levels of organisms

Biological Organization at different levels 

 In order to understand the various phenomena of life, biologists study biological organization at different levels. The list goes from simpler to complex levels. Subatomic particles make atoms and atoms make molecules. Different molecules of life make organelles and different organelles assemble together to form the simplest living unit i.e. the cell.
 Cells are organized in the form of tissues and different coordinating tissues make an organ. Organs performing relative functions make organ system and different organ systems make a complete individual. Individuals of the same species live together and make a population. Populations of different species living in the same habitat constitute a community. 

 Biosphere 

"The part of the Earth inhabited by organisms’ communities is known as biospeher." Biosphere Protons and neutrons are located inside nucleus of atom while electrons orbit in energy levels (electron shells) around the nucleus. The number of electrons in the outermost shell determines the manner.
All types of matter are made up of elements and there are about 92 kinds of elements, found in nature. Each element is made up of a single kind of atoms . These atoms are actually the structures formed by many subatomic particles.
The most stable subatomic particles are electrons, protons and neutrons.Each of these is found in definite number, in a specific atom. Only six (O,C,H,N,Ca,&P makes 99% of the total mass.Other ten (K,S,Cl,Na,Mg,Fe,Cu,Mn,Zn,&I)collectively make one percent of the total mass. Out of the 92 kinds of elements that occur in nature, 16 are called bioelements. 
These take part in making the body mass of a living organism . A molecule is the smallest part combine through ionic or covalent bonding. The stable particles formed by the bonding between compound is called as molecule. Bioelements share their atoms in making biomolecules or molecules of life.

 Formation of organism

 An organism is formed by enormous number of biomolecules of hundreds of different types. These molecules are the building material and are themselves constructed in great variety and complexity due to specific bonding arrangements. 
Biomolecules may be classified as micromolecules and macromolecules. Micromolecules These are with low molecular weight e.g. glucose, amino acids, fatty acids etc. Macromolecules These are with high molecular weights e.g. starch, proteins, lipids etc. Two different molecules, belonging to different categories, usually combine together to form conjugated molecules e.g. glycoproteins, lipoproteins, nucleoproteins etc. 

Level 1-Organelle and Cell level: 

An enormous number of biomolecules become associated in a particular way and form organelles. The organelles are actually sub-cellular structures and when they assemble together, cells are formed. 
 Each type of organelle is specialized to perform a specific function. For example; mitochondria are specialized for cellular respiration and ribosomes are specialized for protein synthesis. In this way, functions of the cell are accomplished by these specialized structures. 
 It is an example of the division of labour within the cell. Prokaryotes have only limited number and types of organelles in their cells. They are made up of simple cells which lack membrane bounded organelles e.g. mitochondria, Golgi complex. Eukaryotes have large number and types of organelles in their cells. They are made up of complex cells which have membrane bounded organelles. 
A cell membrane (outer covering of cell) is however present in all cells, whether prokaryotic or eukaryotic. In the case of bacteria and most protists, the entire organism consists of a single cell. In the case of most fungi, animals and plants, the organism consists of up to trillions of cells. There are some similarities and clear differences between Prokaryotc and Eukaryotic cells Level 2 -

Tissue level: 

In multicellular organisms, similar cells (performing similar functions) are organized into groups, called tissues. Defination of tissue We can define a tissue as" a group of similar cells specialized for the performance of a common function". Each cell in a tissue carries on its own life processes (like cellular respiration, protein synthesis), but it also carries on some special processes related to the function of the tissue.
 On the basis of their structures and functions, plant tissues are divided into two types i.e. Meristematic tissues Permanent tissues. Meristematic tissues These tissues are made of undifferentiated, small cells which have the ability to divide. These tissues are located at the tips of roots and shoots (apical meristem) and between the xylem and phloem tissues (lateral meristem).

 Permanent tissues 

These tissues are made of differentiated cells of different shapes and sizes. They are further divided into Epidermal tissues (the outermost covering of leaf, stem and root), ground tissue (or prarenchyma: prepares food and stores food and water, supporting tissue (i.e. collenchyma / sclerenchyma; provides strength to the plant) and conducting tissue xylem and phloem (transports water and food). 

Animal tissues 

There are four major types of animal tissues i.e. epithelial, connective, nervous and muscular tissues. Epithelial tissues acts as the covering and glandular tissue. Connective tissue acts as the connecting and supporting tissue. Nervous tissue conducts messages and muscular tissue acts as the contracting tissue. 

