Biology

• Cell specialisation

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


  • Have a myelin sheath which is a fatty material that insulates the impulses and allows them to travel faster
• Sperm cells


  • Have a tail for swimming and a middle piece with mitochondria which release energy for movement
• Red blood cells

  • Contain haemoglobin to carry oxygen, have a biconcave disc shape to increase surface area for the movement of oxygen, have no nucleus or other organelles so there is more room to carry oxygen
• Specialised plant cells


  • Leaf palisade cells
  • Guard cells
  • Root hair cells
  • Xylem cells
  • Phloem cells
• Guard cells


  • Have a special shape which results in a pore between cells, the pore is called a stoma and it opens and closes to allow gas exchange between the leaf and its surroundings
• Root hair cells


  • Have a large surface area which allows for the efficient absorption of water and mineral ions
• Xylem cells


  • Gain a thick cell wall as they develop, lose their cell contents to make it easy to transport water from roots to leaves
• Tissues


  Groups of similar cells that work together to perform a specific function
• Tissues


  • Muscle tissue
  • Nerve tissue
  • Palisade tissue
• Organs


  Groups of different types of tissue that perform one or more functions
• Organs in humans


  • Intestines
  • Brain
  • Lung
  • Stomach
• Organs in plants

  • Stem
  • Leaf
• Organ systems


  Groups of organs that work together
• Levels of organisation

  • Cells
  • Tissues
  • Organs
  • Organ Systems
  • Organism
• Plantae


  Kingdom of multicellular, autotrophic organisms (make own food) such as plants and algae
• Animals

  Kingdom of multicellular, heterotrophic organisms (consume other organisms for food) such as animals
• Prokaryotes

  unicellular organisms which have their dna in the free cytoplasm of the cell