# Transport in Plants

> CIE A-Level Biology · CIE A-Level Biology 9700
> Source: https://www.owlsprep.com/study/cie-9700-u7-overview/
> Weight: n/a

This unit explores how vascular plants transport water, minerals, and organic solutes between roots, stems, and leaves, a core physiological process supporting growth, photosynthesis, and survival across diverse habitats.

**Prerequisites:** [Understanding of cell membrane structure and water potential](https://www.owlsprep.com/study/cie-9700-u4-cell-membranes-and-permeability/); [Basic plant tissue organisation](https://www.owlsprep.com/study/cie-9700-u3-cell-structure-and-organisation/)

## Learning objectives

- Identify the structure and function of specialised plant transport tissues
- Explain the mechanisms of water, mineral and organic solute movement through vascular plants
- Evaluate how environmental factors affect transpiration and how plants adapt to water-limited environments

## Unit at a Glance

This unit follows a logical, building sequence: we start with the specialised tissues that enable long-distance transport, then explore how water enters and moves through the plant from soil to leaves. Next, we examine the process of transpiration and the factors that affect it, then cover how organic sugars are moved around the plant via translocation, and end with how plants adapted to dry environments minimise water loss.

Every concept in this unit builds on the previous one: understanding the structure of xylem and phloem is required to explain how movement works, which in turn helps you interpret why xerophyte adaptations are so effective.

Sub-topics in this unit, ordered by learning sequence:
- [Plant transport tissues](https://www.owlsprep.com/study/cie-9700-u7-plant-transport-tissues/) — Covers the structure and function of xylem and phloem in plant vascular bundles.
- [Water uptake and movement](https://www.owlsprep.com/study/cie-9700-u7-water-uptake-and-movement/) — Explores water and mineral uptake by root hairs and the apoplast/symplast pathways.
- [Transpiration](https://www.owlsprep.com/study/cie-9700-u7-transpiration/) — Explains the cohesion-tension theory and environmental factors that affect transpiration rate.
- [Translocation](https://www.owlsprep.com/study/cie-9700-u7-translocation/) — Covers the mass flow hypothesis for transport of organic solutes in phloem tissue.
- [Xerophyte adaptations](https://www.owlsprep.com/study/cie-9700-u7-xerophyte-adaptations/) — Examines structural and functional adaptations that reduce water loss in dry environments.

## Common pitfalls

- **Wrong:** Confusing the structure and function of xylem and phloem
  - Why it fails: These tissues are frequently tested, and their features are easy to mix up
  - Correct: Remember: xylem = water/minerals upwards, dead lignified hollow cells; phloem = solutes bidirectionally, living sieve tube elements
- **Wrong:** Mixing up apoplast and symplast pathways for water movement
  - Why it fails: Students often confuse which pathway moves through which part of the plant tissue
  - Correct: Apoplast = through cell walls (A = outside cytoplasm); Symplast = through connected cytoplasm (sym = shared inside)
- **Wrong:** Thinking translocation only moves sugars from leaves to roots
  - Why it fails: Direction of movement depends on where sugars are needed at different growth stages
  - Correct: Translocation always moves from source (where sugars are produced/stored) to sink (where sugars are used/stored), so direction can vary

## Cheatsheet

| Concept | Key Summary |
| --- | --- |
| Water movement rule | Water moves from higher (less negative) $\Psi$ to lower (more negative) $\Psi$ |
| Xylem function | Transports water and minerals from roots to shoots, made of dead lignified cells |
| Cohesion-tension theory | Transpiration pull relies on cohesion of water molecules and tension in the xylem column |
| Translocation source/sink | Source = site of sucrose production/storage; Sink = site of sucrose use/storage |
| Xerophyte core adaptation | All adaptations work to reduce transpiration rate by limiting water loss to dry air |

## What's next

Begin this unit with the first sub-topic to master the structure of plant transport tissues, which underpins all other concepts in transport. Once you complete all sub-topics in this unit, you can move on to the next unit covering transport in mammals.

- [Plant transport tissues](https://www.owlsprep.com/study/cie-9700-u7-plant-transport-tissues/)
- [Water uptake and movement](https://www.owlsprep.com/study/cie-9700-u7-water-uptake-and-movement/)
- [Transpiration](https://www.owlsprep.com/study/cie-9700-u7-transpiration/)

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From [OwlsPrep](https://www.owlsprep.com) — free study guides for A-Level, IB, AP and IGCSE, written against the official syllabus. Canonical page: https://www.owlsprep.com/study/cie-9700-u7-overview/