I need help with one paragraph. (About the image)

Although there are a limited number of amino acids many different types of proteins exist because..

The circles, or orbits, for electrons are called energy levels. each level can hold only a certain number of electrons. add electrons to each level until you can't add any more. how many electrons can each level hold?

Factors that can increase mutation rates a. high temps b. low temps c. food additives d. uv rays