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Cell Structure and Organisation: Question 2

Syllabus 2.1

Structured Core 5 marks

For a school open day, three students each build a large model of a different specialised cell: a ciliated cell from the lining of the trachea, a root hair cell from a young plant's root, and a palisade mesophyll cell from a leaf.

(a) State the main function of each of these three specialised cells.

(i) ciliated cell [1]

(ii) root hair cell [1]

(iii) palisade mesophyll cell [1]

(b) Describe how the shape of the root hair cell is related to its function. [2]

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Worked solution

Part (a): Functions of three specialised cells

(i) Ciliated cell

Ciliated cells line the trachea and bronchi. Tiny hair-like cilia on their surface beat together in a coordinated wave, sweeping a layer of mucus, along with dust particles and microorganisms trapped in it, up and out of the airways.

(ii) Root hair cell

Root hair cells are found near the tips of plant roots. Their function is to absorb water and mineral ions from the soil, which then move into the rest of the plant.

(iii) Palisade mesophyll cell

Palisade mesophyll cells are found near the upper surface of a leaf. Their function is to carry out photosynthesis, using light energy to make carbohydrates.

A root hair cell has a long, thin, finger-like extension of its cell surface membrane that grows out into the spaces between soil particles. This extension greatly increases the surface area of the cell that is in contact with the surrounding water and soil solution.

Because water and mineral ions move into the cell across its surface (by osmosis and diffusion/active transport), a larger surface area means more water and ions can be absorbed in the same amount of time than if the cell had a simple rounded shape.

Final answers

  • (a)(i) Ciliated cell: sweeps mucus, dust and microorganisms out of the trachea and bronchi.
  • (a)(ii) Root hair cell: absorbs water and mineral ions from the soil.
  • (a)(iii) Palisade mesophyll cell: carries out photosynthesis.
  • (b) The root hair cell’s long, thin extension gives it a large surface area, which increases the rate at which water and mineral ions can be absorbed.