Unit 6 NotesUnit 6 Notes

Flow of Energy Through an Flow of Energy Through an Ecosystem (Food chains and Food Ecosystem (Food chains and Food webs)webs)

OverviewOverview We learned about different We learned about different

symbiotic relationships symbiotic relationships (mutualism, commensalism, (mutualism, commensalism, parasitism) that illustrate how parasitism) that illustrate how organisms interact. organisms interact.

Another way to study the Another way to study the interactions of organisms interactions of organisms within an ecosystem is to within an ecosystem is to follow the energy that flows follow the energy that flows through itthrough it

Organisms differ in how they Organisms differ in how they obtain energy; they are divided obtain energy; they are divided into two categories: into two categories: autotrophs and heterotrophautotrophs and heterotrophss

Autotrophs Autotrophs Autotrophs are organisms that Autotrophs are organisms that

collect energy from the sunlight to collect energy from the sunlight to produce foodproduce food Also called Also called producersproducers (produce (produce

their own food)their own food) Green plants and other Green plants and other

organisms that create their own organisms that create their own food from food from abiotic sourcesabiotic sources

Organisms that contain Organisms that contain chlorophyll (the green pigment chlorophyll (the green pigment found in plants that captures found in plants that captures sunlight)sunlight) absorb energy during absorb energy during photosynthesis and convert it to photosynthesis and convert it to food (like glucose, a type of food (like glucose, a type of sugar)sugar)

If sunlight isn’t available (deep in If sunlight isn’t available (deep in the ocean, for example), organisms the ocean, for example), organisms can use inorganic substances like can use inorganic substances like carbon dioxide to make their foodcarbon dioxide to make their food

HeterotrophsHeterotrophs Heterotrophs – organisms that get Heterotrophs – organisms that get

energy by eating another organismenergy by eating another organism They are called They are called consumersconsumers

A A primary consumer primary consumer eats only eats only plants, plants,

a a secondary consumer secondary consumer eats eats primary consumers (herbivores), primary consumers (herbivores),

a a tertiary consumer tertiary consumer eats secondary eats secondary consumers (carnivores)consumers (carnivores)

Different types: Different types: Herbivores Herbivores – eat only plants– eat only plants CarnivoresCarnivores – eat other animals – eat other animals Omnivores Omnivores – eat both plants and – eat both plants and

animalsanimals DetritivoresDetritivores – eat dead matter and – eat dead matter and

return nutrients to the soil so they can return nutrients to the soil so they can be reused (worms, fungi) – also called be reused (worms, fungi) – also called decomposersdecomposers

Quick Check for Quick Check for UnderstandingUnderstanding In your notes (summary section): In your notes (summary section):

List at least 3 different:List at least 3 different: autotrophs and autotrophs and heterotrophsheterotrophs

List at least 3 different:List at least 3 different: herbivores, herbivores, carnivores, carnivores, omnivores, and omnivores, and detritivoresdetritivores

Models of Energy FlowModels of Energy Flow

Ecologists use Ecologists use food chains and food chains and food websfood webs to model the energy to model the energy flow through an ecosystemflow through an ecosystem

They are simplified They are simplified representations of the flow of representations of the flow of energyenergy

Each step in a food chain or Each step in a food chain or food web is called a food web is called a trophic trophic levellevel

Autotrophs make up the first Autotrophs make up the first trophic leveltrophic level Get their energy from the sun Get their energy from the sun

(usually)(usually) Heterotrophs make up the Heterotrophs make up the

remaining levels, and get their remaining levels, and get their energy from the trophic level energy from the trophic level before itbefore it

Food ChainsFood Chains Food chains show the flow of Food chains show the flow of

energy from one organism to energy from one organism to another in a single lineanother in a single line (simpler (simpler diagrams than a food web)diagrams than a food web)

Arrows represent the one-way Arrows represent the one-way energy flow which usually starts energy flow which usually starts with an autotroph and moves to with an autotroph and moves to heterotrophsheterotrophs

Each organism uses a portion of Each organism uses a portion of the energy it gets from the the energy it gets from the organism it eats organism it eats for cellular for cellular processes to build new cells and processes to build new cells and tissuestissues

The remaining energy is The remaining energy is released into the surrounding released into the surrounding environment (usually as heat) environment (usually as heat) and is no longer available to the and is no longer available to the organismsorganisms

Food WebsFood Webs A food web is a model A food web is a model

representing the many representing the many interconnected food interconnected food chains and pathways in chains and pathways in which energy flows which energy flows through a group of through a group of organismsorganisms Show the flow of energy Show the flow of energy

through connected food through connected food chainschains

Food webs are usually Food webs are usually more complex than a more complex than a single food chain because single food chain because most organisms feed on most organisms feed on more than one species more than one species

Quick Check for Quick Check for UnderstandingUnderstanding Use the following information to make a food web in a meadow Use the following information to make a food web in a meadow

ecosystem:ecosystem: Red foxes feed on raccoons, crayfishes, grasshoppers, red clover, Red foxes feed on raccoons, crayfishes, grasshoppers, red clover,

meadow voles, and gray squirrelsmeadow voles, and gray squirrels Red clover is eaten by grasshoppers, muskrats, red foxes, and meadow Red clover is eaten by grasshoppers, muskrats, red foxes, and meadow

volesvoles Meadow voles, gray squirrels, and raccoons all eat parts of the white oak Meadow voles, gray squirrels, and raccoons all eat parts of the white oak

treetree Crayfishes feed on green algae and dead material, and they are eaten Crayfishes feed on green algae and dead material, and they are eaten

by muskrats and red foxesby muskrats and red foxes Raccoons feed on muskrats, meadow voles, gray squirrels, and white Raccoons feed on muskrats, meadow voles, gray squirrels, and white

oak treesoak trees

Identify all the herbivores, carnivores, omnivores and detritivores in the Identify all the herbivores, carnivores, omnivores and detritivores in the food webfood web

Describe how the muskrats would be affected if disease kills the white Describe how the muskrats would be affected if disease kills the white oak treesoak trees

Ecological pyramids Ecological pyramids Ecological pyramids are Ecological pyramids are

diagrams that can show the diagrams that can show the relative amounts of energy or relative amounts of energy or numbers of organisms at each numbers of organisms at each trophic level in an ecosystemtrophic level in an ecosystem

Only 10 percent of all energy Only 10 percent of all energy is transferred to the level is transferred to the level above itabove it Most of the energy contained in the Most of the energy contained in the

organisms at each level is organisms at each level is consumed by cellular processes or consumed by cellular processes or released to the environment as released to the environment as heatheat

Usually the amount of living Usually the amount of living matter at each trophic level matter at each trophic level decreases as you move up a decreases as you move up a step because there is less step because there is less energy available to support energy available to support organismsorganisms (there are more (there are more mice mice than foxes, for example)than foxes, for example)

Quick Check for Quick Check for UnderstandingUnderstanding

Draw an energy pyramid in the question Draw an energy pyramid in the question column of your notes for a food chain made up column of your notes for a food chain made up of:of:

Grass, a caterpillar, a beetle, lizard, snake, and Grass, a caterpillar, a beetle, lizard, snake, and a roadrunner (bird)a roadrunner (bird) Assume that 100 percent of the energy is available Assume that 100 percent of the energy is available

for the grass.for the grass. At each stage, show how much energy is lost At each stage, show how much energy is lost

and how much is available to the next trophic and how much is available to the next trophic levellevel