HIGH SCHOOL: BIOLOGY
CHAPTER ONE
HOW DO ECOSYSTEMS WORK?
All activities of life are powered by the energy of sunlight.
The molecules of life are constructed of chemical building blocks that
are obtained as nutrients from the environment.
Solar energy is converted into chemical energy and is ultimately
converted to heat energy that radiates back into space. Chemical
nutrients remain on Earth. The nutrients may change in form and
distribution, and may even be transported among different
ecosystems. Nutrients are constantly recycled.
Thus we see energy moves through the communities within
ecosystems in a continuous one-way flow, needing constant
replenishment from an outside source, the sun.
Nutrients constantly cycle and recycle within and among ecosystems.
ENERGY FLOW THROUGH COMMUNITIES
http://www.youtube.com/watch?v=TE6wqG4nb3M
[energy transfer and a song]
http://www.youtube.com/watch?v=YUOl_j2ga7o&feature=related
[ bio animation of a food chain x]
http://www.metacafe.com/watch/237035/food_chain/
Food chain ***
 The sun fuses hydrogen molecules into helium molecules,
releasing tremendous quantities of energy.
 A small fraction of this energy reaches Earth in the form of
electromagnetic waves, including light, heat and ultraviolet
energy.
 Of the energy that reaches Earth, much is reflected by the
atmosphere, clouds, and Earth’s surface. Still more is absorbed
as heat by Earth and its atmosphere, leaving only about 1% to
power all life.
 Of this 1% which reaches Earth’s surface as light, green plants
and other photosynthetic organisms capture 3% or less. The
entire life on this planet is supported by less than 0.03% of the
energy reaching Earth from the sun.
 During photosynthesis pigments such as chlorophyll absorb light
and convert the solar energy into chemical energy. This chemical
energy is stored in chemical bonds, producing sugar and other
high-energy molecules.
 Photosynthetic organisms which can prepare their own food are
called autotrophs or producers, because they can produce food
for themselves using nonliving nutrients and sunlight. They
produce for all other forms of life as well.
 Organisms that cannot prepare their own food and depend on
other organisms or green plants are called heterotrophs or
consumers. They obtain their nutrients from other organisms.
 The energy that photosynthetic organisms store and make
available to other members of the community over a given
period is called net primary productivity.
 The productivity of an ecosystem is influenced by many
environmental variables, including the amount of nutrients
available to the producers, the amount of sunlight reaching
them, the availability of water, and the temperature.
 In the desert, for example, lack of water limits productivity.
 Energy flows through communities from producers through
several levels of consumers. Each category of organisms is called
a trophic level (meaning feeding level)
 Producers -----from redwood trees to cyanobacteria-----form the
first trophic level. They obtain their energy directly from
sunlight.
 Consumers occupy several trophic levels. Some consumers feed
directly and exlusively on producers and are called the
herbivores (meaning “plant eaters”), ranging from grasshoppers
to giraffes. They are also called as primary consumers and form
the second trophic level.
 Organisms that are predators and feed primarily on primary
consumers are called carnivores (meaning “meat eaters”).
Carnivores are also called secondary consumers and they form
the third trophic level. Some carnivores occasionally eat other
carnivores and such consumers occupy the fourth trophic level
and are called the tertiary consumer.
http://www.metacafe.com/watch/237035/food_chain/
Food chain ***
Explain how energy and nutrients, enter, move through and exit a
food chain in an ecosystem.
Energy enters from sunlight
Chloroplast/producers/autotrophs capture sunlight.
Energy flows through the trophic levels in stages in food chain.
Energy transfer is apporixmately 10% from one trophic level to the
next. Heat energy is lost through cell respiration.
Energy loss due to material not consumed/assimilated egested
excreted.
Labeled diagram of energy pyramid
Energy passes to decomposers detritivores saprotrophs in dead organi
matter.
Nutrient cycles within ecosystem nutrients are recycled.
Example of nutrient cycle with three or more links
Nutrients absorbed by producers plants roots
Nutrients move through food chain by digestion of other organisms
Nutrients recycled from decomposition of dead organisms.
