Which one among the fallowing Statements about blood trans- fusion is correct ? Blood group B can give blood to—

1. Composition of Human Blood (basic)

To understand human health, we must first understand the 'river of life' flowing through us. Blood is far more than just a red liquid; it is a specialized fluid connective tissue that acts as the body's primary transport and communication system Science, Class X (NCERT 2025 ed.), Life Processes, p.91. It is essentially a non-uniform mixture where various specialized cells are suspended in a liquid medium Science, Class VIII (NCERT 2025 ed.), Nature of Matter: Elements, Compounds, and Mixtures, p.131. If you were to spin a tube of blood in a centrifuge, it would separate into two main parts: the straw-colored liquid plasma (about 55%) and the formed elements or blood cells (about 45%).

The Plasma is the fluid matrix of the blood. It is composed mostly of water but is packed with vital substances. Plasma is responsible for transporting food (nutrients), carbon dioxide, and nitrogenous wastes in a dissolved form Science, Class X (NCERT 2025 ed.), Life Processes, p.91. It also carries mineral salts, proteins, and hormones, similar to how the cytoplasm of an individual cell contains proteins, fats, and minerals to sustain life Science, Class VIII (NCERT 2025 ed.), The Invisible Living World, p.12.

Suspended within this plasma are three distinct types of cells, each with a 'special function' that allows the entire organism to work Science, Class VIII (NCERT 2025 ed.), The Invisible Living World, p.13:

• Red Blood Corpuscles (RBCs): These are the oxygen-carriers of the body. They contain hemoglobin, which binds to oxygen and delivers it to every tissue Science, Class X (NCERT 2025 ed.), Life Processes, p.91.
• White Blood Cells (WBCs): These function as the body's 'internal police' or defense system, fighting off infections and foreign invaders.
• Platelets: These are essential for the 'repair system' of our circulatory network. If a blood vessel is damaged, platelets trigger the clotting process to plug the leak and prevent excessive blood loss Science, Class X (NCERT 2025 ed.), Life Processes, p.91.

Component	Primary Function	Transport State
Plasma	Transport of nutrients and metabolic wastes	Dissolved form
RBCs	Transport of Oxygen	Bound to Hemoglobin
Platelets	Blood Clotting / Repair	Cellular activation

Sources: Science, Class X (NCERT 2025 ed.), Life Processes, p.91; Science, Class VIII (NCERT 2025 ed.), Nature of Matter: Elements, Compounds, and Mixtures, p.131; Science, Class VIII (NCERT 2025 ed.), The Invisible Living World: Beyond Our Naked Eye, p.12-13

2. Functions of Blood and Hemoglobin (basic)

Think of blood not just as a red liquid, but as the body's internal logistics network. It is a fluid connective tissue that ensures every single cell, no matter how deep inside, receives the supplies it needs and disposes of its trash Science Class X, Life Processes, p.91. Blood is composed of a liquid medium called plasma, in which various cells are suspended. While plasma is excellent at transporting dissolved substances like food (glucose), salts, and nitrogenous wastes, it needs specialized help for gases.

This is where hemoglobin comes in. In small organisms, oxygen can simply move through the body via diffusion (moving from high to low concentration). However, in large animals like humans, diffusion pressure alone is too slow to reach every tissue Science Class X, Life Processes, p.90. To solve this, our Red Blood Corpuscles (RBCs) contain hemoglobin—a respiratory pigment with a very high affinity for oxygen. Hemoglobin acts like a specialized shuttle, picking up O₂ in the lungs and releasing it only when it reaches tissues that are oxygen-deficient Science Class VII, Life Processes in Animals, p.132.

Interestingly, the transport of Carbon Dioxide (CO₂) works differently. Because CO₂ is more soluble in water than oxygen is, it doesn't rely as heavily on a pigment carrier. Instead, most of the CO₂ produced by our cells travels back to the lungs in a dissolved form within the blood plasma Science Class X, Life Processes, p.90.

Component	Primary Transport Function	Method
Plasma	Food, CO₂, Nitrogenous wastes, Salts	Dissolved in liquid
RBCs (Hemoglobin)	Oxygen (O₂)	Bound to respiratory pigment

Sources: Science Class X, Life Processes, p.90; Science Class X, Life Processes, p.91; Science Class VII, Life Processes in Animals, p.132

3. Genetics of Blood Group Inheritance (intermediate)

To understand the genetics of blood group inheritance, we must first look at the surface of our red blood cells (RBCs). These cells carry specific sugar polymers called antigens. In the ABO blood group system, these antigens are determined by a single gene, often called the I gene. This gene has three different versions, or alleles: Iᴬ, Iᴮ, and i. While most genes have only two versions, blood groups are a classic example of multiple alleles existing in a population.

