Question

Which of the following are secondary lymphoid organs?
(a) Bone marrow
(b) Tonsils
(c) Spleen
(d) Thymus
Choose the correct answer from the options given below :

• (a) and (d) only
• (a) and (b) only
• (b) and (c) only
• (b) and (d) only

Hint:

Bone marrow is the principal site of lymphocyte production, where both B and T cell precursors are generated. The spleen acts as a main biological filter, trapping blood-borne microorganisms and worn-out erythrocytes.

Answer 1

The Correct Option is C

Step 1: Read the question.
We must pick the secondary lymphoid organs from: (a) bone marrow, (b) tonsils, (c) spleen, (d) thymus.
Step 2: Recall the two classes.
Primary lymphoid organs are where lymphocytes form and mature. Secondary lymphoid organs are where mature lymphocytes meet antigens and multiply.
Step 3: Classify bone marrow.
Bone marrow is where lymphocytes are made and mature, so it is a primary organ. So (a) is not secondary.
Step 4: Classify thymus.
The thymus is where T-lymphocytes mature, so it is also a primary organ. So (d) is not secondary.
Step 5: Classify tonsils and spleen.
Tonsils and spleen are sites where mature lymphocytes interact with antigens, so both are secondary lymphoid organs. So (b) and (c) are correct.
Step 6: Conclude.
The secondary organs are (b) and (c), which is option (3).
\[ \boxed{\text{(b) and (c) only}} \]