Tissues, Organs and Systems

• In most organisms, cells are arranged into tissues
• A tissue is a group of cells with a similar structure and function, which all work together to carry out a role, e.g.

  • muscle tissue contracts and relaxes to produce movement
  • glandular tissue produces substances such as enzymes and hormones
  • epithelial tissue covers organs.
• Organs are groups of tissues, which all work together to perform a specific job
• Each organ may contain several tissues
• The stomach organ contains:

  • muscle tissue that contracts to churn the contents
  • glandular tissue to produce digestive juices and acid to sterilise food
  • epithelial tissue to cover the outside and inside of the stomach
• Organs are organised into organ systems, which are groups of organs working together to do a particular job
• The digestive system is an example of an organ system, in which several organs work together to digest and absorb food
• All the organ systems work together to make an organism
• Single-celled organisms do not have tissues. Some simple animals do not have organs, only tissues