This document discusses how energy flows through ecosystems, noting that autotrophs like plants capture energy from the sun or inorganic sources and form the base of food chains and webs, while heterotrophs obtain energy by consuming other organisms or their waste. It also examines models for representing energy flow, such as food chains which show linear energy transfer and food webs which illustrate more complex feeding relationships, as well as ecological pyramids which represent biomass and numbers decreasing at higher trophic levels due to less available energy.

1. Flow of Energy in
an Ecosystem
CHAPTER 1.2
P41-44

2. Outline
 Energy in an Ecosystem
 Autotrophs
 Heterotrophs
 Models of Energy Flow
 Food Chains
 Food Webs
 Ecological Pyramids

3. New Vocabulary
 Autotroph
 Heterotroph
 Herbivore
 Carnivore
 Omnivore
 Detritivore
 Trophic Level
 Food Chain
 Food Web
 Biomass

4. What is the original source of the
energy we use to live, move, talk, and
think?

5. Energy in an Ecosystem
 All energy in an ecosystem come from a source and flows
throughout the ecosystem.
 Studying the way energy that flows through ecosystem is one way
scientists study how organisms interact.
 We also classify organisms by how they obtain their energy in an
ecosystem
 Autotrophs
 Heterotrophs

6. Autotrophs
 Definition: All of the green plants and
other organisms that produce their own
food in an ecosystem are primary
producers called autotrophs.
 An autotroph collects energy from
sunlight or inorganic substances to
produce food.

7. Organisms that
contain chlorophyll
absorb energy during
photosynthesis and
use it to convert the
inorganic substances
carbon dioxide and
water to organic
molecules.

8. In places where
sunlight is
unavailable, some
bacteria use
hydrogen sulfide and
carbon dioxide to
make organic
molecules to use as
food.

9. Autotrophs are the
foundation of all
ecosystems
because they
make energy
available for all
other organisms in
an ecosystem.

10. Heterotrophs
 Definition: A heterotroph is an organism that
gets its energy requirements by consuming
other organisms.
 Therefore, all heterotrophs are called consumers.
 There are four types of heterotrophs:
 Herbivores
 Carnivores
 Omnivores
 Detritivores

11. Detritivores
• Detritivores eat pieces of dead matter
in an ecosystem, returning nutrients to
the soil, air, and water where the
nutrients can be reused by organisms.
• Worms, millipedes, flies, and slugs
• Decomposer, similar to detritivores,
break down dead organisms by
releasing digestive enzymes.
• Fungi and bacteria are decomposers
• Decomposers are the primary tool
used to breakdown organic
compounds and make nutrients
available to producers for reuse.

12. State why detritivores are an
important part of the ecosystem.
WB: p1.1

13. Models of Energy Flow
 Ecologists use food chains and food webs to model the energy flow
through an ecosystem.
 Like any model, these are simplified representations of energy flow.
 Defintion: Each step in a food chain or food web is called a trophic
level.
 Autotrophs make up the first trophic level in all ecosystems.
 Heterotrophs make up the remaining levels.
 Organisms at each trophic level get their energy from the trophic level
before it, except for the first trophic level.

14. Food Chains
 Definition: A food chain is a simple model that shows how energy
flows through an ecosystem.
 Arrows represent the one-way energy flow which typically starts
with autotrophs and moves to heterotrophs.
 Each organism in a food chain uses a portion of the energy it
obtains from the organism it eats for cellular processes to build new
cells and tissues.
 The remaining energy is released into the surrounding environment
and no longer is available to these organisms.

16. Food Webs
 Feeding relationships usually
are more complex than a single
food chain because organisms
feed on more than one species.
 Definition: A food web is a
model representing the many
interconnected food chains
and pathways in which energy
flows through a group of
organisms.

17. Describe how food chains are
related to food webs.
WB: p1.2

18. Ecological Pyramids

19. Pyramids are models used to represent trophic levels in
ecosystems.

21. Ecological Pyramids
 Definition: An ecological pyramid is a diagram that can show the
relative amounts of energy, biomass, and numbers of organisms at
each trophic level in the ecosystem.
 In a pyramid of energy, only 10 percent of all energy is transferred
to the level above it.
 Energy is used for cellular processes or released to the environment as
heat.
 Usually, the amount of biomass – the total mass of living matter at each
trophic level – decreases at each trophic level.
 The relative number of organisms at each trophic level also decreases
because there is less energy available to support organism.

22. Predict how the removal of an herbivore
from a food web could affect the entire
community.
WB: p1.5

23. Draw an energy pyramid in which the base
is grass and 100% of the energy is available
for the grass.
Please draw into your notebook.

24. Homework:
Finish WB page 1 and

25. Disturbing Food Web
 https://www.youtube.com/watch?v=FdiCS3bDUN4
 Notebook questions:
 1. What is an invasive species?
 2. How did Asian Carp get to the USA?
 3. Why is Asian Carp a problem?
 4. What would a pyramid of numbers look like for Lake Michigan now
assuming that it was a normal pyramid before?