Topic 2.2:
Communities and
ecosystems
Starter:
Discuss with your
partner what the
word community
means to you
2.2 Significant Ideas
• The interactions of species with their environment result
in energy and nutrient flow.
• Photosynthesis and respiration play a significant role in
the flow of energy in communities.
• The feeding relationships in a system can be modeled
using food chains, food webs, and ecological pyramids.
2.2 Application and Skills
• Construct models of feeding relationships, eg., food
chains, food webs and ecological pyramids, for given data.
• Explain the transfer and transformation of energy as it
flows through an ecosystem.
• Analyse the efficiency of energy transfers through a
system.
• Construct systems diagrams representing photosynthesis
and respiration.
• Explain the relevance of the laws of thermodynamics to
the flow of energy through ecosystems.
• Explain the impact of a persistent/non-biodegradable
pollutant in an ecosystem.
2.3 Knowledge and Understanding
See Pages 64-65 in your textbook or refer
to you IB ESS Guide.
Community, Population, Individual
• Levels of organisation within an ecosystem.
• Ecosystem – a biological community of interacting
organisms and their physical environment.
• Community – a group of interacting species living
within the same ecosystem (does not include
abiotic factors)
• Population – all the individuals of the same species
within a community.
• Individual – a single organism of one species.
In your books:
Write a definition for each of
the new concepts. (C,P and I)
Theory of Knowledge:
Why is there so much specialised vocabulary in this
topic? Why are we spending a lot of time learning
the definitions of these words? Does the use of
specialised vocabulary affect how we learn?
Where does the energy in an
ecosystem come from?
One
interesting
exception
Chemosynthetic
bacteria
How does the energy from the
sun “get into” an ecosystem?
Photosynthesis
• Autotrophs (self feeding)
• Plants and algae (contain chloroplast)
• Primary producers
• Convert carbon dioxide and water into glucose and
oxygen using light energy from the sun.
• Photosynthesis produces the raw material for
producing biomass
• Biomass = the mass of living or recently living
organisms.
Photosynthesis
Light energy
carbon dioxide + water  glucose + oxygen
inputs
outputs
Chemical
potential energy
• Carbon dioxide and water have relatively low chemical energy.
• Plants use sunlight to convert these into glucose (which has a lot more chemical
potential energy).
In your books:
1) Write the word equation for photo synthesis, highlighting the
inputs and output.
2) Explain how the energy from the sun is transformed into
chemical energy which can then be used to produce biomass
How do you know I’m not lying?
carbon dioxide + water  glucose + oxygen
• How could you test for the outputs of
photosynthesis?
• How would you know whether it was
photosynthesis producing these chemicals and not
another process?
Discuss with your
partner – be ready to
feed back to the class
Testing for the products of
photosynthesis
Starch
Once glucose has been
produced a plant rapidly
converts it into starch
which is easier to store.
Oxygen
Using an aquatic plant you will
collect the gas released and test
it.
1. Collect a leaf from
each plant.
2. Make note of the
conditions it was kept
in.
3. Boil the leaf in ethanol
for a few minutes.
4. Remove the leaf from
the ethanol and test
for starch with iodine.
1. Collect a sprig of Cabomba.
2. Set up the equipment as
shown on your sheet
3. Shine a bright light onto the
plant.
4. Notice what happens when
you change the distance of
the light.
5. Test the gas that you have
collected in your test tube
with a glowing splint.
Conclusion
• Using your results write a conclusion to your
experiment.
• Ensure you suggest some improvements.
Respiration
Starter:
In your books:
1) Write the word equation for
photosynthesis.
2) What is respiration?
3) Write the word equation for
respiration.
Respiration
• The process by which living organisms convert
oxygen and glucose into a useful energy form,
releasing carbon dioxide and water in the process.
Respiration
In your books:
Make sure you have the correct equation for
respiration down.
Highlight the input and outputs.
glucose + oxygen  carbon dioxide + water
inputs
chemical
energy (ATP)
outputs
heat energy
• The chemical potential energy of the glucose is released during this reaction.
• It is converted from one form to another.
• The energy is “stored” within the chemical bonds of the glucose, and as the
glucose is broken down the energy released is used to created another
chemical, ATP, which our cells can readily use.
