Question

Which one of the following statements is INCORRECT?

• A. Cnidaria is the first animal group showing true simple nervous system.
• B. Diffused type of nervous system is the first landmark in the development of nervous system.
• C. In plants, control and co-ordination mechanism is brought about by sending chemical signals for chemotactic, phototropic and thigmotactic movements.
• D. Ladder type of nervous system is found in sponges and Hydra.

Hint:

Remember sequence: No nervous system (Porifera) $\rightarrow$ Diffused nerve net (Cnidaria) $\rightarrow$ Ladder type (Platyhelminthes).

Answer 1

The Correct Option is D

Concept:
The nervous system shows evolutionary progression from simple to complex forms:
• Sponges (Porifera) → No nervous system
• Cnidarians (e.g., Hydra) → Diffused nerve net
• Flatworms (Platyhelminthes) → Ladder-type nervous system

Step 1: Understand each statement.
• Cnidaria possess the first simple nervous system (nerve net)
• Diffused nervous system is the earliest form
• Plants use chemical signals (hormones) for coordination

Step 2: Analyze the incorrect statement.
• (A) Correct → Cnidarians are first to show nervous system \checkmark
• (B) Correct → Diffused nerve net is the primitive form \checkmark
• (C) Correct → Plants use chemical coordination \checkmark
• (D) Incorrect → Sponges lack nervous system and Hydra has nerve net, not ladder-type $\times$

Step 3: Conclusion. Thus, the incorrect statement is: \[ \text{Ladder type of nervous system is found in sponges and Hydra} \]