These questions ask you to identify a plant transport tissue from its cargo, direction, structure or job. The most reliable method is to trace where the material entered or was made and where it needs to go.
Trace the journey
Begin with the cargo. Roots take up soil moisture containing dissolved ions. This liquid root load enters xylem and moves towards stems and leaves. Leaves make sugars, which dissolve before entering phloem. Phloem then distributes them to parts that use or store them. This origin test separates the tissues even when a question does not name either one.
| Signal | Transport decision |
|---|---|
| Soil moisture or mineral ions absorbed by roots | Choose xylem and trace a one-way journey upwards. |
| Dissolved sugar moving from a producing or releasing part | Choose phloem and trace the journey from source to sink. |
| Dead, empty tubes with strengthened walls | Identify xylem; lignin prevents collapse and adds support. |
| Living sieve tubes working with companion cells | Identify phloem. |
| A leaf vein | Expect both tissues together in a vascular bundle, providing an inward route and an outward route. |
For phloem direction, do not memorise a fixed arrow. Label the source as the place currently releasing sugar and the sink as the place currently using or storing it. A sink can lie above or below a source, so separate phloem flows can run in either direction. For the xylem stream, evaporation from leaves maintains an upward liquid column. The movement of sugar through phloem has the different name translocation.
Avoid these transport mix-ups
| Tempting route | How to reject it |
|---|---|
| Putting sugar or ready-made food into xylem | Ask what roots actually absorb. They supply soil moisture carrying dissolved ions, while sugars are made within the plant and use phloem. |
| Giving xylem an up-and-down flow | The xylem load enters at the roots and travels towards the leaves. The two-direction rule belongs to source-to-sink transport in phloem. |
| Sending every phloem flow downwards | Locate the source and sink instead. A growing region above a leaf can receive sugar just as a storage organ below it can. |
| Describing phloem as dead, empty piping | That structure suits an unobstructed liquid column. Sugar transport uses living sieve tube cells and companion cells. |
| Choosing a term because it begins with trans | Connect the ending to the process: translocation relocates sugar, whereas transpiration is vapour loss that drives a xylem stream. |
Try it
In translocation, sugar travels from a source to a sink. In a leafy plant in midsummer, which movement fits that description?
- From a photosynthesising leaf to a growing root tip
- From a root upwards to a leaf that is making sugar
- Between two leaves of exactly the same age and size
- From the soil into a root hair and on up to the shoot
A plant takes up nitrate ions at its roots and they arrive in a leaf at the top of the stem. Which statements about that journey are true? Select all that apply.
- Carrying these ions means that xylem is carrying the plant's food
- The ions are dissolved in the water that is moving upwards
- The ions travel as dry particles blown along inside the tubes
- The ions travel in the xylem
- The ions are handed across to the phloem at the base of the stem