THE CARBON AND NITROGEN CYCLES

Cycles of Life

The Carbon Cycle

Carbon is found in four major reserves on earth.Organisms: Inside the body tissues of living

organisms Atmosphere: As CO2 , CH4, (carbon dioxide and

methane)

Oceans: As dissolved CO2 (which becomes carbonic acid)

Earth Bound: Gas and oil locked inside rock deep within the earth. (this carbon is from once living organisms)

Carbon makes up 50% of an organism’s dry weight. This carbon is locked away inside the body in various compounds such as proteins, sugars (carbohydrates), and nucleic acids.

Photosynthesis

Carbon enters the food chain from the atmosphere through the photosynthetic actions of producers. Plants use a special pigment called chlorophyll to carry out photosynthesis.

Photosynthesis extracts inorganic carbon using the sun’s energy and locks it away as useable carbon, making up half of the carbon cycle.

Cellular Respiration

Cellular respiration releases the energy stored in the chemical bonds of carbohydrates during photosynthesis. This energy can be used by organisms to maintain life functions. All cells use cellular respiration in one form or another (plant cells included).

Human Interference in the Carbon Cycle

In the past, the amount of carbon removed from the atmosphere by photosynthesis has tended to equal the amount returned by cellular respiration and decomposition.

When carbon is added to a certain part of the cycle, it can be disrupted with drastic effects.

The burning of fossil fuels by humans (the remains of dead plants and animals) spews extra carbon dioxide into the atmosphere. The atmospheric concentration of CO2 goes up as a result.

Since carbon dioxide is a greenhouse gas, average global temperatures rise

What do we call this effect? _________________

Sinks: Reduce CO2 in the atmosphere

Sources: Add CO2 to the atmosphere

1. The ocean (water absorbs LOTS of CO2)

2. Forests (photosynthesis removes CO2 from air)

3. Algae (these critters remove CO2 from ocean water allowing more to enter it)

4. Sediments (trapped carbon inside dead critters and plants)

the ocean is the largest single carbon sink on earth, holding 50 times the carbon the atmosphere does.

 

1. Respiration in plants and animals

2. Geothermal activity (volcanoes)

3. Manufacturing (cement, plastics manufacturing, tire manufacturing etc.)

4. Hydro carbon burning (burning of coal, oil, and natural gas, even wood)

Sinks and Sources

The Nitrogen Cycle

Another essential element to life is Nitrogen. All living things incorporate Nitrogen into the proteins, and nucleic acids in their cells.

Although the atmosphere is made up of 78% Nitrogen, most organisms (including plants and animals) cannot use it in its atmospheric elemental form. The Nitrogen must be converted into a useable form (an absorbable compound).

Plants and Animals require the Nitrogen to be in either:

 Ammonium Ions: NH4

orNitrate Ions: NO3

Nitrogen Fixation

The process by which Nitrogen is converted from elemental to a biologically useable form is called Nitrogen Fixation.

In nature, the essential process of nitrogen fixation falls to a few species of nitrogen fixing bacteria. In their regular metabolic cycles, they have evolved the ability to convert atmospheric Nitrogen into Nitrates.

Lightning and Nitrogen

A small percentage of nitorgen is fixed through lightning strikes (providing the energy needed to convert the N)

Rhizobia

Rhizobia are the most important nitrogen fixing bacteria in nature. They live in a symbiotic relationship inside special structures on the roots of certain types of plants.

 What does Symbiotic mean? _______________

Nodules: Special structure on the root of certain plants that contains Nitrogen fixing bacteria. These nodules provide protection to the bacteria and ideal conditions, while the plant reaps the benefits of the conversion of Nitrogen to nitrate.

Legumes: Plants which have root nodules. Examples of these are Alfalfa, Peas, Beans, peanuts.

Nitrogen fixation releases nitrate into the soil. Some enters the food chain through absorption into plants (some into the legumes themselves, some into surrounding non-legumes). Some of the nitrate remains in the soil.

NitrificationIf this process continued in non-cyclical fashion,

eventually all Nitrogen would be removed from the atmosphere (the nitrates in the bodies of dead organisms would decompose, re-releasing nitrate into new organisms).

Another process called Nitrification performed by a few species of soil bacteria (e.g. Nitrosamonas) converts free nitrates into ammonium. Ammonium is not nearly as absorbable as nitrate, although some plants can still use it as their nitrogen source.

DenitrificationThis is the last link in the Nitrogen cycle.

Ammonium is converted back into atmospheric Nitrogen through the actions of denitrifying bacteria.

The Nitrogen Cycle can be altered by human activity:

1. The over farming of legumes adds extra nitrate to the cycle.

2. The addition of chemical fertilizers adds nitrate and ammonia to the cycle.