Water travels up a plant in tubes called xylem: in at the root hairs, up the stem and out of the leaves as vapour, which pulls more up behind it. Put this 3D sunflower on the board and watch. It is cut open so the class can see inside: pale arrows carry water up the water tubes from the root hairs to every leaf, and gold beads carry sugar from the leaves up to the flower and down to the roots.
Water in the soil soaks into the root hairs, moves across the root into the water tubes and is carried up the stem. Water only ever goes up. Most of it escapes from the leaves as invisible water vapour through tiny holes underneath, pulling more water up behind it. More detail names it all: osmosis into the root hair cell, minerals by active transport, the xylem, transpiration, stomata and guard cells.
In sunlight the leaves use water and air to make sugar, the plant's food. The sugar travels in its own tubes, the phloem, up to the flower and down to the roots. More detail adds photosynthesis and translocation. Press Stem to see a slice across a real stem, with its ring of bundles: xylem on the inside, phloem on the outside.
In the celery experiment the dye climbs because coloured water is pulled up the plant's water tubes, the xylem, as water escapes from its leaves. After a few hours the leaf veins turn the colour of the dye, and so do the petals of a white flower such as a carnation. Slice the celery across and you find a row of coloured dots: the cut ends of the water tubes. Press Red dye and the board shows the same thing, with the water arrows and leaf veins turning red while the sugar stays as it was. Strictly, a stick of celery is a leaf stalk, not a stem.
Mostly pulled. As water evaporates from the leaves it pulls the thread of water in the xylem up behind it, a bit like drinking through a straw. The roots give a small push too, called root pressure, but most of the movement is the pull from the leaves. That loss of water vapour is transpiration, and the steady flow it causes is the transpiration stream. It is faster on a hot, dry or windy day, when water leaves the leaves more quickly.
No. A plant takes water and minerals from the soil, but it makes its own food, sugar, in its leaves, using sunlight, water and air. That sugar then has to reach the parts that cannot make their own, such as the roots and the flower, which is what the sugar tubes, the phloem, are for. Step 4 shows the leaves making it and step 6 shows it travelling.
Six steps follow the journey, each zooming in on its part. Press a name to look closer and read what that part does. Red dye runs the celery experiment: the water arrows and leaf veins turn red, while the sugar stays as it was. Quiz: press Labels once and every name hides behind a question mark. Draw on the board, and Print a pupil sheet to label or the board as it is.
The words are pitched at ages 7 to 16: Years 3 to 11 in England, 2nd to 10th grade in the United States, where it supports NGSS 4-LS1-1 (stems and roots are among the structures named). In England it fits Year 3 science, "investigate the way in which water is transported within plants", and AQA GCSE Biology 4.2.3.2, the plant organ system.
How does water travel up a plant?
Water in the soil soaks into the root hairs, moves across the root into the water tubes (xylem) and is carried up the stem to the leaves. Water only ever goes up. Most of it escapes from the leaves as invisible water vapour through tiny holes underneath, and that pulls more water up behind it.
What is the difference between xylem and phloem?
Xylem carries water and minerals up from the roots, only upwards. Its tubes are dead, hollow cells strengthened with lignin. Phloem carries dissolved sugar made in the leaves to wherever it is needed, up to the flower or down to the roots. Phloem is made of living cells.
What are transpiration and translocation?
Transpiration is the loss of water vapour from the leaves, mostly through stomata on the underside; guard cells open and close them. Translocation is the movement of dissolved sugar (sucrose) through the phloem.
What does the red dye switch show?
The celery experiment. Stand a stalk in water with food colouring and the colour climbs the water tubes into the leaves. On the board the water arrows and leaf veins turn red, and the sugar is unchanged.
What does the simulation show?
A young sunflower in 3D, cut open lengthways so one water tube and one sugar tube show side by side from every root tip, up the stem, into the leaves and up to the flower. Six steps follow the journey, and More detail adds the proper words. Pressing Stem shows a slice across a stem with its ring of bundles.
What has been simplified?
There is one water tube and one sugar tube, drawn much wider than real. A real stem has many bundles of xylem and phloem in a ring, which the stem slice shows. In a real root the water tubes sit in the middle.
What age is it for?
Ages 7 to 16: the plain steps suit primary science, and the More detail switch adds the words for KS3 and GCSE.
Is it free?
Free to try. Opening Science Simulations uses one token for the whole day, however many times you come back to it. Every account gets 20 free tokens, and Pro gives 50 a day.
Bodies move things through tubes too: the heart simulation follows blood round the body, and the digestive system simulation follows food. All twelve are on the Science Simulations page. For models the class can spin, try 3D Explorer.