yes, you can graft all citrus (exept for kumkuat) on a single tree
No, lemons and limes do not grow on the same tree. They are the fruit of two different species of trees.
Different species of different fruits or plants grow differently. For example, a blueberry tree would grow to about 50cm maximum when a mango tree would grow to about 5m.
Citrus fruits originate in tropical and sub-tropical areas. Nigeria, China, Guinea, Syria, and Japan are the top five producers of citrus fruits in the world. Source: http://en.wikipedia.org/wiki/Citrus
Citrus trees are trees that grow citrus fruits, such as orange, lemon, lime. I don't know how a fruit can help its tree. i am no expert but the fruit can help because as it decomposes it is a natural fertilizer for the tree i have heard that some fruit trees like banana peels on the ground to decompose into fertilizer.
Watermelon
got ask your mama NOW
Yes. Using a technique called bud grafting you can grow any type of citrus from one citrus tree or "rootstock".
Yes. Different fruits and vegetables only grow in one way. If one cherry grows on a tree, all of them do.
non-tree fruits most likely means fruits that don't grow on trees, like strawberrys
coffee, coconuts, palm oil, citrus fruits, cocoa n etc
Mandarin, although the tree is not small. The kumquat has small fruits, usually made into marmalade.
orangutans (correct spelling?) eat different fruiting plants that grow in the forest (rely on fruit) and one of there preferred fruits are from a tree called the durian tree.
marijuana