Levels of Organization (anatomy)

The simplest unit of life is the atom, like oxygen. Two or more atoms is a molecule, like dioxide. Many molecules is a macromolecule, such as a phospholipid. Multiple macromolecules form a cell, like a Clara cell. A group of cells functioning together is a tissue, for example, Epithelial tissue. Different tissues make up an organ, like a lung. Organs work together to form an organ system, such as the Respiratory System. All of the organ systems make a living organism, like a lion. A group of the same organism living together in an area is a population, such as a pride of lions. Two or more populations interacting with each other form a community, for example, lion and zebra populations interacting with each other. Communities interacting not only with each other but also with the physical environment encompass an ecosystem, such as the Savanna ecosystem. All of the ecosystems make up the biosphere, the area of life on Earth.

Level 1: Atoms

Atoms are the smallest part of the cell that is studied in biology.

Level 2: Molecules

Molecules are made of one or more atoms bonded together.

Level 3: Organelles

Organelles are composed of molecules, and carry out specific functions for each cell.

Level 4: Cells

A cell is the smallest functional unit of life. All living organisms are composed of one or more cells.

Level 5: Tissues

Main article: Tissue (biology)

Tissues make up the second level of organization. They are formed by the joining of cells that have similar function or structure.

Level 5 1/2: Structures

Tissues make up structures. Some structures could make up organs

Level 6: Organs

Main article: Organ (anatomy)

An organ is a group of tissues that perform a specific function or group of functions. This is the third level of organization.

Level 7: Organ Systems

Main article: Organ systems

Main article: Biological system

An organ system is a collection of organs that perform a specific function- the circulatory system or digestive system for example. Several organ systems are present in humans, but many other types exist in different organisms. An organ system cannot live by itself and is dependent on other organ systems to form an organism. Here is a list of human organ systems and the organs they are composed of:

• Circulatory system: the heart, blood, and blood vessels
• Digestive system: the salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, rectum, and anus
• Endocrine system: the hypothalamus, pituitary gland, pineal body, thyroid, parathyroids, and adrenals
• Integumentary system: the skin, hair, and nails
• Lymphatic system: the leukocytes, tonsils, adenoids, thymus, and spleen
• Muscular system: the muscles
• Nervous system: the nerves, brain, spinal cord, and peripheral nerves
• Reproductive system: the ovaries, fallopian tubes, uterus, vagina, mammary glands, testes, vas deferens, seminal vesicles, prostate, and penis
• Respiratory system: the pharynx, larynx, trachea, bronchi, lungs, and diaphragm
• Skeletal system: the bones, cartilage, ligaments, and tendons
• Urinary system: the kidneys, ureters, bladder, and urethra

Organ systems may be closely intertwined and called things like the musculoskeletal system or neuroendocrine system.

Level 8: Organisms

Main article: Organism

An organism is a being that's able to perform simple acts of survival. We humans are one for example.

Level 9: Population

Main article: Population

A population is a group of organisms of the same species.

Level 10: Community

Main article: Community

A community is a group of interacting organisms of multiple species sharing a populated environment.

Level 11: Ecosystem

Main article: Ecosystem

Ecosystems has organisms but also includes the land, water, air, rocks, and other non living things in a given area.

Level 12: Biosphere

Main article: Biome

A biome is a major regional or global community of organisms. Biomes are usually characterized by the climate in the given area.

See also

• Biological organization
• Cell Theory
• Basic functions of an organism/ organ system/ organ/ tissue/ cell

References

• Harcourt Science Textbook 2007 Edition
• Science Class
• Cells (a book)