Nutrients from weathering of rocks enter ecosystem
Nutrients lost by leaching sedimentation e.g shells sinking to sea
body.
FOOD CHAIN AND FOOD WEB
The linear feeding relationship is called food chain. Food chain refers
to a series of steps in which organisms transfer energy by eating and
being eaten.
Each step in a food chain or food web is called a trophic level.
Producers make up the first trophic level and the consumers make up
the second, third, or higher trophic levels. Each consumer depends on
the trophic level below it for energy.
A simple marine food chain.
Different ecosystems have radically different food chains.
A food web refers to many interconnecting food chains. Food web
describes more accurately the feeding relationships within a given
community.
Some animals, such as bears, rats, raccoons, and humans, are
omnivores and they at different times act as primary, secondary, and
occasionally as tertiary consumers.
Many carnivores will eat either herbivores or other carnivores, thus
acting as secondary or tertiary consumers, respectively.
An owl for instance, is a secondary consumer when it eats a mouse,
which feeds on plants, but a tertiary consumer when it eats a shrew,
which feeds on insects.
Different ecosystems have radically different food chains.
A food web refers to many interconnecting food chains. Food web
describes more accurately the feeding relationships within a given
community.
Some animals, such as bears, rats, raccoons, and humans, are
omnivores and they at different times act as primary, secondary, and
occasionally as tertiary consumers.
Many carnivores will eat either herbivores or other carnivores, thus
acting as secondary or tertiary consumers, respectively.
An owl for instance, is a secondary consumer when it eats a mouse,
which feeds on plants, but a tertiary consumer when it eats a shrew,
which feeds on insects.
DETRITUS FEEDERS AND DECOMPOSERS
The detritus feeders are an army of small and often unnoticed animals
and protists that live on the refuse of life: molted exoskeletons, fallen
leaves, wastes, and dead bodies (detritus means “debris”). Detritus
feeders includes earthworms, mites, protists, centipedes, some
insects, a unique land-dwelling crustacean called a pillbug, nematode
worms, and even a few large vertebrates such as vultures.
Pillbug
They consume dead organic matter, extract some of the energy
stored within it, and excret it in a further decomposed state. Their
excretory products serve as food for other detritus feeders and for
decomposers.
The decomposers are primarily fungi and bacteria that digest food
outside their bodies by secreting digestive enzymes into the
environment. They absorb the nutrients they need and release the
remaining nutrients. Through the activities of detritus feeders and
decomposers, the bodies and wastes of living organisms are reduced
to simple molecules – such as carbon dioxide, water, minerals, and
organic molecules – that return to the atmosphere, soil, and water. By
liberating nutrients for reuse, detritus feeders and decomposers form
a vital link in the nutrient cycles of ecosystems.
In some ecosystems, such as deciduous forests, more energy passes
through the detritus feeders and decomposers than through the
primary, secondary, or tertiary consumers.
What would happen if detritus feeders and decomposers
disappeared?
This portion of the food web, although inconspicuous, is absolutely
essential to life on Earth. Without it, communities would gradually be
smothered by accumulated wastes and dead bodies. The nutrients
storesd in these bodies would be unavailable to enrich the soil. The
quality of the soild would become poorer and poorer until plant life
could no longer be sustained. With plants eliminatesd, energy would
cease to enter the community; the higher trophic levels including
humans, would disappear as well.
Energy transfer through trophic levels is inefficient.
When a caterpillar (primary consumer) eats the leaves of
tomato plant ( a producer), only some of the solar energy
originally trapped by the plant is available to the insect. Some
energy was used by the plant for growth and maintenance,
and more was lost as heat during these processes. Some
energy was converted into the chemical bonds of molecules
such as cellulose, which the caterpillar cannot digest.
Therefore, only a fraction of the energy captured by the first
trophic level is available to organisms in the second trophic
level.