3-Organ and Organ system level: 

In higher multicellular organisms, particularly in animals, more than one type of tissue having related functions are organized together and make a unit, called organ. Different tissues of an organ perform their specific functions and these functions collectively become the functions of that organ.
 For example stomach is an organ specialized for the digestion of proteins and for storing food. Two major types of tissue are organized in its structure. Epithelial (glandular) tissue secretes the gastric juice and muscular tissue performs contractions of stomach walls for grinding of food mixing of enzymes with food and moving food to posterior end. So two tissues perform their specific function which collectively become the function of stomach. The next level of organization in multicellular organisms is the organs system level. Different organs performing related functions are organized together in the form of an organ system. In an organ system, each organ carries out its specific function and the functions of all organs appear as one process of the organ system. For example, digestive system is an organ system that carries out the process of digestion. 
Major organs arranged in its framework are oral cavity, stomach, small intestine, large intestine, liver, and pancreas. The whole organisms has it's individuality as far as its characteristics are concerned. For ! example; all human beings have same organs and organ systems which are organized in the same pattern. Yet they have different skin colors, heights, voice tones etc. Such characteristics Makes the individuality in a human being. 
The organ system level is less definite in plants as compared to animals .The complexity of organ and organ system level in animals is associated with a far greater range ot functions and activities than in plants. 

4- Individual level: 

Different organs (in plants) and organ systems (in animals) are organized together to form an individual / organism. In organism, various organs and organ systems are organized in such a way that all the functions, processes and activities are coordinated.
For example, when a man is engaged in continuous and hard exercise, not only his muscles are working but also there is an increase in the rate of respiration and heart beat. 
This accelerated rate of respiration and heart beat supplies more oxygen and food to the muscles which they need for continuous work. In animals, regulation of activities (coordination) is achieved by nervous system and hormones while in plants, coordination is brought about only by hormones.
 5- Population level: 
Biologists extend their studies to the population level where they study interactions among member of the same species living in the same habitat. A population is defined as" a group of organisms of the same species located in the same place, at the same time". For examples, number of rats in a field of rice in 2002, number of students in biology class in semester 2008 etc.
 Similarly human population comprises the number of human beings in a particular city or country at a particular time. At population level, biologists study life in a number of new parameters, which cannot be considered at individual (organism) level. For example; gene frequency, gene flow,’ age distribution, population density, population pressure etc. 
6-Community level: 
"A community is an assemblage of different populations, interacting with one another within the same environment". A forest may be considered as a community. It includes different plant species e.g. oak trees, ash trees, grasses, bushes etc; different species of microorganisms and fungi; and different animal species. Communities are collections of organisms, in which one population may increase and others may decrease.
 Usually populations change due to fluctuations in abiotic factors and changes in the size of other populations. Some communities are complex e.g. a forest community, a pond community etc. Other communities may be simpie e.g. a fallen log with various populations under it. 
In a simple community number and size of populations is limited so any change in biotic or abiotic factors may have drastic and long lasting effects. Cellular Organization We have studied that there are two basic types of cells i.e. prokaryotic and eukaryotic cells. In living organisms the ceils organize in three ways to make the bodies of organisms. 
Cells make unicellular, colonials and multicellular organizations and the organisms formed through these organizations are unicellular organisms, colonial organisms and multicellular organisms. In unicellular organisms only one cell makes the life of an organism. All the life activities are carried out by the only cell. We are familiar with Amoeba, Paramecium, and Euglena etc . In colonial type of cellular organization many unicellular organisms live together but do not have any division of labour among them.
 Each unicellular organism in a colony lives its own life and does not depend on other cells for its vital requirements. Volvox is a green alga found in water that shows colonial organization. Hundreds of Volvox cells make a colony. Sometimes a Volvox colony consists of daughter colonies. 
Each cell of the colony has two flagella at the anterior end, which is directed towards the surface of the colony. The colony moves in water by the combined action of the flagella of all the cells. In multicellular organization cells are organized in the form of tissues, organs and orga systems.
 Frog and mustard are the familiar examples of multicellular organization. Mustard plant (scientific name: Brassica campestris) is sown in winter and it produces seeds at the end of winter. The plant body is used as vegetable and its seeds are used for extracting oil. The organs of the body can be divided into two groups on the basis of their functions.
 Root, stem, branches and leaves are the vegetative organs, which do not take part in the sexual reproduction of the plant. Flowers are the reproductive parts of the plant because they take part in reproduction and produce fruits and seeds photomicrographs of different organs.
 Frog (scientific name: Rana tigrina) also shows the multicellular organization. The body is made of organ systems and each organ system consists of related organs. All the organs are made of specific tissues (epithelial, glandular, muscular, nervous etc).