Organisation in Multicellular Organisms

Multicellular organisms, such as plants and animals, are organised into highly complex and structured systems. The order from least complex to most complex is:

  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organisms



Cells are the basic structural and functional unit of a living organism. They are specialised to carry out specific functions.


Tissues are groups of cells with similar structures that work together to perform a shared function. For example, muscle tissue is a group of muscle cells that work together to contract and relax. This leads to movement at a joint.

Examples of tissues include:

  • Muscles
  • The blood
  • Xylem (water carrying tubes in plants)
  • Nervous tissue – involved in transmitting signals


An organ is made up of various tissues that work together to perform specific functions. For example, the heart contains fibrous tissue that makes up the heart valves and muscle tissue to pump the blood.

Some examples of organs are:

  • Kidney
  • Stomach
  • Lungs
  • Brain

Organ systems

An organ system is a group of organs with related functions that work together to perform bodily functions. For example, the circulatory system is responsible for pumping and circulating blood around the body. It includes the heart and blood vessels.

Some examples of organ systems are:

  • Skeletal system
  • Respiratory system
  • Muscular system
  • Circulatory system
  • Digestive system
  • Nervous system

A series of six illustrated human figures showcasing different body systems. From left to right: a figure displaying the skeletal system with visible bones; a figure highlighting the respiratory system with lungs depicted; a muscular figure representing the muscular system; a figure outlining the circulatory system with arteries and veins; a figure emphasising the digestive system with stomach and intestines; and lastly, a figure illustrating the nervous system with a network of nerves.


An organism is made up of several organ systems that perform the processes required for life.

Organisation in plants

1. There are a lot of specialised plant cells that come together to form different plant tissues.

  • For example, the epidermal tissue protects the plant, while vascular tissues like xylem and phloem are responsible for transporting water, nutrients and food.

2. The different plant tissues come together to form organs.

  • The leaves, roots and stems are all examples of plant organs

3. These organs come together to form organ systems.

  • An example of a plant organ system is the reproductive system, which allows the plant to produce offspring

4. These organ systems work together to form the organism, which is the entire plant in this case.

An illustrative representation of the hierarchical structure of plant biology. A sunflower stands in soil, labelled as an 'organism (organ system)'. From the sunflower, an arrow points to a depiction of green leaves, labelled 'organ'. Another arrow leads from the leaves to a magnified view of plant tissue. Further magnification reveals a detailed plant cell, and the last magnification displays a chloroplast, labelled 'organelle (chloroplast)'. The background displays a clear sky above and soil with a few stones below.