Levels of Organisation in Multicellular Organisms

Multicellular organisms, such as plants and animals, are organised into highly complex and structured systems. We can break this down into different layers.

The order from least complex to most complex is:

  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organism

Levels of Organisation

Cells

Cells are the basic structural and functional unit of a living organism. They are specialised to carry out specific functions. Each cell contains subcellular structures, such as a nucleus, mitochondria, and ribosomes.

Tissues

Tissues are groups of cells with similar structures that work together to perform a particular 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.

Epithelial tissue, formed by epithelial cells, lines many parts of the body, including the intestines and the outer layer of skin.

Some other examples of tissue include:

  • Muscles
  • The blood
  • Xylem (Water carrying tubes in plants)
  • Nervous tissue

Organs

Organs are made up of groups of 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 blood.

Some examples of organs are:

  • The kidneys
  • The stomach
  • The lungs
  • The 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

Organism

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

Organisation in plants

1. Many specialised plant cells come together to form various plant tissues. For example, dermal tissue is the outer layer that covers and protects the plant

2. The various plant tissues come together to form organs. Some examples of plant organs are the leaf, roots and stem

3. These organs collectively form organ systems. An example of an organ system is the plant’s reproductive system, which allows the plant to produce offspring

4. Various organ systems work together to form the organism and in this case, it is the whole plant.

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