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GCSE Biology Revision

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GCSE Biology revision

Cell specialisation

Cell structure

AQA 4.1.1.1
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AQA student objectives

Learning pathway

All · Most · Some

ALL 🎯

Identify examples of specialised animal and plant cells and describe their functions.

MOST 🎯🎯

Explain how the structures of specialised cells are adapted to their particular functions.

SOME 🎯🎯🎯

Apply structure–function relationships to explain how an unfamiliar specialised cell is adapted to its role in a tissue, organ or organ system.

Revision summary

Key knowledge

Read on screen, then print for Cornell-style active revision.

What is Cell Specialisation?

  • Most animal cells are specialised, meaning they have specific adaptations that help them carry out a particular function.
  • The process by which cells become specialised is called differentiation.
  • Although all animal cells share a basic structure, their appearance and features vary depending on their role in the body.

Sperm Cell Adaptations

  • The function of a sperm cell is to travel to and fertilise an egg cell (ovum), combining genetic information from both.
  • Sperm cells contain only half the genetic information of a normal adult cell, stored in the nucleus.
  • A long tail and streamlined shape allow the sperm cell to swim efficiently towards the egg.
  • Sperm cells are packed with mitochondria to provide the energy needed for swimming.
  • Enzymes in the sperm cell's head allow it to digest through the outer layer of the egg during fertilisation.

Nerve Cell (Neurone) Adaptations

  • The function of a nerve cell (neurone) is to send electrical impulses around the body.
  • A long axon carries electrical impulses from one part of the body to another over large distances.
  • The axon is covered with a myelin sheath, which insulates it and speeds up the transmission of nerve impulses.
  • Synapses are junctions at the end of the axon that allow impulses to pass from one nerve cell to the next.
  • Dendrites extend from the cell body, increasing the surface area so that more connections with other nerve cells can be made.

Muscle Cell Adaptations

  • The key feature of muscle cells is their ability to contract, meaning they can get shorter.
  • Muscle cells contain protein fibres that can change length; when the cell contracts, these fibres shorten, decreasing the overall length of the cell.
  • Muscle cells are packed with mitochondria to provide the energy required for contraction.
  • Muscle cells work together to form muscle tissue, enabling coordinated movement in the body.

Key Vocabulary Recap

  • Differentiation is the process by which a cell becomes specialised for a particular function.
  • Fertilisation is the joining of a sperm cell and an egg cell, combining their genetic information.
  • The myelin sheath is a fatty layer surrounding the axon of a nerve cell that insulates it and speeds up impulse transmission.
  • Mitochondria are organelles found in both sperm and muscle cells that carry out respiration to release energy.

Cell Specialisation & Differentiation

  • Cells become specialised through a process called differentiation, where they develop specific adaptations to carry out a particular function.
  • Plant cells share key structures including chloroplasts, a cellulose cell wall, and a permanent vacuole.

Root Hair Cells – Structure

  • Root hair cells have a long root hair extension that greatly increases the surface area of the root.
  • The increased surface area allows the root to absorb water and dissolved minerals from the soil more effectively.
  • Root hair cells do not contain chloroplasts because they are underground and cannot access light for photosynthesis.

Xylem Cells – Structure & Function

  • Xylem cells are found in the plant stem and form long tubes that transport water and dissolved minerals from the roots to the leaves.
  • The cell walls of xylem are thickened with a chemical called lignin, which provides structural support to the plant.
  • Lignin seals the cell walls, causing the xylem cells to die, leaving hollow tubes with no nucleus, cytoplasm, vacuole, or chloroplasts.
  • The end walls between xylem cells break down completely, forming a continuous tube that allows water and minerals to flow freely.

Phloem Cells – Structure & Function

  • Phloem tubes transport dissolved sugars both up and down the plant, supplying all living cells with energy.
  • Phloem consists of two types of cells: phloem vessel cells (also called sieve tube elements) and companion cells.
  • Phloem vessel cells have no nucleus and only limited cytoplasm, and their end walls contain pores called sieve plates to allow sugars to move through.
  • Because phloem vessel cells have limited cytoplasm, they have few mitochondria and rely on neighbouring companion cells for energy.

Companion Cells – Supporting Phloem

  • Each phloem vessel cell is connected to a companion cell via pores in the cell wall.
  • The mitochondria in companion cells carry out respiration to provide the energy needed for the phloem vessel cell to function.

Comparing the Three Specialised Plant Cells

  • Root hair cells are specialised for absorption, xylem cells for transport of water and minerals, and phloem cells for transport of sugars.
  • All three cell types lack chloroplasts, reflecting that their functions do not involve photosynthesis.
  • Both xylem and phloem vessel cells lack a nucleus, whereas root hair cells retain a nucleus to control their metabolic activity.