Principles of organisation

• Cells are the basic building blocks of all living organisms
• A tissue is a group of cells with a similar structure and function
• Organs are aggregations of tissues performing specific functions
• Organs are organised into organ systems, which work together to form organisms
• 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 different tissues, which all work together to perform a specific job
• Each organ may contain several tissues. For example, the stomach is an organ that contains:

  • muscle tissue that contracts to churn the contents
  • glandular tissue to produce digestive juices and acid to sterilise food
  • epithelial tissue 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
• Muscle tissue - can contract to bring about movement
• Glandular tissue - can produce substances such as enzymes e.g. amylase and hormones, e.g. insulin
• Epithelial tissue - covers all organs in the body, e.g. the skin