Problem 149 - Objective Biology for NEET

Question

Assertion: Every \(100 \mathrm{ml}\) of oxygenated blood can deliver around \(5 \mathrm{ml}\) of \(\mathrm{O}_{2}\) to the tissues. Reason: Every \(100 \mathrm{ml}\) of deoxygenated blood delivers approx \(4 \mathrm{ml}\) of \(\mathrm{CO}_{2}\) to the alveoli.

Step-by-Step Solution

Answer

The Assertion and Reason are factually correct but the Reason does not directly support the Assertion because the oxygen delivery process and carbon dioxide delivery process, while related, are separate parts of the overall respiration process.

Step 1: Understanding Blood Oxygenation

First, it is key to understand that every \( 100 \, ml \) of oxygenated blood can indeed deliver approximately \( 5 \, ml \) of \( O_2 \) to the tissues. This occurs because hemoglobin in the red blood cells binds oxygen in the lungs and carries it to the body's tissues.

Step 2: Understanding Blood Deoxygenation

Next, grasp that every \( 100 \, ml \) of deoxygenated blood can deliver approximately \( 4 \, ml \) of \( CO_2 \) to the alveoli. Here, deoxygenated blood returns to the heart, is pumped to the lungs, and \( CO_2 \) is released and exhaled.

Step 3: Comparing Assertion and Reason

Finally, the comparison between oxygen delivery and carbon dioxide delivery process needs to be done. Even though these processes are linked in the overall respiration process, they are still distinct and therefore one does not provide straightforward support or reasoning for the other.

Key Concepts

Oxygen Transport

Oxygen transport is a fundamental process in respiratory physiology that ensures the delivery of oxygen to tissues across the body. The primary vehicle for this transportation is hemoglobin, a protein found in red blood cells. Each hemoglobin molecule can bind up to four oxygen molecules, effectively capturing oxygen in the lungs and releasing it in tissues that require it. This interaction is pivotal, as it allows for the efficient movement of oxygen from regions of high concentration, such as the lungs, to areas of lower concentration, like actively metabolizing tissues.

• Oxygen is loaded into red blood cells at the alveoli in the lungs.
• These oxygen-rich red blood cells then travel through the bloodstream to various tissues.
• Hemoglobin releases oxygen where it's needed most, like in muscles during exercise.

Maintaining a gradient for oxygen is crucial for its effective delivery, supported by the varying differences in partial pressures between the lungs and body tissues.

Carbon Dioxide Transport

Carbon dioxide transport away from tissues is just as vital as the delivery of oxygen. Carbon dioxide, a waste product of cellular respiration, needs to be efficiently removed from the body to maintain homeostasis. This process operates mainly via three methods: dissolution in plasma, chemical conversion to bicarbonate, and binding to hemoglobin.

• A portion of carbon dioxide dissolves directly into the blood plasma.
• A significant amount is converted into bicarbonate ions, which are transported in the plasma.
• Some carbon dioxide binds directly to hemoglobin, forming carbaminohemoglobin.

Upon reaching the lungs, these processes reverse, allowing carbon dioxide to be expelled during exhalation, thus keeping the blood pH stable and preventing acidity.

Hemoglobin Function

Hemoglobin's role is central to respiratory physiology, as it not only carries oxygen but also plays a part in transporting carbon dioxide back to the lungs. Structurally, hemoglobin is made of four subunits, each capable of binding one oxygen molecule. This multi-unit configuration allows for cooperative binding. When one oxygen molecule binds, the hemoglobin changes shape slightly, making it easier for additional oxygen molecules to attach.

• Each hemoglobin can carry four oxygen molecules at its full capacity.
• Binding is influenced by several factors including the pH and concentration of carbon dioxide.
• This cooperative nature ensures swift oxygen attachment in the lungs and rapid release in tissues requiring oxygen.

Moreover, hemoglobin's versatility ensures that not only oxygen, but carbon dioxide and protons are transported, playing a role in pH regulation through the buffering system.

Alveolar Gas Exchange

Alveolar gas exchange is a critical process happening within the respiratory zone of the lungs. The alveoli are tiny sac-like structures where the actual exchange of gases occurs. Oxygen from the inhaled air diffuses across the thin walls of the alveoli into the blood in the surrounding capillaries. Simultaneously, carbon dioxide diffuses from the blood into the alveoli to be exhaled.

• This process is driven by differences in partial pressures of gases (known as the concentration gradient).
• The thin walls of the alveoli and extensive capillary networks facilitate efficient gas exchange.
• A higher concentration of oxygen in the alveoli allows this gradient to push oxygen in and carbon dioxide out.

Ultimately, adequate alveolar gas exchange ensures that blood arriving at the lungs becomes oxygenated, ready to supply oxygen to tissues while carrying away carbon dioxide for removal.