Question

1. protein coated container
2. antibodies bind to protein
3. excess washed away
4. second antibody binds to first
5. visual change confirms correct protein is present

choose the step # that shows when the enzyme - linked antibodies were added to the well.
a 5
b 4
c 3
d 1
e 2

Explanation:

In an ELISA (Enzyme - Linked Immunosorbent Assay) - like process, the second antibody (enzyme - linked) is added in step 4, as step 4 is labeled "second antibody binds to first". Step 1 is the protein - coated container, step 2 is the first antibodies binding, step 3 is washing excess, and step 5 is the visual change. So the step where enzyme - linked antibodies (second antibody) are added is step 4.

Answer:

B. 4