Atypical Structures

Certain types of eukaryotic cells and tissues do not conform to the standard organisation of a typical cell

• These cells have developed unique characteristics in order to better to support their specific cellular activities

Striated Muscle Fibres:

• Individual muscle cells fuse together to form long striated muscle fibres

• These fibres are surrounded by a continuous plasma membrane and possess multiple nuclei
  

• Striated muscle fibres challenge the idea that all living things are comprised of discrete cell units

Aseptate Fungal Hyphae:

• Fungi may have filamentous structures called hyphae, which are used for nutrient absorption and growth

• Hyphal cells are typically separated by internal walls (septa), but some hyphae are not partitioned and have a continuous cytoplasm (with multiple nuclei)
  

• Aseptate fungal hyphae challenge the idea that living structures are composed of autonomous cells

Sieve Tube Elements:

• Sieve elements that line the phloem in plants are interconnected by plasmodesmata into supracellular assemblies that transverse the length of a plant

• These sieve elements also lack nuclei and have few organelles, relying on local companion cells for survival
  

• Phloem sieve tube elements challenge the idea that multicellular structures are composed of anatomically independent cells

Red Blood Cells:

• Red blood cells have no nucleus or mitochondria when they are mature (the organelles are ejected to allow more haemoglobin to be stored)

• Without any genetic material, red blood cells cannot independently replicate and new cells must be continually produced within the bone marrow
  

• Red blood cells challenge the traditional definition of a eukaryotic cell as they lack critical structures needed for autonomous survival

Atypical Cell Structures