IB Environmental Systems and Societies

1. Topic 2
2.2 Communities and Ecosystems

2. Ecosystem Structure
• There are 3 main biotic components in any ecosystem:
– Producers
• Plants, algae and cyanobacteria
• They are able to create food using sunlight energy
• Also referred to as photoautorophs
– Consumers
• Obtain energy through eating other organisms
• They do not possess chlorophyll and can’t photosynthesise
• Also referred to as heterotophs
• They may be herbivores or carnivores
– Decomposers
• Bacteria and fungi 1 2 3
• Obtain food though the breakdown of dead organic matter
• Create humic material and are important in recycling nutrients
• Some bacteria are chemoautotrophic decomposers (they use a
similar process to photosynthesis which uses energy from
oxidation reactions rather than sunlight)

3. Food Webs
A simplified food web for savannah biome

4. Energy Flow
• Photosynthesis
• Respiration
6CO2 + 6H2O C6H12O6 + 6O2
C6H12O6 + 6O2 6CO2 + 6H2O
• Energy flow through an ecosystem occurs by 2
processes:

5. Energy Flow
Photosynthesis Respiration
Inputs
Outputs
Transformations
Process
Glucose, O2Light Energy, H2O, CO2
Glucose, O2 Energy, H2O, CO2
Light Energy
Chemical Energy
Chemical Energy
Kinetic Energy + Heat
Chlorophyll traps light
energy, this energy used
to split water molecules,
H from water combined
with CO2 to produce
glucose
Oxidation reactions
inside cells break down
glucose to release
energy

6. Energy Flow
• The sun is the source of energy for the producers in nearly all of the
food webs on Earth
• This is because they are usually dependent on photosynthesis
• However, between 1977 and 1979 scientists from the Woods Hole
Oceanographic Research Institution, using the submersible Alvin,
confirmed the existence of deep-sea hydrothermal vents and
communities in which the producers are use chemosynthesis not
photosynthesis (they live in complete darkness)
Bill Nye - Hydrothermal vent communities

7. Energy Flow
• About half of the Sun’s total radiation is visible
light
• Only visible light is useful for photosynthesis
• Producers use very little of the visible light
available to produce biomass (about 0.06% of the
Sun’s total radiation is captured by producers)
– The remainder is reflected, transmitted or is not the
correct wavelength of light for photosynthesis.
Photosynthesis itself is not an efficient process
(typically 0.1 - 2.0% efficient)
Why do you think photosynthesis hasn’t evolved to become a more efficient process?

8. Energy Flow
• Producers make energy available to consumers in
the form of stored chemical energy (glucose)
• This energy is lost as it passes through each
trophic level due to respiration and defaecation
(typically 90% is lost between each level)
• Eventually all of the initial available energy is lost
by being converted into heat which radiates away
from the Earth. The Sun re-radiates energy to the
Earth (which is therefore an Open System)
Can you see the relevance of the Second Law of Thermodynamics to ecosystems?