Organisation in multicellular organisms

• In complex multicellular organisms...

  eukaryotic cells become specialised for specific functions.

  ~Specialised cells are grouped into tissues, organs and organ systems.
• Tissue:

  Group of specialised cells with a similar structure working together to perform a specific function, often with the same origin.
• Eg: Epithelial tissues

  -Found in animals and consist of sheets of cells.

  -They line the surface of organs and have a protective or secretory function.

  -Thin flat cells that line organs where diffusion takes place, eg: alveoli of lungs and ciliated epithelium that lines a duct such as trachea.
• Organ:

  Aggregation of tissues performing specific functions.
• Eg: Stomach:

  Tissues it consists of include:

  -Muscle to churn and mix stomach contents

  -Epithelium to protect the stomach wall and produce secretions

  -Connective tissue to hold together the other tissues
• Organ system:

  Group of organs working together to perform specific functions.