The way these alleles interact follows the rules of Mendelian genetics, specifically dominance and co-dominance. The Iᴬ and Iᴮ alleles are dominant over the i allele. This means if a person inherits one 'A' allele and one 'O' allele (genotype Iᴬi), their blood type will be A. However, Iᴬ and Iᴮ are co-dominant with each other. If an individual inherits both, they express both antigens equally, resulting in blood group AB. Group O (genotype ii) is recessive, appearing only when no dominant A or B allele is present. This genetic blueprint is why a child's blood type can sometimes differ from both parents, as hidden recessive traits can emerge in the next generation. Science, Class X (NCERT 2025 ed.), Heredity, p.133.

Beyond just inheritance, these groups dictate biological compatibility. Our bodies produce antibodies in the plasma that act as a defense mechanism against 'foreign' antigens. For instance, a person with Blood Group B has B-antigens on their cells and anti-A antibodies in their plasma. If they receive Type A blood, their antibodies will attack the donor cells, causing a dangerous immune reaction.

Blood Group	Genotype(s)	Antigens on RBC	Antibodies in Plasma
A	IᴬIᴬ or Iᴬi	A	Anti-B
B	IᴮIᴮ or Iᴮi	B	Anti-A
AB	IᴬIᴮ	A and B	None
O	ii	None	Anti-A and Anti-B

Because Type O lacks antigens, it is known as the universal donor, while Type AB, lacking antibodies, is the universal recipient. While we often view family through the lens of shared rituals and resources, these biological 'kinfolk' ties are strictly governed by these microscopic markers. Themes in Indian History Part I, Kinship, Caste and Class, p.55.

Sources: Science, Class X (NCERT 2025 ed.), Heredity, p.133; Themes in Indian History Part I, Kinship, Caste and Class, p.55

4. The Rh Factor and Clinical Implications (intermediate)

To understand blood compatibility fully, we must look beyond the ABO system to the Rh (Rhesus) factor. This is a specific protein (antigen) found on the surface of red blood cells. If your blood has this protein, you are Rh-positive (Rh+); if it lacks it, you are Rh-negative (Rh-). While the ABO group is the first check for a transfusion, the Rh factor is the second. An Rh-negative individual should generally not receive Rh-positive blood because their immune system will recognize the Rh protein as a foreign 'invader' and produce antibodies to destroy the donor cells.
The most significant clinical implication of this factor occurs during pregnancy, a condition known as Erythroblastosis Fetalis (or Hemolytic Disease of the Newborn). This risk arises specifically when an Rh-negative mother carries an Rh-positive fetus. During the first such pregnancy, the mother and fetus are usually safe because the placenta acts as a barrier. As noted in Science, class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.124, the placenta provides a large surface area for the exchange of nutrients and waste through villi and blood spaces, but it generally keeps the two blood supplies separate. However, during childbirth, small amounts of fetal Rh-positive blood may enter the mother’s bloodstream.
Once exposed, the mother’s immune system becomes 'sensitized' and starts producing anti-Rh antibodies. While the first child is usually born healthy, the danger escalates in subsequent pregnancies with Rh-positive fetuses. These maternal antibodies are small enough to cross the placenta and attack the red blood cells of the fetus, leading to severe anemia, jaundice, or even heart failure in the newborn. To prevent this, medical professionals administer Anti-D (RhoGAM) injections to Rh-negative mothers after their first delivery to neutralize any fetal Rh-positive cells before the mother's immune system can react.

Sources: Science, class X (NCERT 2025 ed.), How do Organisms Reproduce?, p.124

5. Antigens, Antibodies, and Agglutination (exam-level)

To understand blood compatibility, we must first look at the microscopic "identity tags" on our cells. Every individual's red blood cells (RBCs) carry specific proteins called Antigens on their surface. Think of these as a biological ID card. In the ABO system, these antigens are either A, B, both (AB), or neither (O). Simultaneously, our blood plasma contains Antibodies—protective proteins that act like security guards. A critical rule of nature is that your body produces antibodies against the antigens you do not have. For instance, if you have Blood Group B, your RBCs display B antigens, and your plasma contains Anti-A antibodies to guard against "foreign" A-type cells.

