Integrated Science: Grade 10
Activity: Intro to Energy in Ecosystems
Energy in Ecosystems: Introductory Activities
Guided reading exercise
Use this worksheet as your notes regarding the topics discussed.
Introduction:
We have spent much of this year discussing energy in various forms. We just finished talking about
the flow of energy on a microscopic scale, now it is time to think about energy on a larger scale.
Today you will explore the flow of energy in ecosystems, defining terms and checking your
understanding along the way. Enjoy!
1. Open the associated text reading section 30.2: Special Interactions in Ecological Communities
(page 649-650) and 30.3: Energy Flow in Ecosystems (page 654-656). Read and take notes.
2. Try the “Check Your Thinking” at the end of the section.
3. Go to http://www.sophia.org/tutorials/energy-pyramids--2. Look at the PPT and answer the Quiz
questions.
Define the following terms and answer the questions below. You may find you need to revise these
definitions as you learn more throughout the unit, so do your best and modify and edit as needed
along the way.
1.
2.
3.
4.
5.
6.
Biomass: The
organic matter in an ecosystem (all living things are made
of organic matter and therefore contribute to the biomass in an
ecosystem. What about dead organisms?)
Trophic level: One of the different feeding levels in a food chain,
including producers, primary consumers, secondary consumers and so
on.
Food Chain: a diagram of the relationships between species from
multiple feeding levels/trophic levels, always begins with a producer
Food Web: a diagram of the overlap in feeding relationships within an
ecosystem, a more realistic, complex and accurate depiction of feeding
relationships within ecological communities.
Producers: species that make organic molecules out of inorganic
materials and energy
Consumers: organisms that obtain food (energy) by eating other
organisms
7.
Differentiate between primary, secondary and tertiary consumers.
8.
Primary consumers: organisms
9.
that directly consume producers
Secondary consumers: organisms that consume primary consumers
10.
Tertiary consumers: organisms
that consume secondary consumers
11.
Energy an organism takes in (or produces in the case of plants) goes to what three
aspects of living?
All of the energy may not be consumed eg primary consumers don't
eat ALL the plants, or it may be eaten but not actually digested e.g. the
energy is lost as waste from the body. Lots of the 90% of energy that
isn't passed on is used for maintenance e.g. to allow cellular
respiration, to move muscles. Much of the energy is transformed into
heat as a result of all of the reactions taking place. Therefore, energy
an organism takes in:
Is USED to make new biomass (make new cells and molecules)
and to allow for cellular respiration (extract energy in form of ATP) to
do cellular work (active transport, for example)
Is NOT USED and passes through the organism
Is NOT USED and is lost as Heat from the organism
12.
What energy moves up the food chain?
Only mass that has been converted to biomass (i.e. stored chemical
potential energy) and is CONSUMED by the next trophic level will
move up the food chain.
13.
Approximately how much of the total energy (biomass) at one level of a food chain is
available to the next tropic level?
Only ~ 10% eg if there is 1000 J energy in the autotrophs (“self”
“feeders”, i.e. producers) then only 100J of that energy would be
available to the primary consumers
14.
Wait a minute, we know that energy cannot be create or destroyed, so explain why
energy flow in ecosystems does not violate (prove incorrect) the Law of Conservation
of Energy.
Even though only 10% of energy is passed onto the next trophic level
that doesn't mean that the energy has been destroyed. Rather it is
transformed.
15.
Now, knowing what you know, explain why person may correctly say that becoming
a vegetarian is better for the environment and can actually help stop deforestation.
In becoming a vegetarian, a person becomes a primary consumer rather than a
secondary or tertiary consumer. In doing so, fewer energy conversions have to
take place to access the necessary fuel to allow for their cellular needs. Since
only 10% of energy gets passed from one level to the next, the vegetarian
drastically reduces the number of producers (plants) needed to fuel them,
because the plants don’t need to fuel a cow/pig/chicken in between. Thus, less
land is needed to grow crops that feed animals and less land is needed to put the
animals, overall, reducing the need for more land and thus decreasing
deforestation.
4. Read the next section of your text: Energy Leaks When Organisms Eat (P. 655)
16.
In your own words, explain how the second law of thermodynamics relates to the
notion of the energy pyramid between each trophic level of the ecosystem. Begin by
stating, in your own words, the second law of thermodynamics.
Second law of thermodynamics: Natural systems tend to disperse from
concentrated and organize energy states toward diffuse &
disorganized states or entropy (disorder) will increase in a system
unless energy is added to that system.
First, some of the energy is used by the organisms for maintenance (eg
growth, reactions, movement). When energy from food is used in the
chemical reactions that allow organisms bodies to function energy is
lost as heat – this supports the 2nd law of thermodynamics eg natural
systems move from organized to disorganized (to more dispersed) less
useful heat/thermal energy.
Thermal energy = heat. When energy is transferred from one trophic
level to the next or in one form in your body (food) into another
(ATP) energy is lost as heat. Therefore, the entropy is increased and
the energy state is more disorganized.
This is why the energy flow in an ecosystem is a pyramid, higher
levels cannot have more useful energy than lower levels, because
energy at the lower levels gets converted into less useful thermal/heat
energy, which cannot be captured by the next level.
At the end of the section, be sure to answer these “Check Your Thinking” Questions:
17.
What ultimately happens to the energy that goes into the “maintenance” of a living
organism?
Eventually it all gets converted into thermal energy eg heat.
18.
Does energy move around Earth in cycles the way water, carbon and nitrogen do?
Explain.
No, energy is finite. It will all eventually get converted into thermal
energy e.g. heat, (most entropy/most disordered) and thus we must
constantly add Energy to the system (where does that E come from?)
Putting it all together:
IN A SEPARATE DOCUMENT, titled “Energy Flow in Ecosystems” by (Insert your name)
Write a short (½ to 1 page) essay that uses the Law of Conservation of Energy and the Second Law
of Thermodynamics as it relates to entropy to discuss energy flow in ecosystems. Include the
following points:
i.
the main source of energy for life on Earth (Law of Conservation of Energy – transformations);
ii. how energy is used, by organisms within trophic levels;
ii
the approximate amount passed on to higher trophic levels;
iii. how much is 'lost' from the ecosystem/food chain;
iv. where the 'lost' energy goes (Law of Conservation of Energy – transfers and transformations);
v. why it transforms to that form (Second Law of Thermodynamics as it relates to entropy);
vi whether energy is conserved (Law of Conservation of Energy – transfers and transformations).
When you have completed your essay, SAVE IT AS YOUR NAME, then submit it to the dropbox on
Moodle.