Problem 115 - Objective Biology for NEET

Question

Which one of the following is a possibility for most of us in regard to breathing, by making a conscious effort? (a) One can breathe out air totally without oxygen. (b) One can breathe out air through Eustachian tubes by closing both the nose and the mouth. (c) One can consciously breathe out by moving the diaphragm alone without moving the ribs at all. (d) The lungs can be made fully empty by forcefully breathing out all air from them.

Step-by-Step Solution

Answer

None of these options are a possibility. Breathing involves various physiological mechanisms that aren’t usually under complete conscious control.

Step 1: Evaluate Option A

Breathing out air without any oxygen is not possible because even after gaseous exchange in the lungs, the air we exhale contains around 16% oxygen. Therefore, it is not possible to exhale air totally without oxygen.

Step 2: Evaluate Option B

Eustachian tubes connect the middle ear to the throat. They function mainly in equalizing air pressure on both sides of the eardrum. We cannot breathe out air through Eustachian tubes by closing both the nose and the mouth.

Step 3: Evaluate Option C

In the process of breathing, both the diaphragm and the intercostal muscles (surrounding the ribs) are involved. We can control our diaphragm to an extent but it's not feasible to breathe out by moving just the diaphragm without any rib movement.

Step 4: Evaluate Option D

It's not possible to empty the lungs fully by forcefully breathing out all air from them. Some residual air always remains in the lungs which cannot be expelled.

Key Concepts

Gaseous Exchange

Gaseous exchange is a crucial process in the human respiration system. It primarily occurs in the alveoli, the tiny air sacs in the lungs. This process involves the exchange of oxygen and carbon dioxide between the lungs and the blood.

• Oxygen from inhaled air diffuses through the walls of the alveoli into the surrounding blood capillaries.
• Simultaneously, carbon dioxide from the blood diffuses out into the alveoli to be expelled from the body during exhalation.

This exchange is driven by differences in partial pressures of the gases. Though this exchange efficiently reduces carbon dioxide levels in the blood, the exhaled air still contains about 16% oxygen, which illustrates why we cannot breathe out air totally devoid of oxygen.

Diaphragm Movement

The diaphragm is a dome-shaped muscular partition located between the chest and the abdominal cavity. It plays a key role in breathing by altering the volume of the thoracic cavity. When you inhale, the diaphragm contracts and moves downward.

• This contraction increases the space in the thoracic cavity, reducing the pressure and pulling air into the lungs.
• During exhalation, the diaphragm relaxes and moves upward, decreasing the space in the chest cavity and pushing air out of the lungs.

While it's possible to exert some conscious control over diaphragm movement, it usually works in tandem with the intercostal muscles around the ribs. Meaning, typically the ribs and diaphragm work together during breathing, making it challenging to breathe by moving only the diaphragm.

Residual Volume in Lungs

Residual volume refers to the amount of air that remains in the lungs after a forceful exhalation. It's impossible to completely empty the lungs because of this residual air.

• This volume is crucial as it helps keep the alveoli open and ready for the next breath.
• Maintaining residual air prevents lung collapse and ensures that gas exchange can continue between breaths.

While forceful breathing may expel more air, residual volume ensures that our lungs stay partially filled to maintain proper physiological function. It's an essential part of why lungs can never be totally emptied out.