Which of the following pyramids is always upright and can never be inverted?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Pyramid of energy
Ecological pyramids show the relationship between trophic levels in terms of number, biomass or energy. Pyramids of number and biomass can sometimes be inverted, but the energy pyramid cannot, because some energy is always lost as heat when it flows from one trophic level to the next.
Option (1) Pyramid of biomass — Incorrect. The pyramid of biomass can be inverted. In the sea it is generally inverted, because the biomass of fishes far exceeds that of phytoplankton.
Option (2) Pyramid of energy — Correct. Energy at a lower trophic level is always more than at a higher level, since some energy is lost as heat at each step. So the pyramid of energy is always upright.
Option (3) Pyramid of numbers — Incorrect. The pyramid of numbers can be inverted, for example when many insects feed on one big tree.
NCERT Extract:
Ecological Pyramids – “… The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton. Isn’t that a paradox? How would you explain this? Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.”
Figure 12.4 (d) An ideal pyramid of energy. Observe that primary producers convert only 1% of the energy in the sunlight available to them into NPP