The energy consumed by the caterpillar is in turn partially
used to power the various activities, some of the energy is lost
as heat. All this energy is unavailable to the songbird in the
next trophic level when it eats the caterpillar. The bird loses
energy as body heat, more in flight, and also uses some
energy to convert into feathers, beak and bone. All this energy
used by the bird is unavailable to the hawk that catches it.
http://www.youtube.com/watch?v=NJplkrliUEg
Ecological pyramid meaning and explanation
http://www.brightstorm.com/science/biology/communities-andecosystems/ecological-pyramids/
Ecological pyramids (Good Explanation)
Energy pyramids to illustrate Energy transfer between trophic
levels
Studies of a variety of communities indicate that the net
transfer of energy between trophic levels is roughly 10%
efficient.
This means that, in general, the energy stored in primary
consumers (herbivores) is only about 10% of the energy
stored in the bodies of producers.
In turn the bodies of secondary consumers possess only 10%
of the energy stored in primary consumers.
In other words, for every 100 calories of solar energy captured
by grass, only about 10 calories are converted into herbivores,
and only 1 calorie into carnivores.
This inefficient energy transfer between trophic levels is called
the “ 10% law”.
An energy pyramid show maximum energy at the base and
diminishing amounts at higher levels.
This is the reason why we find the producers to be the
predominant organisms in any ecosystems. Plants have the
most energy available to them, because they trap the energy
directly from the sunlight
The most abundant animals will be those which feed directly
on plants, and carnivores will be relatively large.
The lower the trophic level we utilize, the more food energy is
available to us; in other words, far more people can be fed on
grain than on meat.
Construct a food chain to show food chains magnify toxic
substances.
NUTRIENT CYCLES
Nutrients do not flow down onto Earth in a steady stream
from above. Essentially the same pool of nutrients has been
supporting life for more than 3 billion years.
Nutrients are elements and small molecules that form the
chemical building blocks of life. Some called macronutrients,
are required by organisms in large quantities. These include,
water, carbon, hydrogen, oxygen, nitrogen, phosphorus,
sulfure, and calcium.
Mucronutrients, are required in small quantities, like zinc,
iron, iodine, selenium.
Nutrient cycles also called biogeochemical cycles, describe the
pathways these substances follow as they move from
communities to nonliving portions of ecosystems and back
again to communities.
The source and storage sites of nutrients are called reservoirs.
CARBON CYCLE
http://www.youtube.com/watch?v=c40jebr9jbg
carbon cycle
http://www.youtube.com/watch?v=0Vwa6qtEih8
carbon cycle-2
 Carbon enters the living community from atmosphere
through capture of carbon dioxide during photosynthesis
by producers. Land plants obtain carbon dioxide from the
atmosphere while the aquatic plants get carbon dioxide
dissolved in the
water.
Producers return some of the carbon dioxide to the
atmosphere and ocean during cellular respiration.
 Primary consumers eat the producers and acquire the
carbon stored in their tissues. These herbivores also
release some carbon through respiration and store the
rest, which is sometimes consumed by organisms in
higher trophic levels.
 The carnivores eat the herbivores and acquire the carbon
stored in their tissues.
 All living things eventually die, and their bodies are
broken down by detritus feeders and decomposers.
Cellular respiration by these organisms returns carbon
dioxide to the atmosphere and oceans.
 Mollusks and some marine protists extract carbon
dioxide dissolved in water and combine it with calcium to
form calcium carbonate, from which they construct their
shells. After death, the shells of these organisms collect
in undersea deposits, are buried, and may eventually be
converted into limestone. Limestone may dissolve
gradually as water runs over it, making the carbon
available to living organisms once again.
 Fossil fuels form from the remains of ancient forms of
life. the carbon in the organic molecules of these
prehistoric organisms was transformed by high
temperatures and pressure over millions of years into
coal, oil, and natural gas. The energy of sunlight is also
trapped in these fossil fuels, captured by autotrophs and
converted into high energy hydrocarbons that we burn
today. When people fossil fuels to make use of this
stored energy, carbon dioxide is released into the
atmosphere.
 Human activities such as cutting and burning of Earth’s
great forest also increase the amount of carbon dioxide
in the atmosphere.
