This definitions covers Key Definitions within Plant Transport Systems for GCSE Biology. Xylem and phloem structure, water and sugar transport, root hair adaptations, translocation, and practical investigations It is section 10 of 17 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Topic position
Section 10 of 17
Practice
19 questions
Recall
24 flashcards
Key Definitions
Xylem: A plant tissue made of dead, hollow, lignified cells that transports water and dissolved mineral salts from the roots upwards to the leaves. Flow is one-directional (upward only).
Phloem: A plant tissue made of living cells (sieve tube elements and companion cells) that transports dissolved sugars and amino acids from leaves (sources) to all other parts of the plant (sinks). Flow can be in both directions.
Translocation: The movement of dissolved organic substances (mainly sucrose) through phloem from a source (e.g. leaf) to a sink (e.g. root or growing tip).
Transpiration: The evaporation of water from the surfaces of plant cells, followed by diffusion of water vapour out through the stomata.
Lignin: A tough, waterproof polymer deposited in xylem cell walls. It strengthens the vessel and prevents it collapsing under the negative pressure created by transpiration.
Sieve tube element: A living phloem cell with a perforated end wall (sieve plate) allowing dissolved substances to flow through. Lacks a nucleus in maturity.
Companion cell: A nucleated cell adjacent to a sieve tube element. It provides ATP for the active loading and unloading of sugars into the phloem.
Root hair cell: A specialised epidermal cell with a long projection that greatly increases the surface area of the root for absorption of water (by osmosis) and mineral ions (by active transport).