Wow a 6 marker on that...
Well firstly establish your mutagens. e.g. UV rays, X rays, Nuclear contamination (e.g. atom bombs and Chernobyl)
Then elaborate on the evidence... so for U.V rays you can talk about Australia having the highest rate of skin cancer in the world etc, how U.V radiation actually causes the mutations in DNA and how this effects human health.
Make sure you support it with statistics and facts.
Repeat this for your other mutagens.
e.g. Most first generation radiation therapists died of cancer (due to over exposure to X rays)
e.g. Talk about the mutations of new borns in Hiroshima.
Now depending on the wording of the question (look for the key verb is it describe, evaluate, etc) you may need a concluding statement just to wrap everything up.
Thats all I can really think of... hope I was any help
