Download Living things depend on nonliving things for life. At the organism

6. Stability in an ecosystem is a balance between competing effects. As a basis for understanding this
concept:
d. Students know how water, carbon, and nitrogen cycle between abiotic resources and organic matter in the
ecosystem and how oxygen cycles through photosynthesis and respiration.
Living things depend on nonliving things for life. At the organism level living things depend on natural
resources, and at the molecular level, they depend on chemical cycles. Water, carbon, nitrogen, phosphorus, and
other elements are recycled back and forth between organisms and their environments. Water, carbon, and
nitrogen are necessary for life to exist. These chemicals are incorporated into plants (producers) by
photosynthesis and nitrogen fixation and used by animals (consumers) for food and protein synthesis. Chemical
recycling occurs through respiration, the excretion of waste products and, of course, the death of organisms.
Notes: Chemical Cycling in Ecosystems
The regular movement and exchange of elements between the biotic and abiotic parts of an ecosystem is called a
biogeochemical cycle. Every element used by living things must eventually be recycled or life would soon come to a
halt. Only the most common elements and compounds will be covered including the:
The carbon cycle is essential to all living things. It involves three compounds:
1. carbon dioxide
2. carbonate minerals
3. organic molecules starting with sugar
The carbon cycle also includes 4 processes
1. respiration -- both glycolysis and the citric acid cycle break down sugar -- which produces carbon dioxide
(all living things used glycolysis to produce ATP energy
2. photosynthesis which uses carbon dioxide (and water) to produce sugars and other organic molecules.
3. chemical precipitation which removes carbon dioxide and converts it into carbonate rocks like marble
4. chemical solution which dissolves the carbonates (usually in acidic conditions) releasing CO2 back into the
atmosphere.
The steady increase in the use of fossil fuels has caused a corresponding increase in the amount of carbon dioxide in
the atmosphere. This increase in CO2 concentration is in part responsible for the world wide increase in air
temperatures. This is called the greenhouse effect.
The Nitrogen Cycle Nitrogen is a part of nucleic acids and their nitrogen bases (A,T,C and G) as well as all
proteins and the 20 amino acids.
The nitrogen cycle involves 3 soluble nitrogen compounds, 20 amino acids and the element nitrogen listed below.
1. Nitrogen gas (N2) The element nitrogen is very stable and difficult for living things to convert into usable
form
2. Ammonia (NH3 gas and NH4OH in solution) Nitrogen gas is converted into ammonia by bacteria in the
root nodules of legumes (pea plants)
3. Nitrites and Nitrates (NO2- and NO3-) both anions--negative ions-- are soluble in water and can easily enter
plant root systems. Certain soil bacteria are responsible for converting ammonium ions into nitrites and
nitrates.
4. amino acids (20 varieties) are made first by plants using nitrates or nitrites.
Other processes help to recycle the nitrogen either converting it back to ammonia or even nitrogen gas. Review the
diagram below for greater detail on how these processes are interconnected.
The Phosphorus Cycle This cycle is important because phosphorus like nitrogen is a component of nucleic acids
Phosphorous is involved in two interconnecting cycles.
1. Plants can absorb phosphates dissolved in the soil converting them into organic matter (nucleotides etc.).
Plants die or are eaten by animals which leave phosphate containing wastes which then reenter the soil.
2. Some of the phosphates in the soil enter the marine ecosystem through runoff from rivers and streams.
Once in the ocean the phosphate can be used by algae and other producers and eaten by fish. Eventually
however the phosphate are lock up in sediments and stored as rock. Only by plate tectonics which can
eventually raise the sea floor can the phosphate bearing rocks be exposed and converted back to soil.
The Water Cycle Water is an essential ingredient in all metabolic processes and is an essential part of every
environment. It is the most abundant resource on the earth covering about 70% of its surface. Water maybe
involved in strictly abiotic processes like evaporation and precipitation. It is found in the solid (ice) liquid (water)
and gaseous (vapor and clouds) forms. Water helps to regulate air temperatures and the body temperature of plants
and animals through evaporative cooling and transpiration (plants).