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Biology 2014-2015

Energy Flow
SWS Biology
SWS Life Science

Section 3-2

       The flow of energy through an ecosystem is one of the most important factors that determines the system’s capacity to sustain life.




       Sunlight is the main energy source for life on Earth.

       In a few ecosystems, some organisms obtain energy from a source other than sunlight.

       The energy is stored in inorganic chemical compounds.

       mineral water that flows underground or boils out of hot springs

       undersea vents are loaded with chemical energy

       Autotrophs use energy from the environment to fuel the assembly of simple inorganic compounds into complex molecules.

v      plants, some algae, and certain bacteria are organisms that produce living tissues.

       Organisms that make their own food are also called producers.


Energy From the Sun

       The best-known autotrophs obtain energy through the process of photosynthesis.

       Photosynthesis is the process by which light energy is used to convert carbon dioxide and water into oxygen and energy-rich carbohydrates.

       Oxygen is added to—and carbon dioxide is removed from—the Earth’s atmosphere.

       On land, plants are the main autotrophs

       In freshwater and the upper layer of the ocean, algae are the main autotrophs.

       In tidal flats and salt marshes, cyanobacteria is the most common source.


Life Without Light

       Some autotrophs can produce food in the absence of light.

       These autotrophs rely on energy within the chemical bonds of inorganic molecules.

       Chemosynthesis is the use of chemical energy to produce carbohydrates.

       Several types of bacteria represent a large portion of living autotrophs.




       Some organisms cannot make their food directly and must acquire it from other organisms.

       Heterotrophs are organisms that rely on other organisms for their energy and food supply.

v      animals, fungi and some bacteria fit into this group

       Heterotrophs are also called consumers.

       Types of heterotrophs are:

       Herbivores obtain energy by eating plants.

Ex) cows, caterpillars, and deer

       Carnivores eat animals.

Ex) snakes, dogs, and owls

       Omnivores eat both plants and animals.

Ex) humans, bears, and crows

       Detritivores food on plant and animal remains and other dead matter.

Ex) mites, earthworms, snails, and crabs

       Decomposers break down organic matter

Ex) bacteria and fungi


Feeding Relationships


    Energy flows through an ecosystem in one direction, from the sun or inorganic compounds to autotrophs (producers) and then to various heterotrophs (consumers).


Food Chains

       The energy stored by producers can be passed through an ecosystem along a food chain.

       A food chain is a series of steps in which organisms transfer energy by eating and being eaten.

Ex) grassgrazing antelopecoyote

      (producer)    (herbivore)                     (carnivore)

Ex) algaezooplanktonsmall fishsquidshark

Food Webs

       A food web is a feeding relationship among various organisms in an ecosystem that form a network of complex interactions.

       A food web links all the food chains in an ecosystem together.


Trophic Levels

       A trophic level is each step in a food chain or food web.

       Producers make up the first trophic level.

       Consumers make up the second, third, or higher trophic levels.

       Each consumer depends on the trophic level below it for energy.


Ecological Pyramids


       The amount of energy or matter in an ecosystem can be represented by an ecological pyramid.

       An ecological pyramid is a diagram that shows the relative amounts of energy or matter contained within each trophic level in a food chain or food web.


Energy Pyramid

       There is no limit to the number of trophic levels but, only part of the energy that is stored in one trophic level is passed on to the next level.

       Only about 10 percent of the energy available within one trophic level is transferred to organisms at the next trophic level.

Ex) 100% producers10% first-level consumers1% second-level consumers0.1% third-level consumers

       The more levels that exist between a producer and a top-level consumer, the less energy that remains from the original amount.


Biomass Pyramid

       Biomass is the total amount of living tissue within a given trophic level.

       Biomass is expressed in terms of grams of organic matter per unit area.

       A biomass pyramid represents the amount of potential food available for each trophic level.


Pyramid of Numbers

       A pyramid of numbers is based on the numbers of individual organisms at each trophic level.

       For some ecosystems, such as a meadow, the pyramid of numbers is the same as that of the energy and biomass pyramids.

       For others, such as a forest, there are fewer producers than there are consumers.

       A single tree has a large amount of energy and biomass, but it is only one organism.