In the ABO blood group system, antigens A and B are both absent on the red blood cells of individuals with which blood group?

Introduction / Context:
The ABO blood group system classifies human blood based on the presence or absence of antigen molecules on the surface of red blood cells. This question focuses on recalling which blood group lacks both A and B antigens on its red cells. This knowledge is very important in blood transfusion and clinical practice.

Given Data / Assumptions:

• We are dealing with the ABO blood group system.
• The question asks where both A and B antigens are absent.
• Options list the four main ABO blood groups.

Concept / Approach:
In the ABO system, group A has antigen A on its red blood cells and anti B antibodies in the plasma. Group B has antigen B and anti A antibodies. Group AB has both antigens A and B on red cells but no anti A or anti B antibodies in plasma. Group O has neither antigen A nor antigen B on red blood cells but has both anti A and anti B antibodies in plasma. Therefore, the group without A and B antigens is group O.

Step-by-Step Solution:
Step 1: Recall the antigen profile of blood group A, which has antigen A. Step 2: Recall that blood group B has antigen B. Step 3: Recall that blood group AB has both antigens A and B. Step 4: Conclude that group O, by definition, lacks both A and B antigens.

Verification / Alternative check:
Blood transfusion charts show that group O negative blood is often called universal donor blood because it lacks A and B antigens and is Rh negative. This reduces the risk of immune reaction in recipients of different blood types. This property directly depends on the fact that group O red cells do not carry A or B antigens.

Why Other Options Are Wrong:

• Option B (A): Group A has antigen A on red blood cells, so it does not fit the requirement that both antigens are absent.
• Option C (B): Group B has antigen B, so it also does not fit.
• Option D (AB): Group AB has both A and B antigens, the exact opposite of what the question describes.

Common Pitfalls:
Students may confuse antigens on red cells with antibodies in plasma. It helps to memorise a simple table of the ABO system. Remember that the name of the blood group refers to the antigens present on the red blood cells. Group O is named for the absence of these two main antigens, not for the presence of any special antigen called O.

Final Answer:
Antigens A and B are absent on the red blood cells of people with blood group O.