Cell Specialisation and Organization

• In multicellular organisms cells are specialised to perform specific functions. Each specialised cell will have developed more or fewer of certain organelles and specialised structures to suit the role it carries out. 
• • The first group of cells in an embryo are all initially identical.  
  • As it matures, each cell takes on its own individual characteristics that suit it to the function that it will perform when it is mature
  • It becomes specialized or differentiated.
  • It does this by switching genes on and off. 
• Cells can become specialised by:

  • Changing the shape of the cell, - may have an increased surface area  
  • Changing the number of a specific organelle e.g. a cell may have many mitochondria 
  • Changing the plasma membrane -may have more carrier proteins 
• Red blood cells (erythrocytes) have:

  • No organelles such as a nucleus to maximise the space for haemoglobin
  • A biconcave shape to allow for flexibility to fit through narrow capillaries
• Sperm cells have:

  • A tail (undulipodium/ flagellum) for locomotion
  • A head containing enzymes for the penetration of the female egg
  • A midpiece containing mitochondria- this allows for lots of energy/ ATP for movement
• Tissues

  A collection of cells that are similar to each other and perform a similar function, for example xylem tissue or nervous tissue.
• Organs

  A collection of tissues that work together to perform a particular function, eg heart, lungs, liver, intestine
• Organ systems

  Groups of organs working together e.g. respiratory system, circulatory system, excretory system, digestive system
• Squamous epithelium – flattened cells, very thin, line the inside of blood vessels and tubes to provide smooth surface for passage of fluids.

  The thin walls provide a short diffusion pathway e.g. alveoli for oxygen and carbon dioxide. 
• Ciliated epithelial tissue – made up of column shaped cells. Found on inner surface of the tubes e.g. trachea, bronchi and bronchioles, uterus and oviducts. Goblet cells produce and secrete mucus. Cilia can waft mucus when they move in a synchronised rhythm.  

  Nicotine can paralyse cilia and tar can damage them so they can’t sweep mucus out.