Question

The longest cell in the body of an animal is
A. Osteocytes
B. Neuron
C. Chromatophores
D. Lymph corpuscles

Answer 1

Hint: The specialised cells coordinate various systems of the body easily through their spreaded network throughout the body

Complete answer:
Option A: Osteocytes are cells inside the bone. Size of osteoblasts vary from 5-20 micrometers. Therefore, this is the incorrect option.
Option B: Neuron or nerve cell is the basic unit of the nervous system which coordinates different body systems through transmission of electrical signals. Neurons are spreaded throughout the body to carry out these functions. Size of a neuron can be upto 50 micrometer in diameter (of the cell body) and 1.5 meter in axon length. They are the longest cell in the body of an animal. Therefore this is the correct answer.

A typical neuron body consists of a cell body, axon and dendrites. Cellbody is the compact structure which enclose nucleus and organelle.Axons and dendrites are the proration from it. Neurons receive signals via branched axones and transmit to the next neuron through the long axon. Axones are often covered with myelin sheath which increases the transmission speed of signals. The site of connection between two neurons are known as synaptic knobs. The neurotransmitter molecules present here receive the electric signal from the end of an axon and transmit them in the form of chemical signals to the dendrites of the next neuron.
There are three types of neurons. Sensory neurons which respond to the stimuli such as touch, motor neurons which coordinate the muscle contraction and interneurons which connect the neurons of brain and spine.
Option C: Chromatophores are pigments containing cells of lower vertebrate which are responsible for skin and eye colour. They are very small in size.Therefore, this is the incorrect option.
Option D: Lymph corpuscles are a mononuclear leukocyte formed in lymph nodes and lymphatic tissue with a size of 20-100 micrometer. Therefore, this is the incorrect option.

Hence, the correct answer is option (B)

Note: 1.Neurons are present in all animals except placozoa and sponges.
2.Neurons are absent in plants and fungi.
3.Neurons does not execute cell division.