The Nitrogen Cycle Revision

Página 1

The Nitrogen Cycle Revision

Nitrogen is a vital element for all living things. It is needed to make proteins.

Proteins themselves are needed as raw materials for the building of new cells and repairing the old cells.

Whenever an organism is growing there is a need for nitrogen.

Plants can easily make carbohydrates by photosynthesis. These are converted into fats. But for proteins plants need to absorb nitrogen.

The nitrogen is absorbed from nitrates that are in the soil.

Plants cannot use gaseous nitrogen, which is the most common gas in the atmosphere. Only certain bacteria in the ground can use nitrogen gas; converting it into nitrates, which the plants absorb.

Nitrogen

The Nitrogen Cycle

There is a limited supply of nitrogen on the Earth and so for life to be sustained it has to be recycled.

The cycle is dependent of various bacteria converting nitrogen gas from the atmosphere into nitrates.

The nitrates are then absorbed into the soil, which is then absorbed by the plants roots.

Animals get their nitrogen from eating the plants.

When animals excrete it returns nitrogen back into the soil.

Urea (animal wee) contains a lot of nitrogen.

Nitrogen is also returned to the soil when animals and plants die and their bodies get broken down by decomposers.

Body proteins and urea are converted into ammonia during decomposition.

Soil bacteria can change the ammonia into nitrates, which can then be re-used by plants.

Another type of bacteria changes the soil nitrates back into gaseous nitrogen, which gets released back into the atmosphere to complete the cycle.

Urea and urease

The bacteria which breaks down urea does so by using the enzyme urease.

As it is an enzyme catalyzed reaction, it is influenced by certain factors:

Warm temperatures speed up the action of the enzyme, but if the temperature increases over 60 degrees the enzyme is destroyed. We call this denatured. And the reaction stops.

The optimum pH for urease is about 7. If the pH gets much higher of lower than 7 the enzyme will denature.

Increasing the concentration of the urease or urea can speed up the reaction as long as the other factors allow it.

New Page