The Nitrogen Cycle Organisms require nitrogen to produce amino acids. Nitrogen makes up seventy-eight percent of the atmosphere, but most organisms can not use this form of nitrogen, and must have the fixed form. The nitrogen cycle produces the fixed form of nitrogen these organisms need.

Step 1: A special type of bacteria called nitrogen fixing bacteria take in atmospheric nitrogen and produce ammonia (NH3).

Step 2: Other bacteria use this ammonia to produce nitrates and nitrites, which are nitrogen and oxygen containing compounds.

Step 3: The nitrates and nitrites are used by plants to make amino acids which are then used to make plant proteins.

Step 4: Plants are consumed by other organisms which use the plant amino acids to make their own.

Step 5: Decomposers convert the nitrogen found in other organisms into ammonia and return it to the soil. A few of these type of bacteria return nitrogen to the atmosphere by a process called denitrification, however this amount is small.

Water cycle

Over two thirds of the earth's surface is covered by water. It forms an important component of most life forms, with up to 70% of plants and animals being composed of water. Vast quantities of water cycle through Earth's atmosphere, oceans, land and biosphere. This cycling of water is called the water or hydrological cycle. The cycling of water is important in determining our weather and climate, supports plant growth and makes life possible.

o Evaporation: most water evaporates from the oceans, where water is found in highest abundance. However some evaporation also occurs from lakes, rivers, streams and following rain. o Transpiration: is the water loss from the surface area (particularly the stomata) of plants. Transpiration accounts for a massive 50% of land-based evaporation, and 10% of total evaporation.. o Evapotranspiration: the processes of evaporation and transpiration are often collectively referred to as evapotranspiration. o Condensation: the process by which water vapour is converted back into liquid is called condensation. You may have observed a similar process occurring when dew drops form on a blade of grass or on cold glass. Water in the atmosphere condenses to form clouds. o Precipitation: water returns to earth through precipitation in the form of rain, sleet, snow or ice (hail). When rain occurs due to precipitation, most of it runs off into lakes and rivers while a significant portion of it sinks into the ground. o Infiltration: the process through which water sinks into the ground is known as infiltration and is determined by the soil or rock type through which water moves. During the process of sinking into the Earth's surface, water is filtered and purified. Depending on the soil type and the depth to which the water has sunk, the ground water becomes increasingly purified: the deeper the water, the cleaner it becomes. o Melting and freezing: some water freezes and is "locked up in ice, such as in glaciers, and ice sheets. Similarly, water sometimes melts and is returned to oceans and seas.

Oxygen cycle

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:

o Breathing and respiration: organisms such as animals and plants take in oxygen from the air, during breathing and gaseous exchange processes. The oxygen is used for cellular respiration to release energy from organic nutrients such as glucose. o Photosynthesis: during photosynthesis, plants absorb carbon dioxide from the air to synthesize sugars, and release oxygen. o There is a complementary relationship between photosynthesis and respiration in that the former produces oxygen and the latter consumes oxygen.

Carbon cycle

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. Other reservoirs of carbon include the oceans and atmosphere.

Carbon moves from one reservoir to another by these processes:

o Combustion: burning of wood and fossil fuels by factory and auto emissions transfers carbon to the atmosphere as carbon dioxide. o Photosynthesis: carbon dioxide is taken up by plants during photosynthesis and is converted into energy rich sources, such as glucose, which contains carbon. o Cellular respiration: animals eat plants for food, taking up the carbon. Plants and animals release carbon into the atmosphere as carbon dioxide during gaseous exchange o Metabolism: organisms convert carbon into organic molecules like fats, carbohydrates and proteins when they eat plants or animals. o Precipitate: carbon dioxide in the atmosphere can also precipitate as carbonate in ocean sediments. o Decay: carbon dioxide gas is also released into the atmosphere during the decay of all organisms.

Krebs Cycle

a) Krebs cycle ccurs in matrix of mitochondria. b) Only occurs if O2 present. c) Link Reaction: Pyruvate moves into matrix & loses 1 carbon as 1 CO2. 1 more NADH is made. d) The remaining 2C molecule enters the Krebs Cycle.

In several steps, e) energy & hydrogens are removed from the 2 carbons and changed to more NADH & FADH2. These migrate to Electron Transport. f) 1 more ATP is made. The cell can use this. g) each remaining carbon is removed as CO2 & released to air.

Phosphorus Cycle

Phosphorus (P) is another one of the essential elements that cycle through the ecosystem. It is an element that is found in the ground and then taken up by plants and animals. Phosphorus starts its existence as phosphate ions (PO4) in the rocks of the world. When it rains, the phosphates and other minerals are removed from the rocks and distributed in soils and the water all over the planet.

Plants Need It

Plants on land take in the inorganic (compounds without carbon) phosphorus compounds from the soil. The phosphorus atoms are then incorporated into many organic compounds that are used in cells. Animals can get their phosphorus by eating plants or drinking water. Algae and water plants are able to absorb the ions from the water. Unlike carbon and nitrogen, the phosphorus cycle is not a true cycle. There is a great deal of phosphorus lost.

Losing The Element

Phosphorus has a tendency to wind up at the bottom of the ocean. Once at the bottom, the phosphate ions are lost to the world. Sometimes the phosphates are found in runoff water and go to the bottom and sometimes human poop contains phosphate and those phosphates are returned to the ocean. The problem is that all usable phosphorus sources are on the surface The atoms are useless once they reach the bottom of the ocean. Slowly but surely the surface of the Earth is running out of easy places to find phosphorus.

Elemental Concern

Why is there a sudden concern? Phosphorus only gets into the soil by the weathering process on rocks. When plants die in the natural world, the phosphates return to the soil. In farming, the crops are taken away and then over many years the soil runs out of phosphorus compounds. We have created a situation where we must artificially replenish the nutrients in the land. Phosphorus is heavily used in the farming industry and fertilizersfilled with phosphates are used all over the world to help plants grow.