Biological Organization – Hundreds of chemical reactions are involved in maintaining life of even the simplest organism. In view of this, it is something of a surprise to find that of the 92 naturally occurring chemical elements, only 16 are commonly used in forming the chemical compounds from which living organisms are made. These 16 elements and a few others which occur in a particular organism are called bioelements. In the human body only six bio-elements account for 99% of the total mass.
Biology the six commonest Bioelements account for 99% of body mass.
- Oxygen 65%
- Carbon 18%
- Hydrogen 10%
- Nitrogen 3%
- Calcium 2%
- Phosphorus 1%
Other bioelements include (about 1%) – potassium (0.35%), sulphur (0.25%), chlorine 0.15%), sodium (0.15%), magnesium (0.05%), iron (0.004%), copper (trace), manganese (trace), zinc (trace),
The fact that the same 16 chemical elements occur in all organisms, and the fact that their properties differ from those in the non living world, shows that bioelements have special properties which make them particularly appropriate as basis for life.
Biological organization is not simple. It has high degree of complexity because of which the living organisms are able to carry out a number of processes (some very complicated) which distinguish them from the non living things. A living thing has built-in regulatory mechanisms which interact with the environment to sustain its structural and functional integrity.
A living thing is, therefore, composed of highly structured living substance or protoplasm. In order to understand the various phenomena of life, biologists for their convenience, study the biological organization at different levels starting from the very basic level of sub atomic and atomic particles to the organism itself and beyond which the study of community, population and entire world are included.
Biological organization can be divided into the following levels.
| Biosphere | That part of earth inhabited by living organisms; includes both the living and the nonliving |  |
| Ecosystem | A community together with its nonliving surroundings |  |
| Community | Two or more populations of different species living and interacting in the same area |  |
| Population | Members of one species inhabiting the same area |  |
| Species | Very similar, potentially interbreeding organisms |  |
| Multicellular organism | An individual living thing composed of many cells |  |
| Organ system | Two or more organs working together in the execution of s specific body function |  |
| Organ | A structure normally composed of several tissue types that from a functional unit |  |
| Tissue | a group of similar cells that perform a specific function |  |
| Cell | The unit of life |  |
| Organelle | A structure within a cell that performs a specific function |  |
| Macromolecules and macromolecules | A combination of atoms |  |
| Atom | The smallest particle of an element that retains the properties of that element |  |
| Subatomic particle | Particles that make up an atom |  |
Atomic & Subatomic Levels
All living and nonliving matter is formed of simple units called atoms and sub atomic particles such as protons, electrons & neutrons.
Molecular level
In organisms elements usually do not occur in isolated forms. The atoms of different elements combine with each other through ionic or covalent bonding to produce compounds. This stable form is called a molecule. Hydrogen, carbon, oxygen, nitrogen, phosphorous and sculpture are the most common atoms found in biological molecules. The different types of bonding arrangement permit biological molecules to be constructed in great variety and complexity. These may be macromolecules with low molecular weight like CO2, H2O etc or macromolecules with high molecular weights e.g. starch, proteins etc.
Biological world has two types of molecules: organic and inorganic. An organic molecule is any molecule containing both carbon and hydrogen. Inorganic molecules do not include carbon and hydrogen together in a molecule.
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, nucleotides like ATP, ADP, AMP etc.
Organelles & cell
Different and enormous number of macromolecules and macromolecules arrange themselves in a particular way to form cells and their organelles. In case of simple organisms like bacteria and most protests, the entire organisms consist of a single cell. In most fungi, plants and animals, the organism may consist of up to trillions of cells.
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 whether prokaryotic or Eukaryotic.
Tissue level
In multicellular animals and plants, groups of similar cells are organized into loose sheets or bundles performing similar functions: these are called tissues. Each tissue has a particular function in the life of the organism e.g. muscle tissue glandular tissue, xylem tissue, phloem tissue etc. they are specialized for contraction (movement), secretion, conducting water and for translocation of sugar, proteins etc.
Organ & system
Different tissues having related functions assemble together in a structure to carry out its function with great efficiency. Such structures are called organs and they are specialized to perform particular functions. For example stomach which is an organ has a function of food digestion (protein part) has a secretary epithelium which secretes the gastric juice, and a muscular tissue (smooth) for contracting the walls of the stomach and mixing the food with the enzyme thoroughly and moving the food to the posterior end. The formation of organs also has a selective value because this leads to an efficient accomplishment of their functions both qualitatively and quantitatively. N animal’s organ formation is far more complex and defined. Organs re part of organ systems where total functions involved in one process or phenomenon are carried out.
The organ level of organization is much less definite in plants than it is in animals. At the most. We might distinguish roots, stems, leaves and reproductive structures. Clear cut functions, the distinguishing features, can be assigned to each of these structures. Roots are involved in anchoring the plant while the leaves are primary organs for food manufacture. Flowers of other reproductive structures are involved in producing the next generation (reproduction). The complexity of the organ systems of animals is associated with a far greater range of functions and activities than is found in plants.
Individual (Whole Organism)
Levels of Biological Organization Various organs in plants and various organ systems in animals are assembled together to form an individual – the whole organism. The whole organism has its individuality as far as its characteristics are concerned. It is different from other members of the same species in certain respects. The various functions, processes, activities of an organism are coordinated. In an animal all the systems work in coordination with each other. For instance if a man is engaged in continuous and hard exercise, not only his muscles are working but there is an increase in the rate of respiration and heart beat to supply the muscles with increased oxygen and food which they need for continuous exercise. In animals the coordination is achieved by means of nervous system and endocrine system, whereas in plants only long term regulation of activities is brought about by hormones.
Organism works as a whole and it interacts and responds to the environmental changes as a whole.
Population
A population is a group of living organisms of the same species located in the same place at the same time, examples are the number of rats in a field of rice, the number of students in your biology class, or human population in a city.
Population is a higher level of biological organization than organism (whole because here a group of organisms of the same species is involved. This level of organization has its own attributes which come into being by living together of a group of organisms of the same species.
Some of these attributes are gene frequency, gene flow, age distribution, population density, population pressure etc. all these are new parameters which have appeared due to population of an organism. You will study them in detail n population ecology.
Community
Populations of different species (plants and animals) living in the same habitat form a community. Communities are dynamic collections of organisms, in which one population may increase and others may decrease due to fluctuation in biotic factors. Some communities are complex and well interrelated, other communities may be simple. In a simple community any change can have drastic and long lasting effects.
The foregoing account makes it clear that an organism can be studied at different levels of organization. It can be studied at subatomic, atomic, molecular, macromolecular, organelle, cell, tissue, organ and organ system level. We can also look at it as an individual, as a part of population of similar individuals, as a part of a community that includes other populations and a part of community of an ecosystem which includes abiotic factors as well as living organisms. Fig. 1.2.
The organisms’ interaction can take many shapes. It may be predation, parasitism, commensalism, mutualism and competition.
Living world in space
Living world of today is enormous in size. It has been reproducing and evolving since the time of its origin on this planet. Today almost all parts of the world abounds in living organisms. The distribution of organisms in space can be studied through biomes.
A biome is a large regional community primarily determined by climate. It has been found that the major type of plant determines the other kind of plants and animals. These biomes have, therefore been named after the type of major plants or major feature of the ecosystem. The major biomes of the world you will study in the chapter of ecology.