Nitrogen and Carbon Cycle

Consumers must obtain nitrogen from the organisms they consume. Herbivores receive their nitrogen from the plants that they eat, and carnivores get their nitrogen from the animals they consume. However, all organisms depend on the ability of nitrogen-fixing microorganisms to convert atmospheric nitrogen into a form of nitrogen that plants can assimilate, or take in and use.

Finally, nitrogen is returned to the atmosphere through the combustion of fossil fuels or when decomposers break down the nitrogen found in fertilizers, urine, and dead plants and animals.

CARBON Cycle

Carbon and oxygen are necessary for all organisms. These elements move between producers, consumers, and the atmosphere in a continuous biogeochemical cycle.

The carbon and oxygen cycles are sometimes discussed separately. However, these cycles can also be addressed together since they are dependent upon each other for proper operation. This combined, interdependent cycle is known as the carbon-oxygen cycle.

Processes that Release Carbon Dioxide into the Atmosphere

• Cellular respiration is a natural process in which substances are broken down to create energy.

• Decay is a natural process in which organic matter, like dead organisms, decomposes or breaks down.

• Volcanic activity is a natural process involving the eruption of hot gases and rock material from within the Earth.

• Weathering is the process by which stones at the Earth's surface are broken down, either physically or chemically.

• Combustion is a reaction in which a substance burns in oxygen.

  • It can be natural, such as a forest fire started by lightning.

  • It can be man-made, such as burning wood and fossil fuels.

• Degasification is the release of carbon dioxide, once dissolved in water, into the air. It is a natural process, but it has increased due to higher global temperatures. Warm water can hold less dissolved gases than cooler water. This is why a can of soda goes flat when it gets warm.

Processes that Store Carbon Dioxide

• Photosynthesis is a natural process in which carbon dioxide and water are converted into sugar.

• Sedimentation is a natural process in which pieces of rock and other matter settle out of water and are buried.

• Dissolution is a natural process in which carbon dioxide from the atmosphere dissolves into water.

Photosynthesis & Respiration

The two most important natural processes that drive the carbon-oxygen cycle are photosynthesis and cellular respiration. Each of these processes must take place in order for the cycle to function properly. This is because the end products of one process are starting materials for the other.

Photosynthesis:

carbon dioxide + water → sugar + oxygen

The end products of photosynthesis are sugar and oxygen. These substances are the starting materials of cellular respiration.

Cellular Respiration:

sugar + oxygen → carbon dioxide + water

The end products of cellular respiration are carbon dioxide and water. These substances are the starting materials of photosynthesis.

Life and the Water Cycle

Ecosystems and living organisms depend on the water cycle. Most living organisms, including humans, depend on the water cycle and actually take part in it. Land animals, for example, need to consume fresh water to remain hydrated. Without fresh water to drink, land animals quickly die. But the vast majority of water on Earth is saltwater and undrinkable. Fortunately, the water cycle supplies fresh water on land through the process of evaporation and precipitation. When water from the Earth's saltwater oceans evaporates, it leaves the salt behind. The freshwater travels by wind over land and falls as precipitation. This process makes it possible for animals to survive on land.

Animals, including humans, make use of the water cycle in other ways as well. When a person sweats (perspires) the water on his or her skin evaporates. This has the effect of keeping the person cool. Many other animals, including dogs, use panting to keep cool, which also involves the evaporation of water.