Plant plans, xylem, phloem and translocation
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Two pipes in every plant
- Plan diagrams
Read the transcript of the teaching part
Last time
Before we start: last time, in Transcription, RNA processing and translation, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Two pipes in every plant
A tall tree must lift water a hundred metres from root to leaf, and also send sugar from the leaves down to the roots. It does both with two sets of pipes. Xylem carries water up. Phloem carries sugars to wherever they are needed. Knowing where they sit, and how each is built, is the start of everything in plant transport.
Plan diagrams
A plan diagram shows the arrangement of tissues, not individual cells. Draw clear outlines, no shading, and no single cell drawn in detail. In a dicotyledonous stem, the vascular bundles form a ring near the outside. In each bundle, phloem lies towards the outside, and xylem towards the centre, with cambium between. In a root, the xylem forms a star shape in the very centre, with phloem between the arms. The central core is surrounded by the endodermis. In a leaf, the midrib holds the vascular bundle, with xylem on the upper side and phloem below. Palisade mesophyll lies near the upper surface.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Structure of xylem and phloem · Translocation: loading sucrose and mass flow.
The whole chapter: Transport in Plants, Transport in Plants.
Chapter 7: Transport in plants
- Plant plans, xylem, phloem and translocation 6 min
- Transpiration, root pathways and xerophytes 6 min
Also for A Level Biology 9700
Which topics come up most in A Level Biology 9700 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency, Paper 4 topic frequency.