The flow of energy in an ecosystem typically goes

Answer: Producers → primary consumers → secondary consumers → tertiary consumers → decomposers Energy moves up the food chain, with much lost as heat at each level (10% rule). Decomposers recycle nutrients.

Producers (autotrophs) make their own food primarily by

Answer: Photosynthesis (or chemosynthesis in some prokaryotes) Producers convert solar (or chemical) energy into biomass, forming the foundation of food webs.

Decomposers (e.g., fungi, bacteria) play the critical role of

Answer: Breaking down dead organic matter and releasing nutrients back to producers Without decomposers, nutrients would lock up in dead biomass and halt biogeochemical cycles.

AP Biology · Topic 8.2

Energy Flow Through Ecosystems Practice

Part of Ecology.(ENE-2.A)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$The flow of energy in an ecosystem typically goes$
- A
  $Producers \to decomposers \to primary consumers \to secondary consumers \to tertiary consumers$
- B
  $Decomposers \to producers \to primary consumers \to secondary consumers \to tertiary consumers$
- C
  $Tertiary consumers \to secondary consumers \to primary consumers \to producers \to decomposers$
- D
  $Producers \to primary consumers \to secondary consumers \to tertiary consumers \to decomposers$
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Why
$Energy moves up the food chain, with much lost as heat at each level (10% rule). Decomposers recycle nutrients.$
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Sample 2difficulty 1/5
$Producers (autotrophs) make their own food primarily by$
- A
  $Decomposition of dead material (or absorption from soil minerals)$
- B
  $Cellular respiration (or fermentation in oxygen-poor environments)$
- C
  $Ingestion of consumers (or scavenging in nutrient-rich habitats)$
- D
  $Photosynthesis (or chemosynthesis in some prokaryotes)$
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Why
$Producers convert solar (or chemical) energy into biomass, forming the foundation of food webs.$
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Sample 3difficulty 1/5
$Decomposers (e.g., fungi, bacteria) play the critical role of$
- A
  $Breaking down dead organic matter and releasing nutrients back to producers$
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- B
  $Fixing atmospheric nitrogen and supplying ammonia directly to consumer species$
- C
  $Hunting live prey and transferring energy upward to higher trophic levels$
- D
  $Capturing solar energy and converting it into organic carbon for the food web$
Why
$Without decomposers, nutrients would lock up in dead biomass and halt biogeochemical cycles.$
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Sample 4difficulty 2/5
$What is the primary ecological role of decomposers shown in the figure?$
- A
  $Prey upon top consumers$
- B
  $Fix nitrogen for plants$
- C
  $Recycle inorganic nutrients back to producers$
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- D
  $Photosynthesize directly$
Why
$Decomposers (bacteria and fungi) break down dead matter, releasing inorganic nutrients (e.g., NH4+, PO4 3-) that producers reuse.$
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Sample 5difficulty 2/5
$Carbon enters the food web from the atmosphere via$
- A
  $Volcanic outgassing (CO₂ \to carbonate rocks during weathering)$
- B
  $Photosynthesis (CO₂ \to organic carbon in producers)$
  check_circle
- C
  $Cellular respiration (organic C \to CO₂ released by consumers)$
- D
  $Decomposition (organic C \to CO₂ released by microbial activity)$
Why
$Photosynthesis pulls atmospheric CO₂ into biomass; respiration and combustion release it back.$
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