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.
Create a matrix. A matrix is a rectangular set of numbers that are arranged in multiple rows and columns. Code a matrix by listing a series numbers separated by spaces or commas per row within the command window. For a new row, a semi colon is placed between the values of the old row and new row.