Unit 4 Section 5 - Biogeochemical Cycles

Part a | Part b | Lab | Key terms | Weekly quiz | Quizstar

  1. Biogeochemical cycles
  2. Water Cycle
  3. Evaporation
  4. Transpiration
  1. Precipitation
  2. Nitrogen Cycle
  3. Nitrogen fixation
  4. Ammonification
  1. Nitrification
  2. Denitrification
  3. Carbon Cycle
  4. Oxygen Cycle

Biogeochemical Cycles:
the process by which abiotic materials move from the
atmosphere or soil into organisms and back again.

The abiotic materials (inorganic nutrients) cycle through more than the organisms, they also enter into the atmosphere, the oceans, and even rocks. Since these chemicals cycle through both the biological and the geological world, we call the overall cycles biogeochemical cycles. Each chemical has its own unique cycle, but all of the cycles do have some things in common. Reservoirs are those parts of the cycle where the chemical is held in large quantities for long periods of time. In exchange pools, on the other hand, the chemical is held for only a short time. The length of time a chemical is held in an exchange pool or a reservoir is termed its residence time. The oceans are a reservoir for water, while a cloud is an exchange pool. Water may reside in an ocean for thousands of years, but in a cloud for a few days at best. The biotic community includes all living organisms. This community may serve as an exchange pool (although for some chemicals like carbon, bound in a sequoia for a thousand years, it may seem more like a reservoir), and also serve to move chemicals from one stage of the cycle to another. For instance, the trees of the tropical rain forest bring water up from the forest floor to be evaporated into the atmosphere… The energy for most of the transportation of chemicals from one place to another is provided either by the sun or by the heat released from the mantle and core of the Earth.

click to find the answer to today's question Why is the water in the ocean salty?

The water cycle: link to an Internet Website
  • There are about 1.5 billion km3 of water on Earth.
    • 97% of the water on earth is in the oceans.
    • Only 3% of the water on earth is freshwater.
    • About 2.4% of the water on earth is permanently frozen in glaciers and the polar ice caps.
    • About 1/2 of 1 % of the water on earth is groundwater. link to an Internet Website
    • Only about 1/100 of 1% of the water on earth is in the rivers and lakes.
  • Most cycling occurs through:
    1. Evaporation link to an Internet Website
    2. Transpiration link to an Internet Website
    3. Precipitation link to an Internet Website

Test your knowledgelink to an Internet Websiteof the water cycle.

click for a career


4.5a Assignment - Biogeochemical Cycles
Use the links provided in this assignment and the information on this page to answer the questions.
Scoring criterialink to a local webpage

  1. How much of Earth's water is found in rivers and lakes?
  2. Study this website link to an Internet Website to answer these questions:
    1. Clouds are formed by condensation. What does water condense on to form a cloud?
    2. What type of clouds are made of ice crystals?
    3. Why does water move horizontally through an aquifer instead of downward?

  3. Study this website link to an Internet Website to answer these questions:
    1. During 1995, how many gallons of freshwater were used each day in Arizona?
    2. What were the top four categories for the use of this freshwater?
    3. We all know that the "dust bowl" was caused by the worst drought in history. Officially, during what years did this drought occur?

part b biogeochemical cycles

click to find the answer to today's question Your body must have nitrogen to make what compounds?

link to a local webpage with useful information The nitrogen cycle: link to an Internet Website converts atmospheric nitrogen, N2 , into a form plants and animals can use.  

Nitrogen makes up about 78% of the atmosphere. However, most living things cannot use atmospheric nitrogen and must rely on nitrates (NO3-) and nitrites (NO2-) in the soil.

    The nitrogen cycle, like the carbon cycle, involves a gaseous form, i.e., N2 or nitrogen gas

    1. Nitrogen gas may be removed from the atmosphere, particularly by bacteria, in a process called nitrogen fixing [which is relatively expensive since nitrogen gas is quite stable]

    2. Nitrogen gas may be returned to the atmosphere, again particularly by bacteria, in a process called denitrification (a form of anaerobic respiration);

    3. More typically, bioavailable nitrogen is found as ammonium ion (NH4+), nitrate ion (NO32-), and various organic, nitrogen-containing compounds (e.g., amino acids and nucleic acids)

    4. Nitrate and ammonium ion are converted back and forth between each other (and nitrite, NO22-), also by various bacteria via processes termed nitrification and Ammonification

    5. The nitrogen cycle thus involves

    Steps of the nitrogen cycle:

    1. Nitrogen fixation link to an Internet Website - nitrogen-fixing bacteria, primarily living on the roots of legumes, convert nitrogen gas into NH4OH.

    2. Ammonification - bacteria decomposers break down amino acids from dead animals and animal wastes into NH4OH.

    3. Nitrification - chemosynthetic bacteria oxidize NH4OH to produce nitrates and nitrites. The energy of lightning also causes atmospheric oxygen and nitrogen to combine to form nitrate ions.

    4. Denitrification - anaerobic bacteria break down nitrates, releasing N2 back into the atmosphere.

This is a slow process requiring a lot of energy. Because of this, lack of nitrogen in the soil often limits the productivity of an ecosystem.


 Biogeochemical Cycles (Test Your Concept Understanding)

  1. Study this website link to an Internet Website to answer this question:
    What four activities of humans have severely altered the nitrogen cycle?

click to find the answer to today's question What is the cause of the increase in the amount of CO2 in the Earth's atmosphere?

Oxygen cycle: link to an Internet Websitelink to an Internet Website
  • Photosynthesis adds O2.
  • Cellular respiration removes O2 from the air
  • Photosynthesis and respiration usually balance out.
  • Connected to the Carbon cycle
  • Requires water
  • Most living organisms require its use.


Carbon cycle: link to an Internet Websitelink to an Internet Website


4.5b Assignment - Biogeochemical Cycles

Your assignment is to develop a media display on one of the biogeochemical cycles listed above (days 1-3) that will inform and teach all that view your display about the biogeochemical cycle you have chosen.

  1. Work in teams of 2-3

  2. Decide which of the cycles your group will display and report it to your teacher.

  3. Media display methods:

    1. web page, video, standing cardboard display, poster display, power point

  4. Your Biogeochemical display will be evaluated by myself and other students using this rubric link to a local webpage.

Criteria for media display

  1. How does the cycle work (detailed description/diagram)?

  2. How does the cycle interact with the environment (importance of cycle)?

  3. How does the cycle interact with living organism?

  4. Where is the cycle taking place?

  5. Visuals of the cycle.

  6. Key terms related to the cycle. 

  7. Cite your sources in the correct format.

  8. Remember your goal is to teach others about your cycle.

Honors biology: add this portion to your media display

  1. Describe the impact humans have had on the cycle (positive and or negative) and what overall affect that has or will have on the environment.


Biology Class









Ocean water is "salty" because of its dissolved minerals.
River waters carry dissolved minerals to the ocean. When water evaporates from the ocean, the minerals are left behind. This leads to a continual increase in the concentration of minerals in ocean water.










Your body must have nitrogen to make amino acids.
Amino acids are the building blocks of proteins.










Increasing human population is the reason CO2 levels are increasing in the Earth's atmosphere.
Carbon dioxide is a waste product given off during respiration and the burning of hydrocarbons.