Circulatory System

Step 1: Understanding cloning vectors.
Cloning vectors are DNA molecules used to carry foreign DNA into a host cell for replication.
Step 2: Capacity of different vectors.
Lambda phage and cosmids can carry large DNA fragments.
Plasmids can carry moderately sized DNA inserts.
M13 phage has very limited carrying capacity.
Step 3: Elimination of incorrect options.
Since M13 phage can insert only small DNA fragments, it is unsuitable for large DNA molecules.
Step 4: Conclusion.
Larger DNA molecules cannot be inserted using M13 phage.

Step 1: Understanding pulmonary circulation.
In humans, oxygenated blood from the lungs is carried back to the heart through pulmonary veins.
Step 2: Anatomical detail.
There are two pulmonary veins from each lung, making a total of four pulmonary veins that open into the left atrium.
Step 3: Conclusion.
Hence, the correct answer is (B) 4.

Step 1: Understanding blood pressure variation.
Blood pressure is highest in arteries near the heart and gradually decreases as blood flows through capillaries and veins.
Step 2: Evaluating the options.
(A) systemic aorta: Incorrect. It has the highest blood pressure.
(B) pulmonary artery: Incorrect. It still carries blood under considerable pressure.
(C) renal vein: Correct. Veins have much lower pressure compared to arteries.
(D) coronary artery: Incorrect. It supplies the heart and has high pressure.
Step 3: Conclusion.
The minimum blood pressure is found in the renal vein.