Biological organisation

Biological organization is the way that living things are built, from very small parts to very large systems. It helps us understand how life works by looking at how tiny pieces come together to make bigger and more complex structures. This idea starts with tiny atoms and builds up to entire worlds, including the places where plants and animals live.

Each step in this building process adds more complexity. For example, atoms form molecules, which come together to make cells. Cells work together to create tissues, and tissues form organs. These organs work as systems, and finally, all living things together make up the biosphere.

This way of understanding life is very important for science, especially in medicine. It helps scientists study how diseases work and how the body functions. It also helps us learn about how changes at very small levels, like in cells, can affect entire living systems, such as ecosystems. Without this organization, many areas of science, like brain research and medicine, would not be possible.

Levels

See also: Integrative level

The simple way scientists look at living things starts very small and gets bigger. It begins with tiny parts like atoms and builds up to very big groups like whole ecosystems.

Some ways of looking at living things add even more steps in between. For example, a tiny part called a molecule is made from even smaller things called elements. And atoms can be split into even smaller parts, but these are not usually part of biology. Each step in this big list can be broken down even more. For example, a group of all the DNA in a living thing, called a genome, can be split into smaller parts called genes. At each step, new things happen that only work at that step and not at the smaller steps before it. These are called emergent properties. Not all living things are made the same way. For example, something that is not made of tissues cannot be described using the level called histological (tissue) level.

For levels smaller than atoms see Subatomic particle
Acellular level and Pre-cellular level	Atoms
	Molecule	Groups of atoms
	Biomolecular complex	Groups of (bio)molecules
Sub-cellular level	Organelle	Functional groups of biomolecules, biochemical reactions and interactions
Cellular level	Cell	Basic unit of all life and the grouping of organelles
Super-cellular level (Multicellular level)	Tissue	Functional groups of cells
	Organ	Functional groups of tissues
	Organ system	Functional groups of organs
Ecological levels	Organism	The basic living system, a functional grouping of the lower-level components, including at least one cell
	Population	Groups of organisms of the same species
	Guild	Interspecific groups of organisms carrying the same ecological function (i.e. herbivores).
	Community (or biocoenosis)	Guilds from all biological domains, and their interactions in a specific location.
	Ecosystem	Groups of organisms in conjunction with the physical (abiotic) environment.
	Biome	Continental scale (climatically and geographically contiguous areas with similar climatic conditions) grouping of ecosystems.
	Biosphere or Ecosphere	All life on Earth or all life plus the physical (abiotic) environment
For levels larger than Biosphere or Ecosphere, see Earth's location in the Universe

Emergence of biological organization

Biological organization likely began in the early RNA world when RNA chains started to show basic traits needed for natural selection, as Darwin described. These traits include being able to pass on traits, changing over time, and competing for resources. The success of an RNA replicator would depend on how well it could copy itself, stay stable, and gather resources. These abilities were tied to the RNA's shape and sequence. Over time, as life became more complex, success continued to rely on how well organisms could perform these key functions at different levels of life.

Fundamentals

Many natural systems, like living things, have a layered structure. Scientists noticed this in the 1950s and began studying it more closely. They found that these layers help explain how life works and stays organized.

Life can be thought of as a series of steps, from very small parts to very large systems. These steps help scientists understand how living things grow, change, and stay balanced in nature. One important idea is that layers, or steps, in nature tend to form naturally because they are stable and help things work better.

To motivate this deep idea, he offered his "parable" about imaginary watchmakers.

Parable of the Watchmakers
There once were two watchmakers, named Hora and Tempus, who made very fine watches. The phones in their workshops rang frequently; new customers were constantly calling them. However, Hora prospered while Tempus became poorer and poorer. In the end, Tempus lost his shop. What was the reason behind this? The watches consisted of about 1000 parts each. The watches that Tempus made were designed such that, when he had to put down a partly assembled watch (for instance, to answer the phone), it immediately fell into pieces and had to be reassembled from the basic elements. Hora had designed his watches so that he could put together subassemblies of about ten components each. Ten of these subassemblies could be put together to make a larger sub-assembly. Finally, ten of the larger subassemblies constituted the whole watch. Each subassembly could be put down without falling apart.

Parable of the Watchmakers

There once were two watchmakers, named Hora and Tempus, who made very fine watches. The phones in their workshops rang frequently; new customers were constantly calling them. However, Hora prospered while Tempus became poorer and poorer. In the end, Tempus lost his shop. What was the reason behind this? The watches consisted of about 1000 parts each. The watches that Tempus made were designed such that, when he had to put down a partly assembled watch (for instance, to answer the phone), it immediately fell into pieces and had to be reassembled from the basic elements. Hora had designed his watches so that he could put together subassemblies of about ten components each. Ten of these subassemblies could be put together to make a larger sub-assembly. Finally, ten of the larger subassemblies constituted the whole watch. Each subassembly could be put down without falling apart.

Levels

Emergence of biological organization

Fundamentals

To motivate this deep idea, he offered his "parable" about imaginary watchmakers.

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