Unit Overview
Transport in Plants
CIE A-Level BiologyΒ· 5 min read π n/a
1. 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
Covers the structure and function of xylem and phloem in plant vascular bundles.
β β β± 6 min
Water uptake and movement
Explores water and mineral uptake by root hairs and the apoplast/symplast pathways.
β β β β± 7 min
Transpiration
Explains the cohesion-tension theory and environmental factors that affect transpiration rate.
β β β β± 8 min
Translocation
Covers the mass flow hypothesis for transport of organic solutes in phloem tissue.
β β β β β± 7 min
Xerophyte adaptations
Examines structural and functional adaptations that reduce water loss in dry environments.
β β β± 5 min
2. Common Pitfalls
Wrong move:
Confusing the structure and function of xylem and phloem
Why:
These tissues are frequently tested, and their features are easy to mix up
Correct move:
Remember: xylem = water/minerals upwards, dead lignified hollow cells; phloem = solutes bidirectionally, living sieve tube elements
Wrong move:
Mixing up apoplast and symplast pathways for water movement
Why:
Students often confuse which pathway moves through which part of the plant tissue
Correct move:
Apoplast = through cell walls (A = outside cytoplasm); Symplast = through connected cytoplasm (sym = shared inside)
Wrong move:
Thinking translocation only moves sugars from leaves to roots
Why:
Direction of movement depends on where sugars are needed at different growth stages
Correct move:
Translocation always moves from source (where sugars are produced/stored) to sink (where sugars are used/stored), so direction can vary
3. Quick Reference Cheatsheet
Concept | Key Summary |
|---|---|
Water movement rule | Water moves from higher (less negative) to lower (more negative) |
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.