When a person receives a blood transfusion, the recipient's antibodies must not recognize the donor's antigens as foreign. If a mismatch occurs—such as giving Type A blood to a Type B person—the recipient's Anti-A antibodies will bind to the donor's A antigens. This triggers a process called Agglutination, where the red blood cells clump together. This clumping can block blood vessels and cause severe organ damage. This is a specific form of the body's immune response; just as the body reacts more vigorously upon a second exposure to a pathogen Science, Class VIII (NCERT), Health: The Ultimate Treasure, p.45, an immune mismatch in blood creates a rapid and dangerous defensive reaction.

Understanding these pairings is essential for medical safety. The table below summarizes how antigens and antibodies are distributed across the ABO groups:

Blood Group	Antigen (on RBC)	Antibody (in Plasma)
A	A	Anti-B
B	B	Anti-A
AB	A and B	None
O	None	Anti-A and Anti-B

Because Group AB has no antibodies, they can receive blood from any group (Universal Recipient). Conversely, Group O has no antigens on the cell surface to be attacked, making them the Universal Donor. In clinical settings, checking these levels alongside hemoglobin counts is a standard part of assessing a patient's health and readiness for treatment Science, Class X (NCERT), Life Processes, p.91.

Sources: Science, Class VIII (NCERT), Health: The Ultimate Treasure, p.45; Science, Class X (NCERT), Life Processes, p.91

6. Transfusion Compatibility Rules (exam-level)

To understand blood transfusion, we must first look at the surface of our red blood cells (RBCs). These cells carry specific markers called antigens. Simultaneously, our plasma contains antibodies, which act as the body's security guards. The fundamental rule of compatibility is simple: The recipient's antibodies must not recognize the donor's antigens as foreign invaders. If they do, the antibodies will attack the donor's blood cells, causing a life-threatening reaction called agglutination (clumping).

While organ donation—such as kidneys or lungs—requires complex tissue matching Science, class X (NCERT 2025 ed.), Life Processes, p.98, blood compatibility follows a strict ABO logic. There are four primary blood groups based on these markers:

Blood Group	Antigens (on RBC)	Antibodies (in Plasma)
Group A	A Antigen	Anti-B
Group B	B Antigen	Anti-A
Group AB	A and B Antigens	None
Group O	None	Anti-A and Anti-B

Because Group AB individuals have no antibodies against A or B, they are known as Universal Recipients—they can accept blood from any group. Conversely, Group O individuals have no antigens on their RBCs for a recipient's antibodies to attack, making them Universal Donors. Even in specialized donations like corneal transplants, where identity remains confidential, biological compatibility remains the silent foundation of success Science, class X (NCERT 2025 ed.), The Human Eye and the Colourful World, p.165.

Let's apply this to Blood Group B. An individual with Group B has B-antigens and Anti-A antibodies. Therefore, they can safely donate to other B individuals or to AB (who has no antibodies). However, they can only receive blood from B or O (the universal donor). They cannot receive from A or AB because their own Anti-A antibodies would immediately attack the 'A' markers present in those groups.

Sources: Science, class X (NCERT 2025 ed.), Life Processes, p.98; Science, class X (NCERT 2025 ed.), The Human Eye and the Colourful World, p.165

7. Solving the Original PYQ (exam-level)

Now that you have mastered the fundamental principles of immunology, this question tests your ability to apply the Antigen-Antibody relationship to a practical clinical scenario. Remember the golden rule: the antigen on the donor's red blood cells must not match the antibody in the recipient's plasma. Since an individual with Blood Group B has B-antigens and anti-A antibodies, their blood is compatible only with recipients who won't attack the B-antigen (other B types and AB types) and they can only receive from donors who don't carry the A-antigen (other B types and O types).

To arrive at (B) blood groups B and AB, and receive from group B, you must walk through the logic of compatibility. Group B can donate to its own kind and to group AB, which is the universal recipient because it lacks antibodies against both A and B. Conversely, when receiving, group B must avoid any blood containing 'A' antigens (A and AB) because their own anti-A antibodies would trigger a defensive attack. While group B can also receive from group O, the option provided correctly identifies the safe receipt from its own group, making it the most accurate choice among the four.

UPSC often uses role-reversal traps to confuse candidates, as seen in options (A) and (C). A common mistake is thinking that because AB can receive from everyone, it can also give to everyone; however, AB can only donate to other AB individuals because its antigens would be attacked by any other group. Option (D) presents the ultimate distractor by flipping the role of Group O, which is the universal donor, not a recipient for group B. By systematically checking the antigens against the antibodies as detailed in MedlinePlus Medical Encyclopedia, you can easily filter out these distractors and identify the correct physiological match.