In animal cells, during S-phase (a)_____ begins in the the nucleus and (b)_____ duplicates in the cytoplasm

Answer

To answer the question regarding what occurs during the S-phase in animal cells, we can break it down into two parts:

1. **(a) What begins in the nucleus during S-phase?**
- During the S-phase of the cell cycle, DNA replication begins in the nucleus. This is a crucial process where the cell's genetic material is duplicated to ensure that each daughter cell will have an identical set of chromosomes.

2. **(b) What duplicates in the cytoplasm during S-phase?**
- In the cytoplasm, the centrioles duplicate during the S-phase. Centrioles are cylindrical structures that play a key role in cell division, particularly in the formation of the spindle fibers that separate chromosomes during mitosis.

So, the complete answer to the question is:
(a) DNA replication begins in the nucleus and (b) centrioles duplicate in the cytoplasm.