Science Notes - Chapter 21
Section 1:
Energy Flow in Ecosystems
Energy Roles:
Each of the organisms in an ecosystem fills one
of the energy roles of: producer, consumer, or
decomposer.
Producers:
*Organism makes its own food
*Source of all food in ecosystem
*A few ecosystems originally obtain energy from a
source other than sunlightthis ecosystem is found in rocks deep in the
earth, gets energy from hydrogen sulfide
that is found in their environment
Consumers:
*organism that obtains energy by feeding on other
organism
*classified by what they eat
-Herbivore – consumer that eats only plants
-Carnivore - consumer that eats only animals
– Some are scavengers that feed on the
bodies of dead animals
-Omnivore – consumers that eat plants and
animals
Decomposers:
*break down waste and dead organisms and return
the raw materials to the ecosystem
*known as nature’s recyclers
*mushrooms and bacteria are decomposers
Food Chains and Food Webs:
*Energy enters the ecosystem as sunlight and is
converted into food molecules by the producers
*Shows the movement of energy through an
ecosystem. This can be shown in the diagrams
called food chains and food webs.
Food Chain:
*a series of events in which one organism eats
another and obtains energy
-First organism in food chain is the producer
-Second organism feeds on (or off of) the
producer and is called the first level
consumer
-The Second level consumer eats the first level
consumer
**Food chains show only one possible path, along
which energy can move through the
ecosystems.
Food Webs:
*consist of many overlapping food chains. Can
show multiple ways in which consumers interact.
Energy Pyramids
*When an organism in an ecosystem eats, it
obtains energy. (The energy comes from the
food.)
*The energy pyramid shows the amount of energy
that moves from one feeding level to the next.
*The most energy is available at the producer level
of the pyramid. As you move up the pyramid
each level has less energy available than the
level below it!!!
*Only about 10% of the energy at one level of a
food web is transferred to the next higher
level. The other 90% of the energy is lost at
each step (up on the pyramid) because of this
there is not enough energy to support many
feeding levels in an ecosystem.
*Organism at higher food levels don’t necessarily
require less energy to live than lower levels.
Since so much is lost, the amount of energy at
producer level limits the # of consumers that it
can support. This is why there are fewer
animals at top of the pyramid.
Section 2:
Cycles of Matter
* Water cycle- the continuous process by which
water moves from Earth’s surface to the
atmosphere and back.
- Evaporation, condensation and
precipitation make up the water cycle.
*Evaporation – the process by which molecules of
liquid water absorb energy and change to a
gas.
- Liquid evaporates from oceans, lakes and
living things that give off water and forms
a water vapor (a gas).
- Energy for evaporation comes from the
heat of the sun.
*Condensation – the process by which a gas
changes to a liquid.
- As the water vapor rises in the atmosphere, it
cools down.
- Cool vapor turns back into tiny drops of liquid
water. This is the process of condensation.
- This water vapor collects around particles of
dust and forms clouds
* Precipitation – when water vapor condenses the
drops of water in the cloud grow larger,
eventually the heavy drops will fall from the
cloud resulting in rain, sleet, hail or snow.
-Most precipitation falls back into the
oceans or lakes.
The Carbon and Oxygen Cycles
- Producers, consumers and decomposers play
roles in recycling carbon and oxygen.
- Producers take in carbon dioxide gas from the air
during photosynthesis.
- They use the carbon to make food (sugars and
starches)
- Consumers break down carbon (sugars) to obtain
energy and release CO2.
- When producers and consumers die,
decomposers break down their remains and
return the carbon to the soil.
- Producers release oxygen as a result of
photosynthesis
- Most organisms take in O2 from the air or water
and use it to carry out life processes.
The Nitrogen Cycle
- Nitrogen moves from the air to the soil, into
living things and back into the air.
- Our atmosphere is 78 % Nitrogen gas (free
nitrogen-not combined with other kinds of
atoms). Most organisms cannot use it in this
form.
- Most organisms can use it when it is “fixed” or
combined with other elements (nitrogencontaining compounds)
- Nitrogen fixation the process of changing free
nitrogen into a usable form.
Returning Nitrogen to Environment
- Once nitrogen is fixed, consumers can use it
to make proteins.
- Decomposers break down these complex
compounds in animal wastes and dead
organisms. Decomposition returns simple
nitrogen
compounds to the soil.
- Nitrogen can cycle from the soil to producers,
then to consumers many times.
- Eventually, bacteria break down nitrogen
compounds completely and release “free”
nitrogen back into the air.