Question

Student to attempt either option (A) or (B):
(A) Construct a pyramid of biomass starting with phytoplankton, label its three trophic levels. Is the pyramid upright or inverted? Justify your answer. 
OR 
(B) Draw a pyramid of number where a large population of insects feed upon a very big tree. The insects in turn, are eaten by small birds which in turn are fed upon by big birds.

Hint:

Biomass pyramids can be upright or inverted depending on the ecosystem. In contrast, pyramids of number often become inverted when a single large producer supports many consumers.

Answer 1

Option (A):
Step 1: In an aquatic ecosystem, the biomass pyramid is usually inverted. The three trophic levels are: 
1. Phytoplankton (producers) 
2. Zooplankton (primary consumers) 
3. Small fishes (secondary consumers) 
Step 2: It is inverted because the biomass of phytoplankton is less at any given time, yet they reproduce rapidly to support higher trophic levels. 
OR 
Option (B): 
Step 1: In a pyramid of numbers with one large tree at the base, it supports many insects. 
Step 2: These insects are eaten by fewer small birds, which are in turn consumed by even fewer big birds. 
Step 3: This results in a spindle-shaped or inverted pyramid of numbers.