Biology is a rapidly maturing science, with its roots in the work of Aristotle, who lived from 384-322 BCE.

After many years of observation, experimentation, hypothesizing and revision, we now know the broad outlines of how living things work.

At their root, organisms are systems of macromolecular machines, built using information stored in nucleic acid molecules.

The simplest organisms consist of a single cell. We can think of cells as the atoms of life, the smallest living units.

A paramecium, a singled-celled free living organism.

Single-celled organisms can form communities or be highly integrated to form multicellular organisms.

Organisms, in turn, interact with one another and their physical environment to form ecosystems.

Biologic systems:

Cells
organisms
ecosystems

Cells are defined by a boundary layer, called the plasma membrane. This membrane controls the movement of materials into and out of the cell.

Within the membrane is the cytoplasm, a concentrated solution of molecules, primarily proteins and various smaller molecules.

These molecules capture and transform energy from the outside world and use it to build and maintain the plasma membrane, copy and read the information stored in nucleic acids, build new molecules and so increase the size of the cell. Once the cell is large enough, it can be divided into two.

Replication is a key feature of life.

There is a continuity to life, stretching back to a "last common ancestor" that lived billions of years ago.

We can see the evidence for this history in the fossil record

By looking at what is common among all living organisms, we can deduce what that ancestral organism was like.

Organisms obey the laws of chemistry and physics. They use energy and export entropy to create, maintain and copy themselves.

In contrast to most non-living systems, biologic systems are 'historical' objects - they are produced by evolutionary processes.

During replication, a cell builds a copy of the nucleic acids that store its genetic information.

In the course of building this copy, mistakes can be made. A mistake in the replication of genetic material is known as a mutation.

Sometimes these mistakes are incompatible with life and the cell or organism dies. More often the mistake produces more subtle changes.

As mutations accumulate they lead to differences between organisms. These differences can influence an organism's chances for survival and its ability to reproduce.

With each generation, some organisms produce more offspring than others. Over time, the population of organisms changes, it evolves.

Evolution can lead to the accumulation of information or its loss.

The environment an organism lives in is rarely constant. It consists of other organisms and the physical world.

As the environment changes, organisms either adapt and give rise to ancestors or they do not and become extinct.

The complexity of living things.

Organisms are much more complex and "condensed" than typical chemical systems.

Within a cell, there are thousands to tens of thousands of different types of molecules.

In the cytoplasm, the concentration of these molecules is generally between 300 to 400 milligrams per milliliter (mg/ml).

Another way of thinking about is that 30 to 40% of the space is occupied by these molecules and the rest by water. This is a very thick solution.

While there are many different types of molecules, some are present in rather small numbers.

Under these conditions, statistical fluctuations combine to produce complex and chaotic behaviors.

Given all this complexity, do we really 'understand' biologic systems?

It depends upon what you mean by understanding. What level of detail do you need to do what you want to do.

It is possible to understand the physics of an internal combustion engine without being able to repair one!

Similarly, understanding the basics of biology does not provide nearly enough information to cure a cancer or repair a damaged nervous system.

To rationally manipulate biologic systems we need to know the system in very great detail.

In most cases, we remain very far from such a detailed understanding. Many years of research and experimentation remain before truly rational bioengineering is possible.

But we can already anticipate what such an understanding will look like.

To appreciate biologic systems you need to master their basics -the biofundamentals. That is the goal of this course.

If you pursue a career in biology or medicine, you will find yourself immersed in necessary details.

Part of what makes science different from other human activities is its reliance upon shared experience, logical argument and consensus and the acceptance that our understanding is incomplete and likely to remain so.

The scientific process involves gathering information, building models, testing those models by experiment, and revising both the facts and the models.