2.5 Ecosystem
Functions
Major Functions of An Ecosystem
Producers-Convert sunlight energy into
organic matter
 Consumers- Use living organic matter as
energy to grow and develop
 Decomposers- Break down the dead organic
matter / return nutrients to the soil

ENERGY ENTERS THE ECOSYSTEM
AS SUNLIGHT
Only 2% of the light energy falling
on plant is used to create energy
 The rest is reflected, or just warms
up the plant as it is absorbed

Photosynthesis
Process where plants use sun light energy to
create chemical energy
 Photosynthesis: equation

◦ 6CO2 + 6H2O --> C6H12O6 + 6O2
Inputs: light energy, water, carbon dioxide
 Outputs: oxygen gas, sugar
 Energy transformations: Light to Chemical
 respiration backwards!

Respiration
Process by which animals create energy
through consumption of organic molecules
(sugars)
 Respiration:

◦ C6H12O6 + 6O2 --> 6CO2 + 6H2O
Inputs: oxygen gas, organic molecules
(sugars)
 Outputs: carbon dioxide, energy in ATP,
waste heat
 Energy transformations: chemical to heat
 Photosynthesis backwards!

Photosynthesis and Respiration
Glucose /
Oxygen
CO2/
Water
Energy Transfers in Ecosystem
Energy Flow Diagram
Water Cycle
Nitrogen Cycle
Carbon Cycle
Gross productivity
Total energy captured or
“assimilated” by an organism.
 Measured in joules (J)
 Plant (Gross Primary Productivity)

◦ GPP = sunlight energy used during
photosynthesis

Animals (Gross Secondary
Productivity)
◦ GSP = food eaten - energy in
faeces
Energy is
stored in leaf
as sugars and
starches, which
later are used
to form
flowers, fruits,
seeds,
Net productivity
The energy left over after organisms have used
what they need to survive.
 All organisms have waste energy and respiratory
loss given off as heat, metabolism (R)
 Plants and animals have to use some of the energy
they capture to keep themselves growing:

◦ They both move water and stored chemicals around
◦ Plants make flowers, fruits, new leaves, cells and stems
◦ Animals create cells and need to move muscles.
Net productivity = Gross productivity - Respiration Energy
or using symbols:
NP = GP - R
Net Primary vs. Net Secondary Productivity
(NPP) vs. (NSP)

Calculate Net productivity for plants and animals
 NPP = GPP – R
PLANTS
 NSP = GSP – R
ANIMALS
NSP
GSP
Productivity in Food Web

In a food web diagram, you can assume that:
◦ Energy input into an organism represents the GP
◦ Energy output from that organism to the next trophic level
represents the NP
◦ GP-NP = R (respiration energy ) and/or loss to decomposers
?
Therefore…

The least productive ecosystems are those
with limited heat and light energy, limited
water and limited nutrients.
◦ Example biome:_______________

The most productive ecosystems are those
with high temperature, lots of water light and
nutrients.
◦ Example biome:__________________
Now check you have understood!

Draw a complete food web for an ecosystem of your
choice, which should include:
◦
◦
◦
◦
◦
◦

the sun and its energy
named primary producers (at least 2)
named primary consumers (at least 3)
named secondary consumers (at least 2)
named decomposers (at least 2)
respiration energy loss (use red marker for this arrow)
On your diagram use arrows to show direction of
energy flow
◦ Complete this energy flow diagram:
 Label GPP, NPP and R for the primary producer
 Add arrows to show missing energy pathways
 (5 in total)
 Fill in the blank box to explain why some sunlight is not
fixed by plant
HERBIVORES
PLANT
SUN
………………
…………….
(~98% of energy
is here)
RESPIRATION
DECOMPOSERS

Draw your own energy flow diagram, rather like
the one on the previous slide to show energy flows
through the trophic levels in your food web.
Include the following labels:
◦ Start with sunlight energy
◦ Include all trophic levels from your food web
◦ Include arrows showing energy moving from each trophic
level to another and to decomposers
◦ Show energy lost in faeces
◦ Show Respiration loss (heat energy) USE RED MARKER!
◦ Label each individual arrow with a letter (A,B,C,D,E…)
◦ Use the lettered arrows to write an equation for GPP,
NPP
◦ Write an equation for GSP, NSP for primary consumers
The data in the table below relate to the transfer of energy in a small
clearly defined habitat. The units in each case are in kJ m-2 yr-1



Trophic Level
Gross
Production
Respiratory
Loss
Loss to
decomposers
Producers
60724
36120
477
1° Consumer
21762
14700
3072
2° Consumer
714
576
42
3° Consumer
7
4
1
Respiratory loss
by decomposers
---
3120
---
Construct an energy flow model to represent all these data – Label each arrow with the
appropriate amount from the data table above.
Use boxes to represent each trophic level and arrows to show the flow of energy
Calculate the Net Productivity for
◦ NPP for Producers
◦ NSP for 1°Consumers, 2°Consumers, 3°Consumers
◦ NSP for Decomposers
ENERGY FLOW MODEL
R=36120
60724
Producers
R=576
R=14700
21762
1 Consumer
714
2 Consumer
3072
R=4
7
3 Consumer
42
477
1
Decomposers
R=3120
Productivity Calculations
NPP of Producers:60724 - (36120+477)
NSP of 1 Consumer21762 -(14700+3072)
NSP of 2 Consumer714 -(576+42)
NSP of 3 Consumer7 -(4+1)
NSP of Consumers:
22483 -(15280+3115)
NSP of Decomposers:
(477+3072+42+1)
=24127 kJ.m-2.yr-1
=3990 kJ.m-2.yr-1
=96 kJ.m-2.yr-1
=2 kJ.m-2.yr-1
=4088 kJ.m-2.yr-1
-3120
=472 kJ.m-2.yr-1
How to measure primary
productivity
1.
2.
3.
Harvest method – measure biomass and
express as biomass per unit area per unit
time.
CO2 assimilation- measure CO2 uptake
in photosynthesis and releases by
respiration
02 production-Measure O2 production
and consumption
Measuring productivity continued
4.Radiosotope method-use c14 tracer in
photosynthesis.
5.Chlorophyl measurement- assumes a
correlation between the amount of
chlorophyll and rate of photosynthesis.