 Respiration by producers, and consumers release carbon
dioxide to the atmosphere.
 Burning of fossil fuels release carbon dioxide,
 Use of automobiles also release carbon dioxide to the
atmosphere.
 Burning of wood also release carbon dioxide to the
atmosphere.
b) human activities like deforestation, use of fossil fuels,
burning of wood, industrial waste led to the atmosphere
has lead to the increase in carbon dioxide.
Implications for future climate: carbon dioxide is a green
house gas and absorbs heat. As a result of increase in
carbon dioxide in the atmosphere heat will be trapped and
lead to global warming which can lead to rise in sea level,
climatic changes, and loss of organisms.
NITROGEN CYCLE.
http://www.youtube.com/watch?v=bbDGs43-4WY
Nitrogen cycle(fast)
http://www.youtube.com/watch?v=MGDS6oga_7o&NR=1
 The atmosphere contains about 79% of nitrogen gas and is
thus the major reservoir of this nutrient. (Nitrogen is a
crucial component of proteins, many vitamins, and the
nucleic acids DNA and RNA.) Plants cannot extract this gas
from atmosphere and must be supplied with nitrate or
ammonia.
 Ammonia is synthesized by certain bacteria that engage in
nitrogen fixation, a process that combines nitrogen with
hydrogen. Some of these bacteria live in water and soil.
Others live in symbiotic association with leguminous plants

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(alfalfa, soybeans, clover and peas) where they live in
special swellings in the roots called nodules.
Decomposer bacteria can also produce ammonia from the
amino acids and urea found in dead bodies and wastes.
Some bacteria that live in soil convert ammonia into
nitrites and nitrates.
Producers make use of ammonia and nitrate and use them
to make proteins. Consumers then eat the producers and
reuse the nitrogen to make their own protein.
When organisms die, decomposers return nitrogen to the
soil as ammonia. The ammonia may be taken up again by
producers.
Other soil bacteria convert nitrates into nitrogen gas in a
process called denitrification. This process releases
nitrogen into the atmosphere once again.
THE WATER CYCLE
 All living things require water to survive.
 Water moves between the ocean, atmosphere, and land.
 Water evaporates from the ocean or other bodies of water
like lakes, ponds, and rivers and enter the atmosphere as
water vapor, a gas. The process by which water changes
from liquid form to an atmospheric gas is called
evaporation.
 Water can also enter the atmosphere by evaporating from
the leaves of plants in the process of transpiration.
 During the day, the sun heats the atmosphere. As the
warm, moist air rises, it cools. Eventually, the water vapor
condenses into tiny droplets that form clouds. When the
droplets become large enough, the water returns to
Earth’s surface in the form of precipitation—rain, snow,
sleet, or hail.
 On land much of the precipitation runs along the surface
of the ground until it enters a river or stream that carries
the run-off back to an ocean or lake.
 Rain also seeps into the soil, some of it deeply enough to
become ground water. Water in the soil enters plants
through the roots, and the water cycle begins anew.
6. Decomposers help to break down the organic matter
present in the dead plants and animals and convert them
into simpler substances and return them to the soil to be
used up by plants. Thus they help in recycling of nutrients.
7.
 Carbon is present in the atmosphere in the form of
carbon dioxide.
 Plants take in carbon dioxide and convert them into
sugar/starch during photosynthesis.
 Plants are consumed by herbivores which are then
consumed by carnivores.
 Dead plants and animals are acted upon by
decomposers and they produce carbon dioxide during
decomposition which is returned to the atmosphere.
 Burning of fossil fuels also produce carbon dioxide.
 Respiration by plants and animals liberate carbon
dioxide to the atmosphere.
 b) human activities like deforestation, use of fossil
fuels, burning of wood, industrial waste led to the
atmosphere has lead to the increase in carbon
dioxide.
 Implications for future climate: carbon dioxide is a
green house gas and absorbs heat. As a result of
increase in carbon dioxide in the atmosphere heat
will be trapped and lead to global warming which
can lead to rise in sea level, climatic changes, and
loss of organisms.