Cycling of Materials in Ecosystems Biogeochemical cycles – the circulation of substances through living organisms from or to the environment

The paths of water, carbon, nitrogen, and phosphorus pass from the nonliving environment to living organisms, such as trees and then back to the nonliving environment. In almost all biogeochemical cycles, there is much less of the substance in the living reservoir than in the nonliving reservoir.

The Water Cycle Nonliving Portion of the Water Cycle: (The physical components of an ecosystem.) ex: air, lake condensation – water vapor; clouds precipitation – rain, snow, sleet ground water – the water that is beneath the Earth’s surface evaporation – heated water that reenters the atmosphere

Living Portion of the Water Cycle: (Organisms within an ecosystem.) transpiration – evaporation of water from the leaves of a plant

Water Cycle Ground Water

The Carbon Cycle Carbon dioxide in the air or dissolved CO2 in water is used by photosynthesizing plants, algae, and bacteria as a raw material to build organic molecules.

C atoms may return to the pool of CO2 in the air and water in 3 ways: respiration – O2 is used to oxidize organic molecules during cellular respiration and CO2 is a by product of this reaction combustion – C can return to the atmosphere through combustion, or burning wood; the remains of dead organisms that become buried in sediments may be gradually transformed by heat and pressure into fossil fuels – coal, oil, and natural gas. This C is released when the fossil fuels are burned.

erosion – marine organisms use CO2 dissolved in sea water to make calcium carbonate shells. The shells of the dead organism form sediment, which forms limestone. As limestone is exposed and erodes, the C becomes available to other organisms (see Fig 13)

Carbon Cycle Respiration Combustion Erosion

Carbon Cycle 2. 1. 3. (Erosion)

The Phosphorous and Nitrogen Cycles P and N are needed to build proteins and nucleic acids. P is an essential part of both ATP and DNA. Phosphorous is usually present in soil and rock as calcium phosphate, which dissolves in water to form phosphate ions. This phosphate is absorbed by the roots of plants and used to build organic molecules. Animals that eat the plants reuse the organic phosphorous. (P is cycled through plants into animals.)

Phosphorus Cycle

Nitrogen Cycle The atmosphere is 79% nitrogen gas, N2. However, most organisms are unable to use it in this form. Why? The two N atoms are connected by a strong triple covalent bond that is very difficult to break. However, a few bacteria have enzymes that can break it and they bind N atoms to hydrogen to form ammonia, NH3, (nitrogen gas→ammonia). This process is called nitrogen fixation.

Nitrogen Cycle 1. 2. 3. 4. 5. 6. nitrogen released into atmosphere