A scientist investigates transport in three similar flowering plants. Each labelled substance behaves in the same way as the unlabelled substance.
When labelled carbon dioxide is supplied to a mature leaf, the label becomes part of the sucrose made in that leaf.
| Plant | Label supplied | Tissue tested later | Label detected |
|---|---|---|---|
| 1 | labelled magnesium ions to the soil around the roots | a mature leaf above the roots | labelled magnesium ions |
| 2 | labelled carbon dioxide to a mature leaf below a developing flower | the developing flower | labelled sucrose |
| 3 | labelled carbon dioxide to a mature leaf above a developing flower | the developing flower | labelled sucrose |
Explain how these results show differences between transport in xylem and transport in phloem.
In another plant, a chemical reduces respiration in companion cells. Suggest how this would affect the amount of labelled sucrose reaching the developing flower from a mature leaf.
80 exam-style questions on Edexcel GCSE Biology 6.2 Transport in plants, covering 6.2.1 Root hair cell adaptations, 6.2.2 Structure of xylem and phloem, 6.2.3 Transpiration and stomata, 6.2.4 Translocation of sucrose, 6.2.5 Leaf structure for photosynthesis, 6.2.6 Environmental factors on water uptake, 6.2.7 Rate calculations for transpiration, and 6.2.8 Plant adaptations to extreme environments. Each one has a worked solution and a mark scheme showing where the marks go.