Topic: Fisheries
Theme: Energy

Key Concepts:


  • Photosynthesis is the production of organic substances, cheifly sugars, from carbon dioxide and water, in green plant cells that are supplied with enough light. This light allows chlorophyll (the green-colored substance present in plant cells) to aid in the transformation of the radiant energy (like sunlight) into a chemical form.
  • Oxygen is released to solution during photosynthesis and consumed during respiration.


  • Some types of bacteria can convert carbon dioxide and water to organic matter by using energy from chemical reactions rather than light. This process is called chemosynthesis.
  • Chemosynthesis is mostly used by life near hydrothermal vents on oceanic ridges, but also occurs in ocean water that is vented or seep from ocean sediment near subduction zones.
  • Photosynthetic and chemosynthetic organisms can be called either primary producers or autotrophs because they make their own food.

Length of Food Chain

  • Organisms can be labeled by their position in a who-eats-whom (or what) feeding heiarchy called a trophic pyramid.
    • The primary producers at the base of the pyramid are mostly chlorophyll-containing photosyntheizers.
    • The heterotrophs that eat them are called primary consumers (or herbivores).
    • The animals that eat primary consumers are called secondary consumers.
    • At the top of the trophic pyramid we find the top consumer (top carnivore).
    • Some consumers are referred to as omnivores (eat plants and animals).
  • As organisms at one trophic level are consumed by those at the next higher trophic level, food biomass ingested is not used entirely to create biomass (flesh) of the consumer species at the higher trophic level. An average of ony about ten percent (varies from 1 to 40%) of food consumed is used for growth. The remaining 90% is used during respiration to provide the consumer with energy or excreted as waste.
  • Transfer of food in food chains is clearly inefficient.
  • Long marine food chains that lead to higher trophic level consumers, such as tuna, utilize primary production hundreds of times less efficiently than short marine food chains, such as those that support anchovy or sardine.