Download UNIT 2: Energy Flow and Cycles

Carbon, Nitrogen, and H2O
Energy Flow

Without a constant flow of energy, living
systems cannot function. Sunlight is the
main energy source for life on Earth.
Some types of bacteria rely on the
energy stored in inorganic (non-living)
chemical compounds instead of the sun.
 These organisms use chemical energy
to produce food in a process called
chemosynthesis.

autotrophs, or producers, have the ability
to make their own food.
 Most autotrophs convert light energy to
chemical energy (food). They accomplish
this through photosynthesis.


The bacteria that perform
chemosynthesis are also autotrophs (ex:
bacteria in deep sea thermal vents, hot
springs, and marshes)
Heterotrophs get their energy from the
things they consume (eat) or absorb.
 There are five major types of
heterotrophs.

Herbivores – obtain energy from eating
plants
 Carnivores – obtain energy from eating
animals
 Omnivores – obtain energy from eating
plants and animals (most humans)




Detritivores – feed on plant and animal
remains and other dead matter (detritus)
Decomposers – organisms that break down
organic matter (once living stuff) into simple
products.
Generally, fungi and bacteria are the
decomposers.
FOOD CHAINS AND FOOD WEBS

Energy flows through an ecosystem in
one direction, from the sun or inorganic
compounds to autotrophs and then to
many different heterotrophs.
A food chain is a series of
steps in which organisms
transfer energy by eating
and by being eaten.
 Each step in a food chain
or a food web is called a
trophic level.
 There are basically four
trophic levels to food
chains:

Producers (autotrophs
that perform
photosynthesis or
chemosynthesis)
 Primary consumers
(herbivores)
 Secondary
consumers
(carnivores or
omnivores)
 Tertiary consumers
(carnivores or
omnivores)


A food web shows all the food chains
and relationships in an ecosystem.
Ecological pyramids

An ecological pyramid is a diagram that
shows the amount of energy or matter
within each trophic level in a food chain
or web. There are three major types of
ecological pyramids.

Energy Pyramid – shows
the relative amount of
energy available at each
trophic level.
The 10% Rule – In a food chain, only
about 10% of the energy is transferred
from one trophic level to the next.
 The other 90% is used for things like
respiration, digestion, running away from
predators, etc.
 The producers will have the most energy
in an ecosystem, the tertiary consumer
will have the least energy.

Copyright 2011 – Rachel Miller – No part of this presentation may be duplicated
.1%
3rd Level
CONSUMERS
1%
2nd Level CONSUMERS
10%
100%
1st Level CONSUMERS
Heterotrophs
PRODUCERS
Autotrophs

Biomass Pyramid –
represents the
amount of living
organic matter at
each trophic level.
Typically, the greatest
biomass is at the
bottom of the pyramid
(producers).

Pyramid of
Numbers – Shows
the relative number
of organisms at each
trophic level. This is
not always the same
as the biomass
pyramid.
Hydrological (Water) Cycle

Water vapor is transferred into clouds
through condensation, which leads to
precipitation (rain, snow, sleet, hail).

The process by which water changes
from liquid to water vapor is called
evaporation.

Water can also enter the atmosphere by
evaporating from the leaves of plants in a
process called transpiration.
Carbon Cycle
Animals and plants add carbon dioxide
(CO2) to the atmosphere through respiration.
 Plants take in the atmospheric CO2 to use
during photosynthesis.


When plants and animals remove waste or
die, the carbon in their bodies enters the soil.
Over millions of years the carbon is turned
into fossil fuels.

Humans release carbon dioxide into the
atmosphere when they burn fossil fuels,
mine coal, and cut or burn forests.

Since the industrial revolution, the levels of
atmosphere CO2 have steadily risen. Which
has lead to an increase in the greenhouse
effect.
Greenhouse effect – when heat is trapped in
the Earth’s atmosphere by carbon dioxide,
methane and other greenhouse gases.
 A drastic rise in greenhouse gases could
increase the greenhouse effect and lead to
global climate change.

Nitrogen Cycle

Most of the Earth’s nitrogen exists as
atmospheric nitrogen (N2). Plants and
animals cannot use this form of nitrogen.
Atmospheric nitrogen (N2) is transferred to
the Earth’s soil by precipitation.
 Once in the soil, special bacteria in plant
roots convert N2 into ammonia in a process
called nitrogen fixation.

Other bacteria in the soil then change the
ammonia into nitrate or nitrite.
 Producers (plants) and animals use the
nitrate or nitrite to make proteins.


When organisms die, decomposers
return the nitrogen to the soil as
ammonia.

Other bacteria convert nitrates back into
atmospheric nitrogen (N2) in a process
called denitrification.