Explain two ways in which xylem is modified to carry out its function

The functions of xylem is to transport water, minerals, inorganic ions and other materials needed by the plant and to provide support for the plant. Xylem is adapted to its functions in the following ways:
1. The xylem tube containa a ring of lignin which form a spiral pattern around the xylem tube. Because lignin has high strength capacity, it helps to be a supportive structure for the plant. It also prevent the walls of xylem from collapsing under pressure caused by transpiration pull. 
2. Xylem is made up of water proof, dead cells; this enables it to have high capacity for transporting large quantity of water.

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.