1. Chapter 42 Review: Cool Ecosystem
An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact
An example is the unusual community of organisms, including chemoautotrophic bacteria, living below a glacier in Antarctica 1

2. Conservation of Energy
Laws of physics and chemistry apply to ecosystems, particularly energy flow
The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed
Energy enters an ecosystem as solar radiation, is transformed into chemical energy by photosynthetic organisms, and is dissipated as heat 2

3. The second law of thermodynamics states that every exchange of energy increases the entropy of the universe
In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat
Continuous input from the sun is required to maintain energy flow in Earth’s ecosystems 3

4. Conservation of Mass
The law of conservation of mass states that matter cannot be created or destroyed
Chemical elements are continually recycled within ecosystems
In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water
Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products 4

5. Ecosystems can be sources or sinks for particular elements
If a mineral nutrient’s outputs exceed its inputs it will limit production in that system 5

6. Energy and nutrients pass from primary producers
primary consumers (herbivores)
secondary consumers (carnivores)
tertiary consumers (carnivores that feed on other carnivores) 6

7. Prokaryotes and fungi are important detritivores
Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter
Prokaryotes and fungi are important detritivores
Decomposition connects all trophic levels; detritivores are fed upon by secondary and tertiary consumers 7

8. Energy and other limiting factors control primary production in ecosystems
In most ecosystems, primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period
In a few ecosystems, chemoautotrophs are the primary producers 8

9. Ecosystem Energy Budgets
The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget 9

10. The Global Energy Budget
The amount of solar radiation reaching Earth’s surface limits the photosynthetic output of ecosystems
Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength 10

11. Gross and Net Production
Total primary production is known as the ecosystem’s gross primary production (GPP)
GPP is measured as the conversion of chemical energy from photosynthesis per unit time 11

12. Net primary production (NPP) is GPP minus energy used by primary producers for “autotrophic respiration” (Ra)
NPP is expressed as
Energy per unit area per unit time (J/m2  yr), or
Biomass added per unit area per unit time (g/m2  yr)
NPP = GPP − Ra 12

13. NPP is the amount of new biomass added in a given time period
Only NPP is available to consumers
Standing crop is the total biomass of photosynthetic autotrophs at a given time
Ecosystems vary greatly in NPP and contribution to the total NPP on Earth 13

14. Net primary production (kg carbon/m2 • yr)
Figure 42.6
Net primary production
(kg carbon/m2 • yr) 3 2 1
Figure 42.6 Global net primary production 14

15. Net ecosystem production (NEP) is a measure of the total biomass accumulation during a given period
NEP is gross primary production minus the total respiration of all organisms (producers and consumers) in an ecosystem (RT)
NEP = GPP − RT 15

16. NEP is estimated by comparing the net flux of CO2 and O2 in an ecosystem, two molecules connected by photosynthesis
The release of O2 by a system is an indication that it is also storing CO2 16

17. Nutrient Limitation
A limiting nutrient is the element that must be added for production to increase in an area
Nitrogen and phosphorous are the nutrients that most often limit marine production
In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species
In lakes, phosphorus limits cyanobacterial growth more often than nitrogen 17

18. Energy transfer between trophic levels is typically only 10% efficient
Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time 18

19. Production Efficiency
When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production
Net secondary production is the energy stored in biomass
An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration
Production
efficiency =
Net secondary production × 100%
Assimilation of primary production 19

20. secondary production)
Figure 42.9
Plant material
eaten by caterpillar
200 J
67 J
Cellular
respiration
Figure 42.9 Energy partitioning within a link of the food chain
100 J
Feces
33 J
Not assimilated
Growth (new biomass;
secondary production)
Assimilated 20

21. Insects and microorganisms have efficiencies of 40% or more
Birds and mammals have efficiencies in the range of 13% because of the high cost of endothermy
Insects and microorganisms have efficiencies of 40% or more 21

22. Trophic Efficiency and Ecological Pyramids
Trophic efficiency is the percentage of production transferred from one trophic level to the next, usually about 10%
Trophic efficiencies take into account energy lost through respiration and contained in feces, as well as the energy stored in unconsumed portions of the food source
Trophic efficiency is multiplied over the length of a food chain 22

23. Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer
A pyramid of net production represents the loss of energy with each transfer in a food chain 23

24. Tertiary consumers 10 J Secondary consumers 100 J Primary consumers
Figure 42.10
Tertiary
consumers
10 J
Secondary
consumers
100 J
Primary
consumers
1,000 J
Primary
producers
Figure An idealized pyramid of net production
10,000 J
1,000,000 J of sunlight 24

25. Turnover time is the ratio of the standing crop biomass to production
Certain aquatic ecosystems have inverted biomass pyramids: producers (phytoplankton) are consumed so quickly that they are outweighed by primary consumers
Turnover time is the ratio of the standing crop biomass to production
Turnover time =
Standing crop (g/m2)
Production (g/m2  day) 25

26. Water is essential to all organisms
The Water Cycle
Water is essential to all organisms
Liquid water is the primary physical phase in which water is used
The oceans contain 97% of the biosphere’s water; 2% is in glaciers and polar ice caps, and 1% is in lakes, rivers, and groundwater
Water moves by the processes of evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater
Animation: Carbon Cycle 26

27. The water cycle Movement over land by wind Precipitation over land
Figure 42.13a
Movement over
land by wind
Precipitation
over land
Precipitation
over ocean
Evaporation
from ocean
Evapotranspiration
from land
Figure 42.13a Exploring water and nutrient cycling (part 1: water)
Percolation
through
soil
Runoff and
groundwater
The water cycle 27

28. Carbon-based organic molecules are essential to all organisms
The Carbon Cycle
Carbon-based organic molecules are essential to all organisms
Photosynthetic organisms convert CO2 to organic molecules that are used by heterotrophs
Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, the atmosphere, and sedimentary rocks 28

29. CO2 is taken up by the process of photosynthesis and released into the atmosphere through cellular respiration
Volcanic activity and the burning of fossil fuels also contribute CO2 to the atmosphere 29

30. The carbon cycle CO2 in atmosphere Photosynthesis Photo- synthesis
Figure 42.13b
CO2 in
atmosphere
Photosynthesis
Photo-
synthesis
Cellular
respiration
Burning of
fossil fuels
and wood
Phyto-
plankton
Consumers
Figure 42.13b Exploring water and nutrient cycling (part 2: carbon)
Consumers
Decomposition
The carbon cycle 30

31. Nitrogen is a component of amino acids, proteins, and nucleic acids
The Nitrogen Cycle
Nitrogen is a component of amino acids, proteins, and nucleic acids
The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to NH4+ or NO3− for uptake by plants, via nitrogen fixation by bacteria 31

32. Denitrification converts NO3− back to N2
Organic nitrogen is decomposed to NH4+ by ammonification, and NH4+ is decomposed to NO3− by nitrification
Denitrification converts NO3− back to N2 32

33. The nitrogen cycle N2 in atmosphere Reactive N gases Industrial
Figure 42.13c
N2 in
atmosphere
Reactive N
gases
Industrial
fixation
Denitrification
N fertilizers
Fixation
Runoff
Dissolved
organic N
NO3−
Terrestrial
cycling N2
NO3−
NH4
Aquatic
cycling
Denitri-
fication
Figure 42.13c Exploring water and nutrient cycling (part 3: nitrogen)
Decomposition
and
sedimentation
Decom-
position
Assimilation
NO3−
Fixation
in root
nodules
Uptake of
amino acids
Ammoni-
fication
Nitrification
NH4
The nitrogen cycle 33

34. Phosphate (PO43−) is the most important inorganic form of phosphorus
The Phosphorus Cycle
Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP
Phosphate (PO43−) is the most important inorganic form of phosphorus
The largest reservoirs are sedimentary rocks of marine origin, the soil, oceans, and organisms
Phosphate binds with soil particles, and movement is often localized 34

35. The phosphorus cycle Wind-blown dust Geologic uplift Weathering
Figure 42.13d
Wind-blown
dust
Geologic
uplift
Weathering
of rocks
Runoff
Consumption
Decomposition
Plant
uptake
of PO43−
Plankton
Dissolved
PO43−
Uptake
Leaching
Figure 42.13d Exploring water and nutrient cycling (part 4: phosphorus)
Sedimentation
Decomposition
The phosphorus cycle 35