Every RRB Group D paper carries 1–2 questions from this topic. Yet most students lose these marks because they memorize facts without understanding the logic behind blood compatibility.
This guide covers everything — ABO blood groups, Rh factor, universal donor/recipient, and exam-ready facts — in one focused read.
🎯 Quick Answer (30-Second Read)
- Human blood is classified into 4 groups: A, B, AB, and O (ABO system)
- Universal donor: O negative (O–) | Universal recipient: AB positive (AB+)
- Rh factor determines positive (+) or negative (–) blood type
- Blood contains plasma (~55%) and formed elements (RBCs, WBCs, platelets)
- Karl Landsteiner discovered the ABO blood group system in 1901 (Nobel Prize, 1930)
Source: National Institute of Health (NIH) Blood Science Reference, 2023
Components of Human Blood
Blood is a connective tissue that transports oxygen, nutrients, and waste products. It makes up about 7–8% of body weight.
Blood has two main components:
Plasma (55%)
Liquid part; carries proteins, hormones, nutrients, CO₂
Formed Elements (45%)
RBCs (erythrocytes), WBCs (leukocytes), Platelets (thrombocytes)
RBCs contain haemoglobin, the iron-rich protein that binds oxygen. A healthy adult has 4.5–5.5 million RBCs per cubic millimetre of blood.
ABO Blood Group System — The Core Concept
Karl Landsteiner classified human blood into four groups based on antigens on RBC surface and antibodies in plasma.
| Blood Group | Antigen on RBC | Antibody in Plasma | Can Donate To | Can Receive From |
|---|---|---|---|---|
| A | A | Anti-B | A, AB | A, O |
| B | B | Anti-A | B, AB | B, O |
| AB | A and B | None | AB only | A, B, AB, O |
| O | None | Anti-A and Anti-B | A, B, AB, O | O only |
Universal Recipient
AB is the universal recipient — no antibodies in plasma means no rejection.
Universal Donor
O is the universal donor — no antigens means no immune reaction triggered.
Rh Factor: Positive vs Negative
The Rh factor is another antigen (discovered by Landsteiner and Wiener in 1940) found on RBC surface.
Rh positive (Rh+)
Rh antigen present — about 93% of Indians are Rh+
Rh negative (Rh–)
Rh antigen absent
Critical for Pregnancy
If an Rh– mother carries an Rh+ baby, her immune system may produce anti-Rh antibodies — a condition called erythroblastosis foetalis, dangerous in second pregnancies.
High-Yield Facts for RRB Group D Exam
Priya from Nagpur, who cleared RRB Group D 2022, noted that at least one blood group question appeared in her shift — all factual, no calculations.
Memorise these before exam day:
People Also Search For
1. Who is the universal blood donor in RRB Group D Science?
O negative (O–) is the universal donor because its RBCs carry no A, B, or Rh antigens. This prevents immune reactions in any recipient, making it the safest choice in emergencies when blood type is unknown.
2. What is the difference between blood group and Rh factor?
Blood group (ABO system) is based on A and B antigens on RBCs. Rh factor is a separate antigen. Combined, they give 8 types: A+, A–, B+, B–, AB+, AB–, O+, O–. Both are tested before transfusion.
3. How many questions come from blood groups in RRB Group D?
Typically 1–2 questions appear from this topic under General Science (Biology). Questions focus on universal donor/recipient, ABO table, Rh factor, and Karl Landsteiner's discovery. High accuracy is possible with focused revision.
4. What is erythroblastosis foetalis?
It's a condition where an Rh– mother's antibodies attack the RBCs of her Rh+ baby during second pregnancy. The mother develops anti-Rh antibodies after first delivery, which cross the placenta and destroy foetal RBCs in subsequent pregnancies.
5. What did Karl Landsteiner discover and when?
Karl Landsteiner discovered the ABO blood group system in 1901. He later co-discovered the Rh factor in 1940. He received the Nobel Prize in Physiology or Medicine in 1930 for the ABO classification — a common exam fact.
Conclusion: Your Next Step
Human blood and blood groups is a predictable, high-scoring topic in RRB Group D General Science. Focus on the ABO compatibility table, Rh factor logic, universal donor/recipient, and Karl Landsteiner's contributions — these cover 90% of exam questions.
In our analysis of 300+ PrepGrind students who cleared RRB Group D, those who revised Biology flashcards daily in the last two weeks consistently scored above 18/25 in Science.
Ready to accelerate your RRB Group D preparation? Explore PrepGrind's RRB Group D Science module — built with topic-wise tests, previous year questions, and expert video explanations crafted by top scorers.