Plants and animals, and even humans, have similar organ systems. For example, a plant such as a tree transports nutrients through “veins” called the xylem and the phloem.
The xylem carries water through the roots and up the trunk of the tree. It then branches off into the limbs, into the twigs, and eventually, the leaves. Roots of the tree seem to know their surroundings. If the soil around the root is poor in nutrients, it will lengthen, searching for a mineral-rich patch of soil. If and when the root finds mineral-rich soil, it will branch off, forming what might be analogous to a mini root system, in order to get a hold of the most nutrients possible.
The phloem has always been harder to understand than the xylem, for me, at least. The leaves contain chlorophyll and chloroplasts, giving them a green color while also producing sugar from light that enters the leaf. The tree has a special way of capturing the most light possible. It does this through “phyllotaxy”, which makes sure that the leaves nearer to the top of the tree don’t overshadow the leaves closer to the bottom. The phloem transports the sugar down the trunk, towards the roots. However, in the reproductive phase of a tree, the sugars, or, “photosynthates”, never reach the roots. They instead go to the fruit of the tree, enriching it with sugar and nutrients.
This system is very similar to an animal’s or human’s circulatory system. The soil’s nutrients are the tree’s meal. It eats the meal through the roots, carries it up the trunk through the xylem, and into the leaves, just like an animal’s blood into the skin. Only problem is, animals and humans don’t produce fruit off our arms or legs. So the analogy has a few kinks, but, I think you (the reader) get the point.