Final answer:
A structure composed of nervous tissue that responds to specific stimuli by converting them into nerve impulses is called a 'sense organ'. These organs consist of specialized sensory receptors and can be functionally and structurally classified based on their response to various stimuli. The correct answer is 'a. sense organ'.
Step-by-step explanation:
A structure composed of nervous tissue and other tissues that enhances response to a specific type of stimulus is known as a sense organ. Sense organs are complex structures that include sensory receptors and other cells that assist in the sensory perception process. These organs are specialized to detect a variety of stimuli, such as light, sound, and touch, and convert them into nerve impulses that the brain can interpret.
The sensory receptors involved can be structurally classified as free nerve endings, encapsulated endings, or specialized receptor cells. Free nerve endings are embedded in tissues for general sensations like pain and temperature, while encapsulated endings are wrapped in connective tissues to enhance sensitivity to stimuli like pressure and touch. Specialized receptor cells, such as photoreceptors in the retina, are dedicated to specific types of sensory input.
Functionally, these receptors can be categorized as chemoreceptors, mechanoreceptors, thermoreceptors, and more, depending on the type of stimulus they sense. In general, sensory receptors either work with neurons or constitute the sensory nerve ending that responds to external or internal environmental stimuli. This process of converting a physical stimulus into a nerve impulse is called transduction, and the region where a sensory receptor can respond to a stimulus is called its receptive field.
To answer the student's question, the correct option is 'a. sense organ'.