Tubular secretion allows hydrogen ions, creatinine, and penicillin to be excreted in the distal convoluted tubule. How are these molecules moved across?

Active Transport

Explanation:

Tubular secretion allows hydrogen ions,  and penicillin to be excreted in the distal convoluted tubule. These molecules moved across through a process called active transport.

In Active transport there is movement of ions or molecules from a region of lower concentration to the region of higher concentration through a permeable membrane (cell membrane) with the help of enzymes and energy. So, similar is the process for tubular secretion.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.