1.Which of the following bones produces immune cells?
1 mark
APhalanges.
Why this is wrongThe phalanges are small bones with minimal red-marrow activity and are not a significant site of immune-cell production.
BWrist.
Why this is wrongThe wrist is a joint region made of several small carpal bones rather than a single marrow-rich bone that produces immune cells.
CCarpal.
Why this is wrongCarpal bones are small bones of the wrist with little red marrow and do not serve as a main site of immune-cell production.
DSternum. Correct answer
Why this is correctRed bone marrow in flat bones such as the sternum produces immune cells.
Immune cells (lymphocytes and other white blood cells) are produced by the red bone marrow. Red bone marrow is most active in flat bones and the ends of long bones, and the sternum is a classic flat bone rich in red marrow, which is why the sternum is used clinically for marrow sampling. The phalanges, wrist, and carpal bones contain little active red marrow.
2.A child suffers from a disease called "Cystic Fibrosis "which leads to production of very thick mucus. Which of the following natural lines of defense will directly affected?
1 mark
ASecond line: inflammatory response
Why this is wrongThe inflammatory response is a second-line internal defense; thickened mucus affects a surface barrier, not inflammation.
BFirst line: all natural barriers
Why this is wrongOnly the mucus barrier is impaired, so it is not accurate to say all natural barriers of the first line are affected.
CFirst line : some natural barriers Correct answer
DSecond line: Natural killer cells
Why this is wrongNatural killer cells belong to the second line of defense; thickened mucus affects an external barrier, not these internal cells.
Why this is correctMucus is one of the first-line natural barriers, so only some first-line barriers are directly affected.
The first line of natural defense is made of physical and chemical barriers such as skin, mucus, tears, and gastric acid. Mucus is one specific first-line barrier, so when cystic fibrosis thickens the mucus, only that particular barrier is directly impaired. The problem is therefore localized to some first-line barriers, not the whole first line and not the second-line internal defenses.
3.Which of the following are characteristics of an antibody?
1 mark
ABelongs to the non-histone proteins.
Why this is wrongThe histone and non-histone classification describes proteins associated with chromosomes, not plasma immunoglobulins, so it does not define an antibody.
BAlways consists of two types of polypeptide chains. Correct answer
CInvolved in the construction of specific cellular structures.
Why this is wrongAntibodies bind antigens; they are not used to build specific cellular structures, so this misstates their role.
DIts genetic code is found only in B cells.
Why this is wrongAntibody genes are present in all body cells even though they are expressed in B cells, so the code is not found only in B cells.
Why this is correctA typical antibody has heavy and light polypeptide chains.
The concept is the basic structure of an antibody. Every antibody is built from two types of polypeptide chains, heavy chains and light chains, so two types of polypeptide chains is the true characteristic. The histone and non-histone label applies to chromosomal proteins, antibodies are not structural building blocks, and antibody genes exist in all body cells even though they are expressed in B cells. Method: describe the antibody by its own heavy-and-light-chain structure rather than by properties borrowed from other protein categories.