**Core Concept:** Blood is a complex fluid composed of plasma, red blood cells (RBCs), white blood cells (WBCs), and platelets. Plasma contains essential proteins, clotting factors, and various substances that play crucial roles in blood coagulation, immunity, and transport of nutrients and waste products. Plasma is further divided into two fractions: albumin and globulin.

**Why the Correct Answer is Right:** The correct answer refers to the plasma fraction, specifically the globulin fraction, which is stored at -40°C. Globulins are proteins that are essential for maintaining osmotic pressure, transporting hormones, and acting as antibodies, enzymes, and transport proteins. The primary globulin fractions are α-globulin, β-globulin, and γ-globulin. α-globulin is responsible for transporting Vitamin D and calcium, β-globulin carries red blood cell precursors, and γ-globulin contains antibodies, which are crucial for immune response and defense against infections.

**Why Each Wrong Option is Incorrect:**

A. Albumin is also part of plasma, but it is stored at room temperature (approximately 37°C) and is not stored at -40°C. Albumin plays a crucial role in maintaining osmotic pressure, preventing protein loss, and transporting fatty acids and hormones.

B. RBCs (red blood cells) and WBCs (white blood cells) are not stored as fractions but are essential components of blood cells. RBCs carry oxygen to tissues, while WBCs play a vital role in immune response and defense against infections.

C. Platelets are small cell fragments responsible for blood clotting and wound healing. They are not stored as fractions but exist as a separate entity within the blood.

D. Plasma proteins, including globulins, play essential roles in blood coagulation, immune response, and transport of hormones, nutrients, and antibodies. However, they are not stored as a single fraction at -40°C, but are distributed among various blood components, as explained above.

**Clinical Pearl:** Maintaining proper blood composition, including the storage of globulins and other plasma components, is crucial for proper physiological functioning of the human body. Imbalances in blood fractions can lead to various disorders, such as hypoalbuminemia, hypoglobulinemia, and hemoconcentration, among others. Understanding the storage and role of blood fractions is essential for healthcare professionals, particularly for those involved in blood banking, transfusion medicine, and clinical laboratory analysis.