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3.2 General Biology
Biology is the study of life. All living things are collectively known as organisms.
Living beings are different from non-living beings by seven characteristics explained
in Fig. 3.5.
All living things are made up of microscopic structures called cells. Some organisms have single cell and are called unicellular organisms. Organisms made up of
multiple cells are called multicellular organisms. Figure 3.6 shows an illustration of
the complex arrangement of chemicals that makes up an organism.
Atoms combine to form the molecules. Small molecules bond together to form
larger molecules and these larger molecules form organelles of cells that perform
specific activities. These organelles form the cells.
Some simple organisms are made up of single cell, which are called unicellular
organisms, while others are made up of many cells that are similar in nature.
In complex organisms, cells form tissues, which make their organs. The organs
form organ systems, which in turn make complex multicellular organisms including
the humans.
Fig. 3.3 Alteration of environment for human benefit
3 Fundamentals of Biology for Environmental and Medical Professionals