Translocation sim
Place aphids on a willow stem, ring the bark with a scalpel, cut the stylets, push ¹⁴CO₂ into a leaf chamber, then count the radioactivity in each stylet's sap every 4 minutes, work out the speed of translocation and make an autoradiograph to see which sinks the sucrose reached.
Translocation: sucrose and amino acids moved in the phloem from source to sink, up or down the stem; evidence from ringing, aphid stylets and ¹⁴CO₂ labelling with an autoradiograph · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Willow shoot model: one leaf is given ¹⁴CO₂; labelled sucrose leaves the leaf after about 4 min and moves in the phloem at about 10 mm per min, up to the shoot tip and down to the roots. A ring of bark (the phloem) blocks it. Simplified: illustrative counts, speed (10 mm per min ≈ 0.6 m per hour) and loading time (≈ 4 min); one speed in every direction; real speeds vary along the stem; the labelled sucrose's front spreads over 8 min; real fronts spread more; the sap is counted without any loss of droplets, and background is a steady 24 counts per minute; aphids feed only at set places, 40 mm apart; the ring blocks the phloem at once and completely; the swelling above a ring takes weeks and is shown as a separate view; the autoradiograph is shown at once; a real film takes days in the dark, and the shoot stays drawn on the bench after it is pressed; the plant and the close-up are not to scale.
- Lit: the syringe plunger (push it in to give the leaf ¹⁴CO₂)
- Close-up: inside the stem, and the autoradiograph (schematic, not to scale)
- Amber in the close-up: labelled sucrose (a colour key; radioactivity has no colour)
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
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