Pyramid of life: hierarchical structure of life

The pyramid of life is a representation of the different hierarchical levels in which life, as we know it, is organized. From the point of view of terrestrial biology, life is organized in such a way that the broadest and most inclusive levels are at the base, and as you climb up the pyramid, the levels narrow and become increasingly ever more specific. If the point of view of the analysis were the physical sciences, the components of subatomic particles would be found at the apex of the pyramid. And if the perspective were astronomy, the base would be formed by the universe as a whole.

Let’s take a look at this hierarchical structure for the organization of life, beginning with the biosphere at the bottom and culminating with the atom at the top.

hierarchical structure of life

From the top to the bottom, the pyramid of life is divided into 12 levels that are:

• Atom
• Molecule
• organelle
• Cell
• Tissue
• Organ
• organ system
• Organism
• Population
• Community
• Ecosystem
• biome
• Biosphere

Each level of the pyramid is made up of the union of different units belonging to the level immediately above. In this way, the base level, the biosphere, includes all the life we ​​know on earth, while the top level is made up of the fundamental units of matter, that is, atoms. Let’s look at each of these levels in descending order:

The atom

The atom represents the fundamental unit of matter, that is, everything that has mass and that occupies a place in space. There are different types of atoms that make up the different elements of the periodic table. This includes elements like carbon, hydrogen, oxygen, and nitrogen, all of which are essential parts of life. Atoms are not only present in organic substances (those from living beings) but also in all inorganic matter, from rocks to stars.

Despite the fact that atoms can be divided into other smaller subatomic particles, such as electrons, protons or neutrons, and that these in turn can be divided to form quarks and other more exotic particles, from the biological point of view, that is the one we use, atoms represent the smallest and most specific unit of this hierarchical structure.

Some examples of atoms include oxygen (O), hydrogen (H), carbon (C), and nitrogen (N) atoms.

the molecule

Atoms come together and bond with each other to form molecules. These can exist in an immense diversity of sizes and compositions. From the smallest and simplest hydrogen molecule (H ₂ ), to biological macromolecules containing hundreds of thousands and sometimes millions of atoms linked one after the other.

Both inorganic and organic molecules can be found in living beings. The latter include biomolecules such as carbohydrates, lipids, proteins, and nucleic acids, all of which have been studied in great detail by biochemists. Individual molecules can be organized into large molecular structures to form chromosomes, multiprotein complexes, and more. As will be seen later, some of these large biological molecules can clump together to become the organelles that make up cells.

Some specific examples of molecules include the water molecule (H ₂ O), glucose (C ₆ H ₁₂ O ₆ ), hemoglobin, and DNA.

the organelle

The association of certain biological molecules, such as lipids, proteins and nucleic acids, can give rise to small structures with specific functions within cells, called organelles. These structures are responsible for all kinds of functions, from housing, transcribing and copying the genetic information of a living being, to producing energy.

In some cases, the organelles can float freely in the cytoplasm of a cell (as in the case of prokaryotic cells), while in others, the organelles are usually enclosed by a membrane (as in the case of eukaryotic cells).

Some examples of organelles include the nucleus, mitochondria, ribosomes, and chloroplasts.

The cell

The cell is the simplest unit of life. The processes that occur within the body of all living beings take place within cells. For example, when a leg moves, nerve cells are responsible for transmitting signals from the brain to muscle cells in the leg, and these, in turn, translate the nerve impulse into a series of chemical reactions that give rise to contraction of some muscles and relaxation of others.

There are different types of cells, including plant cells, animal cells, and bacterial cells. In addition, between animal or plant cells not all are the same. For example, there are several different types of cells within the body, including blood cells, fat cells, and stem cells, to name a few.

Tissue

The association of multiple cells with shared structure and function gives rise to what is called a tissue. For obvious reasons, only multicellular living things like plants and animals form tissues. Tissues can be very diverse and fulfill a wide variety of highly specialized functions.

In the case of animal tissue, this variety of functions leads to the existence of four different types of tissue:

• Epithelial tissue
• Connective tissue
• Muscle tissue
• Nervous tissue

Some examples of tissues are skeletal muscles, skin and, strangely enough, blood, which is a connective type of tissue.

The organs

Different types of tissues with complementary functions can be associated with each other to give rise to a unit in which a series of very specific complex functions are carried out. These units are called organs. In other words, organs are made up of different types of tissue arranged together to perform specific tasks.

Examples of organs in the human body are the heart, lungs, kidneys, skin, and ears.

organ system

Organ systems are interconnected groups of organs within an organism that have related functions and are generally regulated together. Some examples are the circulatory, digestive, nervous, skeletal, and reproductive systems.

Within an organism, the various organ systems work together to maintain the normal functioning of the body. For example, nutrients obtained by the digestive system are distributed throughout the body by the circulatory system. Likewise, the circulatory system distributes the oxygen that is ingested by the respiratory system.

The organism

A living organism refers to a single individual of a species that exhibits the basic characteristics of life. This means that they are living units capable of growing, developing and reproducing. Each of us represents a single living organism. Complex organisms, including humans, are made up of different organ systems, all of which work together, cooperating to carry out the functions of life.

The population

Populations are groups of organisms of the same species that live and reproduce in a specific community. Populations can increase in size or shrink depending on a number of environmental factors. A population is limited to a specific species. A population can be a plant species, an animal species, or a bacterial colony.

Community

When different populations (groups of organisms of the same species) interact with each other in a given geographic area, a community is formed. From people and plants to bacteria and fungi, communities include the living organisms in an environment. Different populations interact with each other and influence their respective community.

The ecosystem

The interaction between different communities of different species and the natural environment in which they live, gives rise to an ecosystem. In other words, ecosystems involve the interactions between living organisms and their environment, including both living and non-living material. An ecosystem contains many different types of communities, all linked through a complex chain of food and energy flows.

Some examples of ecosystems are the savannah, the polar ecosystem, and the tropical forests, among others.

the biome

Biomes consist of the union of multiple ecosystems that share a wide geographical area, as well as certain climatic and biodiversity characteristics. Organisms in each biome have acquired special adaptations to live in their specific environment. According to Heinrich Walter’s classification, the following 9 biomes can be distinguished on planet earth:

• Equatorial
• Tropical
• Subtropical
• Mediterranean
• Warm temper
• Nemoral
• Continental
• Boreal
• Polar

the biosphere

Finally, we come to the bottom of the pyramid of life, the biosphere. The biosphere includes all the biomes on Earth and, therefore, all the living organisms within them.

In other words, the biosphere corresponds to the system formed by all living beings on the planet, including all their complex interrelationships and their interrelationships with the environment in which they live. This includes all areas on the Earth’s surface, below the Earth’s surface, in water, and in the atmosphere.