Specialisation of Eukaryotic Cells (AQA A Level Biology): Revision Note

Adaptations of eukaryotic cells

• In multicellular organisms, eukaryotic cells become specialised to perform specific functions

• Their structure is adapted to their role, which explains why different cell types can look very different

• Structural adaptations may include:

  • Cell shape

  • Presence or absence of specific organelles

  Examples:

  • Red blood cells are biconcave and lack a nucleus, creating more space for oxygen transport

  • Protein-producing cells contain many ribosomes to support high levels of protein synthesis

• Other examples include:

Neurones (nerve cells)

• Function: Conduction of nerve impulses

• Adaptations:

  • Cell body contains most organelles and is the site of protein synthesis

  • Dendrites receive signals; axons transmit them to other cells

  • Long axon (up to 1m) enables fast, long-distance transmission

  • Myelin sheath insulates axon and increases speed of impulse conduction

Muscle cells

• Function: Contraction for movement

• Adaptations:

  • Three types in animals: skeletal, smooth, and cardiac

  • Protein filaments (actin and myosin) slide over each other to cause contraction

  • High density of mitochondria for ATP production via respiration

  • Skeletal muscle cells fuse during development to form multinucleated fibres

Sperm cells

• Function: Fertilisation of the egg and delivery of the father's DNA

• Adaptations:

  • Head contains haploid nucleus with genetic material

  • Acrosome contains digestive enzymes to penetrate the egg

  • Mid-piece packed with mitochondria to provide energy for movement

  • Tail rotates to propel the sperm towards the egg

Root hair cells

• Function: Absorption of water and mineral ions from the soil

• Adaptations:

  • Root hair increases surface area to maximise absorption

  • Thin cell wall reduces diffusion distance

  • Vacuole contains concentrated cell sap to maintain a water potential gradient

  • Mitochondria provide ATP for active transport of mineral ions

  • No chloroplasts as they are found underground and not exposed to light

Xylem vessel cells

• Function: Transport of water and dissolved mineral ions

• Adaptations:

  • No end walls between cells forming a continuous tube

  • Cells are dead and lack organelles for unimpeded water flow

  • Walls thickened with lignin for strength and structural support

Phloem vessel cells

• Function: Transport of sugars and amino acids (translocation)

• Adaptations:

  • Living cells joined end-to-end with sieve plates for solute flow

  • Few subcellular structures to aid transport

  • Companion cells provide ATP and regulate transport processes