Question

Draw a rough sketch of the carbon cycle and explain the chemical transformations shown in your cycle.

Short answer

In the carbon cycle, carbon moves from atmospheric CO₂ through photosynthesis, respiration, decomposition, and fossil fuel combustion, continually changing form.

Step-by-step solution

Identify the Key Components

In the carbon cycle, the primary components include carbon dioxide in the atmosphere, photosynthesis by plants, respiration by organisms, decomposition of organic matter, and fossil fuel combustion. Write these down as they will be the basis for drawing your cycle.

Draw the Atmospheric Carbon

Start your sketch with a circle labeled 'Atmospheric CO₂.' This represents the carbon dioxide present in the air, which is central to the carbon cycle.

Illustrate Photosynthesis

Connect the 'Atmospheric CO₂' to another labeled area called 'Plants.' Use an arrow to show that plants take in CO₂ for photosynthesis, a process where carbon dioxide and water are transformed into glucose (C₆H₁₂O₆) and oxygen (O₂).

Show Respiration Process

Draw another arrow from 'Plants' to 'Atmospheric CO₂,' and label it as 'Respiration.' This indicates that both plants and animals convert glucose back into CO₂ and water during respiration, releasing energy.

Depict Decomposition

Connect 'Plants' to 'Soil,' where dead plant and animal matter breaks down in a process called decomposition. This process transforms organic carbon into carbon dioxide and sometimes methane (CH₄) if in anaerobic conditions, releasing it back to the atmosphere.

Include Fossil Fuels Combustion

Illustrate an arrow from a labeled section 'Fossil Fuels' to 'Atmospheric CO₂.' This arrow represents the burning of fossil fuels, which releases stored carbon as CO₂ into the atmosphere.

Finalize and Review Your Diagram

Ensure that all components and arrows are labeled correctly and that they flow logically. The carbon moves in a cycle continuously changing form between atmospheric carbon dioxide, organic matter, and fossil fuels.

Key concepts

Photosynthesis

Photosynthesis is a vital process in the carbon cycle where green plants, algae, and some bacteria transform carbon dioxide into organic compounds, primarily glucose, using sunlight. This process takes place in the chloroplasts of plant cells.
During photosynthesis, carbon dioxide \[ 6CO_2 \] from the atmosphere and water \[ 6H_2O \] are converted into glucose \[ C_6H_{12}O_6 \] and oxygen \[ 6O_2 \] through the presence of chlorophyll and light energy.
This can be summed up in the equation:

• \[ 6CO_2 + 6H_2O + ext{light energy} \rightarrow C_6H_{12}O_6 + 6O_2 \]

Photosynthesis not only provides their energy but also produces oxygen, which is essential for most living organisms.
This process helps reduce the concentration of carbon dioxide in the atmosphere, thus playing a crucial role in balancing the earth's carbon levels. Plants act as carbon sinks by absorbing more CO₂ than they release.

Respiration

Respiration is another key process in the carbon cycle. It occurs in all living organisms including plants, animals, and microorganisms.
During respiration, these organisms convert glucose and oxygen back into carbon dioxide and water, releasing energy necessary for various biological activities.
The chemical equation for respiration is the reverse of photosynthesis:

• \[ C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ext{Energy} \]

This process releases CO₂ back into the atmosphere, completing the carbon cycle loop.
Plants perform respiration all the time, but at night when photosynthesis stops, respiration becomes the dominant process in plants. It’s important as it balances out the oxygen production via photosynthesis and keeps the carbon cycle in equilibrium.

Decomposition

Decomposition is the process where complex organic material from dead organisms is broken down into simpler substances. This is carried out by decomposers such as bacteria and fungi.
Through decomposition, organic carbon in the forms of proteins, cellulose, and other compounds are converted back into carbon dioxide and other nutrients.
If the conditions are anaerobic, which means without oxygen, decomposition can also produce methane \( CH_4 \).
This process is crucial for recycling carbon and nutrients in ecosystems, enabling them to be reused by plants and other organisms.

• Carbon returned to soil enriches it, supporting plant growth.
• Aids in maintaining the balance of carbon granules on earth.

The continuous process of decomposition ensures that carbon is not locked away indefinitely, allowing it to enter back into the carbon cycle.

Fossil Fuels Combustion

Fossil fuels combustion refers to the burning of coal, oil, or natural gas, created from the ancient remains of organisms.
This process releases significant amounts of carbon dioxide into the atmosphere as fossil fuels contain high amounts of carbon.
When burned, the chemical reaction is as follows:

• \[ ext{Fuel} + O_2 \rightarrow CO_2 + ext{other products + Energy} \]

Combustion of fossil fuels is a principal contributor to increased carbon dioxide levels in the atmosphere, influencing global climate change.
Human activities like driving cars, generating electricity, and running industries are primarily fueled by fossil combustion, intensifying this effect.
Reducing reliance on fossil fuels and transitioning to renewable energy sources is vital to mitigate these impacts on the carbon cycle and climate.