BIO 2 GO!
Interactions of Organisms in an Ecosystem
3525 – Energy and Biomass Pyramids
Interrelationships and Interdependencies among different organisms in
an ecosystem are affected by factors in the environment.
These relationships contribute to the stability of an ecosystem.
Pyramids of Energy and Biomass
3525
Upon successful completion of this unit, you should be able to do the
following:
1.
2.
3.
4.
5.
Describe an energy pyramid.
Explain how an energy pyramid is useful.
Relate a food chain to an energy pyramid.
Describe a biomass pyramid.
Explain how a biomass pyramid is useful.
6. Use the following words in their correct context:
Energy pyramid
Biomass pyramid
Food chain
Producer
Herbivore
Carnivore
Omnivore
Decomposer
Pyramids of Energy and Biomass
3525
Energy Pyramid
An energy pyramid is an easy way to see the amount of energy loss
from one trophic level to the next. Each layer in the pyramid represents
one trophic level. Producers (green plants) are always located at the
bottom. Herbivores (like a cow) contain less energy and make up the second
level from the bottom. Carnivores (wolves) that feed on herbivores form
the next level. At the top level are carnivores that feed on other
carnivores (like humans). Note that organisms on the top layers of the
pyramid store less energy than those located at the base.
REMEMBER THIS!!!
The total amount of energy available is reduced when moving up the
energy pyramid.
As you know energy from the sun is used by plants in photosynthesis to
make food (glucose) for all other organisms. When we and all organisms on
earth eat we get energy. If we did not eat, we would not have any energy,
and we would die. A car needs gas, which is its energy, in order to work.
Without gas, the car would not do anything or go anywhere. Our bodies are
just like that! We can show how the energy moves through an ecosystem
by drawing a food chain or by an energy pyramid.
Energy pyramids are cool because they show us with a picture how much
energy we get by what we eat. Think about it! Some things that you eat will
give you more energy than others. Have you every wondered why?
Energy pyramids are related to food chains. Look at the example of a
food chain:
Sun---Producer---Herbivore---Carnivore---Carnivore---Decomposer
The food chain tells us the order that organisms are consumed by other
organisms. This is useful information if you are studying an ecosystem.
However, an energy pyramid provides even more information because the
energy pyramid also shows how much energy is transferred to the next
organism. Remember, one of the main reasons any organism eats is to
gain energy. No energy, no life.
An energy pyramid is a diagram that shows the trophic levels as blocks
that are stacked on top of each other. The lowest trophic level
(producers) is at the bottom. The width of the block shows how much
energy is available at that level. Take a look!
Top Carnivore
Carnivore
Herbivores
Producers
Question 1: Look at the energy pyramid above. Which trophic level contains
the most available energy? Which trophic level contains the least amount of
available energy?
The bottom has the most
The top has the least
Only about 10% of the energy is passed to the next level. The rest is
used or is lost as heat. That means that 90% of the energy is used by the
organisms to live.
REMEMBER THIS!!!
Only 10% of the available energy is passed from one trophic level to the
next.
Since most of the available energy is lost between trophic levels,
organisms at the top of the pyramid have to constantly search for more
food. Most humans expect to eat three times every day!
Question 2: How much available energy is lost when a carnivore consumes an
herbivore?
90%
Question 3: Assume that a field of green plants produced 1,000 calories of
energy. A cow was allowed to eat all of the green plants in that field.
How much of the 1,000 calories of energy would the cow receive?
100 calories
Question 4: From question #3, assume that the cow was then taken to the
market and sold as beef. How much of the original 1000 calories of
energy are now available to the person who purchases the beef?
10 calories
Biomass Pyramid
The pyramid of biomass looks exactly the same as the energy pyramid.
What is biomass? Biomass is the dry weight of tissue and other organic
matter in an ecosystem.
REMEMBER THIS!!!
Biomass is the amount of organic matter that is found in an area.
Biomass pyramids are often more useful than energy pyramids.
Ecologists sometimes use biomass pyramids to more accurately determine
the amount of energy in an ecosystem. The results though are the same as
the energy pyramid. Only 10% of the biomass is available to use at the
next higher trophic level.
TEST YOURSELF
True or False
__T__ 1. The lowest trophic level of any ecosystem is occupied by the
producers.
__F_ 2. The number of organisms in a trophic level is always directly
proportional to the amount of energy at that level.
__T__3. An energy pyramid shows the trophic levels as blocks stacked on
one another.
__T__ 4. An energy pyramid shows how much energy is transferred from
one organism to the next.
__F__ 5. Energy pyramids are not related to food chains at all.
__F__ 6. Biomass pyramids have little use when determining how much
energy is in an ecosystem.
__T__ 7. Only 10% of the biomass is available to organisms at the next
higher trophic level.
__F__ 8. There is more energy available at the top of the energy pyramid
than at the bottom.
__F__ 9. An example of a carnivore is a cow.
__T__ 10. Biomass is the amount of organic matter found in an area.
Matching
A. Model that shows the available
energy in a trophic level.
__D__ 1. Producers
__B__ 2. Consumers
__A__ 3. Energy Pyramid
__C__ 4. Decomposer
__H__ 5. Omnivore
__F__ 6. Carnivore
__E__ 7. Food Chain
__G__ 8. Biomass Pyramid
B. Organisms that get their food
by eating other organisms.
C. Breaks down dead organisms in
the environment.
D. Organisms that make organic
nutrients for an ecosystem
using energy from the sun.
E. Tells us the order that
organisms are eaten by other
organisms
F. Eats only meat.
G. Shows the amount of
organisms in an ecosystem by
measuring their dry weight.
H. Eats both plants and meat.
Fill in the Blank
decomposers
trophic
food chain
herbivores
biomass
energy
1. The term _DECOMPOSERS____________ is given to the bacteria
that break down dead tissue.
2. In an ecosystem, __ENERGY____________ decreases at each higher
trophic level.
3. A path of energy through the trophic levels of an ecosystem is called
a(n) __FOOD______________ _____CHAIN__________.
4. An energy pyramid shows the amount of energy contained in the
bodies of organisms at each ___TROPHIC__________ level.
5. _HERBIVORES______ are organisms that eat only plants.
6. _BIOMASS_______ is the dry weight of tissue and other organic
matter in an ecosystem.
Answer the following:
1. Examine the energy pyramid and explain why most ecosystems seldom
have more than four or five trophic levels.
BECAUSE THERE IS NOT ENOUGH ENERGY TRANSFERRED TO
HE NEXT LEVEL IF YOU GO BEYOND FIVE.
2. From an energy or biomass viewpoint, is it better to for humans to be
vegetarians or carnivores? Explain your answer in terms of available
energy and biomass.
Vegetarians- there is more energy available to them at he lower
trophic level.