Question

Johnston’s organ found in
a. Antenna of mosquito
b. Head of cockroach
c. Abdomen of housefly
d. Abdomen of spider

Answer 1

Hint: We must remember that a group of sensory cells contained in the pedicel (the second segment) is Johnston's organ. In the flagellum (third and usually final antennal segment), Johnston's organ senses motion. It consists of scolopidia, each of which comprises a mechanosensory chordotonal neuron, arrayed in a bowl shape.

Complete answer:
We have to remember that the Johnston organ is located in the pedicels of the mosquito antenna. It's the gathering of sensory cells. It senses flagellum motion. In homopterans, there are 25 - 79 scolopidia in the Johnston organs. A distinguishing feature that distinguishes the class Insecta from the other hexapods belonging to the group Entognatha is the presence of Johnston's organ. The organ of Johnston was called after Christopher Johnston, the doctor's father and the Assyriologist Christopher Johnston.

Sound waves vibrate the insect's antenna and Johnston's organ senses these vibrations. As an insect can sense the sound of a mate's wing beats, the Johnston's organ is widely used to locate a mate. It is the presence of the organ of the Johnston that distinguishes insects from the hexapods of the non-insect.

Hence, the correct answer is option (A).

Note: We must know that one feature of Johnston's organ is to detect the frequency of a mate's wing beat. Sound output in the air results in two components of energy: the element of pressure, which is the change in the air pressure originating from the source of the sound; and the element of particle displacement, which is the back and forth vibration, which oscillates in the path of the propagation of sound. The displacement of particles has greater energy loss than the pressure component. So only within one wavelength of the origin is the displacement component called "near-field sound" audible.