Highlight Row based on data on separate sheet - Macro or Conditional Formatting?

I'm trying to find a quick way to search a large list of information on two separate sheets in the same workbook for different data.

Example:

Sheet1:
a1: Test1
a2: Test2
a3: Test3
a4: Test4
a5: Test5

Sheet2:
a1: Test1
a2: Test2

Basically I'd like the macro or conditional formatting (whichever is easier?) to search the data on sheet1 vs sheet2 and highlight any rows on sheet1 that aren't on sheet2. So in the example, after running the macro, Sheet1 row 3, row 4,and row 5 would all be highlighted because the values for a3, a4, and a5 are not on sheet2.

Any help with this would be great.

Thank you so much in advance!

RichWW2

Not sure if I did it right or not, but it highlighted all the blank cells in sheet1 column A, but not Row 3, 4, or 5. I don't think the ISNA function works here because I'm looking it to highlight all the cells that don't match, even ones with values, not just the ones that are blank.