Agarose gels have very large pore size and are used primarily to separate very large molecules with a molecular
mass greater than $200\; K$ Da.
Spectrophotometry is a method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution.
Tissue culture involves the growth in an artificial medium of cells derived from living tissue.
$PCR$ is a technique used to make multiple copies of a segment of $DNA$.