The xylem xylem cell is specialised to transport water up the stem and into the leaves. Xylem vessels are made up of a series of connectedxylem cells. The end walls of the dead cells are broken to allow water to move through. A substance called lignin lignin strengthens the cell walls of xylem cells.

depends on if you on plato or not

c.) polymerase chain reaction

- "unlike the original dna fingerprinting method, dna profiling does not use restriction enzymes to cut the dna. instead it uses the polymerase chain reaction (pcr)? to produce many copies of specific str sequences. pcr is an automated procedure that generates lots of copies of a specific sequence of dna."

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.