Question

The narrowest and most numerous tubes of lungs are termed as
(a) Bronchus
(b) Alveoli
(c) Bronchioles
(d) Hilum

Answer 1

Respiration is the process of formation of energy for the purpose of completing the various metabolic reactions where the energy is produced and may sometimes be required to complete the process and result in the formation of certain end products. This is done through various passages.

Complete answer
The respiratory system involves the intake of oxygen and the removal of carbon dioxide. The nostrils inhale the air or oxygen which then reaches the nasal cavity. From the nasal cavity, the sir reaches the pharynx (a part of the throat with rings of cartilages), and then to the larynx (the voice box). The air is then carried to the trachea from where it finally reaches the lungs. The trachea that reaches the lungs is divided into smaller tubes or branches called trachea called bronchi which are further divided into smaller and branches structure called bronchioles. They are the narrowest and most numerous tubes of lungs. The bronchioles end to form a balloon-like structure called alveoli which helps in gaseous exchange resulting in the diffusion of the gases in the blood. They are also called the air sac as they contract and relax when the air is inhaled or exhaled. They are composed of various blood vessels that help in the process of transportation of air to various body organs. The transportation occurred through the respiratory pigment called hemoglobin present in the red blood cell of the blood that stores oxygen and transports it throughout the body.

Additional information
Every individual needs the energy to perform various processes of the body. This energy is produced through respiration. The molecules of carbohydrates that are stored in the body will break down into simpler molecules during the process of respiration and help in the production of energy. Respiration is of two types based on the presence or absence of oxygen, aerobic respiration (oxygen present), and anaerobic respiration (oxygen absent).
During respiration in living organisms, the oxygen is inhaled while the carbon dioxide is exhaled through the lungs mostly, this process is termed breathing. There are three respiratory surfaces present on the body of the frog which are used during the process of exchanging gas with the environment, they are; the skin, the lungs, and the lining of the mouth.

So, the correct answer is ‘Bronchioles’.

Note:
The process of respiration is not the same in various organisms. In unicellular animals, the exchange of gases takes place through the cell surface such as amoeba. In man, it takes place through the lungs. Earthworms use their skin for the exchange of gases. In insects like cockroaches, transportation of gas takes place in tracheae. The respiration in aquatic animals mostly occurs through gills.