On which plant did Taylor and his colleagues perform experiments using radioactive thymidine to prove the semi-conservative mode of $DNA$ replication?

Given below are two statements,one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R).$
Assertion $(A):$ $\text{DNA}$ replication occurs within a small opening of the $\text{DNA}$ helix,referred to as the replication fork.
Reason $(R):$ During transcription,the discontinuously synthesized fragments of $\text{DNA}$ are joined by the enzyme $\text{DNA}$ ligase.
In the light of the above statements,choose the most appropriate answer from the options given below:

The growth of Okazaki fragments in a $DNA$ strand is .....

During replication of $\text{DNA},$ Okazaki fragments are formed in the direction of :

If a normal $DNA$ molecule replicates in an $N^{15}$ medium for consecutive generations,what is the percentage of light $DNA$ in the $4^{th}$ generation (in $\%$)?

In the process of $DNA$ replication,deoxyribonucleoside triphosphates act as: