Biology 20 Chapter 2_keyed Mrs. Steinbrenner Chapter Two: Cycles of Matter (pages 32 - 65)
2.2 Biogeochemical Cycles (pages 42 – 52)
In order to survive and grow, organisms must obtain nutrients that serve as sources of energy or
chemical building blocks, or both. The cycling of matter through the biotic and abiotic
components of the biosphere allows all organisms to obtain nutrients.
All biogeochemical cycles involve some substances that are temporarily stored in nutrient
reservoirs for various amounts of time, while some substances are moving through the
environment between reservoirs.
The substances that are involved
in biogeochemical cycles are:
• water
• carbon
• oxygen
• sulfur
• nitrogen
• phosphorus
Each substance can be considered
to be part of its own cycle, while
all of the cycles are said to be
interconnected.
Substances may be part of a rapid cycle or part of a slow cycle depending on the amount of time
spent in a reservoir.
Nutrient reservoir:
A nutrient reservoir is a component in the biosphere in which nutrients temporarily accumulate.
Examples include: soil, water and organisms
The four nutrient reservoirs are
categorized with respect to whether they
involve biotic or abiotic components of
the ecosystem and whether the nutrients
they contain are directly available to
living things.
Nutrients that are directly available to
living things are said to be part of a rapid
cycle. Nutrients that are not available to
living things are said to be part of a slow
cycle.
1 Biology 20 Chapter 2_keyed Mrs. Steinbrenner Rapid Cycle
What to do: read the information on pages 42-43 of the text. Summarize the information
in the table below.
Definition: Substances cycle between nutrient reservoirs relatively
quickly.
Examples: Carbon moves from producer to consumer to decomposer,
and back into the atmosphere through rapid cycling.
how substances move into and out of nutrient reservoir
photosynthesis, cellular respiration, decomposition, excretion
Definition: Substances accumulate and are unavailable to organisms.
Slow Cycle
It can take millions of years for these substances to again become
available to organisms.
Examples: Organic carbon in the matter of living organisms is
fossilized. The burning of fossil fuels millions of years later puts the
carbon into the atmosphere.
how substances move into nutrient reservoir
fossilization, formation of sediments
how substances move out of reservoir
erosion, burning of fossil fuels, weathering
The Carbon and Oxygen Cycles (pages 43 – 46)
Rapid Cycling of Carbon
Plants and animals play an important role in the rapid cycling
of oxygen and carbon dioxide. Plants consume much greater
amounts of carbon in the process of photosynthesis than plants
and animals release in the process of cellular respiration.
Much of the carbon in forest reservoirs is released back into
the atmosphere as carbon dioxide from forest fires and the
breakdown of organic matter by decomposers.
Rapid Cycling of Oxygen
Plants, animals, and decomposers also play an important role
in the cycling or oxygen. Photosynthesis produces oxygen gas,
which is needed for cellular respiration. 2 Biology 20 Chapter 2_keyed Mrs. Steinbrenner The Carbon and Oxygen Cycle
The Slow Cycling of Carbon
Living organisms also play an important role in the slow cycling of carbon. Organic
carbon that is stored in the dead bodies of organisms may enter into a slow cycle if the
carbon is not made immediately available by decomposers.
Over millions of years, organic material that is not broken down by decomposers may
become incorporated into rocks or contribute to petroleum (fossil fuel) deposits.
Human activities influence the slow cycling of carbon in a number of ways. The
combustion of petroleum deposits quickly releases carbon back into the atmosphere.
Since the industrial revolution, levels of carbon dioxide in the atmosphere has increased
by about 30%.
Question 1. Using the
diagram to the right, list the
major carbon sinks
(reservoirs) on the Earth.
Major carbon sinks
include: ocean, forests,
petroleum deposits,
limestone (CaCo3)
* note that the “slow
cycling” of carbon is shown
in bold against a darker background.
3 Biology 20 Chapter 2_keyed Mrs. Steinbrenner The Sulfur Cycle (pages 46 – 48)
The sulfur cycle is a biogeochemical cycle that shows how sulfur is converted into
