Question

Assertion: Human breathing is negative pressure breathing. Reason: Air drawn in lungs because of pressure less than atmospheric pressure in lungs during inspiration

Short answer

The assertion and reason are correct and the reason correctly explains the assertion. Human breathing is negative pressure breathing because during inhalation, the pressure within the lungs drop below atmospheric pressure, leading to inflow of air.

Step-by-step solution

Understanding Negative Pressure Breathing

Negative pressure breathing is a type of breathing in which the pressure inside the lungs is less than the atmospheric pressure. This pressure difference is due to the contraction of the diaphragm, which increases the volume of the lungs and, thus, decreases their internal pressure.

Understanding Inhalation Process

Inhalation, or inspiration, is the intake of air into the lungs. It is initiated by the diaphragm and supported by the external intercostal muscles. During inhalation, the diaphragm contracts, resulting in the enlargement of the thoracic cavity. This enlargement leads to a decrease in pressure inside the lungs compared to the outside atmosphere, causing air to flow into the lungs.

Comparing Assertion and Reason

The assertion states that human breathing is negative pressure breathing, which is indeed correct, as explained in step 1. This is because the pressure within the lungs becomes less than the pressure in the atmosphere during inhalation, causing air to flow into the lungs. The reason given correctly explains this process, providing the physiological mechanism behind negative pressure breathing.

Key concepts

Diaphragm Contraction

The diaphragm is a large, dome-shaped muscle located at the base of the lungs. It plays a critical role in the breathing process. During inhalation, this muscle contracts and moves downward, expanding the chest cavity.
When the diaphragm contracts, it flattens and creates more space in the chest. This process is vital as it directly influences the pressure inside the lungs.

• The contraction of the diaphragm increases the volume of the thoracic cavity.
• As the volume increases, the pressure within the lungs decreases.

The decrease in pressure inside the lungs relative to the outside atmosphere is what enables air to flow into the lungs easily. The synergy between the diaphragm and other breathing muscles ensures that breathing is an efficient process.

Inhalation Process

Inhalation is the process by which air is drawn into the lungs, a crucial phase in breathing. It begins with the contraction of the diaphragm, followed closely by the action of the external intercostal muscles.
As the diaphragm contracts and moves downward, the ribs are lifted by the intercostal muscles, further enlarging the space in the chest cavity.

• This enlargement reduces the air pressure inside the lungs.
• A lower pressure inside the lungs compared to the atmosphere outside prompts air to enter.

This entire process hinges on the creation of negative pressure within the lungs, demonstrating the intricate balance and coordination required for simply taking a breath. It underscores how our bodies harness natural physical forces, like differences in pressure, to facilitate a crucial life-sustaining function.

Atmospheric Pressure

The concept of atmospheric pressure is pivotal to understanding how breathing functions, particularly in relation to negative pressure breathing. Atmospheric pressure is the weight of the air above us exerted on everything at the Earth’s surface, including our bodies.
This pressure is what drives air into the lungs during inhalation.

• When the diaphragm contracts and the chest cavity enlarges, the lung pressure drops below atmospheric levels.
• Air naturally travels from areas of higher pressure, like the atmosphere, to areas of lower pressure inside the lungs.

Without the atmospheric pressure as a reference point, the mechanism of negative pressure breathing, which draws air into the lungs, would not be possible. Understanding atmospheric pressure offers insight into the mechanics of how and why we inhale, illustrating the invisible yet powerful forces at work every moment as we breathe.