Tuesday, October 16, 2007


This was the Lesson for Monday and Tuesday!!!

So far we have talked about the three Domains and the different Kingdoms. These encompassed living organisms and their populations. Now we are jumping into the part of the world which includes both the biotic and abiotic factors. An
Ecosystem is all the organisms in a community plus the abiotic factors. Ecosystems need three processes to occur in order to to be self-sustaining:

  1. Capture of energy

  2. Transfer of Energy

  3. Cycle of Nutrients

There are Two Inputs in an ecosystem which are necessary. They are:

  1. Energy
  2. Nutrients
There is a constant source of energy that life of earth gets and that source is the sun. Sunlight is needed in order for there to be life. Energy flows through an ecosystem. Energy is lost through each trophic level. Producers have the greatest amount of energy and primary consumers receive less energy, then seconday consumers get a lesser amount and so on.

Nutrients on the other hand cycle through a system. There are a limited amount of nutrients on this earth and they are recycled because according to the first law of thermodynamics matter can neither be created nor destroyed. Both nutrients and energy go through a series of trophic levels. In general the nutrients are in an abiotic reservoir of some kind. They then are made available to producers, which then goes to consumers. Decomposers are the key to recycling most nutrients. They take the stored nutrients and put them back into the ecosystem to circulate the process. There are various elements that can be cycled. A couple important cycles are the carbon cycle, nitrogen cycle, phosphorus cycle, and the water cycle.

Carbon Cycle:

The Carbon cycle is the most known and famous cycle because of its importance. Organisms on earth are carbon based so carbon is essential for life. Carbon is found in the atmosphere and is made usable by the process of photosynthesis. Producers take carbon and in the process of photosynthesis make it usable to the rest of the biotic community. Carbon is returned back into the atmosphere with respiration as animals exhale it out as a byproduct of respiration. Carbon can also be returned into the atmosphere when humans burn fossil fuels which are the deposition of dead material.

Nitrogen Cycle:

The Nitrogen cycle is different in that nitrogen is mostly found in an unusable form. The triple bond of N2 prevents most processes from breaking down the compound. Bacteria are the only ones that can break down nitrogen into a usable form. Nitrogen-fixing bacteria make nitrogen available in the soil which consumers eat where nitrogen is then return to the soil with either decomposition or excretion. Denitrifying bacteria are the only ones that can return nitrogen back into the atmosphere. The nitrogen cycle is important because nitrogen is included in the base pairs of DNA as they are called nitrogen bases. Nitrogen also is important for the production of amino acids which code for proteins which enzymes are. Enzymes take part in many processes.

Phosphorus Cycle:

Phosphorus is found in rocks and minerals, usually igneous rock. Phosphates are leeched by water and are available in the water or soluble soil which are then absorbed by plants. Phosphorus cannot be returned to the abiotic reservoir but decomposers cycle the phosphorus. Sugar phosphates line DNA and phosphates are included in Adenosine Triphosphate.

Water Cycle:

The reservoir for water is usually the ocean, lakes, groundwater, or water vapor in the atmosphere. Precipitation transfers water from the atmosphere to the ground. Evaporation transfers some water from the ground to the atmosphere but transpiration does most of the job. Transpiration is the evaporation of water from plants as water escapes the stomates. The stickiness of water which causes one molecule of water to pull another molecule up a plant is called transpirational pull.

Deforestation has been breaking the water cycle. Groundwater is not transpired to the atmosphere, so precipitation is not created. This has led to desertification. Deforestation has caused nitrate levels in runoff to increase by 600% as shown by studies done in the Hubbard Brook forest region. There are people out there in the world trying to make a difference. The Greenbelt Movement in Kenya has been influenced by Wangari Maathai who has restored sustainable ecosystems and has won a Nobel Peace prize in 2004.

Deforestation in Eastern Angola

Deforestation in Middle Land, ParĂ¡ Brazil

Wangari Maathai planting a tree at the Outspan Hotel, Nyeri, Kenya, to mark the launch of her autobiography, Unbowed

Deforestation Video:

Ecological Pyramid and Trophic Structure:

Food webs are linked into food webs because there is a complex connecting system of producers, preys, and predators. Depending on what a species eats or its niche, it can weave into the web at different levels. All levels are connected by decomposers who put the dead matter back into the cycle. The length of a food chain is limited by inefficiency of energy transfer. Energy is always lost at each level. in various processes. 50% of energy is passed the organism and is given off as waste. 33% of energy goes to cellular respiration and the rest of the 17% goes to growth. The loss of energy at each level creates an ecological pyramid in both energy amount and population size. The bottom of the pyramid has a lot of energy so it can hold a greater population while the top has very little energy so it can hold only a small population.


  1. Energy flows through a system

  2. Nutrients cycle through a system
  3. Both energy and nutrients are needed to support an Ecosystem

More Information on Hubbard Brook Research go to: http://www.hubbardbrook.org/

More Info on the Grenbelt Movement go to: http://www.greenbeltmovement.org/

Tomorrow's Sherpa will be Kristen

1 comment:

Carl said...

Excellent blog post!

Your information about the nitrogen cycle was especially interesting, which is my field of research. There is so much misinformation currently available about nitrification and de-nitrification.

Carl Strohmeyer; Aquarium Nitrogen Cycle