Question 21N.1A.SL.TZ1.32

This question required candidates to know that phloem transports sugars and then also either recognise phloem tissue in a micrograph or know its relative position in a vascular bundle. Of the tissues labelled, A and D were not part of the vascular bundle and C was easily recognizable as xylem. To a well-prepared candidate, the small, thin-walled cells labelled B were clearly phloem, with the characteristic pattern of larger sieve tubes and smaller companion cells just about visible. Areas of sclerenchyma and cambium in the micrograph were not labelled as they would have been more confusable with phloem. A G2 comment was made that all living tissue would eventually have received radioactive sugars in this experiment, but the candidate’s task is always to choose the best answer, and phloem would become radioactive first and reach the highest levels.