Level of detail:
Definition / Description:
Knowledge of basic science includes
the distinction between atoms and molecules, and elements, mixtures and compounds.
- Elements are chemical substances
that include only one type of atom.
- Mixtures and compounds include more than one type of atom, the difference
between these being that mixtures consist of discrete
(not attached together) combinations of atoms
and molecules, which can therefore often be separated easily. Conversely, compounds consist of at
least two different types (elements) of atoms that have joined together via chemical
bonds to form molecules. Although molecules can also be formed from two or more atoms of the same type (same element),
e.g. the gaseous molecules of oxygen (O2)
and nitrogen (N2), unless atoms of different elements have joined together, the molecule is that of an
element, not a compound.
Some scientific disciplines, such as particle
physics, include consideration of atoms and sub-atomic
particles (that is the even smaller parts that,
together, form atoms). In most cases biologists and health scientists
concentrate on studying structures from the size of molecules
(i.e. "molecular scale") upwards in
The human body needs a wide range of
specific elements, which are sometimes
The different elements have different functions,
work in different ways, are required in different
quantities, and received in different ways, e.g.
we breathe in oxygen but receive sodium from the
salt in food.
are required by the human body in sufficient quantities
that they are known as:
The following are also important
but required in lower quantities, hence known
The size of molecules
varies enormously depending on the type of molecule.
The smallest consist of only two tiny atoms. Others,
such as certain modern plastics, consist of extremely
long chains of carbon atoms together with groups
of atoms of other elements.
Other scientific disciplines, such as particle
physics, are interested in atoms and sub-atomic
particles (that is the even smaller parts that,
together, form atoms).
Biologists and health scientists usually
study structures from the size of molecules (i.e.
"molecular scale") upwards in size.
Molecules may be considered as the "building
blocks" of animals such as humans. In most
cases they must be obtained in the diet or manufactured
(by the body) from dietary components.
example, the amino acid called alanine (whose molecule is indicated below) is a sub-unit that forms part of proteins such as actin and myosin, and also the enzyme ATPase.
As indicated by its structure, alanine includes the elements Hydrogen, Carbon, Nitrogen and Oxygen.
Organelles are sub-cellular structures
specialised to perform specific functions within
The relative quantities of the types
of organelles within cells depends the type
of cell. There are many different types of cells in the body that are specialised for performing specific tasks.
following organelles are found in animal cells
- click on the clicks for further information
For example, there are several types of nerve cells, also known as neurons or neurones:
Cells are units of living matter.
One of the first units taught in many biology
courses includes the structures of, and differences
between, animal cells and plant cells. Such comparison might be omitted from courses in specifically Human Biology because the human body includes
only "animal cells" (unless the digestion
of plant-matter is discussed at a cellular level).
Animal cells are surrounded by a cell membrane
and are generally specialised for particular
tasks within the body. When viewing animal
cells in photographs or on microscope
slides, they are therefore usually labelled
according to the particular type of cell, which often relates to its location in the body.
A tissue is group of similar and closely
associated cells that are specialised to perform
a particular function (or group of functions).
Each of the
4 basic types of animal tissue listed on the left
can be sub-divided into even more specialised
For example, there are three
(3) distinctly different types of muscle
tissue. They are:
(Biological) organs are groups of physically
associated tissues that operate together (as one
unit) to perform a specific function with great efficiency.
There are many organs
within the body. Examples include:
- The Heart
- The Lungs
- The Stomach
- The Liver
- The Kidneys
- The Intestines
Groups of organs
and associated tissues that operate together are
called "Organ Systems", see below.
An organ system is defined as
a group of organs and tissues that operate together
in a co-ordinated way to perform a gross function.
The example of the Urinary
System shown on the right illustrates:
Other examples of "Organ
Systems", also known as "Body Systems"
Introductory courses in Human Biology, Anatomy
& Physiology, or similar often begin with
a general introduction to sub-structures such
as cells and tissues then progress to cover each
of the major organ systems as separate units.
More advanced study may then include consideration
of interactions between the systems of the body.
(the whole body)
The human organism refers to a whole (complete) human.
It is obvious that every example is different, although some may be very similar such as identical twins and triplets, etc..
To see a
perfect example, just look in a mirror, or if
you are reading this in a group, at the person
next to you.