(modified from Foundation Notes)
* Definition of Biology
* Characteristics of Life
* Levels of Organization
* SI Units and Relative Size
* Scientific Method
* Classification and Binomial Nomenclature
Definition of Biology
Biology can be broadly defined as the “study of life” or the “study of living things”. It includes molecules that are made, used by, or derived from living things. It also includes certain groups like viruses, prions, and virions that lack a complete cellular structure but which are agents of infection.
Characteristics of Life
WHAT IS LIFE?
If biology is the study of life, how do we know when something is living? There are 8 main characteristics of living things. These are:
Feeding – The taking in, digestion, and assimilation of food. 2.
Excretion – The removal of wastes that result from metabolism. 3.
Respiration – The production and use of energy in the form of ATP. 4.
Growth – By increasing the size of one cell, or by cell division to create more cells. 5.
Movement – The ability to move from A to B or to move one part into a new position. 6.
Sensitivity – The ability to sense and respond to stimuli from the environment. 7.
Reproduction – The production of offspring and passing of heritable characteristics from generation to generation. 8.
Cells – All living things are made of cells.
Please note that many non-living things possess some of these characteristics, but only living things possess all of them. Certain groups, like viruses, also lack some of these characteristics because they have taken up an extreme parasitic existence and use a host cell to carry out the functions of life for them.
THE BASIC UNIT OF LIFE
The cell is the basic unit of life; this means that a cell is the simplest level of organization that is able to carry out all the characteristics of living things. The development of a simple bilayered membrane is probably the most critical event that allowed the first cells to form (perhaps 4 billion years ago).
Levels of Organization
We can study biology and biological processes at various levels. The broadest (biome) is at top left.
BRANCHES OF BIOLOGY
Biology is a huge subject and cannot be studied by a professional scientist in its entirety. Thus, a scientist will choose a branch of biology in which to specialize. A few are mentioned below, but there are many applied areas of biology (such as medicine and agriculture) and many subjects with strong links to biology (such as pharmacology and geology) so that any list is necessarily inadequate and a gross simplification. Also, it is now virtually impossible to study one branch of biology without knowing something about other branches.
An ecologist studies the levels organism to biosphere. *
An ethologist studies the behavior of organisms and populations. *
A physiologist studies organs and organ systems.
A histologist studies tissues.
A cytologist studies organelles, cells, and tissues.
A biochemist studies molecules and organelles.
Fig. 1: Relationships Between Sizes and the Resolution of the Human Eye/Light Microscope/Electron Microscope
PREFIXES AND SYMBOLS
Students are sometimes confused by size. This section compares the sizes of items commonly mentioned in biology. It is first important to know the main prefixes, or SI units, in the Système Internationale. The same SI units are used in mass and volume, the basic units of which are the gram and the liter respectively.
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