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.