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Ecology - Nutrient Cycles (Carbon and Nitrogen)

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Carbon Cycle describes the process in which carbon atoms continually travel from the atmosphere to the Earth and then back into the atmosphere. This includes reservoirs like the oceans, soil, and living organisms.

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Photosynthesis is the process by which autotrophs (plants) take in CO2CO_2 from the atmosphere and convert it into glucose (C6H12O6C_6H_{12}O_6) using light energy.

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Cellular Respiration is the biological process where organisms break down C6H12O6C_6H_{12}O_6 in the presence of O2O_2 to release energy, producing CO2CO_2 and H2OH_2O as byproducts.

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Combustion occurs when fossil fuels or biomass are burned in the presence of O2O_2, releasing stored carbon back into the atmosphere as CO2CO_2.

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Nitrogen Fixation is the conversion of atmospheric nitrogen (N2N_2), which is unusable by most organisms, into ammonia (NH3NH_3) or ammonium (NH4+NH_4^+) by specialized bacteria like Rhizobium or by lightning.

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Nitrification is a two-step aerobic process where bacteria convert NH4+NH_4^+ into nitrite (NO2−NO_2^-) and then into nitrate (NO3−NO_3^-), which is the form of nitrogen most easily absorbed by plants.

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Assimilation refers to the process by which plants absorb NO3−NO_3^- or NH4+NH_4^+ from the soil to build proteins and nucleic acids.

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Denitrification is the process, usually occurring in anaerobic (oxygen-poor) soils, where bacteria convert NO3−NO_3^- back into N2N_2 gas, completing the cycle.

📐Formulae

6CO2+6H2O+light energy→C6H12O6+6O26CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2

C6H12O6+6O2→6CO2+6H2O+ATP (energy)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP (energy)}

N2→NH3/NH4+N_2 \rightarrow NH_3 / NH_4^+

2NH4++3O2→2NO2−+2H2O+4H+2NH_4^+ + 3O_2 \rightarrow 2NO_2^- + 2H_2O + 4H^+

2NO2−+O2→2NO3−2NO_2^- + O_2 \rightarrow 2NO_3^-

💡Examples

Problem 1:

During a period of heavy rain, a farmer's field becomes waterlogged (anaerobic conditions). Explain which process of the nitrogen cycle will increase and what the effect will be on soil fertility.

Solution:

The process of Denitrification will increase. NO3−→N2NO_3^- \rightarrow N_2.

Explanation:

In anaerobic conditions, denitrifying bacteria thrive. They convert nitrates (NO3−NO_3^-) in the soil back into nitrogen gas (N2N_2), which escapes into the atmosphere. This reduces the amount of nitrogen available for plant uptake, thereby decreasing soil fertility.

Problem 2:

Identify the chemical change that occurs during the combustion of methane (CH4CH_4), a common fossil fuel component.

Solution:

CH4+2O2→CO2+2H2OCH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

Explanation:

Combustion is a chemical reaction where a hydrocarbon reacts with oxygen (O2O_2) to produce carbon dioxide (CO2CO_2) and water (H2OH_2O). This process moves carbon from the geosphere (fossil fuels) to the atmosphere.

Problem 3:

How does the process of 'Assimilation' differ from 'Nitrogen Fixation' in terms of the nitrogen compounds involved?

Solution:

Nitrogen Fixation: N2→NH3N_2 \rightarrow NH_3. Assimilation: NO3− or NH4+→Organic Nitrogen (Proteins)NO_3^- \text{ or } NH_4^+ \rightarrow \text{Organic Nitrogen (Proteins)}.

Explanation:

Nitrogen fixation converts inorganic atmospheric gas (N2N_2) into reactive compounds like ammonia. Assimilation is the intake of those reactive compounds (NO3−NO_3^- or NH4+NH_4^+) by plants to build biological molecules like amino acids.