Q.Match the following list of animals with their level of organisation. Division of Labour / Animal
Column I: A. Organ level, B. Cellular aggregate level, C. Tissue level, D. Organ system level
Column II: i. Pheretima, ii. Fasciola, iii. Spongilla, iv. Obelia Choose the correct match showing division of labour with animal example.

The correct option is (C) D-i, A-ii, B-iii, C-iv.

• Pheretima (earthworm, Annelida) shows the organ-system level of organisation (D-i).
• Fasciola (Platyhelminthes) shows the organ level of organisation (A-ii).
• Spongilla (Porifera) shows the cellular level of organisation (B-iii). …

The level of organisation rises in four steps — cellular, tissue, organ, and organ-system — and each animal in the list is a standard representative of one level.

• Pheretima, the earthworm, is an annelid, and annelids are described as having the organ-system level of organisation, the most advanced of the four — matching D (organ-system level) with i (Pheretima).
• Fasciola, the liver fluke, is a Platyhelminth, and Platyhelminthes show the organ level of organisation, where tissues combine into distinct organs but not yet full organ systems — matching A (organ level) with ii (Fasciola). …

Method: The organisation-ladder approach

Instead of matching each animal to its level one pair at a time, first arrange the four levels of organisation into their fixed ladder (cellular → tissue → organ → organ-system), then place each named animal onto the correct rung by recalling its phylum's position on that same ladder.

Step 1 — fix the ladder in order of increasing complexity:

1. Cellular level (loosest organisation) — Porifera.
2. Tissue level — Coelenterata.
3. Organ level — Platyhelminthes.
4. Organ-system level (most complex) — Annelida and beyond.

Step 2 — place each named animal by recalling its phylum, then reading its rung straight off the ladder:

• Spongilla → Porifera → rung 1 (cellular aggregate level) → matches B.
• Obelia → Coelenterata → rung 2 (tissue level) → matches C.
• Fasciola → Platyhelminthes → rung 3 (organ level) → matches A.
• Pheretima → Annelida → rung 4 (organ-system level) → matches D.

Step 3 — assemble the full match: D-i (Pheretima), A-ii (Fasciola), B-iii (Spongilla), C-iv (Obelia). …