Special Fields of Biology and levels of Biological Organization

Fields of Biology

There are the following major Biology Fields:

Molecular Biology

It is a new and modern branch of biology in which structures and functions of those molecules studied help in the biological processes of living organisms, such as nucleic acid, gene structure, function, protein, and protein synthesis. It is the foundation of genetic engineering.

“The study of the molecular structure of the organisms, their cells or the organelles of the cells is called Molecular Biology.”

Micro Biology

“It deals with the study of microorganisms, such as viruses, bacteria, microscopic algae, protozoans, etc.”

Environmental Biology

“It deals with the study of the environment and its effects on the body of organisms.”

The study of the relationship between organisms and their environment is called Environmental Biology. The interaction between the organisms and their inorganic and organic environments is studied in this branch. The relationship between these interactions with human activities is also studied.

Marine Biology

“It deals with the study of living organisms, which are found in seawater or ocean water. It also deals with the physical and chemical characteristics of their environment.”marine biology

Fresh Water Biology

“It deals with the study of life found in freshwaters like rivers, lakes, ponds, streams, etc. with physical and chemical characteristics of their environment and its effect on life.

Parasitology (Fields of Biology)

“It deals with the study of the parasitic living organisms, their life cycle, method of disease transmission and interaction with their hosts.”

Human Biology

It includes all aspects of human life such as anatomy, physiology, health inheritance, evolution, etc. The study of Humans is called Human Biology. The structure, functions, histology, anatomy, morphology, evolution, genetics, cell biology, and ecology of human beings are studied in this branch.

Social Biologysocial biology

“It deals with the study of social activities of certain animals within a population, especially human beings. It is also concerned about different types of behavior, which are either inherited from their parents or developed in their body due to their experience.”


It is a very modern and recent branch of biology. It deals with the study of the tools and techniques of engineering and technology for the improvement of life and solutions to problems related to living organisms, especially human beings.

The use of living organisms, their systems, or processes in the manufacturing and services industries is called Biotechnology.

Biological Organization

The study of biology at different levels is called biological organizations. The biological level starts from the very basic level of sub-atomic and atomic particles to the organism itself. After that, the community, population, and the entire world are studied. The organisms have to perform different complicated processes. Therefore, the biological organization is not simple. It is highly complex.

These processes differentiate living things from non-living things. A living thing has a regulatory mechanism. This mechanism interacts with the environment. So it maintains the structures and functions of the organism.


The elements found in living organisms are called Bioelements. A living thing is composed of a living substance called protoplasm. Hundreds of chemical reactions take place in this protoplasm of simple organisms. There are 92 chemical elements. Only 16 elements are called Bioelements.

The properties of these 16 elements are different from the properties of the elements present in non-living organisms. Due to these special properties, these elements form the basis of life. There are two types of these elements:

levels of biological organizationMajor Bioelements

The elements present in larger quantities in the body are called major elements. These are only 6 bio elements. They form 99% of the body of humans. These are oxygen (65%), carbon (18%), hydrogen (10%), nitrogen (3%), calcium (2%), and phosphorus (1%).

Trace Bioelements

The elements present in smaller quantities in the body are called trace elements. These are 10 bio elements. These are potassium (0.35%), sulfur (0.25%), chlorine (0.15%), sodium (0.15%), magnesium (0.05%), iron (0.004%), copper, manganese, zinc, and iodine.


Levels of Biological Organization

The body of living organisms is highly developed and well organized. There are different levels of this well-organized body, called levels of biological organization.

The levels of Biological Organization are as follow:-

  1. Atomic and Sub-Atomic Level
  2. Molecular Level
  3. Cell and Organelles Level
  4. Tissue Level
  5. Organ and Organ System Level
  6. Individual and Whole Organism Level

Atomic and sub-Atomic Level

This is the smallest level of biological organization. The smallest particles of elements having the properties of elements are called atoms. The atoms have sub-atomic particles, like protons, electrons, neutrons, positrons, etc.

Molecular Level

When atoms are combined together, the molecule is formed in the cell. These molecules unite together to form compounds.

Types of Molecules:

  • Simple Molecules

These molecules are smaller and are formed naturally in a systematic way. They may have low molecular weights. Simple inorganic molecules are Carbon Dioxide and water etc.

Simple Organic Molecules are sugar, glycerol, fatty acids, amino acids, purines, and pyridines.

  • Complex Moleculescomplex molecules

These are the larger molecules with higher molecular weights. These are also called Macromolecules.

In the body of living organisms complex, organic molecules are formed from simple organic molecules. There are three types of complex molecules:

  1. Carbohydrates
  2. Proteins
  • Lipids
  1. Organic Molecules

The molecules containing both carbon and hydrogen together are called organic molecules.

