Biology is the study of interactions of life. It covers a number of subjects, like plants (botany), animals (zoology), marine animals and plants (marine biology), microorganisms (microbiology), genes (genetics), and many more. A biologist investigates biological processes and phenomena, that helps build a correlation between all living things. There are certain characteristics of life that are considered the very core of the subject. Characteristics of Life The first characteristic of life is the cell. A cell is the basic unit of life, be it for animals, plants, or single-celled organisms. All living organisms, single-celled and multicellular, are made up of cells. Cells make up tissues that form organs, and organs lead to an organ system. An organ system is contained within the organism. The next characteristic of life is energy transformation. All living things require energy to function. This energy is transferred from the environment to the organism in the form of food. Metabolic processes are therefore, very important for maintenance of life. The third is reproduction. If an organism is alive, it will reproduce. Reproduction can be asexual or sexual. A few organisms undergo binary fission. Only living organisms have the ability to reproduce. When there is reproduction, then comes the next characteristic of life, which is growth. Living organisms need to grow in order to complete their life cycle. Single-celled organisms grow by increasing their cell volume. Multicellular organisms tend to add more cells to their body in order to grow. As an organism grows, it begins to respond to the environment. This brings us to our next characteristic of living things, that is sensation. Living organisms respond to external stimuli, like heat, cold, pain, etc. A few reactions to the environment take place instantly, and some take place over time. This response can occur on a cellular level called homeostasis. When a set of complex reactions takes place, it is called behavior. It also includes the last characteristic, that is adaptation. Organisms, mostly over thousands of years, begin to adapt to their environment. This adaptation leads to permanent genetic changes in them. This process of adaptation is vital for the survival of species, and is called evolution. If the organism fails to adapt, it will perish. To understand the subject, it is essential to understand the basic principles of biology. These principles form its foundation. Cell Theory Cell theory proves and states that a cell is the fundamental unit of life. All living organisms are made of one or more cells. In some cases, organisms are made of the secreted products of cells, like shells. All cells contain hereditary information of life, that is, DNA and RNA. Gene Theory The gene theory states that genes are inherited by all organisms from their parents. All organisms from a tiny virus or bacteria to a multicellular organism like an elephant follow the same process of copying and translating DNA to proteins. The progeny will contain sets of similar genes transferred from the parent. Evolution The theory of evolution states that all organisms have descended from a common ancestral gene pool on Earth. Over thousands of years, genetic changes have led to the formation of different species. Over thousands of generations, changes take place in an organism, that may be small or large, and in some cases, visible or inconspicuous. Homeostasis All living organisms are able to maintain homeostasis. This means, regulation of their internal environment to maintain equilibrium with the environmental changes. Thermodynamics Energy is transferred from one form to another with the help of food and metabolic processes. Thus, energy transformation is not always efficient, but energy will forever remain constant. Careers Associated with Biology There are different branches of biology. Some of the enriching careers in the field of biology are as follows:

• Aerobiology
• Agriculture
• Anatomy
• Astrobiology
• Biochemistry
• Bioengineering
• Bioinformatics
• Biomathematics or Mathematical Biology
• Biomechanic
• Biomedical jobs
• Biophysics
• Biotechnology
• Building biology
• Botany
• Cell biology
• Conservation Biology
• Cryobiology
• Developmental biology
• Ecology
• Embryology
• Entomology
• Environmental Biology
• Epidemiology
• Ethology
• Evolutionary Biology
• Genetics
• Herpetology
• Histology
• Ichthyology
• Integrative biology
• Limnology
• Mammalogy
• Marine Biology
• Microbiology
• Molecular Biology
• Mycology
• Neurobiology
• Oceanography
• Oncology
• Ornithology
• Population biology
• Paleontology
• Pathology
• Parasitology
• Pharmacology
• Physiology
• Phytopathology
• Psychobiology
• Sociobiology
• Structural biology
• Virology
• Zoology

As you can see, biology is simply the study of life and all the processes of life. You get to learn about genes, reproduction, evolution, adaptation, and behavioral changes in an organism. This is the field that will help you answer many questions like What came first, the chicken or the egg? and Why do we yawn when sleepy?