One of the interesting Biology Topics is the study of animal behavior and how it is influenced by genetics and the environment.
What are Living Things Made of?
Our earth is inhabited by different kinds of living organisms, that look very different from each other. These living organisms are archaebacteria, eubacteria, protista (Amoeba, Chlamydomonas), fungi, plants, and animals. The bodies of living organisms are made up of microscopic units called cells. The cell has the same central position in biology as an atom in the physical sciences. The cell is the basic structural and functional unit of living organisms.
Present-day cells share common fundamental properties. For instance, all cells employ DNA as their genetic material, are surrounded by a plasma membrane, and use the same basic mechanisms for energy metabolism. On the other hand, present-day cells have evolved a variety of different lifestyles. Many organisms, such as bacteria (both archaebacteria and eubacteria), protozoa (e.g., amoeba), and yeasts, consists of single cells (called unicellular organisms) that are capable of independent self-replication.
More complex organisms, called multicellular organisms, are composed of collections of cells that function in a coordinated manner, with different cells specialized to perform particular tasks. The human body, for example, is composed of more than 200 different kinds of cells, each specialized for such distinctive functions as memory, sight, movement, and digestion. The diversity exhibited by the many different kinds of cells is striking; for example, consider the differences between bacteria and the cells of the human brain.
All cells, whether they exist as one-celled organisms (unicellular organisms) or as a part of multicellular organisms are capable of carrying out certain basic functions such as nutrition, respiration, growth, and reproduction. These functions are essential for the survival of the cells.
Differences between Unicellular and Multicellular Organisms
| Unicellular Organisms | Multicellular Organisms |
| 1. An unicellular organism is represented by a single cell. | 1. A multicellular organism consists of a large number of cells. |
| 2. All activities of the organisms are performed by a single cell. | 2. A single cell performs one or a few activities of the organisms. |
| 3. There is no division of labour as the single cell performs all life activities. | 3. Cells are specialized to perform different functions of the body so that there is a division of labour within cells. |
| 4. Reproduction consumes a single cell. | 4. Only some cells of the body called germ cells take part in reproduction. Other cells (somatic cells) remain intact. |
| 5. The life span of an individual is short. | 5. The life span of an individual is long. |
The most important and fundamental level in the organisation of the living world is the cellular level. Cells are the fundamental structural and functional units of living organisms and are the basic unit of life. Cell biology is the study of cells in all aspects of structure and functions.