converted into carbohydrates (potential energy) using water and carbon dioxide. Oxygen is released in the process.

Question 7

Nitrogen Cycle

Answer 7

(Gaseous Cycle)
Nitrogen Cycle ==> Nitrogen → (N2 Fixing/Ammonification) → Ammonia/Ammonium Ions → (Nitrification) → Nitrite → → Nitrate → (Denitrification) → Nitrogen

Question 8

Conversion of nitrogen into oxides how?

Answer 8

Nitrogen in Atmosphere: Exists as N₂ (two nitrogen atoms with triple covalent bond).

Nitrogen Oxides (NO, NO₂, N₂O): Formed by lightning, UV radiation, industrial combustion, forest fires, vehicle exhausts, and power plants.

Question 9

Ammonification

Answer 9

a process that converts organic nitrogen into ammonia or ammonium. from atmosphere by N2 fixers or from urea/uric acid waste by bacteria.

Question 10

N2-fixers

Answer 10

Nitrogenase: Enzyme in prokaryotes that fixes atmospheric nitrogen into ammonia (NH₃) and ammonium ions (NH₄⁺).

N₂-fixers: Microbes that fix nitrogen, including:
1. Free-living (non-symbiotic): Soil bacteria like Azotobacter, Beijemickia, Clostridium, Rhodospirillum.
2. Symbiotic: Bacteria like Rhizobium that form partnerships with leguminous and non-leguminous plants.
3. Cyanobacteria: Blue-green algae such as Nostoc, Anabaena, Spirulina (N-fixation in oceans).

Question 11

Nitrification

Answer 11

Ammonium converted to nitrites and nitrates

Ammonium → Nitrite: By Nitrosomonas and Nitrococcus.
Nitrite → Nitrate: By Nitrobacter.
Nitrates ultimately absorbed by plants

Question 12

Importance of Nitrification

Answer 12

In Agriculture for fertilizers
Ammonia → Nitrate (NO₃⁻), increases nitrogen leaching, water solubility.
In Wastewater Treatment:
Nitrification followed by denitrification.

Question 13

Denitrification

Answer 13

Nitrate → Nitrogen (N₂)
Denitrifying Bacteria: Pseudomonas, Thiobacillus
Converts nitrates/nitrites to elemental nitrogen, which escapes to the atmosphere, completing the nitrogen cycle.

Question 14

Methane

Answer 14

More potent GHG than CO₂, short-lived in atmosphere.
Contributes to ground-level ozone formation (air pollutant).
Oxidizes to CO₂ after 1-2 decades.

Question 15

Methane Cycle

Answer 15

Natural Sources: Decomposing biological matter, wetlands, oceans, termite digestion.

Human Activities: 50-65% of global CH₄ emissions, primarily from:
Agriculture (40%: livestock, rice)
Fossil Fuels (35%)
Waste (20%: landfills, wastewater)

Methane Sinks:
Soils: Methanotrophic bacteria (Methane Oxidation).
Hydroxyl Radicals (OH): Atmospheric cleanser, methane sink.
Clathrate Deposits:

Previously methane sinks in oceans/permafrost, now melting due to warming, releasing methane.

Question 16

Methane release by Wetlands

Answer 16

Methanogens: Microorganisms producing methane (CH₄) during organic matter decomposition. Wetlands: Hypoxic habitat for methanogens, contributing ~80% of global natural CH₄ emissions.

Question 17

Methane release by Oceans

Answer 17

anaerobic digestion in marine zooplankton and fish and from methane produced in sediments/drainage areas in coastal regions.

Question 18

Methane release by Termites

Answer 18

Microbes in the guts of termites produce methane through anaerobic (lack of oxygen) fermentation as part of their normal digestive process.

Question 19

Methane mass extinction

Answer 19

Ocean acidification, climate change wtc can destabilize the clathrates ( in the ocean) and lead to the release of an immense amount of methane — can lead to mass extinction. Also cited as one of the factors in Permian–Triassic Extinction 250 mya.

Question 20

Phosphorus Cycle

Answer 20

(Sedimentary cycle). Occurs as phosphate rocks, weathering, erosion, and mining release phosphates into rivers, then oceans. In oceans, phosphates accumulate on continental shelves as insoluble deposits. After millions of years, crustal plates rise, bringing phosphates back to the crust, repeating the cycle.

Question 21

Importance of phosphorus

Answer 21

Central to aquatic ecosystems and water quality, main cause of phytoplankton blooms in lakes, leading to eutrophication.

Question 22

Sulphur Cycle

Answer 22

Enters atmosphere as sulfur dioxide (SO₂) from volcanic eruptions, fossil fuel combustion, ocean (DMS), and decomposition. Atmospheric hydrogen sulfide (H₂S) oxidizes to SO₂, which returns to Earth as sulfuric acid (acid rain). Sulfates are absorbed by plants, pass through the food chain, and return to soil, ponds, lakes, and seas through excretion and decomposition.

Question 23

Impact of high organic matter on soil water holding capacity

Answer 23

A high content of organic matter (humus) in the soil increases its water-holding capacity.

Question 24

Irrigation over a period of time can contribute to the salinization of some agricultural lands. Why?

Answer 24

groundwater level rises, capillary action brings up salt. And water itself has salt that is left behind when it gets absorbed.