How can aphids be used to measure translocation rate? (6)

1) used to collect sap at various sites of the plant's length 2) plant grown w' leaves in radioactively labelled CO2 3) CO2 becomes radioactively labelled sugars 4) once stylet is severed the sap continues to flow 5) sap is analysed for radioactively labelled sugars translocation rate is calculated based on time taken for the radioisotope to be detected in diff positions of the plant's length