Question

Which of the following processes releases carbon dioxide to the atmosphere? (A) photosynthesis (B) the formation of fossils and fossil fuels (C) respiration by plants and animals (D) burying waste matter in landfills

Short answer

The process that releases carbon dioxide to the atmosphere is (C) respiration by plants and animals. During respiration, glucose is broken down in the presence of oxygen, releasing energy, water, and carbon dioxide as by-products, which contributes to the release of carbon dioxide to the atmosphere.

Step-by-step solution

Understanding Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert sunlight, water, and carbon dioxide into glucose and oxygen. During this process, carbon dioxide is removed from the atmosphere and used as a component in the formation of glucose. Therefore, photosynthesis does not release carbon dioxide into the atmosphere.

Formation of Fossils and Fossil Fuels

Fossils and fossil fuels are formed over millions of years from the remains of dead plants and animals. Over time, these remains get buried and are subjected to heat and pressure, which turn them into fossil fuels like coal, oil, and natural gas. While the carbon in these remains is eventually stored in the form of fossil fuels, the formation process itself does not release carbon dioxide into the atmosphere.

Respiration by Plants and Animals

Respiration is the process by which plants, animals, and other organisms release energy from glucose. During respiration, glucose is broken down in the presence of oxygen, releasing energy, water, and carbon dioxide as by-products. Since respiration involves the release of carbon dioxide as a by-product, this process contributes to the release of carbon dioxide to the atmosphere.

Burying Waste Matter in Landfills

In landfills, waste material is buried to decompose and break down. When organic waste decomposes under anaerobic conditions (i.e., without oxygen), it produces methane gas, which is another greenhouse gas but not carbon dioxide. While some decomposition can also occur under aerobic conditions (with oxygen), leading to the release of carbon dioxide, the main greenhouse gas produced in landfills is methane, not carbon dioxide.

Conclusion

Among the given processes, only respiration by plants and animals releases carbon dioxide to the atmosphere. Therefore, the correct answer is (C) respiration by plants and animals.

Key concepts

Photosynthesis

Photosynthesis is an incredible process carried out by plants, algae, and some bacteria. Through this natural phenomenon, these organisms harness sunlight, combining it with water and carbon dioxide to produce glucose and oxygen.
This remarkable transformation not only provides essential nutrients to plants but also plays a vital role in balancing atmospheric gases. During photosynthesis, plants absorb carbon dioxide from the air. Thus, it does not emit but rather absorbs carbon dioxide.
Photosynthesis is crucial for removing carbon dioxide from the environment, making it a key component in addressing elevated levels of this gas.

Respiration

Respiration happens in plants, animals, and many microorganisms. Unlike photosynthesis, respiration involves breaking down glucose to release energy. This process occurs in the presence of oxygen and results in the production of carbon dioxide and water as by-products.

The Process of Respiration

• Glucose combines with oxygen in cells.
• Energy is released, used by living organisms for various activities.
• Carbon dioxide and water are expelled.

As carbon dioxide is released during respiration, it contributes significantly to the carbon cycle by adding this gas back into the atmosphere.

Fossil Fuels

Fossil fuels such as coal, oil, and natural gas have accumulated over millions of years. These energy resources are formed from the remnants of ancient plants and animals, buried and subjected to heat and pressure.

Fossil Fuel Formation

• Organic material accumulates and gets buried.
• Heat and pressure transform this material over geological timescales.
• The process results in the formation of substances rich in carbon, like coal.

While the formation doesn’t directly release carbon dioxide, burning fossil fuels for energy liberates carbon stored for millennia back into the atmosphere, contributing to carbon emissions.

Greenhouse Gases

Greenhouse gases are essential components of the Earth's atmosphere that trap heat, maintaining the planet’s temperature range. Too much of these gases can lead to global warming, affecting climate patterns.

Examples of Greenhouse Gases

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Nitrous oxide (N₂O)

Carbon dioxide and methane play major roles in this effect. While CO₂ is a by-product of respiration and burning fossil fuels, methane is notably produced in landfills and from agricultural practices. Managing emissions of these gases is critical for mitigating climate change.