Transcript Notes: Food Webs - Highline Public Schools

What Eats What
Mrs. Dignan’ss Science Class
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Take a minute to think about the last meal
you ate. What kinds of organisms did you
eat?
 Plants?
– fruits, veggies, chips, bread
products
 Animals? – meat and seafood
 Fungi? – mushrooms, bread products, some
sodas
 Bacteria? – yogurt, sauerkraut, miso, some
cheeses
Omnivores – Humans are omnivores,
which means we eat both plants and
animals (omni=every, vore=eat)
 Carnivores – Some organisms, such as
cats and dogs, only eat other animals
(carni=meat)
 Herbivores – Some organisms, such as
deer and rabbits, only eat plants
(herbi=plant)
 Detritovores – Some organisms, such as
worms and insects, only eat
dead/decaying plants and animals
(detritus=waste

Trophic Level - a species’ position on the food
chain. What it eats and what eats it. (troph=food).
There are 2 major categories:

Autotrophs produce
their own food
(auto=self)

Heterotrophs
consume food from
other organisms
(hetero=different)
Trophic levels are further divided
by the energy pyramid
Producers/Primary Producers – Organisms that produce
their own food through photosynthesis (or
chemosynthesis). Mostly plants and algae, some
bacteria.
 Primary Consumers – Organisms that eat producers.
Mostly herbivores and small omnivores (bugs).
 Secondary Consumers – Organisms that eat primary
consumers. Often small omnivores and carnivores (birds,
rodents, reptiles).
 Tertiary Consumers – Organisms that eat secondary
consumers. Often larger carnivores (snakes, wild cats)
 Quaternary Consumers – Organisms that eat tertiary
consumers. These don’t exist in many food webs
because there aren’t enough tertiary consumers to eat.

Examples of Energy Pyramids in
Different Ecosystems
Examples of Energy Pyramids in
Different Ecosystems
Examples of Different Energy
Pyramids in Different Ecosystems
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Trophic levels tell us about
biomass and energy.
Biomass – the overall mass
of a particular group of
organisms. Depends on
both size and population
Energy – the amount of
energy that can be
obtained by eating a
particular organism.
The lowest level of an
ecosystem always contains
the most biomass and
chemical energy.
The highest level always
has the least of both.
Trophic Levels
Why is this?
 With the exception of deep sea
vents, all energy on earth comes
from sunlight.
 Producers contain the most energy
and mass because they are only 1
step removed from the sun
(photosynthesis).
 Every time a plant or animal gets
eaten some of its chemical energy
gets wasted by being converted to
heat.
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Trophic Levels
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Every time a plant
or animal gets
eaten most of its
chemical energy
gets wasted by
being converted to
heat (about 90%).
Typically only 10%
of the organism’s
energy makes it
into the next
organism.
For example, the average American ate about
2,000 lbs of food in 2010. If you were 200 lbs,
that would be 10 times your body weight.
 Most of this is used for energy and heat, only
some is stored as muscle and fat (chemical
energy).
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