Transcript Phosphorus cycle

Ch. 5
How Ecosystems Work
Chapter 5 Objectives
List two examples of ecological succession.
Explain how a pioneer species contributes
to ecological succession.
Explain what happens during old-field
succession.
Describe how lichens contribute to primary
succession.
I. Energy Flow in Ecosystems
 A. Life Depends on the Sun
 Photosynthesis – when plants use sunlight to make
sugar molecules
 performed by plants, algae, and some bacteria
 6CO2 + 6H2O + solar energy = C6H12O6 + 6O2
I. Energy Flow in Ecosystems
 Result of photosynthesis is energy rich
molecules called Carbohydrates
 When an animal eats a plant, some
energy is transferred from the plant to the
animal, and use this energy to grow,
move, and reproduce.
I. Energy Flow in
Ecosystems
 Producer – an organism that makes its own
food – an Autotroph
-organisms that perform photosynthesis
 Consumer – organisms that get their energy
by eating other organisms – heterotrophs
 All organisms get their energy from the sun
either by using it directly through
photosynthesis like producers, or indirectly by
eating producers or other consumers
I. Energy Flow in
Ecosystems
 In 1977 scientists discovered areas on the
bottom of the ocean that were full of life even
though sunlight did not reach

-deep ocean communities got their energy
from bacteria who could use hydrogen sulfide
from the hot water vents to make their own
food

