What is an organism that lives on or in another organism and derives its nutrition from that organism?

A parasite

Explanation:

Parasitism is a form of symbiosis where one organism lives on/in another organism, as in the question, and gets a benefit from that organism, while the other organism is harmed. This is denoted by +/-, which means that one is positively impacted and one is negatively impacted, as opposed to commensalism, which is +/0, or mutualism, which is +/+.

An example is tapeworms, which are flatworm parasites that live in the human  intestine; they benefit while the host suffers.

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."