Name:
Worksheet 7: Ecosystems
Chapter 24
1. Define ecosystem. Differentiate between abiotic and biotic, providing examples for each.
2. Consider the general way in which ecosystems work:
a. Define each of the following terms as they relate to ecosystems:

Energy

Nutrients
b. Why does energy flow whereas nutrients cycle though an ecosystem?
3. Consider energy capture in ecosystems:
a. What are the two (2) primary sources of energy?
b. What is the main way in which energy is captured?
c. Once captured, energy is converted and stored as what major type of
macromolecule? (Hint: see also worksheet #1).
d. How is this energy transferred to other organisms?
4. The net amount of energy in the form of organic macromolecules available for
consumption, or net primary productivity (NPP), varies substantially across the globe.
a. What areas have relatively high productivity?
b. What areas have relatively low productivity?
c. What factors determine NPP in a given area?
5. Energy conversion in a community can be represented as an energy pyramid.
a. Diagram a simple energy pyramid for a lake community.
b. At what trophic level(s) do humans belong in your diagram? Briefly explain.
6. Energy is lost at every level in the energy pyramid where energy is transferred – for
example, from primary producers to primary consumers. It is estimated that only 1% of
the solar energy striking plants is converted to chemical energy, only 50-90% of gross
primary productivity (GPP) becomes net primary productivity (NPP) and only about 10%
of the energy available to each trophic level transfers to the next level (as biomass).
a. Restate the preceding information in your own words. Be sure to explain how
GPP and NPP relate to the percentage of energy transfer from one trophic level to
the next.
b. Where does the “lost energy” go? Is it correct to say that energy is “lost” in these
transfers? If not, what would be a better way of expressing this?
c. What is the role of decomposers in ecosystems?
7. Biogeochemical cycles describe the patterns of nutrient transfer between biotic and
abiotic components of the ecosystem (i.e. how do nutrients cycle through ecosystems?).
Consider the general nutrient cycle (Figure 24.8):
a. Where are nutrients stored for long periods of time?
b. Where are nutrients that are accessible for producers?
c. Where are nutrients that are accessible for consumers and decomposers?
8. Biogeochemical cycles can be categorized based on the form of the chemical. Nutrients
that can take on gaseous form may be stored and exchanged via the air. This is known as
the atmospheric cycle. Nutrients that cannot be found in gaseous form must be stored and
exchanged via land and water only. This is known as the sedimentary cycle.
Of these two types of cycles, which would cycle more slowly? Why?
9. Consider the various nutrient cycles. For each nutrient, identify their biological
significance, the forms that are usable by organisms, their common reservoirs as well as
the processes that drive their cycle:
Nutrient
Water
Carbon
Nitrogen
Biological
Significance
Essential for life!
Influences primary
productivity and
decomposition
Usable Forms
Liquid or vapor
Evaporation,
condensation, and
precipitation
Ammonium (NH4+),
nitrate (NO3-),
amino acids
Phosphate (PO43-)
Phosphorous
Oceans, glaciers,
lakes, rivers, and
streams
Processes
Photosynthesis,
respiration,
volcanic activity
Basis of organic
molecules!
Part of amino and
nucleic acids
Reservoirs
Weathering,
leaching, primary
productivity,
decomposition
10. Humans alter ecosystems through activities that affect net primary productivity. Briefly
describe a situation in which humans increase NPP and a situation in which humans
decrease NPP. What are the consequences of these ecosystem alterations?
11. Humans also alter nutrient cycles. Briefly discuss how nitrogen and phosphorous cycles
are affected by human activities. What are the consequences of these alterations? (Be sure
to use Figure 24.15).
12. Consider the ecosystem processes that benefit humans, or ecosystem services.
a. What are some examples of ecosystems services?
b. What is the estimated value of ecosystem services?