Water pathway: dye in celery sim
Lower a celery stalk into red dye, read the dye front on a ruler every 10 minutes and plot it, then cut thin sections on a white tile to find the stained xylem, and follow the water from the soil to the air through the root, stem and leaf.
Transport in plants: the pathway of water through a plant shown with a red dye in a celery stalk; stained xylem in transverse sections; the position of the xylem in a root, a stem and a leaf; water up the xylem by transpiration pull (evaporation, diffusion of water vapour through the stomata, cohesion); faster with leaves and in bright light · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Water pathway: dye in celery. A fresh celery stalk (a leaf stalk, with its leaflets at the top) is held in a clamp above a beaker of red food dye, 20 mm deep. Lower it into the dye, then press Wait 10 min and read the height of the dye in the stalk on the ruler beside it, whose zero is level with the dye surface: the red lines show through the pale stalk. Type each reading, and the graph plots your readings against time with a best-fit line; work out the rate (rate = height / time, in mm per min). Try the lamp on and off, and a stalk with its leaves cut off. Then take the stalk out, lay it on the white tile and drag the scalpel along it to cut thin sections across it: below the dye front only the xylem, on the inner side of each vascular bundle, is red, so water travels up the xylem. Follow the water from the soil to the air, one click per step: into a root hair by osmosis, across the root to the xylem in its centre, up the xylem of the stem, into the leaf veins, out into the mesophyll cells, where it evaporates and leaves through the stomata as water vapour (transpiration). Water molecules cling together (cohesion), so as water is lost from the leaves the whole column in the xylem is pulled up behind it: the transpiration pull. Simplified on purpose: the rates are illustrative (≈): real rates depend on the celery, the dye, the light, the warmth and the air, and real values differ; the dye front rises in 10 minute steps, each at the conditions during that step, with a small seeded wobble (up to 1 mm) so the same run gives the same readings if you do it again; the dye is taken to rise with the water, as fast as the water; in a real stalk some dye sticks to the xylem walls, so the dye front is a little behind the water; every vascular bundle carries dye to the same height; in a real stalk some bundles carry it higher than others; the cut sections are drawn as if seen with a hand lens, not to scale, and a few bundles stand for the many in a real stalk; the stalk is cut, so it has no roots: the root, stem and leaf sections in Follow the water are drawn from a whole plant; the bench apparatus is drawn to scale, and the close-up is not to scale.
- Lit: the scalpel, which cuts the sections
- Close-up: the dye front against a magnified ruler, the section you cut, and the water's path
- Dashed line: where the scalpel will cut
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