'All the pyramids, of number, of energy and biomass are upright''.
(i) Grass land (ii) A big tree
(iii) A sugarcane field (iv) The Arabian Sea
Find the option which correctly tells the ecosystem (s) for which the above statement doesn't hold true.

Options

A. (ii), (iii) and (iv)
B. (i) & (ii)
C. (ii) and (iv)
D. (iii) & (iv)

Answer

To solve the question regarding the ecological pyramids of number, energy, and biomass, we will analyze each of the given ecosystems to determine which ones do not have upright pyramids.

### Step-by-Step Solution:

1. **Understanding Ecological Pyramids**:
- Ecological pyramids represent the distribution of energy, biomass, or number of organisms at each trophic level in an ecosystem.
- There are three types: pyramid of number, pyramid of biomass, and pyramid of energy.

2. **Analyzing Each Ecosystem**:
- **(i) Grassland**:
- In a grassland ecosystem, the pyramid of number is upright because there are many plants (producers), fewer herbivores (like deer), and even fewer carnivores (like tigers).
- The pyramid of biomass is also upright as the biomass of plants is greater than that of herbivores, which in turn is greater than that of carnivores.
- The pyramid of energy is always upright as energy decreases at each trophic level.

- **(ii) A Big Tree**:
- In a parasitic ecosystem involving a big tree, the pyramid of number can be upright (one tree, many birds, many parasites).
- The pyramid of biomass is also upright since the tree has more biomass than the birds, and the birds have more biomass than the parasites.
- The pyramid of energy remains upright as well.

- **(iii) A Sugarcane Field**:
- A sugarcane field is similar to a grassland ecosystem. The pyramid of number, biomass, and energy are all upright for this ecosystem as well.

- **(iv) The Arabian Sea**:
- In an aquatic ecosystem like the Arabian Sea, the pyramid of number can be upright (many small fish, fewer larger fish, and very few top predators).
- The pyramid of biomass, however, can be inverted because the biomass of large fish can exceed that of the numerous small fish due to their size.
- The pyramid of energy remains upright.

3. **Identifying the Correct Answer**:
- The question asks for the ecosystems where the statement "all the pyramids are upright" does not hold true.
- From the analysis, the Arabian Sea is the only ecosystem where the pyramid of biomass can be inverted, making it the correct answer.

### Final Answer:
The ecosystems for which the statement does not hold true are:
- (iv) The Arabian Sea.