A flowering plant has two separate transport tissues. Xylem carries water and mineral ions up from the roots and helps hold the plant up; phloem carries sucrose and amino acids to wherever they are needed. Knowing where each tissue sits in a root, stem and leaf lets you read any section diagram. How xylem vessels are built for their job is Extended content.
Xylem transports water and mineral ions and gives the plant support. Phloem transports sucrose and amino acids. In a root the xylem forms a star in the centre with phloem between its arms; in a stem the xylem and phloem are grouped in vascular bundles arranged in a ring, xylem towards the centre; in a leaf they run in the veins, xylem on the upper side. Extended: xylem vessels have thick walls with lignin, no cell contents and no cross walls, forming long continuous tubes.
Pick a section in the sim and rotate it. Each section is a thin slice of the organ, so you can see the blue xylem and the orange phloem running through it as tubes. Compare the pattern in the root, the stem and the leaf.
| Tissue | Transports | Other job |
|---|---|---|
| Xylem | water and mineral ions, from the roots upwards | support: its strong walls help hold the plant up |
| Phloem | sucrose and amino acids, up or down the plant | none needed at IGCSE |
Do not mix up the cargoes. Xylem never carries sucrose and phloem never carries the plant's water supply up from the roots. A quick memory aid: phloem carries food (sucrose and amino acids).
Extended. Choose inside a xylem vessel in the sim. A xylem vessel is made from a column of cells that have died, lost their contents and their end walls, leaving a hollow pipe. Each feature links to a function.
| Feature of a xylem vessel | How it helps |
|---|---|
| thick walls containing lignin | strong and waterproof, so the vessel does not collapse as water is pulled up, and it supports the plant |
| no cell contents (no cytoplasm, no nucleus) | nothing blocks the flow of water and mineral ions |
| cells joined end to end with no cross walls | forms a long continuous tube from root to leaf, so water flows without interruption |
Lignin makes xylem strong; it does not make it "living" or help it carry sugar. A xylem vessel is dead and empty: that is exactly what makes it a good pipe.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the root section of the sim, where is the xylem?
In the stem section of the sim, how are the xylem and phloem arranged?
In the leaf section, which tissue is on the upper side of the midrib?
Extended: the sim's view inside a xylem vessel shows rings in the wall and no end walls. What do the thickened walls contain?
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Which row shows the substances transported in xylem and in phloem?
A transverse section of a young stem shows tissue A towards the centre and tissue B towards the outside in each vascular bundle. Which is correct?
Extended: why do xylem vessels have no cross walls between the cells?
Extended: which feature of xylem vessels helps to support the plant?
This skill is now recorded on your profile. Keep the chain going.