Question

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe the reservoirs that play a role in the carbon cycle and how carbon transfers among reservoirs. (C)

Short answer

The carbon cycle involves four main reservoirs: atmosphere, oceans, living organisms, and Earth's crust. Carbon is transferred among these reservoirs through processes such as photosynthesis, respiration, decomposition, and human activities. Photosynthesis transfers carbon from the atmosphere into living organisms, while respiration returns carbon from living organisms back to the atmosphere. Decomposition breaks down dead organic matter, returning some of its carbon to the atmosphere and incorporating some into the Earth's crust. Oceans store carbon in various forms, including carbonate rocks and marine sediments. Human activities like burning fossil fuels, deforestation, and cement production increase atmospheric carbon dioxide levels and contribute to global climate change.

Step-by-step solution

1. Identify the major reservoirs in the carbon cycle

In the carbon cycle, there are four main reservoirs where carbon is stored: 1. Atmosphere 2. Oceans 3. Living organisms 4. Earth's crust (includes fossil fuels, carbonate rocks, and terrestrial sediments)

2. Explain the transfer of carbon through photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria take in carbon dioxide from the atmosphere and convert it into glucose, a form of organic carbon. During this process, the plants, algae, and bacteria also release oxygen into the atmosphere. By taking in carbon dioxide and producing organic carbon, photosynthesis plays an essential role in transferring carbon from the atmosphere to living organisms.

3. Describe the transfer of carbon through respiration

Respiration is the process by which living organisms, including plants, animals, fungi, and bacteria, break down organic carbon (in the form of glucose) and release carbon dioxide back into the atmosphere. This transfer of carbon from living organisms back to the atmosphere helps to complete the carbon cycle within the biosphere.

4. Explain the role of decomposition in the carbon cycle

Decomposition is the process by which dead organic matter is broken down by decomposers, such as bacteria and fungi, back into its constituent elements, including carbon. Some of this carbon is returned to the atmosphere as carbon dioxide through the process of respiration by decomposers, while some of it is incorporated into the soil as organic matter, contributing to the Earth's crust as a carbon reservoir.

5. Discuss the transfer of carbon in oceans

Oceans play a major role in the carbon cycle, as they can store large amounts of carbon in different forms. Carbon dioxide from the atmosphere dissolves into the surface of the ocean, forming carbonic acid. This can then react with calcium ions present in seawater to form calcium carbonate, which precipitates and forms carbonate rocks, such as limestone, on the ocean floor. Additionally, marine organisms can fix carbon through photosynthesis, converting it into organic carbon within their bodies and shells. When these organisms die and sink, their carbon-containing remains can accumulate on the seafloor and become part of marine sediments.

6. Highlight the role of human activities in the carbon cycle

Human activities, such as burning fossil fuels, deforestation, and cement production, have a significant impact on the carbon cycle. Burning fossil fuels, like coal, oil, and natural gas, releases stored carbon from the Earth's crust back into the atmosphere as carbon dioxide. Deforestation reduces the number of plants that can take in carbon dioxide through photosynthesis, while cement production releases carbon dioxide by breaking down calcium carbonate from limestone. Overall, these human activities contribute to an increase in atmospheric carbon dioxide levels and global climate change.

Key concepts

carbon reservoirs

Carbon reservoirs are the various natural systems where carbon is stored, and they play a critical role in the carbon cycle. There are four main carbon reservoirs:

• Atmosphere: This is the reservoir that holds carbon as carbon dioxide ( CO_2 ). It plays a central role in regulating Earth's climate.
• Oceans: Oceans are the largest and most significant carbon reservoirs. Carbon is present in dissolved form in seawater and also as carbonate compounds within marine organisms.
• Living Organisms: Plants, animals, and other organisms store carbon in various organic compounds like glucose. This is a dynamic reservoir with continuous carbon exchange.
• Earth's Crust: This includes fossil fuels (like coal, oil, and natural gas), carbonate rocks (e.g., limestone), and terrestrial sediments which store carbon over long periods.

Together, these reservoirs ensure a balanced flow of carbon through natural processes, maintaining ecological harmony.

photosynthesis

Photosynthesis is the process that enables plants, algae, and certain bacteria to transform light energy into chemical energy.
During photosynthesis, these organisms absorb carbon dioxide ( CO_2 ) from the atmosphere, and using sunlight, convert it into glucose ( C_6H_{12}O_6 ). Oxygen ( O_2 ) is a byproduct.
This process is essential for transferring carbon from the atmosphere into living organisms, forming the basis of the food chain.

• Light Absorption: The chlorophyll in plants captures sunlight.
• Carbon Fixation: Plants use the absorbed light to convert CO_2 into glucose, storing energy.

Overall, photosynthesis not only supports life by providing energy and nutritional content but also contributes to maintaining balance within the carbon cycle.

respiration

Respiration is a vital biological process through which living organisms, including plants, break down glucose into carbon dioxide ( CO_2 ) and water, releasing energy necessary for life.
During respiration, carbon stored in organic forms is converted back to carbon dioxide and released into the atmosphere. This is essential for completing the cycle of carbon within ecosystems.

• Plants: While plants photosynthesize during the day, they respire both day and night, balancing energy use and production.
• Animals: They primarily depend on respiration to release the energy stored in their food, made up of carbon compounds.
• Microorganisms: Decompose organic matter through respiration, contributing to nutrient cycling and soil fertility.

Respiration connects living organisms with the atmospheric carbon pool, ensuring a cyclical movement of carbon.

decomposition

Decomposition addresses the breakdown of dead organic matter by decomposers, which primarily include bacteria and fungi.
This process transforms the organic carbon in dead organisms into simpler forms, returning some carbon to the atmosphere and some to the soil.

• Carbon Release: Decomposers respire as they break down material, releasing CO_2 into the air.
• Soil Enrichment: Some carbon remains in the soil as organic matter, enhancing soil quality and serving as a reservoir.

Decomposition ensures that carbon is recycled naturally, contributing to the Earth's sustenance systems. It is nature's way of managing waste, supporting new life growth.

human impact on carbon cycle

Human activities significantly alter the natural carbon cycle, affecting global environmental health.

• Fossil Fuel Combustion: The burning of fossil fuels releases large amounts of CO_2 , stored for millions of years in the Earth's crust, into the atmosphere.
• Deforestation: Removing forests decreases the number of trees available to absorb CO_2 , reducing the capacity for carbon sequestration.
• Cement Production: This process releases carbon by breaking down limestone (calcium carbonate) into calcium oxide and CO_2 .

These actions lead to increased atmospheric CO_2 , contributing to climate change. Understanding these impacts is crucial for developing strategies to mitigate environmental damage.