Trophic levels: Ecology: Biology: GCSE (9:1)

• Trophic levels

  The different levels of organisms in a food chain, each level is represented by a specific number

  
• Food chain


  A diagram to show simple relationships in an ecosystem with a focus on the food sources of organisms, an arrow shows the transfer of energy or biomass along the food chain

  
• Trophic level 1

  Plants and algae occupy this trophic level, they make their own food via photosynthesis and are called producers

  
• Trophic level 2

  Herbivores occupy this trophic level, they eat plants or algae and are called primary consumers

  
• Trophic level 3

  Carnivores that eat herbivores are called secondary consumers, they occupy this trophic level

  
• Trophic level 4

  Carnivores that eat other carnivores are called tertiary consumers, they occupy this trophic level

  
• Prey


  A herbivorous or carnivorous animal that is eaten by another animal called a predator

  
• Predator


  A carnivorous consumer that kills or eats other animals known as prey

  
• Apex predator


  A carnivorous animal at the top of a food chain, the apex predator has no predators of its own

  
• Decomposer


  A microorganism that breaks down dead plant and animal matter by secreting enzymes into the environment, small soluble food molecules can then diffuse into the microorganism

  
• Pyramids of number


  A pyramid that is constructed to represent the number of individuals in each level of a food chain, trophic level 1 is at the bottom of the pyramid

  
• Pyramids of biomass


  A pyramid that is constructed to represent the relative amount of biomass in each level of a food chain, trophic level 1 is at the bottom of the pyramid

  
• Biomass


  The mass of living organisms in an ecosystem which is composed of all of the molecules an organism synthesises or gains from the consumption of other organisms

  
• Reasons for loss of biomass in a food chain

  Not all ingested material is absorbed and some is egested as faeces, some absorbed material is lost as waste such as carbon dioxide and water during respiration or water and urea in urine

  
• Respiration

  Requires large amounts of glucose to release energy, causing the levels of biomass in an organism to decrease

  
• Energy in producers

  Plants and algae transfer about 1% of the incident energy from light for photosynthesis

  
• Transfer of biomass

  Only about 10% of the biomass from each trophic level is transferred to the level above it

  
• Efficiency of biomass transfer calculation

  Percentage efficiency transfer = (Biomass transferred to the next level/biomass available at the previous level) x 100

  
• Reasons for numbers of organisms

  Less biomass and resources are available at higher trophic levels, which explains why there are far fewer individual apex predators than individuals at lower trophic levels