The Pyramid of Life

When you look at a pyramid, you'll notice that its broad base gradually narrows as it extends upward. The same holds true for the organization of life on Earth. At the base of this hierarchical structure is the most inclusive level of organization, the biosphere. As you climb the pyramid, the levels become less encompassing and more specific. Let's take a look at this hierarchical structure for the organization of life, starting with the biosphere at the base and culminating with the atom at the peak.

Hierarchical Structure of Life

Biosphere: The biosphere includes all of the Earth's biomes and all living organisms within. This includes areas on the Earth's surface, below the Earth's surface, and in the atmosphere.

Biome: Biomes encompass all of the Earth's ecosystems. They can be divided into regions of similar climate, plant life, and animal life. Biomes consist of both land biomes and aquatic biomes. The organisms in each biome have acquired special adaptations for living in their specific environment.

Ecosystem: Ecosystems involve interactions between living organisms and their environment. This includes both living and nonliving material in an environment. An ecosystem contains many different types of communities. Extremophiles, for example, are organisms that thrive in extreme ecosystems such as salt lakes, hydrothermal vents, and in the stomachs of other organisms.

Community: Communities consist of different populations (groups of organisms of the same species) in a given geographic area. From people and plants to bacteria and fungi, communities include the living organisms in an environment. The different populations interact with and influence one another in a given community. Energy flow is guided by the food webs and food chains in a community.

Population: Populations are groups of organisms of the same species living in a specific community. Populations may increase in size or shrink depending on a number of environmental factors. A population is limited to a specific species. A population could be a species of plant, species of animal, or a bacterial colony.

Organism: A living organism is a single individual of a species that exhibits the basic characteristics of life. Living organisms are highly ordered and have the ability to grow, develop, and reproduce. Complex organisms, including humans, rely on the cooperation between organ systems to exist.

Organ System: Organ systems are groups of organs within an organism. Some examples are the circulatory, digestive, nervous, skeletal, and reproductive systems, which work together to keep the body functioning normally. For instance, nutrients obtained by the digestive system are distributed throughout the body by the circulatory system. Likewise, the circulatory system distributes oxygen that is taken in by the respiratory system.

Organ: An organ is an independent part of the body of an organism that carries out specific functions. Organs include the heart, lungs, kidneys, skin, and ears. Organs are composed of different types of tissue arranged together to perform specific tasks. For example, the brain is composed of several different types including nervous and connective tissues.

Tissue: Tissues are groups of cells with both a shared structure and function. Animal tissue can be grouped into four subunits: epithelial tissue, connective tissues, muscle tissue, and nervous tissue. Tissues are grouped together to form organs.

Cell: Cells are the simplest form of living units. Processes that occur within the body are carried out on a cellular level. For example, when you move your leg, it is the responsibility of nerve cells to transmit these signals from your brain to the muscle cells in your leg. There are a number of different types of cells within the body including blood cells, fat cells, and stem cells. Cells of different categories of organisms include plant cells, animal cells, and bacterial cells.

Organelle: Cells contain tiny structures called organelles, which are responsible for everything from housing the cell's DNA to producing energy. Unlike organelles in prokaryotic cells, organelles in eukaryotic cells are often enclosed by a membrane. Examples of organelles include the nucleus, mitochondria, ribosomes, and chloroplasts.

Molecule: Molecules are composed of atoms and are the smallest units of a compound. Molecules can be arranged into large molecular structures such as chromosomes, proteins, and lipids. Some of these large biological molecules may be grouped together to become the organelles that compose your cells.

Atom: Finally, there is the ever so tiny atom. It takes extremely powerful microscopes to view these units of matter (anything that has mass and takes up space). Elements such as carbon, oxygen, and hydrogen are composed of atoms. Atoms bonded together to make molecules. For example, a water molecule consists of two hydrogen atoms bonded to an oxygen atom. Atoms represent the smallest and most specific unit of this hierarchical structure.