Trophic levels

• What are trophic levels?

  Different stages of a food chain. They consist of one or more organisms that perform a specific role in the food chain
• What is on the first trophic level?

  • producers are the organisms at the starting point of a food chain
  • they're called producers because they make their own food by photosynthesis using energy from the sun
• What is on the second trophic level

  • primary consumers
  • herbivores that eat the plants and algae that are primary consumers
• What is on the third trophic level?

  • secondary consumers
  • carnivores eat the primary consumers are secondary consumers
• What is on the fourth trophic level?

  • tertiary consumers
  • carnivores that eat other carnivores are tertiary consumers
  • carnivores that have no predators are at the top of the food chain, so they're always in the highest trophic level
  • they're known as apex predators
• How do bacteria and fungi decompose dead animals/plants?

  They secrete enzymes that break the dead carcasses down into small soluble food molecules that then diffuse into the microorganisms. This process also releases nutrients into the environment, which the producers need in order to grow
• What does each bar on a pyramid of biomass represent?

  relative mass of living material at a trophic level - how much all the organisms at each level would "weigh" if you put them all together
• How much energy from the sun is transferred for photosynthesis in producers

  about 1%
• What is some of the glucose that producers make used for?

  • biological molecules
  • they make up the plant's biomass which stores energy
• How much biomass is transferred between trophic levels

  about 10%
• Why is biomass lost?

  • Organisms don't always consume every single part of the organism they're consuming. Some material that makes up plants and animals, like bone, is inedible. So not all the biomass can be passed to the next stage of the food chain
  • Organisms don't absorb everything they ingest - which is egested as faeces
  • Some of the biomass taken in is converted into other substances that are lost as waste.
• How is biomass lost as waste?

  • Organisms use a lot of glucose (obtained from biomass) in respiration to provide energy for movement and keeping warm. This process produces lots of waste carbon dioxide and water as bi-products.
  • Urea is another waste substance, released in urine with water when the proteins in the biomass are broken down
• what products are needed for photosynthesis?

  carbon dioxide and water
• Explain how making dog food from insects could improve human's food security

  • less land required
  • so more space for crops for humans
  • less methane from animals therefore less global warming
  • therefore less harmful effects of global warming on human food production
  • like less flooding of farmland
• Why does the total biomass of Daphnia in a pond different from the total biomass of the algae

  • non-digestible parts of algae lost in faeces
  • not all absorbed
  • lost in urine
• A large amount of untreated sewage entered a river. Many fish died.

  Untreated sewage contains organic matter and bacteria

  Explain why many fish died

  • bacteria decay organic matter/algae
  • by digestion
  • and bacteria respire anaerobically
  • which lower oxygen concentration in water
  • so reduced energy supply causes death of fish
• Why is it more efficient to rear cows indoors rather than outdoors?

  • warmer indoors so less energy wasted in keeping warm
  • less movement indoors so less energy wasted
• What abiotic factors affect the food chain?

  • light intensity
  • temperature
  • moisture levels
  • soil pH
  • mineral/ion content of soil
  • wind speed
  • wind direction
  • carbon dioxide levels
  • oxygen levels
• Why is photosynthesis important in the food chain?

  • absorption of light/energy
  • transfers to chemical energy
  • which provides energy for animals
• why might a students' value for the percentage of biomass lost between snails and thrushes only 66% (rather than 90%)

  • thrushes eat other things
  • thrush numbers like to vary
  • thrushes were not present all the time
  • thrushes feed on a much bigger area