Answer: B - They are cycled through ecosystems.
Elements such as carbon and oxygen play a fundamental role in the composition of organic molecules, which are integral to the structure and function of living organisms. The reason why these crucial elements are not permanently removed from the environment is that they are cycled through ecosystems via biogeochemical cycles. These cycles involve the continuous movement and transformation of elements between different environmental reservoirs, including the atmosphere, living organisms, water bodies, and the Earth's crust.
For instance, the carbon cycle describes how carbon atoms are exchanged between various components of the environment. During the process of photosynthesis, plants and photosynthetic algae capture carbon dioxide (CO2) from the atmosphere and convert it into energy-rich organic compounds. These compounds are then utilized by organisms as a source of energy and building material. When organisms undergo cellular respiration, CO2 is released back into the atmosphere as a byproduct. Additionally, when organisms die, their remains are decomposed by microbes, further contributing to the release of carbon into the environment. Carbon is also sequestered in long-term reservoirs such as rocks, soils, and fossil fuels, and can be released through natural processes like volcanic eruptions and weathering.
Similarly, the oxygen cycle involves the movement of oxygen between the atmosphere and living organisms. Oxygen is produced during photosynthesis when plants and algae convert CO2 and water into organic compounds and release oxygen as a byproduct. This oxygen is then utilized by organisms for cellular respiration, which produces energy and releases CO2 and water. Oxygen can also be dissolved in water and is used by aquatic organisms for respiration.
Overall, the cycling of elements such as carbon and oxygen through ecosystems ensures their continuous availability and prevents their permanent removal from the environment. This cycling is essential for maintaining the stability of ecosystems and supporting life on Earth.
