Why is it important to only change 1 variable at a time?

Which class of molecules contains the amino group, nh2 (a) sugars (b) water (c) proteins (d) hydrocarbons

Sammi is studying the interaction of the digestive and circulatory systems in the human body. she has listed various processes that occur in each of the systems. put the processes in order to describe the interaction between these two systems. tiles nutrients diffuse through the villi of the small intestine.digestive processes break nutrients down in the mouth, stomach, and small intestine.blood is pumped through the circulatory system to deliver nutrients to other organs.nutrients are ingested at the mouth.nutrients enter the capillaries of the circulatory system. sequence

How are mutations continually being generated in a population (what are some of the causes of mutatuions? ) explain