what is the puprose of flame-sterilizing the inoculating loop or needle before and after using it?

Answer 1

Read your question.....
You are sterilising it! You are going to do something with a microscopic organism, for example, plate it up to grow it. You want to keep it sterile, free from contamination.

Answer 2

You heat to sterilize it and not introduce any thing into the culture. After transfer with the loop, you again sterilize the loop to prevent possible contamination from the loop to the environment.

Answer 3

To kill any bacteria prior to and after innoculation. To stop any carryover or contamination of other bacteria.