Structure of transport tissues
Cambridge A-Level Biology (9700) · Unit 7: Transport in plants · 8 flashcards
Structure of transport tissues is topic 7.1 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 7 — Transport in plants , alongside Transport mechanisms.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 8 flashcards — 8 key concepts — covering the precise wording mark schemes reward.
What the Cambridge 9700 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Draw plan diagrams, from photomicrographs and microscope slides, of transverse sections through the leaves, roots and stems of herbaceous dicotyledonous plants.
- Describe where xylem and phloem are located in transverse sections of the stem, root and leaf of herbaceous dicotyledonous plants.
- Draw and label xylem vessel elements, companion cells and phloem sieve tube elements as seen on microscope slides, in photomicrographs and in electron micrographs.
- Relate structure to function for companion cells, xylem vessel elements and phloem sieve tube elements.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Structure of transport tissues
- › Remember that while sieve tube elements lose their nucleus and most organelles, they must retain a thin layer of cytoplasm.
Draw a plan diagram of a transverse section of a herbaceous dicotyledonous stem, labeling the epidermis, cortex, vascular bundles (including xylem and phloem) and pith.
Diagram should show a circular arrangement with the epidermis as the outermost layer, cortex filling the space between the epidermis and vascular bundles, vascular bundles arranged in a ring, and pith in the center. Xylem should be located towards the inside of the vascular bundle, and phloem towards the outside.
Describe the distribution of xylem and phloem in a transverse section of a herbaceous dicotyledonous root.
Xylem forms a central core (often a star shape) in the root. Phloem is located in discrete groups between the arms of the xylem core, often alternating with the xylem.
Describe the distribution of xylem and phloem in a transverse section of a herbaceous dicotyledonous leaf.
Xylem and phloem are located together in vascular bundles within the leaf veins. Xylem is usually positioned towards the upper surface of the leaf, and phloem towards the lower surface.
Draw and label a xylem vessel element.
Diagram should show elongated, hollow cells with thickened walls containing lignin. Pits (small unlignified areas) should be visible in the walls. End walls are absent or heavily modified (perforated).
How does the structure of xylem vessel elements relate to their function?
Lignified walls provide strength and prevent collapse under tension. The hollow lumen and absence of cell contents allow for efficient water transport. Pits allow lateral water movement between vessels. Perforations or absent end walls allow unimpeded vertical flow.
Draw and label a phloem sieve tube element and companion cell.
Sieve tube element should be elongated with sieve plates at the ends. Companion cell should be smaller and adjacent to the sieve tube element, containing a nucleus and dense cytoplasm. Plasmodesmata should be visible connecting the two cells.
How does the structure of phloem sieve tube elements relate to their function?
Sieve plates allow for the flow of assimilates (sugars) between cells. The lack of a nucleus and other organelles maximizes space for translocation. They rely on companion cells for metabolic support.
What is the function of companion cells in the phloem?
Companion cells provide metabolic support to sieve tube elements. They have a nucleus and many mitochondria to carry out active transport of sugars into and out of the sieve tube elements, maintaining the concentration gradient for translocation.
Review the material
Read full revision notes on Structure of transport tissues — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 7 — Transport in plants
Structure of transport tissues sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
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