1. Lect 02
Energy and Biomass

2. Forms and Conservation of Energy
Potential Energy: stored energy
chemical bonds  bodies of organisms
concentration gradients across a cell membrane
Kinetic Energy: energy of motion
being used to do ‘work’
Light, heat, motion

3. First and Second laws of Thermodynamics apply to living things
1st: Energy is neither created nor destroyed
2nd: Energy transfers tend to decrease the ‘quality’ of energy
At each transfer some energy is ‘lost’ as heat – or -
Entropy (disorder) tends to increase

4. Energy Flow in Ecosystems:
Energy flows through trophic (feeding) levels:
Autotrophs: ‘self feeder’ - an organism that can capture light energy … store in organic molecules
Photosynthesis – anabolic reaction
Plants, algae and certain bacteria
Heterotrophs: ‘other feeder’:
rely on breakdown of organic molecules produced by an autotroph as an energy source – catabolic
Trophic, or feeding level: organisms feeding at the same energy level

5. Trace in a linear path passage of energy through an ecosystem
Food chain
Trace in a linear path passage of energy through an ecosystem
Arrows indicate direction of energy flow
Two types
Grazing food chain
Detrital food chain
Both pathways are important in accounting for the energy budget of the ecosystem.

6. simplified by isolating a portion of a community
food web:
branching food chain
complex trophic interactions
Species may play a role at more than one trophic level
simplified by isolating a portion of a community

7. Sea nettle Juvenile striped bass Fish larvae Fish eggs Zooplankton
Figure Partial food web for the Chesapeake Bay estuary on the U.S. Atlantic coast
Fish larvae
Fish eggs
Zooplankton

8. Biomass available at the next trophic level
About one order of magnitude of available energy is lost from one trophic level to the next (10% rule)
Limits food chains to 3 or 4 steps only
Biomass available at the next trophic level
How heterotrophs use food energy
Energy loss in an ecosystem
Cayuga Lake
In NY

9. Ecological or Trophic Pyramids
A plant fixes about 1% of the sun’s energy that falls on its green parts
Fixed energy is used to build chemical bonds (energy stored)
What happens to the other 99% that was not captured to drive photosynthesis?
Of the fixed energy only +/-10% is available to organisms that eat the plant (next trophic level)
Successive members of a food chain incorporate ~ 10% of energy available in organisms they consume
Fewer individuals at higher tropic levels
Ecological or trophic pyramid

10. Heterotrophs
Plants= Autotrophs

11. Photosynthesis: (Chapter 29)
Light energy captured by pigments
Used to build bonds forming various complex molecules – anabolic processes
Carbon dioxide absorbed/oxygen waste product
Within PAR specific wavelengths of light are most important in driving photosynthesis

12. Light-dependent reactions
1. Pigments capture energy from sunlight
Water is split, O2 released
2. Using energy to make high energy transfer molecules: ATP and NADPH
3. Using ATP and NADPH to power the synthesis of carbohydrates from CO2
Light-dependent reactions
Light-independent reactions
The Calvin cycle +
12 H2O
water +
Light energy +
6 H2O
water +
6 O2
oxygen
6 CO2
carbon
dioxide
C6H12O6
glucose

13. Absorption spectra of chlorophylls and carotenoids

14. Primary production (or primary productivity):
Overall rate of photosynthesis or total energy captured by photosynthesis
Limits to primary productivity:
Temperature
intensity of PAR
Precipitation/availability of water
CO2
Nutrients
Limiting nutrient

15. Primary productivity Limits to primary productivity:
Gross Primary Productivity (GPP):
total amount of photosynthetic energy captured in a given period of time.
Limits to primary productivity:
Temperature
intensity of PAR
Precipitation/availability of water
CO2
Nutrients
Limiting nutrient
Net Primary Productivity (NPP):
the amount of plant biomass (energy) after cell respiration has occurred in plant tissues.
NPP = GPP – Plant respiration
plant growth/ total photosynthesis/
unit area/ unit area/unit time
unit time

16. Temperature and precipitation primarily limit terrestrial production.
Figure 10
Temperature and precipitation primarily limit terrestrial production.
Primary productivity in terrestrial ecosystems. Primary productivity in terrestrial ecosystems is often related to average annual temperature and precipitation. The colored bars represent the ranges for representative high latitude (tundra), middle latitude (temperate forests) and equatorial (rain forests) biomes. Note the overlap between the precipitation of the rain forest and temperate forest. This is likely due to the presence of temperate rain forests and seasonal tropical forests, which are both wetter and drier, respectively, than typical temperate and tropical forests.

17. Gross primary productivity
Gross primary productivity. MODIS image shows the gross primary productivity, or the total amount of chemical energy converted by primary producers from solar energy.

18. Experimental introduction of iron to the open ocean
Figure 8
Experimental introduction
of iron to the open ocean
Changes in productivity in enriched and control areas. In this graph, open circles and diamonds (◊) represent productivity in control areas where no iron was added, while filled circles and diamonds represent productivity in areas where iron particles were added.
Although nitrogen and phosphorus are usually the most important limiting nutrients, sometimes other nutrients become most limiting.
In open oceans, iron addition can greatly increase production.

20. Figure 7
Nutrients play an especially important role in limiting productivity in aquatic ecosystems.
Nutrient pollution from agricultural runoff can dramatically alter aquatic ecosystem structure.
Phytoplankton bloom in the Bay of Biscay. This satellite image shows the phytoplankton bloom in the Bay of Biscay. The light blue swirls are the phytoplankton.

21. Secondary Productivity
Secondary productivity – the rate at which consumers convert the chemical energy of the food they eat into their own new biomass
Involves heterotrophs
Essentially reverse of photosynthesis - May occur with or without oxygen
Aerobic – most efficient
Anaerobic  fermentative pathways (in anoxic environment)
ATP immediate cellular energy form

22. Glycolysis With Oxygen aerobic Fermentation- anaerobic
Electron Transport most ATP generated here

23. Disruptions in Energy Flow/Ecosystem Productivity
Eutrophication: Addition of excess nutrients
Introduction of non-native species
Removal of species -

24. Nutrient pollution causes eutrophication.
Decrease in dissolved O2.
Change in species composition.
Often reduction in biodiversity.
High nutrient inputs
Low nutrient inputs
Eutrophic versus oligotrophic freshwater. a) A highly eutrophic wetland in Florida, as indicated by greenish-colored water and large amounts of floating algae. b) An oligotrophic wetland in Florida as indicated by relatively clear water with far less floating algae.