Question

In cockroach, identify the incorrectly matched pair:

• A. Ommatidium -- chordotonal organ
• B. Rhabdome -- light sensitive structure
• C. Crystalline cone -- Transparent conical structure
• D. Cornea -- refractive region

Hint:

Remember that chordotonal organs are for hearing and vibration sensing, usually located in legs and antennae.
Always relate ommatidia to vision and compound eyes.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks us to identify the incorrectly matched anatomical pair from the compound eye and sensory systems of a cockroach.

Step 2: Key Concept and Approach:
The compound eye of a cockroach contains approximately 2000 individual photoreceptive units called ommatidia.
Each ommatidium has specific functional parts, such as the outer cornea, the crystalline cone, and the light-sensitive rhabdome.
We need to evaluate each pair and check if the structure matches its described function or characteristics.

Step 3: Detailed Explanation:

• Ommatidium -- chordotonal organ: This is incorrect.
An ommatidium is a visual receptor unit of the compound eye.
A chordotonal organ is a specialized mechanoreceptive organ in insects that detects stretch, vibration, and sound.
Since chordotonal organs are not part of the ommatidium, this pair is incorrectly matched.

• Rhabdome -- light sensitive structure: This is correct.
The rhabdome is the central rod-like photoreceptive element in each ommatidium, receiving light focused by the lens system.

• Crystalline cone -- Transparent conical structure: This is correct.
The crystalline cone lies beneath the cornea and serves as a transparent conical lens focusing light onto the rhabdome.

• Cornea -- refractive region: This is correct.
The cornea is the outermost transparent cuticle layer that acts as a biconvex lens, providing the primary refraction of light.


Step 4: Final Answer:
The incorrect match is Ommatidium -- chordotonal organ because chordotonal organs are mechanoreceptors, not visual receptors.