Transfer of Biomass | Biology for Grade 10 PDF Download

Biomass Transfer

• The arrows in a food chain show the transfer of biomass from one organism to another. An example of a food chain is:
  maize → locust → lizard → snake
• Some of the energy from the Sun absorbed by maize when it photosynthesises is transferred to the locusts when they eat the plant. So biomass is transferred. Then some of the biomass in the locust is transferred to the lizards when they are eaten and so on.

Energy transfer: A pyramid of biomass

• Not all of the biomass is passed from the maize plants to the locusts. In fact, only about ten per cent of the biomass is transferred from each trophic level to the next. The remaining 90 per cent is used by the trophic level to complete life processes. Biomass can be lost between stages because not all of the matter eaten by an organism is digested. Some of it is excreted as waste such as solid faeces, carbon dioxide and water in respiration and water and urea in urine.
• Because only around 10% of the biomass at each trophic level is passed to the next, the total amount becomes very small after only a few levels. So food chains are rarely longer than six trophic levels.

We do not put the Sun at the bottom of a food chain even though the producing plants or algae transfer energy from the Sun during photosynthesis. This is because the Sun is not a living organism.

• In fact, only about one percent of the energy from the Sun that reaches the plant's leaves is used by the plant during photosynthesis. This sounds small but is still enough to power almost all food chains on our planet.

Calculating efficiency of biomass transfers

• The efficiency of biomass transfer is a measure of the proportion of biomass transferred from a lower trophic level to a higher one. Usually around ten per cent of biomass is transferred between trophic levels in a healthy ecosystem and the remaining ninety per cent is used by the organisms during life processes.
• This is an example of a food chain:
  phytoplankton → zooplankton → herring → sea lion

The total biomass within the phytoplankton is 14.6 kg. The total biomass within the zooplankton is 1.3 kg. What is the efficiency of this transfer?

• To complete this calculation, we divide the amount from the higher trophic level by the amount from the lower trophic level and multiply by one hundred. That is, we divide the smaller number by the bigger one (and multiply by one hundred).

The amount of biomass contained within each trophic level is shown in the table below.

Example 1: Calculate the efficiency of the transfer of energy between each trophic level.

Example 2: A bullock has eaten 10 kg of biomass in the form of grass, and excreted 6.3 kg in the form of faeces, urine and gas. The increase in its body tissues is 0.4 kg. So how much biomass has been used up in respiration?

The biomass use in respiration = 10 - 6.3 - 0.4 = 3.3 kg
Only 0.4 kg of the original biomass available to the bullock is available to the next stage, which might be humans. The efficiency of this transfer is:
Efficiency  = 0.4/10 x 100 = 4%