different forms as it is transported through the air, water, and soil. All organisms require
sulfur as an important component of proteins and vitamins
What to do: Read the information of the sulfur cycle on pages 46 – 48 of the text.
Summarize the information in the table below and answer the questions that follow.
Component of Summary of information:
the Biosphere
Sulfur in the
Air
Sulfur in the
Water
Sulfur in the
Soil
 The decomposition of organic matter, volcanic offgassing, and human activities all release sulfur into the
atmosphere.
 Rain and snow soon return sulfur to Earth’s surface via
acid deposition.
 Plants and algae take up sulfur in the water-soluble
form of sulfate (SO42 ).
−
 Decomposers quickly return sulfur to the soil or air as
hydrogen sulfide (H2S).
 Soil bacteria use sulfur compounds in photosynthesis or
cellular respiration, thus playing an essential role as
they convert one form of sulfur to another.
 Some sulfur is taken out of rapid cycling when bacteria
convert sulfur to forms that are layered down as
sediments, eventually becoming part of rocks.
4 Biology 20 Chapter 2_keyed Mrs. Steinbrenner The Nitrogen Cycle (pages 48 – 49)
The nitrogen cycle is a biogeochemical cycle that shows how nitrogen is converted into
different forms as it is transported through the air, water, and soil. All organisms require
nitrogen to make proteins and genetic material (DNA).
What to do: Read the information of the nitrogen cycle on pages 48 – 49 of the text.
Summarize the information in the table below and answer the questions that follow.
Component of
the Biosphere
Nitrogen in the
Air
Nitrogen in the
Water
Summary of information:
 Nitrogen gas (N2) makes up 78.1 percent of Earth’s atmosphere
by volume.
 Most organisms, however, cannot use atmospheric nitrogen.
 Nitrogen gas is removed from the atmosphere via nitrogenfixing cyanobacteria, which convert it into a form plants can
use—ammonium (NH4+).
 Some types of aquatic bacteria then convert the ammonium into
nitrate (NO3 ), which plants can also use.
 Other bacteria convert nitrate back into nitrogen gas via
denitrification.
 Nitrogen-fixing soil bacteria live in close association with
plants. They convert nitrogen gas into ammonium. Decomposers
also break down organic matter to produce ammonium.
 Soil bacteria then convert the ammonium into nitrite (NO2 ) and
then nitrate.
 Denitrifying bacteria then convert these compounds back into
nitrogen gas.
−
Nitrogen in the
Soil
−
5 Biology 20 Chapter 2_keyed Mrs. Steinbrenner The Phosphorus Cycle (pages 49 – 50)
The phosphorus cycle is a biogeochemical cycle that shows how phosphorus is converted
into different forms as it is transported through the water and soil. All organisms require
phosphorus as a part of cellular DNA and ATP (the energy carrier essential to all cells).
What to do: Read the information of the phosphorus cycle on pages 49 – 50 of the text.
Summarize the information in the table below and answer the questions that follow.
Component of the
Biosphere
Phosphorus in the
Air
Phosphorus in the
Water
Summary of information:

 The growth of algae in aquatic ecosystems is limited by the
amount of available nutrients.

Phosphorus in the
Soil
Unlike carbon, nitrogen, and sulfur, phosphorus does not cycle
through the atmosphere.
Because it is scarce in the environment, excess phosphorus in
aquatic ecosystems can result in algal overgrowth, known as an
algal bloom.
 Weathering gradually releases phosphorus trapped in rocks and
makes it available to organisms.
 Plants and algae can only use phosphorus in the form of
phosphate (PO43 ).
−

Phosphorus is scarce in the environment. This keeps the growth
of producers in balance, but it can also limit the growth of crops.
6 Biology 20 Chapter 2_keyed Mrs. Steinbrenner Question 2. Human activities can greatly affect many of the biogeochemical cycles. The
increase in phosphates due to agricultural run-off can be a major problem for near-by
aquatic environments. Use the phrases below and re-order to show how an increase in the
amount of phosphorus in the environment can cause ecosystem damage.
•
•
•
•
•
•
Algal bloom and overgrowth occurs
Decomposer population grows quickly, depleting oxygen
Excess phosphorus enters the aquatic system
Fish and other organisms requiring oxygen die
Plants below the surface can no longer photosynthesize and die
Sunlight cannot penetrate below the surface
7