Section 3
Review
 primary source of energy
for photosynthetic
organisms is the sun/light.
 Food web
 Food chain
 Biomass
Gross Primary Production (GPP)
 calculate the % of incident light energy which appears
as energy of newly synthesised organic substances
 The total energy captured by primary producers = GPP
 respiration (R)
 Net primary production (NPP) - Remaining organic
substances

Transferred to higher trophic levels
 NPP = GPP – R
 ~10% energy available at one trophic level is
transferred to the next trophic level
Energy Losses Along Food Chains
 Of total energy from Sun, only
 3 reasons:
 Respiration/heat
 Waste/feces

Excretion (feces) or egestion
(from cells)
 Some parts of organism not
eaten
a small percentage is captured
and used for synthesis
(NOT ALL ENERGY BECOMES
AVAILABLE AS NET
PRODUCTION)
 Reflected back from surfaces
 Pass straight through a
producer – not absorbed
 Inefficiencies of photosynthesis
 NPP = GPP – R
Energy Flow in a Food Chain
BIG reason why RARELY have more
than 5 levels
 Energy losses
between trophic
levels
 “loss of heat
energy”
 Insufficient energy
available to
transfer to more
than 5 trophic
levels
Efficiency of Energy transfer between
trophic levels
 Net productivity of plants in a food chain is 36,000
kJ/m2 per year
 Net production of herbivores is 1,700 kJ/m2 per year
 Efficiency of transfer of energy from the producers to
herbivores
(1,700 / 36,000) x 100 = 4.72%
 Energy losses: heat from respiration, losses in urine,
undigested plant material (fecal matter)
 Energy of production of herbivores represent total
energy available to carnivores (next trophic level)
Example
 3.5%
 Show work! [1 point]
 Productivity can be measured as mass of carbon incorporated




into biological molecules per unit area per unit time
The primary productivity of the phytoplankton in this food
web is 90 g of carbon per m2 per year.
The efficiency of transfer between phytoplankton and
herbivores is approximately 10%.
Assuming that zooplankton and bottom-feeding herbivores
eat equal quantities of phytoplankton, calculate the amount of
carbon incorporated into zooplankton per m2 per year. Show
your working.
....................................................... g C m–2 year–1 [2]
 Answer: 90/10% = 9/2 = 4.5
Ecological Pyramids
 Graphical representation of food chain
 Producers at base
 Horizontal bars represents successive trophic levels
 Width of bar proportional to numbers, biomass or
energy
 Impossible to have more energy in higher trophic levels
Ecological Pyramid
Example
 Draw a pyramid of biomass for the following food chain:
Phytoplankon  krill  fish  penguins  killer whales [2]
Answer:
 pyramid with 5 levels;
 each level named; (trophic)
4th, 5th, 6th, 7th
4th, 5th, 6th
4th, 5th, 6th
3rd, 4th
4th, 5th, 6th
3rd, 4th, 5th
3rd, 4th , 5th
2nd, 3rd
1st trophic level
3rd, 4th, 5th
2nd
4th, 5th
3rd, 4th, 5th
3rd, 4th
3rd
2nd
3rd, 4th
2nd
1st trophic level
3rd