-these bacteria served as the food for other
organisms so a whole ecosystem could be
supported
B. What Eats What
 Organisms can be classified by the source of their energy
 Herbivores – consumers that eat only producers – planteaters
 Carnivores – consumers that eat other consumers –
meat-eaters
 Omnivores – consumers that eat both producers and
consumers – all-eaters
 Decomposers – consumers that get their food by
breaking down dead organisms -bacteria and fungi
C. Cellular Respiration:
Burning the Fuel
 Your body gets the energy out of the food
by using the oxygen you breathe to break
down the food
 -you are then able to use the energy
stored in the food
 Excess energy is stored as fat or sugar.
C. Cellular Respiration:
Burning the Fuel
 Cellular respiration – process of
breaking down food to yield energy
-occurs inside cells of most organisms
including plant and animals
 You use the energy to walk, breathe,
think, or play a sport, to make more body
tissues, fight disease, grow, stay healthy
D. Energy Transfer
 Each time one organism eats another, a
transfer of energy occurs
 According to the second law of
thermodynamics – at each energy
transfer only 10% is available at the next
level, the rest is lost as heat
 You can trace the transfer of energy as it
travels through an ecosystem by studying food
chains, food webs, and trophic levels
 Food chain – a sequence in which energy is
transferred from one organism to the next as
each organism eats another organism
 In an ecosystem, energy flow is usually more
complex because there are so many species
interacting
 Food web – shows many feeding relationships
that are possible in an ecosystem
Food Web
Food Chain
Trophic Levels
 Trophic level – each step in the transfer of
energy through a food chain or web
 -each time energy is transferred from one
organism to another, some of the energy is lost
as heat and less is available to organisms at
the next level
 90 percent of the energy at each trophic level
is used to carry out the functions of living
Trophic Levels
 10 percent becomes used as part of the
organisms body and stored in its molecules –
this is what is available to the next trophic level
when one organism consumes another
 Energy pyramid is used to visualize the loss of
energy from one trophic level to the next
 -each layer represents one trophic level
Trophic Levels
 producers form the base because they
contain the most energy
 -herbivores make up the next level
because they contain less energy
 -carnivores that feed on herbivores make
up the next level
 -omnivores that feed on carnivores and
producers make up the top level
Trophic Levels
 The decreased amount of energy at each trophic
level affects the organization of an ecosystem
 -because so much energy is lost at each level,
there are fewer organisms at the higher trophic
levels
 -the loss of energy limits the number of trophic
levels in an ecosystem
Objectives
 List the three stages of the carbon cycle.
 Describe where fossil fuels are located.
 Identify one way that humans are affecting the
carbon cycle.
 List the three stages of the nitrogen cycle.
 Describe the role that nitrogen-fixing bacteria
play in the nitrogen cycle.
 Explain how the excess use of fertilizer can
affect the nitrogen and phosphorus cycles.
II. The Cycling of Materials
 A. The Carbon Cycle
 Carbon is an essential part of all living
things
 Carbon cycle – a process by which
carbon is cycled between the
atmosphere, land, water, and organisms
 Carbon is the essential component of
proteins, fats, and carbohydrates, which
make up all organisms.
The Carbon Cycle
The Long & Short Cycles
of Carbon
 a short term cycle is when producers like plants
convert CO2 in the air into glucose during
photosynthesis
 -some carbon enters a long-term cycle if carbon
is converted into carbonates which make up
the hard parts of bones and shells
As a Long Term Cycle
 over millions of years carbonate deposits
produce huge formations of limestone rocks
-limestone is one of the largest carbon
sinks or carbon reservoirs on Earth
 -carbon can be released into the soil or air after
an organism dies and decomposes and form
deposits of coal, oil, and natural gas
underground called fossil fuels
Humans affect the carbon
cycle
 When we burn fossil fuels, we release
carbon into the atmosphere as carbon
dioxide
-cars, factories, and power plants rely
on these fossil fuels to operate
 -about 6 billion metric tons of carbon a
year are released as CO2
B. The Nitrogen Cycle
 All organisms need protein which is
essential for new cells - nitrogen is needed
for proteins.
 Nitrogen makes up 78% of the gases in the
atmosphere, but organisms cannot take in
and use atmospheric nitrogen
Nitrogen Fixation
 Nitrogen must be altered, or fixed, before
organisms can use it
 The only organisms that can fix nitrogen is
bacteria called nitrogen-fixing bacteria
 -all organisms depend on these bacteria to
supply nitrogen
 Bacteria are an important part of nitrogen cycle
Nitrogen Cycle
Nitrogen cycle
 Nitrogen cycle– a process in which nitrogen is cycled
between the atmosphere, bacteria, and other
organisms
 -bacteria take nitrogen from the air and transforms it
into molecules that living things can use
 -the bacteria live within nodules on the roots of plants
called legumes – beans, peas, clover
 -they use sugars provided by the legumes to produce
nitrogen-containing compounds like nitrates
 -the excess nitrates are released into the soil
 Animals get nitrogen by eating plants or other
animals
 After nitrogen cycles from the atmosphere into
living things, it is returned to the atmosphere by
bacteria
 -decomposers are essential to the nitrogen cycle
because the break down wastes such as urine,
dung, leaves, and other decaying plant and animal
matter and return the nitrogen that these organisms
and wastes contain to the soil
 -after decomposers return the nitrogen to the soil,
bacteria transform a small amount of the nitrogen
into nitrogen gas which returns to the atmosphere
C. The Phosphorus Cycle
 Phosphorus is part of many molecules
that make up the cells of living organisms
 Essential in forming bones and teeth
 Plants get phosphorus from soil and
water, and animals get it by eating plants
or plant-eaters
Phosphorus cycle
 Phosphorus cycle – the movement of
phosphorus from the environment to organisms
and then back to the environment
 -this cycle is slow and does not normally occur
in the atmosphere because phosphorus rarely
occurs as a gas
 -phosphorus enters the cycle when rocks
erode, small amounts of phosphorus dissolve
as phosphate in soil and water
 -plants absorb phosphates in the soil through
their roots
Phosphorus cycle
 -phosphorus also enters the cycle when added
to soil and water when excess phosphorus is
excreted in waste
 from organisms and when organisms die and
decompose
 -some phosphorus also washes off the land
and eventually ends up in the ocean
 -phosphate salts are not soluble in water and
so they sink to the bottom of the ocean and
accumulate as sediment
Phosphorus Cycle
Human effects
 Humans effect the Nitrogen and Phosphorus
cycle
 -people often apply fertilizers to stimulate and
maximize plant growth
 -fertilizers contain both nitrogen and
phosphorus
 -the more nitrogen and phosphorus available to
a plant, the faster and bigger the plant tends to
grow
 If excessive amounts of fertilizer are used, the
fertilize can enter terrestrial and aquatic
ecosystems through runoff
Phosphorus cycle
 -this can cause rapid and over-abundant
growth of algae resulting in an algal bloom – a
dense, visible patch of algae that occurs near
the surface of the water
(Eutrophication)
 -bacteria break down the dead algae and
plants depleting the oxygen from the water
causing fish and other aquatic organisms to die
Nutrient Cycles can be
harmful
 When we burn coal, wood, or oil, a large
amount of nitric oxide is release into the
atmosphere
 -this is a harmful gas and when it
combines with oxygen and water vapor to
form nitric acid (NOX)
 -nitric acid dissolves in rain and snow
contributing to acid precipitation
Bellringer
Objectives
 List two examples of ecological
succession.
 Explain how a pioneer species
contributes to ecological succession.
 Explain what happens during old-field
succession.
 Describe how lichens contribute to
primary succession.
III. How Ecosystems Change
 A. Ecological Succession
 Ecological succession – a gradual
process of change and replacement of
the types of species in a community
 Primary succession – a type of
succession that occurs on a surface
where no ecosystem existed before
-rocks, cliffs, sand dunes
Secondary succession
 Secondary succession – the more common
type of succession where succession occurs
on a surface where an ecosystem has
previously existed
-areas that have been disturbed by
humans, animals or natural processes such
as storms, floods, fires, earthquakes,
volcanoes
 Example – Mount St. Helens eruption wiped
out everything
Mount St. Helens Succession
 the first species to regrow were pioneer
species – the first organisms to colonize any
newly available area and begins the process of
ecological succession
 -pioneer species makes the area habitable for
other species
 -tend to be smaller species like mosses and
grasses
 -they are replaced by larger and larger
organisms
climax community
 -climax community – a final and stable
community
 Natural fires caused by lightening are a
necessary part of secondary succession
 -some trees release seeds only when exposed
to the heat of a fire
 -minor fires remove the brush and deadwood
that would otherwise contribute to major fires
burning out of control
 -some animal species feed on vegetation that
only sprouts after fires
Ecological Succession
Old-field succession
 Example of secondary succession is old-field
succession
 Old-field succession – occurs when farmland
is abandoned when a farmer stops cultivating a
field




-grasses and weeds quickly build up
-over time taller plants move into the area
-taller plants gradually replace smaller ones
-finally the slower growing trees like oaks,
hickory, beech, and maple take over
Primary succession
 Primary succession is much slower than
secondary succession because it begins where
there is no soil
 -it can take several hundred to several
thousand years to produce fertile soil
 -lichens are usually the first pioneer species
because they can live with no soil
 Lichens are composed of a fungus and an
algae
How it happens
 as the lichen grows it breaks down the rock and
soil slowly accumulates as dust particles in the
air are trapped in cracks in the rock
 -dead remains of lichens and bacteria
accumulate in the cracks
 -mosses may grow larger and break the rock
even more, then they die and decay and add
material and nutrients to the growing soil
 -fertile soil is formed from broken rock, decayed
organisms, water, and air
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