eyeball. 1  Photoreceptors are the cells in the retina that respond to light. Their distinguishing feature is the presence of large amounts of tightly packed membrane that contains the photopigment rhodopsin or a related molecule.
In chemical analysis,  matrix refers to the components of a sample other than the analyte of interest. The matrix can have a considerable effect on the way the analysis is conducted and the quality of the results obtained; such effects are called matrix effects. For example, the ionic strength of the solution can have an effect on the activity coefficients of the analytes.
A matrix is a rectangular array of numbers arranged in rows and columns. The array of numbers below is an example of a matrix. The number of rows and columns that a matrix has is called its dimension or its order. By convention, rows are listed first; and columns, second.