(h) how cells of multicellular organisms are specialised for particular…

The idea

Multicellular organisms build many cell types from one fertilised egg. Specialisation means a cell becomes adapted, in shape, organelle content and membrane features, to carry out one function efficiently. Differentiation is the process producing these adaptations, usually through selective gene expression rather than loss of genes. Learn to link structure to function: a red blood cell loses its nucleus and packs haemoglobin for oxygen transport; a sperm cell keeps many mitochondria and a flagellum for motility; a root hair cell extends a long projection to increase surface area for water and mineral uptake; a palisade mesophyll cell holds many chloroplasts near the leaf surface for photosynthesis; a neurone is elongated with many ion channels for conduction.

What earns the marks

• Specialisation is an adaptation of cell structure, including shape, organelle number and membrane features, that suits a particular function.
• Differentiation is the process by which unspecialised cells develop these adaptations, typically through selective gene expression.
• Red blood cells lose their nucleus and are packed with haemoglobin, increasing capacity for oxygen transport.
• Sperm cells retain many mitochondria and a flagellum, supporting the energy supply and movement needed for fertilisation.
• Root hair cells have an elongated projection that increases surface area for absorption of water and mineral ions.
• Palisade mesophyll cells contain many chloroplasts positioned to absorb light for photosynthesis.
• A correct option must link the named structural feature directly to the function stated in the question stem.

Common mistakes and how to put them right

• Assuming specialised cells lose genes they no longer use.

  Put it right: They generally retain the full genome and express different genes selectively.

• Choosing an option that names a real adaptation but does not serve the function asked about.

  Put it right: Check the feature against the specific function in the stem.

• Treating all cells in an organism as identical.

  Put it right: Recognise that differentiation produces many distinct cell types with different structures.

Exam tips

• Read the stem to identify the exact cell and function before looking at the options.
• Eliminate options where the structural feature cannot plausibly support the stated function.
• For each remaining option, state the structure-to-function link in one sentence to confirm it holds.