Cycles within ecosystems

Elements move about within our environment, from organism to organism. It’s strange to think that all of the atoms inside of us have at one point formed stars, bacteria, the ocean, trees, flowers, fish and right now they happen to be sitting hanging around inside of you. This page outlines the different forms in which nitrogen, carbon and water move within ecosystems.

 
 

The nitrogen cycle

Plants can only absorb nitrogen in the form of nitrate so they depend on nitrogen-fixing bacteria to convert nitrogen in the air into nitrate in the soil. These bacteria either live freely in the soil or inside root nodules, forming a symbiotic relationship with the plant.

The Haber process is used to convert nitrogen into ammonia which is used in fertilisers. Nitrifying bacteria convert the ammonia into nitrates. Plants absorb the nitrates and incorporate the nitrogen into amino acids which are used to build proteins. The breakdown of proteins in our bodies produces urea which is removed from our body in our urine. Nitrogen is also returned to the soil by the decomposition of dead matter by microorganisms such as bacteria and fungi.

In some conditions, denitrifying bacteria convert nitrates in the soil into nitrogen in the air. This usually happens in soil which is lacking oxygen, such as waterlogged soil. Therefore, improving drainage can make soil more fertile by retaining more nitrates.

The nitrogen cycle describes the movement of nitrogen through an ecosystem. Nitrogen in the air is converted into nitrates in the soil by nitrogen-fixing bacteria. Plants absorb nitrates and use the mineral to make proteins. Decomposition of animal waste or dead matter converts nitrogen in amino acids into ammonium ions, which are turned into nitrates by nitrifying bacteria. Denitrifying bacteria decreases the amount of nitrates in the soil by converting nitrates into atmospheric nitrogen.

The carbon cycle

Carbon is added to the atmosphere when respiration of living organisms and combustion of fossil fuels release carbon dioxide into the air. The carbon dioxide is removed from the air by plants and converted into carbohydrate during photosynthesis. When animals eat the plants, they incorporate the carbon into their own biological molecules, such as carbohydrate, proteins and lipids. When animals and plants decompose, carbon is released into the atmosphere through the respiration of decomposers, such as bacteria and fungi. The carbon in any remaining dead material will eventually form fossil fuels after millions of years of compression beneath the Earth’s surface.

The carbon cycle shows the movement of carbon through an ecosystem. Carbon dioxide is removed from the atmosphere and converted into organic carbon by photosynthesis. The carbon-containing compounds are passed along the food chain when one organism …

The carbon cycle shows the movement of carbon through an ecosystem. Carbon dioxide is removed from the atmosphere and converted into organic carbon by photosynthesis. The carbon-containing compounds are passed along the food chain when one organism eats another. Respiration of plants and animals returns carbon dioxide to the atmosphere, along with the combustion of fuels. Decomposition of organic matter releases carbon dioxide because the microorganisms which decompose the organism are respiring.

The Water Cycle

Water is essential to life on Earth and is constantly moving through our environment. Some of the water on the Earth’s surface, for example in oceans, lakes and puddles, evaporates when exposed to heat energy from the Sun, forming water vapour in the atmosphere. This condenses to form clouds which are easily blown by winds to other areas. Precipitation of the water droplets within clouds returns water back to the Earth’s surface, which is either absorbed into the ground (infiltration) or runs along the surface of the ground (surface run-off) and into streams and rivers. Some of the water that has been absorbed by soil is taken up by plants for photosynthesis. Some water evaporates from the surface of the leaf, through the stomata, in a process called transpiration. Transpiration creates a pulling force (transpiration pull), resulting in the movement of water through the plant.

The water cycle shows the movement of water through an ecosystem. Evaporation of water from oceans, rivers and streams along with the loss of water vapour through the leaves of photosynthesising plants increases the amount of water vapour in the atm…

The water cycle shows the movement of water through an ecosystem. Evaporation of water from oceans, rivers and streams along with the loss of water vapour through the leaves of photosynthesising plants increases the amount of water vapour in the atmosphere. The water vapour condenses into clouds, which are moved by the wind to other parts of the ecosystem. Water returns back to the ground during precipitation (rainfall).

Did you know..

A single tree can release up to one thousand litres of water each day through transpiration. Large-scale deforestation reduces the amount of transpiration resulting in fewer clouds and less rainfall which has a negative impact on several plant and animal species which rely on fresh water for their survival.