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Biology 2nd Baccalaureate

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1.1. Levels of organization of the human body

Levels of organization of the human body

To facilitate the study of an organism as complex as the human being, we analyze living matter from the simplest to the most complex, but it is necessary that we consider it as a whole formed from other simpler particles that join to form other more complex.

Various levels of complexity or organization can be distinguished of the human body:

  • Atomic level. The atoms are the smallest particles of matter that retain the chemical properties of the chemical element to which they belong. The atoms that make up living matter are bioelements. As you will see in Physics and Chemistry, atoms are made up of other subatomic particles, such as protonsneutrons, and electronsDue to its abundance, two types are distinguished:

Los átomos se unen para formar moléculas

El estado gaseoso de la materia. (s. f.). Recuperado 19 de julio de 2013, a partir de
Alphabet soup: Main bioelements.
Interactive activity: Games with the periodic table.
Test yourself (it will be good for you for chemistry): Atomic structure exam.
Simulator: Learn by playing what an atom is like by building it.
Interactive activity: Interactive periodic table.
  • Molecular level. Atoms are joined together by chemical bonds to form a more complex structure, the molecule. The bioelements are grouped to form biomoleculesThe most important biomolecules are:
    • Inorganic biomolecules: present both in living beings and in inert matter.
      • Water: formed by the union of two atoms of hydrogen and one of oxygen (H2O). It is the majority component of living beings and has many functions, such as transporting molecules, supporting the chemical reactions that occur in the body,solvent for molecules, thermoregulator, etc.
      • Mineral salts: they can be found in the solid state forming hard structures, suchas bonesteeth, mollusk shells, or dissolved, intervening in the maintenance of the internal environment, and in many chemical reactions, suchas the transmission of the nerve impulse or the contraction of the muscles.
    • Organic biomolecules: exclusive to living beings, rich in carbon.

Simulator: Learn by playing that a molecule is made up of atoms.

As you can see, some molecules join with others to form a higher level, the macromolecular levelFor example, when monosaccharides join to form more complex carbohydrates, or amino acids join to form proteins.

Macromolecules unite to form cellular organellesFor example, lipids and proteins associate to form cell membranes.

All these lower levels of organization of matter are abiotic levels but, from the next level, the cellular level, the biotic levels begin, with life.

  • Cell level. The cell is the basic unit of all living things. The molecules and macromolecules are grouped to form organelles and cells, which are able to perform the vital functions: nutrition, relation and reproductionTherefore, the cellular level is the first to have life. Some examples of cells are white blood cells, neurons, muscle cells, etc.

            The unicellular beings have this level of organization, but multicellular are more complex.

  • Tissue. A tissue is formed by the association of specialized cells that have the same structure and function. For example, bone tissue, blood tissue, muscle tissue, etc.

Interactive activity:  What is a tissue?.

  • Body. Several tissues that collaborate to perform a certain function form the organs of the human body. For example, the heart is made up of epithelial, nervous and muscular tissue, and its function is to pump blood. The kidney, the liver, a bone, the ovaries, would be other examples of organs.
  • SystemsThe organs are associated in higher structures (systems of the human body) to perform a specific vital function:
    • The apparatuses are formed by the association of very different organs, with different functions, different structures, but that collaborate together. For example, the digestive system is made up of very different organs, such as the teeth, tongue, or liver, but they all work in a coordinated way in the digestion of food and absorption of nutrients.
    • The systems consist of bodies formed by the same type of tissue with the same structure, as in the skeletal, nervous or muscular system.

Each level of organization forms more complex structures, interacting with the rest until giving rise to the organism, where all the devices and systems that make up the multicellular individual are integrated, such as a plant, a fungus, or the human being.

Las partículas subatómicas forman partes de los átomos, éstos de las moléculas, éstas de los orgánulos, células, tejidos, órganos, aparatos, población, comunidad, ecosistema y biosfera.

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Above the organism level it would be the population level and the ecosystem level.

Interactive activity: Word search about the tissues of the human body.

Interactive activity: Word search about the organs of the human body.

Interactive activity: Crossword on the levels of organization of the subject.

Interactive activity: Levels of organization.

Video and test: Exercises of organization of living beings.

Interactive activity: Levels of organization.

Interactive activity: Check if you know the levels of organization of living matter.

Song "Rap & Reggae of Biology" (IES Ramón Pignatelli): Levels of organization of the human body.

Politicians and science: Cristina Fernández de Kirchner, former president of Argentina, almost knows the formula for water.

Answer in your notebook

1.1.- What are the levels of organization of the human body? Explain how tissues, organs, and systems differ.

Answer in your notebook

1.2.- It indicates to what level of organization a neuron, the heart, DNA, carbon, a sperm and blood belong.

Answer in your notebook

1.3.- What molecules make up living matter?

Reinforcement activities

What are the chemical elements that are part of living beings called?

What is the structure formed by the union of various bioelements called?

Where do we get the biomolecules we need to live?


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.