Question

The majority of oxygen is transported in the blood of vertebrates a. by binding to plasma proteins. b. by binding to hemoglobin in erythrocytes. c. as dissolved gas in the plasma. d. as dissolved gas in the cytoplasm in the erythrocytes. e. by binding to hemoglobin in the plasma.

Short answer

The correct answer is option b. Most of the oxygen is transported in the blood of vertebrates by binding to hemoglobin in erythrocytes.

Step-by-step solution

Understanding the Role of Plasma Proteins

Plasma proteins mainly play the role in clotting, defending the body against diseases, and maintaining the osmotic pressure. They are not primarily involved in oxygen transport.

Understanding the Role of Erythrocytes and Hemoglobin

Red blood cells, or erythrocytes, contain a protein named hemoglobin. This hemoglobin has a high affinity to oxygen and binds with oxygen to form oxyhemoglobin. This process occurs in the lungs.

Considering Dissolved Gas in Plasma

Although oxygen can dissolve in plasma and cytoplasm, the major portion of oxygen is not transported this way because it is not efficient.

Considering Hemoglobin in plasma

Hemoglobin is located inside red blood cells rather than free in the plasma.

Deciding the best choice

Considering all the information about the roles of plasma, erythrocytes, and hemoglobin, the correct choice is the one that correctly states that most of the oxygen is transported by binding with hemoglobin in erythrocytes.

Key concepts

Hemoglobin

Hemoglobin is a remarkable protein found within red blood cells. Its primary purpose is to transport oxygen from the lungs to various parts of the body.

• Structure: Hemoglobin is composed of four subunits, each capable of binding one oxygen molecule.
• Functionality: It functions by binding to oxygen molecules. This creates a compound called oxyhemoglobin, which circulated to tissues where oxygen is needed.
• Other Roles: Hemoglobin also plays a role in transporting carbon dioxide, a waste product from metabolism, back to the lungs where it can be exhaled.

Its efficiency at picking up and releasing oxygen is one of the main reasons it's critical in the respiratory processes of vertebrates.

Erythrocytes

Erythrocytes, commonly known as red blood cells, are the vehicles for transporting oxygen in the bloodstream. They are uniquely designed to ensure efficient oxygen transport.

• Shape: Their biconcave shape increases the surface area for oxygen uptake and release.
• Composition: Erythrocytes are packed with hemoglobin, providing the capacity to bind a vast amount of oxygen.
• Life Span: Red blood cells have a life span of about 120 days, after which they are broken down and recycled in the body.

Erythrocytes play a vital role in maintaining adequate oxygen levels and thus, support cellular and tissue functions across the body.

Plasma Proteins

Plasma proteins are an essential component of blood plasma, but they do not primarily contribute to oxygen transport.

• Roles: These proteins aid in clotting, immune responses, and maintain osmotic balance in the bloodstream.
• Types: The main plasma proteins include albumin, globulins, and fibrinogen.

Their main function is to manage bodily functions related to defense and circulation, rather than being directly involved in the transportation of oxygen.

Oxyhemoglobin

Oxyhemoglobin is the form of hemoglobin that is bound to oxygen. It represents a critical phase in the oxygen transport process.

• Formation: It is formed when oxygen binds to the iron atom in the heme group of hemoglobin molecules in the lungs.
• Release: Once the hemoglobin reaches tissues that need oxygen, the molecule releases oxygen as oxyhemoglobin converts back to deoxyhemoglobin.

This binding and releasing mechanism allow for efficient oxygen delivery throughout the body, playing a crucial role in cellular respiration and energy production.