Answer:
What goes up let's of a load and come back down
I know a word of letters three, add two and less there will be.
I'm a starchy plant tuber that is one of the most important food crops, cooked and eaten fried, such as french fries.
These are believed to be found at the end of rainbows
if I drink I die if I eat I am fine what am i
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.