OVERVIEW

This chapter discusses the systems and cycles of the biosphere - the domain of living organisms.

• Ecology studies the interaction between life forms and their environments.
• An ecosystem is defined as the total assemblage of components entering into the interaction of a group of organisms. These systems import and export matter and energy.
• Biogeographers study the nature and function of ecosystems and their variability from place to place.
• The food web or food chain refers to the flow of energy from one level to another in an ecosystem.
• Primary producers are plants and animals that are able to create carbohydrates from carbon dioxide, water and light energy through the process of photosynthesis.
• In the food web, consumers feed on the primary producers or on other consumers and transfer energy through the different levels in this manner.
• Decomposers ( microorganisms and bacteria) feed on decaying organic matter at all levels in the ecosystem.
• Solar energy is absorbed initially by the primary producers and stored as chemical energy which is digested by consumers. Only 10% to 50% of the energy at any level is passed on to the next level, consequently the amount of organic matter and consumers must decrease with each level.
• Photosynthesis is a biochemical reaction which results in the production of carbohydrates and oxygen using water, carbon dioxide, and light energy. A simplified chemical reaction is:

• In the respiration process carbohydrate is broken down and combined with oxygen to create carbon dioxide, water, and chemical energy. A simplified chemical reaction is

• Photosynthesis is dependent on light and heat. Photosynthesis only occurs when light is available so that longer days produce more plant growth. Photosynthesis also increases with temperature to about 20 degrees Celsius and then levels off.
• Net photosythesis is measured as the carbohydrate remaining after respiration takes up carbohydrate to feed the plant. Net photosynthesis increases with temperature until approximately 18° C, after which it declines as the rate of respiration increases faster than the rate of photosynthesis.
• Net primary production is the annual amount of useful energy produced by an ecosystem. It is controlled by light intensity and duration, temperature and water availability. Net primary production is measured as biomass, the dry weight of organic matter per unit area within an ecosystem.
• Biochemical cycles are the pathways of particular nutrients or materials through the earth's ecosystem.
• The macronutrients hydrogen, carbon, and oxygen account for 99.5% of all living matter.
• The Carbon Cycle
  • most carbon lies in storage pools as carbonate sediments.
  • only 0.2% is available as CO2 or as decaying biomass in active pools.
  • carbon exists as carbon dioxide in the atmosphere and oceans, carbohydrate in organic matter, hydrocarbon compounds in rock and as mineral carbonate compounds.
  • CO2 is added to the earth system by volcanic eruptions and by industry, it is taken out of the earth system by plants in photosynthesis, and by phytoplankton in the oceans.
• The Oxygen Cycle
  • oxygen is added to the earth system by volcanic activity and is lost to the system through organic respiration, mineral oxidation, industrial and natural combustion, and dissolved in ocean water.
• The Nitrogen Cycle
  • the atmosphere is a large storage pool of nitrogen.
  • nitrogen can only be utilized through nitrogen fixation and is lost to the biosphere through denitrification.
  • human influence has increased the amount of nitrogen in the biosphere through the use of nitrogen fertilizers and fuel combustion.
• Many macronutrients such as calcium, magnesium, iron, potassium, sodium and phosphorus move from the land surface to the ocean and subsequently return to land surfaces by tectonic uplift. Storage pools include sea water, sediments and sedimentary rocks. Eventually these macronutrients are released into the earth system through weathering.

KEY TERMS

biosphere         photosynthesis      active pools          
ecology           respiration         storage pools         
ecosystem         detritus            macronutrients        
biogeography      gross               carbon cycle          
food chain        photosynthesis      oxygen cycle          
primary producer  net photosynthesis  nitrogen cycle        
consumer          net primary         sedimentary cycles    
decomposers       production                                
                  biomass                                   
                  biogeochemical                            
                  cycles                                    

STUDY QUESTIONS

1. Why are geographers interested in the biosphere?
2. What plants and animals would be found at the different levels of the food web in an ecosystem close to your home?
3. What inorganic compounds would be part of this ecosystem?
4. Describe how photosynthesis works. How is photosynthesis affected by heat and light?
5. Describe the process of respiration. How it respiration affected by heat and light?
6. How does net photosynthesis respond to increasing light intensity and increasing heat? Why?
7. What climatic factors affect rates of net primary productivity?
8. What is a biogeochemical cycle? Define sedimentary cycle, gaseous cycle, active pool and storage pool.
9. Where are the storage pool of carbon in the earth system? Where are the active pools of carbon?
10. How does human activity reduce the amount of oxygen in the atmosphere?
11. Why is nitrogen fixation important? What is denitrification?
12. What impact has the use of fertilizers had on the nitrogen cycle?