Which ecological pyramid is always straight ?

Explanation

**Step-by-Step Text Solution:**

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

2. **Definition of Upright Pyramids**: An upright or straight pyramid indicates that the values increase as you move from the base (producers) to the top (top predators). However, not all ecological pyramids maintain this structure.

3. **Analyzing Each Type of Pyramid**:
- **Pyramid of Numbers**: This pyramid can be upright or inverted depending on the number of organisms at each trophic level. For example, one tree can support many insects, making it inverted.
...