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Biology - Carbon Cycle

Grade 9IGCSE

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

🔑Concepts

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The Carbon Cycle describes how carbon atoms continually travel from the atmosphere to the Earth and then back into the atmosphere.

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Photosynthesis is the primary process that removes carbon dioxide (CO2CO_{2}) from the atmosphere. Green plants and algae capture CO2CO_{2} and convert it into glucose (C6H12O6C_{6}H_{12}O_{6}).

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Respiration is the process by which all living organisms (including plants) release energy from food. This process returns CO2CO_{2} to the atmosphere as a byproduct.

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Feeding/Consumption: Carbon is transferred as organic compounds (carbohydrates, fats, proteins) when animals eat plants or other animals.

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Decomposition: Decomposers like bacteria and fungi break down dead organic matter. Through their own respiration, they release CO2CO_{2} back into the atmosphere.

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Combustion: The burning of fossil fuels (coal, oil, and gas) or organic matter like wood reacts with oxygen (O2O_{2}) to release stored carbon as CO2CO_{2}.

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Fossilization: In specific conditions where decomposers cannot function (e.g., acidic bogs), dead matter may be compressed over millions of years to form fossil fuels.

📐Formulae

6CO2+6H2O→light, chlorophyllC6H12O6+6O26CO_{2} + 6H_{2}O \xrightarrow{\text{light, chlorophyll}} C_{6}H_{12}O_{6} + 6O_{2}

C6H12O6+6O2→6CO2+6H2O+EnergyC_{6}H_{12}O_{6} + 6O_{2} \rightarrow 6CO_{2} + 6H_{2}O + \text{Energy}

Fuel (Hydrocarbon)+O2→CO2+H2O+Heat Energy\text{Fuel (Hydrocarbon)} + O_{2} \rightarrow CO_{2} + H_{2}O + \text{Heat Energy}

💡Examples

Problem 1:

Calculate the mass of carbon dioxide (CO2CO_{2}) produced from the aerobic respiration of 180 g180\text{ g} of glucose (C6H12O6C_{6}H_{12}O_{6}), given that the molar mass of glucose is 180 g/mol180\text{ g/mol} and the molar mass of CO2CO_{2} is 44 g/mol44\text{ g/mol}.

Solution:

Moles of Glucose=180180=1 molFrom the equation, 1 mole of glucose produces 6 moles of CO2Mass of CO2=6×44=264 g\begin{array}{r} \text{Moles of Glucose} = \frac{180}{180} = 1 \text{ mol} \\ \text{From the equation, 1 mole of glucose produces 6 moles of } CO_{2} \\ \text{Mass of } CO_{2} = 6 \times 44 = 264\text{ g} \end{array}

Explanation:

According to the balanced chemical equation for respiration, the molar ratio of glucose to carbon dioxide is 1:61:6. Therefore, 11 mole of glucose yields 66 moles of CO2CO_{2}.

Problem 2:

Explain how deforestation and the increased use of fossil fuels disrupt the natural carbon cycle.

Solution:

Deforestation reduces the rate of photosynthesis, meaning less CO2CO_{2} is removed from the atmosphere. Simultaneously, combustion of fossil fuels adds CO2CO_{2} that was stored underground for millions of years. Both actions lead to a net increase in atmospheric CO2CO_{2} concentration.

Explanation:

The carbon cycle is a balance between 'sinks' (processes that absorb carbon) and 'sources' (processes that release carbon). Increasing sources while decreasing sinks leads to global warming via the greenhouse effect.