III. Cycles of Matter
*While energy is crucial to an ecosystem,
all organisms need water, minerals, and
other life-sustaining compounds to survive.
In most organisms, more than 95% of the
body is made up of oxygen, carbon, hydrogen,
and nitrogen that must be broken down into
a chemical form that the cells can take up.
A. Recycling in the Biosphere
*Energy and matter move through the
biosphere very differently. Matter is recycled
within and between ecosystems.
Elements, compounds, and other forms
of matter are passed through biogeochemical
cycles that connect the biological, ecological,
and chemical aspects of the biosphere.
Cycles of Matter
-Matter cycles over and over
again through the biosphere
because biological systems don’t
use up matter but transform it.
It is assembled into living tissue
or passed out of the body as
waste products.
B. The Water Cycle
-The water that living things
need to survive moves
between the ocean,
atmosphere, and land.
The Water Cycle
Entering the atmosphere – water
molecules enter the atmosphere
as water vapor (a gas) when they
evaporate from the ocean, other
bodies of water, or when they
evaporate from the leaves of
plants.
Evaporation – the process by
which water changes from liquid
form to an atmospheric gas.
Transpiration – loss of water
from a plant through its leaves
of plants.
The Water Cycle
Leaving the atmosphere – the sun heats
the atmosphere throughout the day,
causing warm, moist air to rise and cool.
The water vapor condenses into tiny
droplets that form clouds. Once large
enough, the water droplets fall to the
surface in the form of precipitation :
rain, snow, sleet, hail, etc.
Traveling on the surface – most precipitation
runs along the surface of the ground until it
enters a river or stream that carries the runoff
back to an ocean or lake. Some rain will
seep into the soil and become ground water.
Water in the soil enters plants through the
roots, restarting the cycle.
C. Nutrient Cycles
Nutrients – all the chemical
substances that an organism
needs to sustain life (chemical
“building blocks” that come from
food).
-Every living organism needs
nutrients to build tissues and
carry out essential life functions.
Like water, nutrients are passed
between organisms and the
environment through
biogeochemical cycles.
3 Major biogeochemical cycles
1. Carbon cycle – cycle that
moves carbon through the
biosphere. Carbon is found in
several large reservoirs in the
biosphere : in the atmosphere
as CO2 gas, in the oceans as
dissolved carbon dioxide, on
land in organisms, rocks, and
soil, & underground as coal,
petroleum, and calcium
carbonate rock.
The Carbon Cycle
Carbon’s role in the biosphere :
 Makes up living tissue &
animal skeletons
 Makes up rock
 It forms CO2 gas in the atmosphere
 Carbon dioxide is taken in by plants
during photosynthesis and is given
off by both plants and animals
during respiration.
Four main types of processes move carbon through its cycle :
 Biological processes, such as
photosynthesis, respiration, and
decomposition, take up and release
carbon and oxygen.
 Geochemical processes, such as
erosion and volcanic activity, release
carbon dioxide to the atmosphere and
oceans.
 Mixed biogeochemical processes, such
as the burial and decomposition of
dead organisms and their conversion
under pressure into coal and
petroleum (fossil fuels), store carbon
underground.
 Human activities, such as mining,
cutting and burning forests, and
burning fossil fuels, release carbon
dioxide into the atmosphere.
The Nitrogen Cycle
2. Nitrogen Cycle – cycle that
moves nitrogen through the
biosphere. The atmosphere is
the main reservoir of nitrogen
in the biosphere (78% of the
atmosphere). It also cycles
through the soil and through
the tissues of living organisms.
Nitrogen’s role in the biosphere :
All organisms need nitrogen to
make amino acids, which are
used to build proteins.
How nitrogen moves through the biosphere :
 Nitrogen gas from the
atmosphere is taken in by
bacteria in the soil/on the
roots of plants and
converted into ammonia.
Nitrogen fixation – process of
converting nitrogen gas into
ammonia.
 Other bacteria in the soil
convert ammonia into
nitrates and nitrites.
How nitrogen moves through the biosphere :
 Producers use nitrates and
nitrites to make proteins.
 Consumers eat the producers
and reuse the nitrogen to make
their own proteins.
 When organisms die, decomposers
return nitrogen to the soil as
ammonia for producers to use.
-Some soil bacteria release nitrogen
into the atmosphere by
denitrification converting nitrates
into nitrogen gas.
The Phosphorous Cycle
3. Phosphorous Cycle – cycle that
moves phosphorous through the
biosphere. Phosphorous in the
biosphere cycles among the land,
ocean sediments, and living
organisms. Although important, it
is not common because it doesn’t
enter the atmosphere. It is mostly
within rock and soil minerals on
land, and in ocean sediments.
Phosphorous’ role in the biosphere :
Phosphorous is essential to living
organisms because it forms part of
important life-sustaining molecules
such as DNA and RNA.
How phosphorous moves through the biosphere :
 Rocks and sediments wear
down, releasing phosphate –
some phosphate stays on land
and cycles between organisms
and the soil.
-When plants absorb phosphate
from the soil or from water, the
plants bind the phosphate into
organic compounds, which move
through the food web from
producers to consumers to the
rest of the ecosystem.
How phosphorous moves through the biosphere :
 Phosphate washes
into rivers &
streams & dissolves.
 Phosphate makes
its way to the ocean,
where it is used
by marine
organisms.
D. Nutrient Limitation
*One key point of interest to
ecologists is primary productivity –
the rate at which organic matter is
created by producers.
-One factor that controls the primary
productivity of an ecosystem
is the amount of available nutrients.
If a nutrient is in short supply,
it will limit an organism’s growth.
When an ecosystem is limited
by a single nutrient that is scarce or
cycles very slowly it is referred
to as a limiting nutrient.
D. Nutrient Limitation
*The ocean is nutrient-poor
compared to the land and
when aquatic ecosystems
receive large amounts of a
limiting nutrient (ex :
runoff from heavily
fertilized fields)algae &
other producers increase
quickly and can lead to
algal blooms which can
disrupt ecosystem
equilibrium.