Question

\(\mathrm{CO}_{2}\) is transported (a) By RBC (b) As bicarbonates (c) In dissolved state through plasma (d) All of these

Short answer

The correct answer is (d) All of These. CO2 is transported in the human body by RBC, as bicarbonates, and in a dissolved state through plasma.

Step-by-step solution

Understand the Mechanisms

Firstly, understand that in the human body, CO2 is transported in three main ways: it dissolves directly into the blood, it binds to proteins in the red blood cells (RBCs), and it changes into bicarbonate.

Match the Options to the Mechanisms

Then, match each option to one of the three mechanisms of CO2 transport. (a) By RBC refers to CO2 being carried by proteins in the red blood cells, (b) As bicarbonates refer to CO2 being transformed into bicarbonate, and (c) In dissolved state through plasma refers to CO2 dissolving directly into the blood.

Evaluate 'All of These'

Lastly, determine if CO2 is transported in all of these ways. The three mechanisms of transport match up with options (a), (b), and (c), which means CO2 is indeed transported in all of these ways. Therefore, (d) 'All of These' is the correct answer.

Key concepts

Red Blood Cells

Red blood cells (RBCs) play a crucial role in the transport of carbon dioxide (CO₂) in the body. These cells contain a protein called hemoglobin, which is primarily known for carrying oxygen, but it also participates in transporting CO₂.

When CO₂ enters the bloodstream, a portion of it diffuses into RBCs. Inside these cells, CO₂ binds with hemoglobin to form carboaminohemoglobin. This process facilitates the transport of CO₂ from the tissues back to the lungs, where it can be exhaled.

RBCs are highly efficient in handling gases, not only because of hemoglobin but also due to their flexible, biconcave shape. This unique form increases the surface area for gas exchange, making them indispensable in maintaining the body's physiological balance.

• CO₂ binds with hemoglobin forming carboaminohemoglobin
• Efficient transport back to the lungs
• Vital for removing CO₂ from the body

Bicarbonate

In addition to transportation by RBCs, carbon dioxide is also converted into bicarbonate ions in the blood. This transformation is an important aspect of maintaining acid-base balance in the body.

When CO₂ reacts with water ( >H₂O) in the presence of the enzyme carbonic anhydrase, carbonic acid (H₂CO₃) is formed. This weak acid quickly dissociates into bicarbonate (HCO₃⁻) and hydrogen (H⁺) ions. Most of the CO₂ in the blood is carried in this way, as bicarbonate, which is highly soluble in plasma.

This bicarbonate mechanism not only helps in CO₂ transport but also plays a key role in buffering the blood pH. By controlling the levels of bicarbonate, the body can regulate the acidity of the blood effectively.

• CO₂ reacts with water forming carbonic acid
• Dissociates into bicarbonate (HCO₃⁻) and H⁺ ions
• Crucial for acid-base balance

Blood Plasma

The third method by which carbon dioxide is transported in the blood is through its dissolution in blood plasma. Although a smaller proportion compared to other methods, it is still significant for the process of gas exchange.

Dissolved CO₂ in plasma accounts for about 5-7% of the total CO₂ transported. This dissolved form can easily diffuse out of the blood into the alveoli in the lungs, where it is expelled from the body during exhalation.

The presence of dissolved CO₂ in plasma contributes to maintaining a gradient that facilitates the movement of CO₂ from tissues into the blood. This is essential, as it ensures a continuous removal of carbon dioxide from metabolically active tissues.

• Accounts for a smaller fraction of CO₂ transport
• Important for maintaining CO₂ gradients
• Essential for efficient gas exchange in lungs