Biology 12

Chapter 13 Ecological Principles • MHR 443

SECTION REVIEW

1. Explain why some ecosystems can support
   highly complex food webs while others can support
   only relatively simple ones.


2. Draw a chart to illustrate a food web that could
   be found in a typical pond ecosystem (show at least
   three distinct trophic levels). Identify the organisms
   and label each trophic level.


3. Explain how the same species can occupy
   more than one trophic level within the same food
   web. Explain how this type of ecological interaction
   can enhance the stability of a food web.


4. Describe the types of biotic and abiotic factors
   that can lead to the collapse of a food web in an
   ecosystem.
   5. Explain why autotrophs rather than
   decomposers occupy the lowest level of a food chain.
   6. Could photosynthetic producers exist in the
   absence of consumers in an ecosystem? Explain
   your answer.
   7. Describe the typical energy sources that
   decomposers rely on in an aquatic ecosystem
   (such as a pond or lake).
   8. Describe the difference between a food chain
   and a food web. Which is more realistic in its
   depiction of what actually exists in nature?
   9. Explain why producer organisms that live
   deep below the surface of Earth’s oceans rely on
   chemosynthesis rather than photosynthesis to
   manufacture high-energy food molecules.

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Figure 13.16A simplified food web. There are many other species that feed with
or on the ones shown in the diagram. Which species eat organisms on more than
one trophic level?

Tertiary and

secondary

consumers

Secondary

and primary

consumers

Primary

consumers

Primary

producers

Decomposers

(bacteria, fungi,

certain animals)

wastes and

dead organisms

(plants, algae,

cyanobacteria)