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2.2Structures and Functions in Living Organisms

Cell Structure — Edexcel Linear - OL Revision Notes & Topical Questions

10 min read 12 parts Lesson 17 of 25 1 quiz

📚 Edexcel Linear - OL Hub / Topical Revision
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Lesson summary

Cell Structure, Plant and Animal Cells and Specialised Cells — EDEXCEL LINEAR - OL notes: Describe the functions of cell structures, compare plant and animal cells, and explain how cells differentiate and are adapted to their functions.Cells are surrounded by a cell membrane, whi…

  • organelles
  • Cell differentiation
  • Worked example 1
  • Worked example 2
  • Worked example 3
  • Worked example 4

Part 1 of 5Structures in cells and their functions

Cells are surrounded by a cell membrane, which separates them from the external environment.

Structures in cells and their functions
Inside it is the cytoplasm, a jelly-like substance of water with dissolved substances.
Organelles
Eukaryotic cells have organelles within the cytoplasm.
Some structures, like ribosomes and mitochondria, are too small to be seen with a light microscope but can be seen with an electron microscope.
Mitochondrion refers to one organelle and mitochondria to more than one (muscle cells contain many mitochondria).
StructureFunction
NucleusContains genetic material (chromosomes)
CytoplasmSite of many chemical reactions; contains water and solutes
Cell membraneControls substances entering and leaving the cell
Cell wall (plants)Cellulose; gives extra support and shape, prevents bursting
MitochondriaSite of aerobic respiration
ChloroplastsSite of photosynthesis; contain chlorophyll
RibosomesSite of protein synthesis
Permanent vacuoleContains cell sap; supports plant cells keeping them firm (turgid)

Part 2 of 5Animal and plant cells compared

StructureAnimal cellPlant cell
Nucleus, cytoplasm, cell membraneYesYes
Mitochondria, ribosomesYesYes
Cell wallNoYes (cellulose)
ChloroplastsNoYes (in leaves and stems)
VacuoleSmall and temporaryLarge and permanent

A plant cell showing chloroplasts would be found in the leaves of a plant.

Part 3 of 5Cell differentiation and specialised cells

Cell differentiation is the process by which a cell changes to become specialised, developing the structure and subcellular structures it needs for its function.

1
Genes in the nucleus control this.
2
For example, to form a nerve cell the cytoplasm and cell membrane elongate to form connections over long distances.
3
As an organism develops, cells differentiate into different types.
4
Most animal cells differentiate early; adult stem cells keep the ability to replace and repair cells like blood and skin cells.
5
In plants, many cells retain the ability to differentiate throughout life.
Specialised cellAdaptationFunction
Ciliated cellHair-like cilia that beatMove mucus and trapped particles in the trachea and bronchi towards the throat
Nerve cellLong, with extensionsConduct impulses over long distances
Red blood cellBiconcave shape, no nucleus, packed with haemoglobinTransport oxygen efficiently
Root hair cellLong extension, thin wallAbsorb water and minerals with a large surface area
Palisade mesophyll cellColumn-shaped, many chloroplasts, packed beneath the upper epidermisPhotosynthesis

Part 4 of 5Using the microscope and reading cell diagrams

A light microscope shows the nucleus, cytoplasm, cell membrane, cell wall, chloroplasts and the vacuole, but not ribosomes or the detailed structure of mitochondria, which need an electron microscope with much higher magnification and resolution.

Using the microscope and reading cell diagrams
When you draw a cell, use a sharp pencil, draw clear continuous lines, label with ruled lines and do not shade.
Magnification = size of the image ÷ size of the real object; for example, an image of 40 mm for a cell of 0.02 mm gives a magnification of ×2000.
  • Cell size in plants is usually larger than in animal cells, and the regular shape of plant cells is due to the cell wall.

When comparing cells, always give a similarity before a difference, for example: both animal and plant cells have a nucleus, but only plant cells have a cell wall. Always link an adaptation to its function, such as many mitochondria in a sperm tail for energy.

Part 5 of 5Worked examples

  1. State the function of the mitochondria. [1]1 mark

  2. Give three structures found in plant cells but not in animal cells. [3]3 marks

  3. Explain how a red blood cell is adapted to carry oxygen. [3]3 marks

  4. Define differentiation. [1]1 mark

  5. Explain why palisade cells contain many chloroplasts. [2]2 marks

Key terms

TermMeaning
OrganelleA structure inside a cell with a specific function.
MitochondrionOrganelle where aerobic respiration takes place.
ChloroplastOrganelle where photosynthesis takes place.
DifferentiationThe process of a cell becoming specialised.
Specialised cellA cell with adaptations for a particular function.
TurgidFirm because the vacuole is full of water.

Avoid these mistakes

1
Saying mitochondria produce energy — they release energy from respiration.
2
Saying plant cells have no mitochondria.
3
Saying all plant cells contain chloroplasts — root cells do not.
4
Confusing the cell wall (support) with the cell membrane (controls what passes).

Last updated:

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.