  1. Inorganic Molecules

The molecules without carbon and hydrogen together are called inorganic molecules.

An organism is usually formed by an enormous number of micro and macro molecules of hundreds of different types. Some most important and abundant organic molecules in organisms are glucose, amino acids, fatty acids, glycerol, nucleotides (like ATP, ADP, and AMP), etc.

3. Organ and Organ System Level

A group of different tissues, performing the same functions is called an organ. Organ performs specific functions. For example, the stomach is an organ. It digests protein food. It has different tissues: its secretary epithelium tissue secrets gastric juice. Its muscular tissues contain the wall of the stomach. So food is mixed with the enzymes.

  • Organ Formation in Animals

Cells form different organs in the bodies of animals. These organs function efficiently. Organ formation is more complex in animals. Animals form organ systems like the digestive system. Different organs in an organ system complete one process of digestion. The organ system of animals performs more functions and activities than plants.

  • Organ Formation in Plantsorgan formation in plants

Plants have less complex organ-level organization than animals. There is no organ system formation in the plant body. Mostly, the body of a plant can be divided into roots, stems, leaves, and reproductive structures. Each of these structures performs a specific function. Root fixes the plant. It also stores food and absorbs minerals. The shoot or stem supports all the plants. The levels synthesize food. Flowers or other reproductive structures are used for reproduction.

The complexity of the organ system of animals is associated with a far greater range of functions and activities than is found in plants.

4. Tissue level

A Group of similar cells, having the same origin and performing the same function are called tissues. Each tissue performs a specific function, e.g.

  • Muscle tissues are used for contractions.
  • Gland tissues are used for secretions.
  • Xylem tissues are used for the conduction of water.
  • Phloem tissues are used for the transport of food. i.e. sugar.

5. Cell and Organelles System Level

Different and enormous numbers of micro-molecules and macro-molecules arrange themselves in a particular way to perform cells and their organelles. In the case of simple organisms like bacteria and most protists, the entire organism consists of a single cell. In most fungi, plants, and animals, the organism may consist of up to trillions of cells.

A cell is a unit of structure and functions of organisms. Different types of micro and macro-molecules arrange to form the cells and their organelles.

There are two types of organisms:

  • Unicellular Organisms

They are composed of single cells like bacteria and protozoans.

  • Multicellular Organisms

These are composed of many cells like fungi, plants, and animals. The cell membrane is present in all cells. There are two types of cells: prokaryotic and eukaryotic cells. Therefore the organisms are divided into two groups on the basis of this difference:

  • Prokaryotes

The organisms without a well-defined nucleus are called prokaryotes. They have a few organelles.

  • Eukaryotes

The organisms with well-defined nuclei are called eukaryotes. They have a large number of membranous organelles.

Numerous sub-cellular structures like mitochondria; Golgi-complex, endoplasmic, reticulum, ribosomes, etc. have been studied for their structure and function. It has become clear that the functions of the cells are accomplished by these specialized structures comparable to the organs of the body. These structures are called organelles.

The arrangement of the organelles speaks of the division of labor within the cell. Prokaryotes have only a limited number and type of organelles in their cytoplasm. Eukaryotes are rich in number and kinds of membranous organelles. A cell membrane is however present in all cells whether prokaryotic or eukaryotic.


The sub-cellular structures of the cell are called organelles. These organelles are mitochondria, Golgi complex, endoplasmic reticulum, ribosome, etc. These organelles perform different functions in the cells. Organelles are arranged specifically in the cells. Thus there is a division of labor within the cell.

6. Individual and Whole System Organism Level

The various organs and organ systems join to form an individual or whole organism. The whole organism has certain special characteristics. Therefore, each individual looks different from the members of the same species. All the systems in an organism coordinate with one another. For example, if a man exercises continuously, the working of muscles increases. His molecules need more oxygen. So the rate of respiration and heartbeat increases.

The nervous system and endocrine systems are used for coordination in animals. On the other hand, in plants, some hormones are involved in the regulation of long-term activities. The organism acts as a whole. It also shows the response to change in the environment as a whole.

Broader Levels of Organization

The broader levels of the organization are as follows:

  • Species:

The organisms with similar characteristics having the same number of chromosomes and can interbreed with their opposite sex are called species.

  • Population:

When members of the same species are found in the same area, it is called a species population.

  • Community:

A group of similar or dissimilar species living together under more or less the same environmental conditions is called a community.

  • Biosphere:

The area where both living and non-living organisms are found is called Biosphere.

  • Ecosystem:

When in a particular area both living and non-living organisms are present, the living organisms and environment exchange materials between them and influence each other. The system is called an ecosystem. The interaction between living and non-living environments in a particular area is known as an ecosystem.

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