Carbon and Nitrogen Cycles

Carbohydrates and fats are primarily composed of carbon, hydrogen, and oxygen. Proteins and DNA also contain nitrogen, but C, H, and O are the fundamental building blocks present in all four categories.

Both carbon and nitrogen are essential nutrients that animals obtain by consuming other organisms. Plants do not get both from the air, and animals do not get them through respiration.

Atmospheric nitrogen (N2) is inert and cannot be used directly by plants. It must be 'fixed' by bacteria into forms like ammonia or nitrates to be biologically useful.

Nitrogen-fixing bacteria convert atmospheric nitrogen (N2) into ammonia or other compounds in the soil that plants can absorb.

Denitrifying bacteria convert nitrates in the soil back into nitrogen gas (N2), releasing it into the atmosphere.

The atmosphere is composed primarily of nitrogen gas, which exists as a diatomic molecule with the formula N2.

Aquatic ecosystems involve the same fundamental biological processes as terrestrial ones. Photosynthesis occurs in algae and plants, respiration occurs in all living organisms, and decomposition breaks down organic matter.

Consumption is the process where heterotrophs ingest organic matter, such as starch from plants, to obtain energy and nutrients. Combustion is a chemical burning process, while photosynthesis is the production of starch by plants.

Combustion is the chemical reaction of a substance with oxygen, releasing heat and often carbon dioxide, which is exactly what happens when fossil fuels are burned. The other options refer to biological or geological processes.

Yeast performs alcoholic fermentation, which releases carbon dioxide as a byproduct. While plants perform cellular respiration, they primarily use aerobic respiration; however, in the context of many biology curricula, yeast is the classic example of an organism that releases CO2 via anaerobic processes.

Carbon is stored in various reservoirs on Earth, including the ocean (dissolved carbon), the atmosphere (as CO2), and underground in fossil fuels. Therefore, all these locations serve as carbon sinks or storage areas.

Decomposers break down organic matter, and during this metabolic process, they release carbon dioxide back into the atmosphere as a byproduct of their cellular respiration.

Photosynthesis is the process by which autotrophs (like plants) take inorganic carbon dioxide from the atmosphere and convert it into organic carbon (glucose), effectively moving carbon into the living world.