8.5 3.1.6 nutrient cycles

Nutrient cycles

Organisms rely on nutrients in order to survive. These include carbon, oxygen, nitrogen, water and mineral salts.

These nutrients need to be cycled through the ecosystem so that they can be re- used. This is called nutrient recycling . In biology, this is the movement of nutrients from the physical environment into living organisms and back into the environment. The flow of energy you sawbefore from the sun to herbivores and then to carnivores is part of this process. In any environment the flow of nutrients must be stable and balancedso that organisms can survive. If the cycle stops at any point, nutrients will become locked in place and cannot be used in the next step.

The water cycle, carbon cycle, oxygen cycle and nitrogen cycle are examples of nutrient re-cycling.

Video: (External Link)

Here is a simple video explaining nutrient cycling

Water

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The earth is sometimes known as the "water planet" because over 70 percent of its surface is covered by water. All living organisms need water for theirsurvival.

In this cycle, water is transported between water reservoirs in the environment and living organisms. This happens through these processes:

• Liquid water in oceans and lakes is converted to water vapour by evaporation . This is caused by heating of the water by the sun. The water vapour rises into the atmosphere.
• Plants release water into the air as vapour during photosynthesis, this is called transpiration .
• When water vapour in the atmosphere cools, it can transform into tiny droplets of liquid water to form clouds by the process of condensation
• When condensed water droplets grow so large that the air can no longer support them against the pull of gravity, they fall to the earth through precipitation . If the water droplets fall as liquid, it is called rain. If the temperature of the surrounding air is cold enough to freeze the water droplets, then the waterfalls as snow, sleet or hail.
• Water that falls onto the earth runs into lakes, rivers or oceans.

Animation: (External Link)

This is an animation of the water cycle

Oxygen

Oxygen is one of the main gases found in the air, along with nitrogen.

Oxygen is re-cycled between the air and living organisms in the following ways:

• Organisms take in oxygen during respiration , which they use for cellular processes to break down energy rich nutrients.
• When wood or fossil fuels burn, they consume oxygen and release carbon dioxide and water into the atmosphere through combustion .
• Plants release oxygen into the air as a by-product of photosynthesis .

Because animals trap oxygen during respiration, the release of oxygen by plants during photosynthesis is the main way oxygen is released into the atmosphere.

Video: (External Link)

This is a video explaining the oxygen cycle

Carbon

Carbon is the basic building block of all organic materials, and therefore, of living organisms. Most of the carbon on earth can be found in the crust. Otherreservoirs of carbon include the oceans and atmosphere.

Carbon moves from one reservoir to another by these processes:

• Combustion of wood and fossil fuels transfers carbon to the atmosphere as carbon dioxide.
• Carbon dioxide is taken up by plants during photosynthesis and gets converted into energy rich sources, such as glucose, that contain carbon.
• Animals eat plants for food, taking up the carbon. They release carbon into the atmosphere as carbon dioxide during respiration .
• Organisms convert carbon into organic molecules like fats, carbohydrates and proteins when they eat plants or animals.
• Carbon dioxide in the atmosphere can also precipitate as carbonate in ocean sediments. These ocean sediments are melted by the movement of tectonic plates and then returned to the surface during volcanicactivity.
• Carbon dioxide gas is released into the atmosphere during volcanic eruptions.

Photosynthesis and respiration are the main carbon cycling processes involving living organisms.

GAME: (External Link)

This is a game you can play to learn more about the carbon cycle

Nitrogen

Nitrogen (N2) makes up most of the gas in the atmosphere (about 78%). Nitrogen is important to living organisms and is used in the production of amino acids,proteins and nucleic acids (DNA, RNA). Only a few single-cell organisms, like bacteria can use nitrogen from the atmosphere directly. For multi-cellularorganisms, like plants and animals, nitrogen has to be changed into other forms, eg. nitrates or ammonia. This process is known as nitrogen fixation .

The nitrogen cycle involves these steps:

During decomposition , bacteria and fungi break down proteins and amino acids from plants and animals into nitrogen in the form of ammonia (NH3) by the process of ammonification and convert the ammonia to nitrate (NO3-) by nitrification .

Nitrogen can be changed to nitrates directly by lightning . The rapid growth of fungi and algae after thunderstorms is because of this process, which increases the amount of nitrates that fall onto the earth inrain water, acting as fertilizer.

Ammonia and nitrates are absorbed by plants through their roots.

Humans and animals get their nitrogen supplies by eating plants or plant-eating animals.

The nitrogen is returned to the cycle when bacteria decompose the waste or dead bodies of these higher organisms, and in the process, convert organic nitrogen into ammonia.

In a process called denitrification , other bacteria convert ammonia and nitrate into nitrogen and nitrous oxide (N ₂ O). Nitrogen is returned to the atmosphere to start the cycle over again.

SIMULATION: http://www.teachersdomain.org/asset/lsps07_int_nitrogen/

You can play with this simulation to learn more about the Nitrogen cycle.

Animation:

Here are some animations of the nitrogen cycle:

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