Energy is never created or
destroyed. It is just converted
from one form to another.
A lot of heat is lost during
respiration. • How could we test for this?
Planning an investigation.
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Question/problem – what have you noticed or observed?
Hypothesis – what do you think is going to happen?
Hypothesis explanation – why do you think that?
Variables – what are the variables?
• Independent – Which are you changing?
• Dependant – Which are you measuring?
• Control – Which are you keeping the same?
Equipment – List of all equipment, and possibly set up diagram.
Method – Clear and precise instructions, written in present tense.
Results – A clear table and appropriate graph of your results.
Discussion – A detailed discussion of what your results show.
Evaluation – Limitation of the experiment, sources of error,
improvements.
Conclusion – Short summary of your findings.
Homework
• Explain how the type of energy changes through
the processes of respiration and photosynthesis.
Trophic Levels
Starter:
In your books:
Draw the food chain and add
the following labels.
Think…
Why are we unlikely to have
a food chain longer than 5
species?
Quaternary consumer
Primary consumer
Primary producer
Tertiary consumer
Secondary consumer
Food chains and webs
• Show the flow of energy between organisms.
Producers
(Autotrophs)
Boxes represent
stored energy and
the arrows
represent a
transfer of energy.
Consumers
(Heterotrophs)
Decomposers
Ecological pyramids
Pyramid of Numbers
Snake 50
Frog 500
Grass hopper 300,000
GrassTree
1,000,000
Oak
1
Pyramid of Biomass
Snap shot into a community, total mass of
each species (per m2)
Snake 1.5g/m2
Frog 11g/m2
Grass hopper 37g/m2
Grass 807g/m2
Unit is g/m2 or gm-2
Pyramid of Biomass
May show greater quantities at higher tropic levels
because they are a snap shot, and seasonal
variation may be prevalent.
Snake 1.5g/m2
Frog 11g/m2
Grass hopper 37g/m2
Grass 30g/m2
Unit is g/m2 or gm-2
Pyramid of Productivity (Energy)
• Show the amount of energy flowing from each trophic
level to the next, not just a snapshot, but dynamic.
• Energy is lost at each stage due to heat lost.
Snake 600 J/m2/yr
Frog 3000 J/m2/yr
Grass hopper 9000 J/m2/yr
Grass 35000 J/m2/yr
Unit is J/m2/yr or Jm-2yr-1
In your books:
Using the table below draw a pyramid of numbers, biomass
and productivity.
Species
Number of
Individuals
Biomass
(gm-2)
Productivity
(Jm-2yr-1)
Kelp
100
2000
100,000
Sea Urchin
2500
250
10,000
Saddle Wrasse
1500
100
1,000
Caribbean reef
shark
5
25
100
In your books:
Calculate the efficiency of energy transfer through each tropic
level.
Why is the efficiency this value?
In your books:
Using the iPads research the following:
What are the advantages/disadvantages of each pyramid
type?
Use this research to explain which pyramid you think best
represents an ecosystem.
I expect a detailed explanation (about half a page).
https://www.youtube.com/watch?v=Ipbc-6IvMQI
You will be writing an essay next lesson on the ecological
effects of these two phenomenon.
What are the ecological effects of bioaccumulation and
biomagnification? Use examples to support your explanation.
Again using the iPads to help make some research notes:
1) Define bioaccumulation and biomagnification (they are different).
2) Research two examples:
• What were these chemicals used for?
• How did they enter ecosystems?
• What are the effects on the organisms within the ecosystem?
• What effect does this have on humans?
• Are there any solutions to the problem?
3) Record the names of any papers/websites you and use these to
reference parts of your essay.
Clues: Minamata Bay disaster, DDT, PBDE
You will be bringing these notes into the lesson with you.
• Mercury in sea
life.
• Industrial waste
• Bioaccumulation
as well as
biomagnification
• DDT was used
as an insecticide
heavily in the
1940-60s.
• Found to cause
cancer in
humans and
was banned in
1972.
In your books:
Explain the impact of a
persistent or nonbiodegradable pollutant in
an ecosystem.
What are the ecological effects of bioaccumulation and biomagnification? Use examples to
support your explanation.
How do we structure an essay?