Transport in plants – root uptake, xylem and phloem
BiologyPlant PhysiologyAges 16–17
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Sign in to playFollow water from the soil into root hair cells, across the cortex and endodermis to the xylem, and up to the leaves by transpiration pull and cohesion, while sucrose moves in the phloem from source leaves to sinks (fruit and roots) by pressure flow. Includes root, stem and leaf cross-sections, a ringing experiment, a ¹⁴C tracer and two practicals: a potometer and celery in coloured water.
Lesson: Transport in plants: xylem and phloem
What it shows
Water enters root hair cells by osmosis, crosses the cortex through cell walls (apoplast) or cytoplasm (symplast), and at the endodermis the Casparian strip forces it through living cells into the xylem. Evaporation from the leaves pulls a continuous water column up the xylem, held together by cohesion between water molecules; root pressure adds a small push. In the phloem, sucrose loaded at a source lowers the water potential, water follows by osmosis, and the pressure difference drives mass flow to sinks.
How to use
Use the four tabs. In Whole plant, change Light, Humidity, Wind, Temperature, Soil water and Sucrose loading, tap the root, stem or leaf for a cross-section, and try Ring the stem or the ¹⁴CO₂ button. Root uptake shows both pathways; untick Aerated soil or Casparian strip. Practicals runs a potometer or celery in dye and records each trial in a results table.
Parameters you can change
- Screen Whole plant, Root uptake, Phloem (pressure flow), Practicals
- Light intensity 0–100 %
- Air humidity 10–100 %
- Wind speed 0–8 m/s
- Air temperature 5–40 °C
- Soil water content 5–100 %
- Sucrose loading at the source leaf 0–100 %
- Sink Fruit and roots, Fruit only, Roots only
- Ring the stem (remove a ring of phloem)
- Aerated soil (O₂ for root respiration)
- Practical Potometer, Celery in coloured water
Questions to explore
- Why can drops of water form on leaf edges at night, when transpiration is almost zero?
- After a ring of bark is removed, why do the leaves stay fresh while the stem above the ring swells?
- Why does waterlogged soil reduce mineral uptake even though the roots are surrounded by water?
