Introduction to Biology: Living Staircase

The Cellular Level. At the cellular level, atoms, the fundamental elements of matter,
are joined together into clusters called molecules. Complex biological molecules are
assembled into tiny structures called organelles, part of cells, which are assembled
together to form cells. Nucleus and mitochondria are the basis of organelles. As
mentioned above, the cell is the basic unit of life and many organisms are composed of
single cells in the world. Bacteria are single cells, for example. All animals and plants, as
well as most fungi and algae, are multicellular-composed of more than one cell. More
descriptions can be learnt from cell and gene chapter.

The Organismal Level. Cells are organized into three levels of organization. The most
basic level is that of the tissues, which are groups of similar cells that act as a functional
unit such as muscle tissues and blood tissues. Tissues, in turn, are grouped into organs,
which are body structures composed of several different tissues grouped together in a
structural and functional unit such as heart and brain. Your brain is an important organ
composed of zillions of nerve cells and a variety of connective tissues. At the third level
of organization, organs are grouped into organ systems. The nervous system, for
example, consists of sensory organs, the brain and spinal cord.

The Populational Level. Individual organisms are organized into several hierarchical
levels within the living world. The most basic of these is the population, which is a group
of organisms of the same species living in the same place such as human population and
fish population. All the populations of a particular kind of organism together form a species, its members similar in appearance and able to interbreed. At a higher level of
biological organization, a biological community consists of all the populations of the
different species living together in one place. At the highest tier of biological
organization, a biological community and the physical habitat within which it lives
together constitute an ecological system, or ecosystem.

Emergent Properties
Many new properties emerge at the higher level of living hierarchy as we climb up the
level from lower to higher level. These are called emergent properties. For example, we
can see the properties and energy in a cell that has been formed from the aggregates of so
many molecules, which are not present in single molecule. For example, there are
properties in molecule such as protein that are not present in atoms that comprised it.
That is, if we take a simple example of diamond and coal that are composed of same
carbon molecule and even though they are formed differently and yet they have so much
difference in terms of their properties and characteristics. We can know from the
hierarchy nature of life from the emergent property of life.