Which one of the following criteria is/are essential and form the basis of classical taxonomic studies?

Options

A. Ecological information of organisms
B. Development process
C. External and internal structure
D. External structure

Answer

To answer the question regarding the essential criteria that form the basis of classical taxonomic studies, we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Understanding Taxonomy**: Taxonomy is the science of classification of living organisms. It involves organizing species into a structured framework based on shared characteristics.

2. **Classification Levels**: The classification of organisms follows a hierarchical structure:
- **Kingdom**: The broadest category (e.g., Animalia, Plantae).
- **Phylum**: Groups organisms based on major body plans (e.g., Chordata, Arthropoda).
- **Class**: Further divides phyla into smaller groups (e.g., Mammalia, Aves).
- **Order**: Groups related families (e.g., Carnivora).
- **Family**: Groups related genera (e.g., Canidae).
- **Genus**: Groups species that are closely related (e.g., Canis).
- **Species**: The most specific level, identifying individual organisms (e.g., Canis lupus for wolves).

3. **Criteria for Classification**: The essential criteria for classical taxonomic studies include:
- **Morphological Characteristics**: The external and internal structures of organisms, such as shape, size, and anatomical features.
- **Physiological Characteristics**: Internal processes like digestion, circulation, and reproduction.
- **Genetic Characteristics**: Although more modern, genetic information can also play a role in classification.

4. **Observation and Analysis**: Taxonomists observe and analyze these characteristics to determine the relationships among different organisms, which helps in placing them in the correct taxonomic hierarchy.

5. **Conclusion**: The essential criteria that form the basis of classical taxonomic studies are primarily morphological and physiological characteristics, which are vital for the classification of organisms.