Special Fields of Biology and levels of Biological Organization

Fields of Biology

There are following major Biology Fields:

·        Molecular Biology

It is new and modern branch of biology in which structures and function of those molecules are studied that help in biological processes of living organisms, such as nucleic acid, gene structure, and 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 virus, bacteria, microscopic algae and protozoans etc.”

·        Environmental Biology

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

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

·        Marine Biology

“It deals with the study of living organisms, which are found in sea water 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 fresh water like rivers, lakes, ponds, streams etc. with physical and chemical characteristics of their environment and its effection the 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 the 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, specially 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.”

·        Biotechnology

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 of problems related with living organisms specially in 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. Biological level starts from the very basic level of sub-atomic and atomic particles to the organism itself. After that, community, population and entire world are studied. The organisms have to perform different complicated processes. Therefore, biological organization is not simple. It is highly complex.

These processes differentiate the living things from the 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 the 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 the simple organisms. There are 92 chemical elements. Only 16 elements are called Bioelements.

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

levels of biological organization

  •   Major Bioelements

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

  • Trace Bioelements

The elements present in smaller quantity in the body are called trace bioelements. These are 10 bioelements. These are potassium (0.35%), sulphur (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

1.     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 proton, electron and neutron, positron etc.

2.     Molecular Level

When atoms are combined together, 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 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, and nucleotides (like ATP, ADP, and AMP) etc.

3.     Organ and Organ system Level

A group of different tissues, performing same functions is called organ. Organ performs specific functions. For example, 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 stomach. So food is mixed with the enzymes.

  • Organ Formation in Animals

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


  • Organ Formation in Plantsorgan formation in plants

The plants have less complex organ level organization than the animals. There is no organ system formation in the plant body. Mostly, the body of a plant can be divided in to roots, stem, 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

Group of similar cells, having same origin and performing same function is 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 number of micro-molecules and macro-molecules arrange themselves in a particular way to perform cells and their organelles. In case of simple organism 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.

Cell, is unit of structure and functions of the 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 cell like bacteria and protozoan.


  • Multicellular Organisms

These are composed of many cells like fungi, plants and animals. 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 well-defined nucleus are called prokaryotes. They have a few organelles.

  • Eukaryotes

The organisms with well-defined nucleus are called eukaryotes. They have 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 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 labour within the cell. The 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 wether prokaryotic or eukoryotic.


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 labour 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 heart beat increases.


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

Broader Levels of Organization

The broader levels of organization are as follow:

  • Species:

The organisms with similar characters having the same number of chromosomes and can inter breed with their opposite sex are called species.

  • Population:

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

  • Community:

The group of similar or dissimilar species living together under more or less same environmental conditions is called 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 environmental exchange materials between them and influence each other. The system is called ecosystem. The interaction between living and non-living environment in a particular area is known as ecosystem.

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