10.3.5 Food Chains, Webs & Pyramids

• What is the definition of a producer in an ecosystem?

  An organism that makes its own organic nutrients, usually through photosynthesis.
• What is a primary consumer?

  A primary consumer is an organism that feeds on producers.
• What is the role of a secondary consumer?

  A secondary consumer feeds on primary consumers.
• What does a tertiary consumer do?

  A tertiary consumer feeds on secondary consumers.
• What is a herbivore?

  An animal that gets its energy by eating plants only.
• What is a carnivore?

  An animal that gets its energy by eating other animals.
• What is a decomposer?


  An organism that gets its energy from dead or waste organic material.
• What is a trophic level?


  The position of an organism in a food chain, web, pyramid of number, or biomass.
• What does biomass refer to?

  The dry mass of an organism once water has been removed.
• What is a population in ecological terms?

  A group of organisms of one species living in the same area at the same time.
• What is a community in ecology?

  All of the populations of different species in an ecosystem.
• What is an ecosystem?

  A unit containing the community of organisms and their environment acting together.
• What do food chains illustrate?

  Food chains show the flow of energy between organisms in an ecosystem.
• What do food webs represent?

  Food webs show the interconnected food chains in part of an ecosystem.
• What is the ultimate source of energy for most communities of living things?

  The Sun.
• Why are producers usually not shown in food chains or food webs?

  Because green plants are usually the producers in a food chain.
• What does a pyramid of numbers show?


  The population of each trophic level at each stage in a food chain.
• How is a pyramid of numbers represented?

  It is drawn as a bar chart with the bars stacked on top of each other.
• Why might a pyramid of numbers not look like a pyramid?

  If the producer is a large plant or if one of the animals is very small.
• What does a pyramid of biomass show?


  The biomass at each trophic level in a food chain or food web.

  
• How does biomass change from one trophic level to the next?

  The biomass goes down from one trophic level to the next.
• Why can it be difficult to obtain valid data for a pyramid of biomass?

  Because measuring dry biomass requires removing all the water from the organisms.
• What is one reason energy is lost at each trophic level?

  Each organism respires, using energy for movement and active transport.
• How much energy is typically passed on to the next trophic level?

  Only 10% of the energy is passed on.
• What happens to the biomass at the top of the food chain?

  The biomass is too small to sustain another group of organisms.
• Why are food chains often not longer than four steps?

  Because the biomass at the top of the food chain is too small to sustain another group of organisms.
• What are some reasons energy is lost in ecosystems?

  Energy is lost as heat, through respiration, and because consumers rarely eat the whole organism.
• What happens to light energy during photosynthesis?

  Some light passes through the leaves, some is reflected, and some is not the correct wavelength to be absorbed by chlorophyll.
• What are the key components of food chains and webs?

  • Producers: Organisms that make their own nutrients.
  • Consumers: Organisms that feed on others (primary, secondary, tertiary).
  • Decomposers: Organisms that break down dead material.
  • Trophic levels: Positions in the food chain/web.
  • Energy flow: Illustrated by arrows in chains and webs.

  
• What are the strengths and weaknesses of using pyramids of numbers and biomass?

  Strengths:

  • Visual representation of populations or biomass at each level.
  • Easy to understand the energy flow.

  
  

  Weaknesses:

  • Pyramids of numbers can be misleading if producers are large.
  • Pyramids of biomass can be difficult to measure accurately.