Levels of Organization in Living Things

• ​Unicellular organisms are a system of only one cell.

• ​Multicellular organisms are a made up of multiple subsystems that work together.

• ​All living things are made up of cells.

• ​The cells of unicellular organisms can do all of the things needed for survival because they have organelles that perform different jobs.

• ​Multicellular organisms have many different types of cells that perform different roles in the body.

• ​Specialized cells are grouped together to form tissues.

• ​A TISSUE is a group of similar cells that are organized to perform a specific function.

• ​For example, a plant's vascular tissue is made up of cells that are small and hollow. They connect to each other to form tubes that carry water and nutrients throughout a plant. You can see these tissues as the "strings" in celery. .

• ​Different types of tissues work together to form an ORGAN.

• ​For example, the stem of a plant is made up of vascular tissue that transports nutrients and water, ground tissue that provides support, and epidermal tissue that protects the outside of the stem.

• ​In animals, blood vessels are considered organs because they're made of more than one type of tissue.

  • ​Epithelial tissue helps control the passage of blood cells.

  • ​Smooth muscle tissue helps control the diameter of the blood vessel.

  • ​Connective tissue is very tough and protects the outside of the blood vessel.

• ​An ORGAN SYSTEM is a group of organs that work together to perform important body functions.

• ​The leaves, stems, and flowers of a plant are all organs that make up the shoot system of a plant.

• ​Roots make up a different system below ground.

• ​The heart and blood vessels in animals are organs that form the circulatory system. 

• ​These organs work together to move blood throughout the body. 

• ​If one organ isn't working properly, the entire organ system may be affected.

  • ​People with a heart disorder may have low blood pressure.

An organism can have many organ systems that work together to perform all the functions the organism needs to survive.