Hey.. I really dont know to much about the cycles because I didnt pay attention to how they were connected…I did a term paper on employment at will.But this website seemed to know what you were talking about..it explains how the carbon and oxygen cycle work and how we are affected and stuff. http://www.p2pays.org/ref/03/02426/primer3.html

I hope it works!

The water cycle is the only one of those three that takes place completely independent of life. So if you are asking what is critical fro life to arise, I suppose that would be it. But life forms on Earth really only need water in liquid form, and without the water cycle, there would still be plenty of liquid water to last a while. Similarly, the C-O cycle replenishes and maintains a balance, but isn’t critical per se. So my vote is for the nitrogen cycle. Without nitrogen fixation, we can’t make use of the molecular nitrogen in the atmosphere. That would mean no DNA, RNA, or proteins, pretty much undermining life as we know it.

By carbon/oxygen, I assume you mean carbon dioxide. The way that works is that we humans inhale oxygen and exhale carbon dioxide. Then the plants photosynthesize the carbon dioxide and produce more oxygen, which we then breathe. I can’t help with the others, though, sorry!

In addition to energy, organisms require a supply of materials to live. These chemical elements are available in the biosphere but must be constantly recycled in order to maintain their availability. This is done by Biogeochemical cycles.

Biogeochemical cycles (bio meaning ‘life’, geo for ‘earth’ and chemical for the changing of matter from one form to another) are natural processes that recycle elements in various chemical forms from the environment, to organisms, and then back to the environment. Water, carbon, oxygen, nitrogen, and other elements pass through these cycles, connecting the living and non-living components of the Earth. The element cycles are one of the basic life support systems of the biosphere.

The water cycle (or hydrological cycle) is the circulation of the waters of the Earth between land, freshwater lakes and rivers, the salt seas and oceans, and the atmosphere. This cycle collects, purifies, and distributes the Earth’s fixed supply of water.

Water cycle follows these steps

1Through evaporation, water on the land and in the oceans is converted by solar energy into water vapour. Winds then move masses of water vapour around the Earth.

2 Through condensation, water vapour is turned into water droplets, which form clouds or fog.

3 Through precipitation, water returns to the Earth in the form of dew, rain, hail, or snow.

4 Through transpiration, water is absorbed by the roots of plants, passed through their stems and other structures, and released from their leaves as water vapour.

5 Through run-off, water moves from the land to the sea, or else from the land into the ground where it is stored (from which it eventually returns to the surface or to lakes, streams, and oceans).

Carbon is an essential component of all living things. It exists mostly as carbon dioxide in the atmosphere, oceans, and in fossil fuels stored beneath the Earth’s surface. The major steps of the carbon cycle are the following:

1 Carbon dioxide in the atmosphere is absorbed by plants and converted into sugar, by the process of photosynthesis.

2 Animals eat plants, breaking down the sugars and releasing carbon into the atmosphere, oceans or soil.

3 Other organisms break down dead plant and animal matter, returning carbon to the non-living environment.

4 Carbon is also exchanged between the oceans and the atmosphere. This occurs in both directions at the interface between the air and water. When the level of carbon dioxide in the oceans (atmosphere) exceeds a certain level, it will flow from the higher concentration in the oceans (atmosphere) to the lower concentration in the atmosphere (oceans), maintaining equilibrium.

Oxygen composes nearly 21% of the atmosphere. It combines chemically with a multitude of other elements to form important substances such as water, carbon dioxide, plant nutrients and organic substances. The steps of the oxygen cycle are the following:

1 Plants release oxygen into the atmosphere as a by-product of photosynthesis.

2 Animals take in oxygen and, by the process of respiration, use it to break down sugars obtained from food.

3 Carbon dioxide is released by animals and used by plants in photosynthesis.

4 Oxygen is also cycled between the oceans and the atmosphere, maintaining oxygen equilibrium.

Two process connect oxygen and carbon cycles

1 Photosynthesis- Photosynthesis is the process by which most autotrophic organisms organisms that manufacture their own food nourish themselves. Green plants, for example, are photosynthetic. Energy from the sun is used to convert carbon dioxide and water into sugars. Sugar is used to form tissues, allowing the organism to grow and reproduce. It is also used as a source of energy.

2 Respiration- Respiration is a process carried out in the cells of both plants and animals. Sugars, whether obtained through photosynthesis or consumption, contain stored (potential) energy which is released when they are burned. This burning takes place in a slow, controlled way within cells, fuelling basic life processes. This conversion of sugars into energy is called respiration; it uses oxygen and produces carbon dioxide.

Through photosynthesis, carbon dioxide is converted into sugar and oxygen, whereas through respiration, oxygen and sugar are converted back into carbon dioxide.

Nitrogen Cycle

Nitrogen is essential for life; living things need it to make proteins and DNA. Nitrogen gas constitutes about 78% of the atmosphere, but it is useless to most living things in this form. There are three main steps in the cycle that converts nitrogen gas into proteins and DNA and back into nitrogen gas again:

1 Certain kinds of organisms (mainly a type of bacteria called cyanobacteria) are able to transform nitrogen gas into water soluble compounds that can be taken up by the roots of plants; this process is called nitrogen fixation.

2 Plants then convert these compounds into protein and DNA. Animals get the nitrogen they need by eating plants or other animals.

3 When plants and animals die, a series of processes, again mediated by bacteria, converts the nitrogen compounds in the dead matter back into nitrogen gas, completing the cycle.

How do humans affect the cycling of oxygen and carbon?

We breathe, taking oxygen out of the air and adding carbon dioxide.

We burn fossil fuels, thereby decreasing oxygen levels and adding carbon dioxide to the atmosphere.

We cut down forests without sufficient replanting. This leaves less vegetation to release oxygen and to absorb carbon dioxide.

We pollute our oceans, destroying photoplankton (microscopic aquatic plants). This has the same effect less oxygen, more carbon dioxide.

We burn fossil fuels. This releases nitrogen compounds into the atmosphere; these compounds can in turn be converted to nitric acid, a component of acid rain.

We fertilize our crops and lawns. The nitrogen contained in fertilizer is important for agricultural productivity, yet much of it seeps into groundwater or runs off into lakes and rivers. An excessive supply of this nutrient causes rapid growth of algae, beginning a chain of effects that disrupts life in aquatic ecosystems

I have provided you the source. Do go to these sites. You will find more information