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Organisms cannot survive w/o a constant supply of energy.

The ultimate source of energy for almost all organisms is the sun.  Life depends on the sun.

Photosynthesis – plants harness sunlight to make sugar (carbohydrates, energy-storing molecules)

Organisms consume food and use the energy form carbohydrates.  The energy travels form one organism to another.


Energy in an ecosystem moves from producers to consumers.

Producer – organism that makes its own food (autotrophs, self-feeders).  Energy comes directly form the sun.

Consumers – organisms that get their energy by eating other organisms (heterotrophs, other-feeders).  They eat producers or other consumers.  Energy comes indirectly from the sun.

Deep-ocean ecosystems are an exception

Bacteria that use hydrogen-sulfide from the thermal vents to make their own food are the producers.  No sunlight.

Different kinds of consumers in an ecosystem:

      1. herbivore – eat producers (vegetarians)

      2. carnivore – eat other consumers (meat-eaters)

      3. omnivore – eat both producers and consumers (everything-eaters)

      4. decomposers – get their food by breaking down dead things – important b/c they allow the nutrients in the rotting material to go back into the soil, water, and air.


This is how they get the energy… but how do they use it?

Organisms are able to use the fuel they get from eating by cellular respiration.

Cellular respiration = breaking down food to yield energy.

ALL ORGANISMS DO IT.  Even the producers use it to break down the food they make.


Every time an organism eats another organism, energy is transferred.

-food chain – sequence where energy is transferred form one org to the next as they eat each other.  Simple.

-Food web – closer to what really happens.  More organisms and multiple food chains linked together.  Shows a lot of the feeding relationships possible in an ecosystem.

-the trophic level describes the transfer of energy in each step of a food chain.

-Each time energy is transferred, some is lost as heat, and less is available to the organisms in the next trophic level.  90% of the energy is used by the organism.  Only 10% gets passed on to the next level.  In other words, 10% goes into making more meat on the organism.

-Energy pyramids help you see the energy loss. Producers form the base of the pyramid, they have the most stored energy, and are the biggest trophic level.  Herbivores have less energy and make up the next level.  Organisms in the upper levels store even less energy.


Energy loss affects how the ecosystem is set up.

-Since energy is lost at each level, there are less and less organisms at the higher trophic levels.

-The loss of energy from level to level, limits the number of trophic levels in an ecosystem.  4 or 5 is the max.

Materials in the ecosystem are constantly reused.  

The carbon cycle

-carbon gets cycled through the atmosphere, land, water, and organisms.

-short-term carbon cycle:

-producers convert CO2 in the air into carbohydrates

-consumers eat producers and get carbon form the carbohydrates

-consumers break down the food so they can use the energy, and CO2 is released

-long-term carbon cycle: 

-carbon may be converted into carbonates which make up bones and shells.  They don’t break down easily.  Carbonates form huge carbon sinks (long-term storage) in limestone deposits.

-when an organism dies, the carbon in its body is released into the soil and air.  When these particles are released underground, they can form deposits of coal, oil, and natural gas – fossil fuels.

-fossil fuels are stored carbon left over form dead bodies from millions of years ago 

How we affect the carbon cycle:

-when we burn fossil fuels we release huge amounts of CO2 into the atmosphere.  More than would be released by the natural cycle.

-Increased levels may contribute to global warming – an overall increase in the temperature of the earth. 

-The carbon that’s not absorbed by the atmosphere is dissolved in the ocean (another sink) or absorbed by plants

-therefore deforestation and cutting down the trees and plants that absorb carbon is an issue


The nitrogen cycle

-Where nitrogen cycles between the atmosphere, bacteria, and other orgs.

-organisms need N to build proteins, which are used to make new cells.

-N2 makes up over 70% of the atmosphere, but most organismss can’t use atmospheric nitrogen. 

-It has to be fixed (turned into a useable form).  Nitrogen-fixing bacteria do the job.

Nitrogen fixing bacteria live in the soil and on nodules on the roots of certain plants. 

They release the N they fix into the soil. 

Plants get it from the bacteria or from the soil. 

Other organisms get it from the plants and it gets passed up the food chain.

-Nitrogen is returned to the atmosphere by bacteria. 

They decompose dead things and waste, the N is  returned to the soil and other bacteria turn it back into N gas, completing the cycle. 

o  W/o bacteria, most N would be locked up in poop and corpses.


The phosphorous cycle

Phosphorous cycles from the environment to organisms then back to the environment.

-it happens slow and doesn’t happen in the atmosphere, since P rarely occurs as a gas

-P is an element that is a part of many important molecules in cells of living organisms

-Plants get it from the soil and water, animals get it by eating plants or other animals

-Phosphorous comes from eroding rocks, goes into soil and water, plants absorb it.

-It also comes from waste and decomposing organisms.  Stuff that washed off the land into the ocean sinks to the bottom

Fertilizers put excess N and P into the ecosystem.  If it gets into bodies of water, it causes algal bloom

Burning full releases nitric oxide into the atmosphere – it combines w/ O and H2O and forms nitiric acid which contributes to acid precipitation.


ENV CHAPTER 5.3:  HOW ECOSYSTEMS CHANGEEcosystems are constantly changing


Ecological succession – gradual process of change and replacement of types of species in a community.  It takes hundreds or thousands of years.


Types of succession:

Primary succession occurs on a surface where no ecosystem existed before.  Occurs on rocks, cliffs, sand dunes.

Secondary succession occurs on a surface where an ecosystem has previously existed – occurs where ecosystems have been disturbed either by humans or by natural processes (like where there used to be a forest but it burned down)  

Pioneer species are the first organisms to colonize a newly available area and start succession.  They make the new area habitable for other species to come in.


The climax community is the final and stable community that results from succession.  It changes a little, but for the most part it’s stable and stays that way unless it’s disrupted.


Fire is an important part of secondary succession in some ecosystems.

Natural fires release the seeds of some conifers, clear out accumulated brush and deadwood and make room for other things to grow.


Old-field succession – occurs when farmland is abandoned

Grasses and weeds take over, then taller plants grow in the area and shade-out the pioneer grasses, over time they are deprived of light and water by growing trees.  Climax community can eventually return


Primary succession is much slower than secondary succession, because it begins where there is no soil. 

-         Lichens and bacteria can colonize b/c they don’t need soil. 

-         Their growth breaks down the rock. 

-         Soil eventually accumulates from broken down rock, trapped sand and dust, dead bacteria and lichens. 

-         Mosses may eventually grow and break down the rock further, they decay and add nutrients to the soil. 

-         Soil is made form broken rock, decaying things, air and water. 

-         This can also happen in a city street!