Astudent examining leaf cross sections under a microscope finds many loosely packed cells with relatively thin cell walls. the cells have numerous chloroplasts. what type of cells are they?

The answer is spongy mesophyll.

Explanation:

Between the upper and lower epidermis of a leave, you can find the so called mesophyll tissue which is rich in chloroplasts. There are two types of mesophyll tissue: the palisade and the spongy mesophyll. Whereas the cells of the palisade mesophyll are tightly packed, the cells of the spongy mesophyll are loosely packed.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.