IB Environmental Systems and Societies

1. Topic 2
2.3 Flows of Energy and Matter

2. 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)

3. The Fate of Solar Radiation
• Energy takes 8 minutes to radiate from the Sun to the Earth
• The energy leaving the Sun is about 63 million J s-1 m-2
• Only about 40% of this energy reaches ground level on Earth
• Photosynthesis is only 30 – 40% efficient

4. Productivity
• Primary Productivity (PP)
– The gain in energy or biomass by producers per
unit area per unit time
• Secondary Productivity (SP)
– The gain in energy or biomass by heterotrophs per
unit area per unit time
PP involves the conversion of solar energy – it is dependent on the amount
of sunlight, temperature, CO2 etc.
SP involves feeding or absorbtion – it is dependent on how much food is
available and how efficiently it can be turned into biomass
Productivity is
measured in
kJ m-2 yr-1

5. Gross Productivity
• Gross Primary Productivity (GPP)
– The total gain in energy or biomass by producers per
unit area per unit time, not taking any losses due to
respiration into account
• Secondary Productivity (GSP)
– The gain in energy or biomass by heterotrophs per
unit area per unit time, not taking any losses due to
respiration and defaecation into account
Losses are caused at each trophic level by respiration
You could compare this idea to money flow
- your GROSS income is the total amount of money you earn
- your NET income is the amount of money you have after losses due to
taxation etc.

6. Net Productivity
• Net Primary Productivity (NPP)
– The total gain in energy or biomass by producers per
unit area per unit time, taking losses due to
respiration into account (R)
• Net Secondary Productivity (NSP)
– The gain in energy or biomass by heterotrophs per
unit area per unit time, taking losses due to
respiration (R) and defaecation (F) into account
The net productivity values are more useful as they give you
information about how much energy or biomass is available from one
trophic level to the next

7. Maximum Net PP in Some Biomes
0
20
40
60
80
100
120
NetPrimaryProductivity(103kJm-2yr-1)

9. Calculations
NPP = GPP – R
NSP = GSP – F – R
NPP
GPP (from
photosynthesis)
R
R
F
NSP
Energy flow in ecosystems

10. Howard Odum
• Ecologist who made the first full analysis
of a whole ecosystem – Silver Springs, a
stream system in Florida
• He measured all inputs and outputs in
terms of organic matter and energy
• He calculated productivity in kcal m-2 yr -1
• He represented his data as a productivity
diagram and an ecosystem model
• In his models he developed a symbol
language similar to that used in
electronics

11. Transfers and Transformations
• The simple movement of energy or matter is a transfer
• The change of energy or matter from one form to
another is a transformation
• Transfers are simpler, require less energy and are
therefore more efficient
• We usually think of energy as being transferred and
chemicals (like nutrients) being transformed
• Nutrients are transformed into different chemical
forms as they pass through trophic levels
• You need to know 3 natural cycles:
– The carbon cycle (transformation of matter)
– The nitrogen cycle (transformation of matter)
– The water cycle (transfer of matter)

12. The Carbon Cycle
http://www.youtube.com/watch?v=2D7hZpIYlCA

13. https://www.youtube.com/watch?v=K5EOZenSSB8
The Nitrogen Cycle
Haber
Process
Ammonia
Artificial
inorganic
fertilizer

14. The Water Cycle
(The Hydrological Cycle)

15. Questions
1. Without referring to your notes, draw an
outline of the carbon, nitrogen and water
cycles
2. Why is not all of the energy assimilated by
one trophic level available to the next one?
3. Without referring to your notes, write
formulas for the calculation of NPP and NSP
(defining each term)

16. Questions
4. If a forest has a gross primary productivity of
6.5 gm-2d-1 and a net primary productivity of
4.0 gm-2d-1, what are its energy losses due to
respiration?
5. A field of cows has a gross secondary
productivity of 5.0 tonnes C m-2yr-1, produces
0.5 tonnes C m-2yr-1 in cowpats and loses 2.1
tonnes C m-2yr-1 in respiration. What is its net
secondary productivity?

17. Questions
Biome Mean NPP
(kg m-3 yr-1)
Desert 0.003
Tundra 0.14
Temperate grassland 0.60
Savannah 0.90
Temperate forest 1.20
Tropical rainforest 2.20
6. Compare and
contrast the NPP
of each biome
7. Why is there a
difference
between the NPP
of temperate
grassland and
savannah?