The part of the leaf which is connected to the transport system of the stem and roots is the

Phloem conducts food and Xylem conducts water.

Explanation:

The xylem is in charge of the transport of water and supplements from the roots to the leaves. In the leaf, the xylem proceeds with this vehicle to the cells in the leaf to guarantee that enough water is available for photosynthesis to happen.  

The Phloem. ~ As it is the two way transport framework in a leaf.  

In a leaf, there are two cylinders: xylem and phloem. The xylem conveys water and the phloem conveys minerals and starches.  

There are two tissues inside those veins, xylem and phloem. Xylem conveys water from the roots up to the cells in the leaf. Phloem conveys the nourishment delivered in the leaf to the remainder of the plant. Primary concern is the leaf has veins for a similar explanation we have conduits and veins, to move stuff around to where we need it.

i'm not sure, but can you answer my most recent question?

these are common warning signs of overtraining syndrome:

washed-out feeling, tired, drained, lack of energy

mild leg soreness, general aches, and pains

pain in muscles and joints

sudden drop in performance

insomnia

headaches

decreased immunity (increased number of colds, and sore throats)

decrease in training capacity/intensity

moodiness and irritability

depression

loss of enthusiasm for the sport

decreased appetite

increased incidence of injuries.

a compulsive need to exercise