Andhra Pradesh Board Class 9 Biology Chapter 6 is an interesting chapter, because it deals with the topic of sense organs in humans. Besides, the sense organs are important as well as fascinating things, and they basically define who we are. We also experience everything mostly because of the power of sense organs. But the question is how well do we know our sense organs? Chapter 6 is all about answering this question and this unit will help students understand everything from the structure of the sense organs, its various functions and more.
Sense organ is generally defined as an organ, which responds to external stimuli by conveying impulses to the sensory nervous system. There are usually five sense organs in the body, and they work together for particular sensations. The five organs are, eyes, nose, ears, tongue and skin.
Eyes are responsible for sight. However, its main ability is to take the information from light waves and then transform the characteristics of light into neural signals which the brain processes. Eyes consist of several parts like the retina, pupil, iris, cornea, lens, vitreous, sclera, macula, and conjunctiva.
Ears are organs that help in hearing. However, another important function of ears is that they help in maintaining the equilibrium of our body. The ear is divided into three main parts – external ear, middle ear and internal ear. The ear also consists of the auditory canal, eardrum, semicircular canals, Cochlea, Vestibular nerve, Cochlear nerve, Eustacian tube, Ear Asslcles and Outer ear (Pinna).
Nose is responsible for the sense of smell. The nose consists of two nostrils and it basically leads to the nasal cavity. The Nasal septum divides the nasal cavity into two halves. The nasal cavity is lined with a mucous membrane and small hairs and olfactory receptors are also present in the mucous membrane.
The tongue, which is responsible for the sensation of taste is made up of voluntary muscles and it consists of about 10 thousand taste buds. The taste buds are all present in the walls of the papillae.
The skin is a sense organ for touch. It contains cutaneous receptors for touch and is mainly made up of two main layers called dermis and epidermis. Some of the other constituents include hair, oil gland, blood vessel, sweat gland, nerve, fat lobules, endodermis, epidermis, and pores.
Students can have a look at some of the questions below and further understand about some of the important chapter topics.
Question 1: Where does the image from in the Eye?
Answer: The image, usually forms in the retina.
Question 2: How many bones do that middle ear contain?
Answer: The middle ear contains three bones, called malleus, incus and stapes that amplify sound.
Question 3: Explain the relationship between the sense organs and the brain.
Answer: Sense organs are responsible for sending messages to the brain through sensory pathways. The brain processes the messages and the information is then sent to the required sense organs to function through motor pathways.
Question 4: Which are the five main sense organs?
Answer: The five main sense organs are the eyes, ears, skin, nose and tongue.
Question 5: Which are the three main layers of the eye?
Answer: Eye has three main layers. They are a sclerotic layer or sclera, choroid layer and retina.
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