Question

The pyramid which cannot be inverted in a stable ecosystem is that of
A) Biomass
B) Number
C) Energy
D) All of the above

Answer 1

Hint: Ecological pyramid is referred to as a graphic representation of biomass or bio productivity at each trophic level present in an ecosystem. They generally begin with the producers at the bottom and proceed through other trophic levels. Pyramids are generally of two types, i.e., inverted and upright.

Complete answer:
Ecological pyramids are used to express the flow of food and energy in the chain. The base of a pyramid is generally broad and it narrows down at the apex. One, gets a similar shape, whether you express the food or energy relationship between the organisms at different trophic levels. The base of each pyramid represents the producers or the first trophic level while the apex represents the tertiary or top-level consumer.

Relationships are expressed in number, biomass and energy. Any calculations of energy content, biomass or number has to include all organisms at that trophic level. If we take a few individuals at any trophic levels into account, we cannot make a true generalisation for it. There are some organisms that may occupy more than one trophic level simultaneously. A trophic level is said to represent a functional level, not a species as such. There are some species of an animal that may occupy more than one trophic level in the same ecosystem at the same time.

Let us study each of the pyramids:
A) Biomass- The pyramid of biomass is generally inverted because the biomass of the first trophic level far exceeds that in the higher energy level.
B) Number- The pyramid of the number represents the number of organisms that are present in each trophic level. This shows the total number of organisms that are involved at each level. It is also inverted.
C) Energy- The pyramid of energy is always upright, and 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. Each bar in the energy pyramid helps us to know the amount of energy that is present at each trophic level in a given time.

The energy pyramid is the only pyramid that is upright as energy flows in one direction only. According to the 10% law of energy, the energy that is transferred from one trophic level to another always decreases. Only 10% of energy is transferred in successive trophic levels, thus the energy decreases with an increase in trophic level.

Therefore, the correct answer is option C, Energy.

Note: There are certain limitations that the ecological pyramids have. There are some pyramids that do not take into account the same species that belong to two or more trophic levels. At times, it has assumed a simple food chain that almost never exists in nature and did not accommodate a food web. There is a group of species called sporophytes, even though they play a vital role in the ecosystem but are not given any place in the ecological pyramid.