General Biology 101
Chapter Outlines
Starr & Taggert
10 th
edition
Chapter 48:
Section 48.6
Biogeochemical Cycles – An overview
Biogeochemical Cycles – when ions or molecules of a nutrient are transferred from the environment into organisms and continues in a cycling fashion.
Four factors that affect these cycles.
1) Mineral elements available for plants are usually ions i.e. charged particles.
2) Decomposers and detritivores maintain an ecosystems reserve or minerals.
3) The actual amount of a nutrient that is cycled through ecosystems/organisms is greater than the amount entering and leaving per year.
4) Weather and weathering of rocks are common inputs of nutrients into an ecosystem. Nitrogen fixation (carried out by living organisms) is also a method of input.
Outputs or losses of nutrients occur because of erosion and similar processes.
Types of cycles:

Hydrologic – water

Atmospheric – gaseous forms e.g. nitrogen and carbon

Sedimentary – solid forms e.g. phosphorous – source is the Earth’s crust.
Section 48.7
Hydrologic Cycle – movement of water on a global scale.
- Affected by ocean currents and prevailing wind patterns.
- Involves evaporation, transpiration and precipitation.
- Water is important for moving nutrients through other cycles.
Watershed – A region in which precipitation is funneled into a single stream or river.
Measuring inputs and outputs of a watershed is important for monitoring usage of water and regional influences such as vegetative cover.
Reservoirs of water:

Ocean (most significant)
 Atmosphere (in the form of vapor)

Land (including ground water sources)


Deforesting an area was studied in Hubbard Brook Valley, what was discovered is that this practice increases loss of nutrients such as calcium at highly accelerated rates.
Therefore plants are very necessary to stabilize the soil and absorb dissolved minerals.
Section 48.8
Carbon Cycle
CO
2
– Carbon dioxide is the most abundant form of “available” carbon and is found primarily in the atmosphere (the main reservoir for carbon).
When CO
2
dissolves in the ocean it is converted to:
bicarbonate
carbonate
Dissolved CO
2 is deposited into the deep ocean reservoir rather than just in the water because it flows with ocean currents. It sinks in cold, salty, Northern Atlantic water.
* Most carbon is held in sedimentary rock formations.
Other forms and sources of carbon include:
 held in living organisms in food webs.

Held in organic wastes (feces)

Held in the remains of dead organisms such as fallen leaves & carcasses

Peat (accumulations of bog plants).

Calcium carbonate shells of marine life, deposited like the white cliffs of
Dover.

Fossil fuel accumulations (remains of ancient forests).

fossil fuels are converted to coal, petroleum and gas reserves in the rock.
Excess liberation of CO
2 from the burning of fossil fuels is thought to contribute to and amplify the greenhouse effect, leading to imbalance on a global scale and is thought to contribute to mass scale global warming trends. See Section 48.9 for further details.
Section 48.9
From Greenhouse Gases to a Warmer Planet?
Molecules that play a role in global temperature include:

Carbon Dioxide

Water
 Ozone

Methane

Nitrous Oxide

Chlorofluorocarbons

Together they help keep incoming solar radiation trapped inside the atmosphere and near the surface of the Earth.
Greenhouse effect – the name of the warming action that occurs on Earth due to these atmospheric gases.
Global warming – A long-term increase in world-wide average temperatures. Caused by greenhouse gases. U.S. and other developed nations are contributing disproportionately to this effect.
* CO
2 concentration levels are the most significant gases contributing to the effect.
Scientists have been monitoring the rise in CO
2
levels since the 1950’s and they have seen an increase in these levels since that time. These increases are attributed to an increase in the burning of fossil fuels.
Evidence – the past decade has been the hottest on record, which is thought to cause an intensified destabilization of weather events.
Projected possible consequences of global warming trends.
Rising sea levels
Glaciers and polar ice caps melting
Water expands when warmed, so oceans are rising/expanding.
Higher tides and storm waves
Increased rainfall and flooding
Summer droughts will be more severe.
Interior of continents will get dryer, increased spread of deserts may result.
Heat waves and wildfires
Crop failures, resulting in increased malnutrition and famine.
Increased occurrences of contagious diseases e.g. malaria and W. Nile Virus
Water wars
Section 48.10
Nitrogen Cycle
Nitrogen is contained in all proteins and nucleic acids.
Source/Reservoir is the atmosphere.
Other reservoirs such as seafloor sediments, ocean and soil also play a part.
Nitrogen is usually the scarcest (most limiting) nutrient for plants.

Cycling Processes:
1) Nitrogen fixation – done by bacteria. They convert nitrogen gas (N
2
) to ammonia (NH
3
). When ammonia dissolves in water it becomes ammonium
(NH
4
+)
which is what plants can readily use for their nitrogen source.
2) Decomposition and Ammonification – decomposers degrade nitrogenous wastes and remains of dead organisms. Plants can readily take up ammonia and ammonium from their natural environment.
3) Nitrification – Action carried out by bacteria as well to strip electrons from compounds. Product of this process is called nitrite (NO
2
). Other bacteria produce nitrate (NO3-), which plants can then take up, by their roots.
Root nodules (lumps) found in legume plants contain mutualistic relationships with bacteria that fix nitrogen.
Nitrogen is lost in the forms of (NH
4
+
), (NO
2
), and (NO3-), and these are necessary for plants, but unfortunately they are easily lost by a process called leaching (which happens when water runs off or percolates repeatedly through the soil).
Denitrification – Nitrogen lost to the atmosphere by bacteria that convert usable forms of nitrogen to nitrogen gas and nitrous oxide. Said to be “reduced” i.e. electrons are accepted via this form.
*Plants that “contain” nitrogen fixing bacteria in their roots “pay out” to the bacteria by giving them sugar.
Human Impact:
Loss of Nitrogen is accelerated by:
Deforestation
Conversion of grasslands to agriculture
Soil erosion
Leaching (overly irrigating)
Stabilizing measures (to help maintain nitrogen).
1) Crop rotation
2) Nitrogen rich fertilizers
> Overuse of nitrogen based fertilizers can interfere with uptake of other minerals such as calcium because of a change in the acidity levels of the soil.
> Can also lead to pollution of fresh water ecosystems like lakes and streams.
> Nitrogen stimulated growth in trees can outstrip the availability of phosphorous so that they show nutrient deficiencies such as premature yellowing in the leaves and leaf drop.
> Nitrogen oxides from fossil fuel emissions can affect the fertility of trees in areas that don’t normally have much nitrogen thus destabilizing the trees nutrient balance.

3
-
4
+

Section 48.11 Sedimentary Cycles
Phosphorous cycle
Land > Ocean Sediments > Land
Very slow cycling, but once in the food chain quite rapid cycling.
Phosphate ions PO
4
3-
are weathered out of rock.
Organisms use phosphates in:
Cell membranes
Energy molecules like ATP
DNA molecules
Phosphates released by living organisms (animals) via wastes/feces.
Plants take it up as a mineral (via the roots).

Phosphorous is the most limiting factor in natural ecosystems (especially aquatic ecosystems)!
Phosphorous is depleted when humans:
Clear cut
Clear grasslands for agriculture.
In developed countries there is an overuse in fertilizers that can lead to pollution of fresh water, leading to algae bloom; this process of over abundance in aquatic settings is called:
Eutrophication – the name given to describe nutrient enrichment of an ecosystem that is usually low in nutrients. Can lead to green waters and a loss of dissolved oxygen in the water due to decomposers using it all up during cellular respiration.