Plant Structure & Function

Revise Plant Structure & Function for Biology 2 (IAL) WBI12 (AS Level) — revision notes and instant AI marking.

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Edexcel International A Level (IAL) Biology

Plant Structure & Function

🌱 The Big Idea: Plant cells are built like tiny engineered factories — every extra structure a plant cell has (that an animal cell doesn't) exists to solve one of two problems: how do I stay strong without a skeleton? and how do I move water, sugar, and minerals over long distances without a heart?

What's inside

Summary — every concept at a glance
1. Plant Cell Structure & Ultrastructure
2. Recognising Plant Cells in Electron Micrographs
3. Starch & Cellulose — Structure & Function
4. Properties of Cellulose & Plant Fibres
5. The Vascular Structure of Plants
6. Core Practical 7 — Identifying Tissue Types in Stems
What to Memorise
Concepts Checklist
Exam Tips & Common Mistakes

📋 Summary — The Whole Chapter in One Scan

Plant cells have a cell wall (cellulose, freely permeable, gives shape/support) and a middle lamella (pectin "glue" between cells).
Plasmodesmata are cytoplasmic threads connecting neighbouring cells — together they form the symplast.
Pits are thin, un-thickened regions of the cell wall (line up in pairs) that allow lateral transport — crucial in xylem.
Chloroplasts: double membrane, thylakoids stacked into grana, joined by lamellae, contain their own DNA and ribosomes — site of photosynthesis.
Amyloplasts store starch granules (abundant in storage organs like potato tubers).
Vacuole + tonoplast: stores cell sap, keeps cells turgid, isolates waste, tonoplast controls what enters/leaves.
In electron micrographs: chloroplasts, vacuoles, and cell walls are the giveaway signs you're looking at a plant cell, not an animal cell.
Starch = plant storage polysaccharide, made of amylose (unbranched helix) + amylopectin (branched) — compact and insoluble, so no osmotic effect.
Cellulose = long chains of β-glucose, alternate molecules rotated 180°, forming straight chains held together by hydrogen bonds → huge tensile strength → cell wall support.
Plant fibres (sclerenchyma, xylem) are strong because of mesh-like microfibril arrangement + secondary thickening with lignin.
Xylem: dead, hollow, lignified tubes — transport water & minerals up the plant, provide support (one-way flow).
Phloem: living tissue (sieve tube elements + companion cells) — transports organic compounds (translocation), can go up or down.
Arrangement of vascular bundles differs between root (centre), stem (ring near edge, xylem inside phloem), and leaf.
Core Practical 7 involves sectioning a stem, staining with TBO, and drawing tissue plan diagrams following strict drawing conventions.

1. Plant Cell Structure & Ultrastructure

Plant cells share a lot with animal cells (nucleus, mitochondria, ER, ribosomes, Golgi...) but they have a handful of extra structures that animal cells simply don't need. Here's the trick to remembering them: don't memorise them as a random list — group them by the problem they solve.

Structural support
(no skeleton!)

Cell-to-cell
communication

Making & storing
food

Water balance &
waste storage