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4.1.1Unit 4: Energy, Environment, Microbiology and Immunity

Plant Cell Structure — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 3 parts Lesson 8 of 28 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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Part 1 of 4Wall and Connections

4.1.1 Plant Cell Structure

The wall and the links between neighbouring plant cells give plants their support and communication routes.

Cell wall
  • Built of cellulose outside the cell membrane, it is rigid, freely permeable, and gives the cell its regular shape and support.
Middle lamella
  • The outermost layer, made mainly of pectin, which acts like glue to stick adjacent plant cells together.
Plasmodesmata
  • Narrow cytoplasmic threads lined by membrane that pass through walls and link neighbouring cells into one connected system, the symplast.
Pits
  • Thin regions of wall lacking secondary thickening, found in matching pairs,
    • which allow substances to pass sideways between cells such as xylem vessels.

Part 2 of 4Plant Organelles

Several organelles are characteristic of plant cells.

Plant Organelles
Chloroplast
  • A double-membrane organelle larger than a mitochondrion, with stacks of thylakoids called grana, and the site of photosynthesis.
Chloroplast contents
  • The stroma contains small circular DNA and ribosomes,
    • which are used to make proteins for chloroplast replication and photosynthesis.
Amyloplast
  • A small membrane-bound organelle packed with starch granules, abundant in storage organs such as potato tubers.
Vacuole and tonoplast
  • A large permanent sac of cell sap bounded by the selectively permeable tonoplast, which keeps the cell turgid.

Part 3 of 4Function Summary

Link each structure to the job it does.

1
Cellulose in the wall resists the pressure of water entering the cell, preventing bursting and keeping the plant upright.
2
Plasmodesmata allow transport of substances and cell-to-cell communication without the materials crossing a membrane twice.
3
Chlorophyll in thylakoid membranes captures light, while the stroma carries out the later stages of photosynthesis.
4
Amyloplasts store starch and release glucose when the plant needs it for respiration.
5
The vacuole keeps cells turgid and also stores pigments and waste, and can break down unwanted chemicals.

Part 4 of 4Exam Checklist & Tips

4.1.1 – Key Points for the Exam

  • Cell wall A rigid layer of cellulose outside the plasma membrane that supports a plant cell.
  • Middle lamella A pectin-rich layer cementing adjacent plant cells together.
  • Plasmodesmata Cytoplasmic channels linking the cytoplasm of neighbouring plant cells.
  • Tonoplast The membrane surrounding the permanent vacuole.
  • Amyloplast An organelle that stores starch in plant cells.

Common Mistakes

  • Saying the cell wall is the same as the cell membrane;
    • the wall is outside the membrane and is freely permeable.
  • Stating that plasmodesmata are gaps in the membrane without cytoplasm, when they are cytoplasmic threads lined by membrane.
  • Writing that only plant cells contain mitochondria; plant cells have both mitochondria and chloroplasts.
  • Forgetting that chloroplasts have a double membrane and an internal system of thylakoid membranes.

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Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.