11
Chapter 2
Organisms and
Environmental Factors
2.1 CATEGORIES OF ORGANISMS
Every living organism is an open system that exchanges matter and energy
with the environment. In various ways the organism takes all the chemical
substances it needs for the composition of its body from the environment
and casts off into the environment the substances that are no longer useful for its functions. In addition, the organism takes from the environment
energy in appropriate forms, which it uses to carry out the chemical reactions of synthesis, to move about, and to regulate its temperature; it casts
off energy into the environment, mainly in the form of heat.
The sum of the physical and chemical processes occurring inside an organism, through which cellular matter is composed and decomposed, is called
metabolism. The matter taken in by the organism and used to make cellular
material or to produce energy is known as food. The processes of metabolism constitute basic links connecting the living organism with its environment and are fundamental elements of the functioning of ecosystems.
A feature of organisms is that they are composed of one or more cells,
which are either similar to or different from each other and perform different functions. There is, however, another type of living things, the viruses,
which are not composed of cells. Viruses are elementary forms of life; they
cannot independently carry out the basic biological functions but are capable only of attacking the cells of various organisms and exploiting cellular
functions in order to reproduce.
Organisms are classed in categories using various criteria such as:
• The complexity of biological organisation
• The source of carbon, which is the most basic component of organic
matter and divides them into autotrophs and heterotrophs
• The source of energy, which divides them into photosynthetic and
chemosynthetic organisms
DOI: 10.1201/b14609-2
Chapter 2
Organisms and
Environmental Factors
2.1 CATEGORIES OF ORGANISMS
Every living organism is an open system that exchanges matter and energy
with the environment. In various ways the organism takes all the chemical
substances it needs for the composition of its body from the environment
and casts off into the environment the substances that are no longer useful for its functions. In addition, the organism takes from the environment
energy in appropriate forms, which it uses to carry out the chemical reactions of synthesis, to move about, and to regulate its temperature; it casts
off energy into the environment, mainly in the form of heat.
The sum of the physical and chemical processes occurring inside an organism, through which cellular matter is composed and decomposed, is called
metabolism. The matter taken in by the organism and used to make cellular
material or to produce energy is known as food. The processes of metabolism constitute basic links connecting the living organism with its environment and are fundamental elements of the functioning of ecosystems.
A feature of organisms is that they are composed of one or more cells,
which are either similar to or different from each other and perform different functions. There is, however, another type of living things, the viruses,
which are not composed of cells. Viruses are elementary forms of life; they
cannot independently carry out the basic biological functions but are capable only of attacking the cells of various organisms and exploiting cellular
functions in order to reproduce.
Organisms are classed in categories using various criteria such as:
• The complexity of biological organisation
• The source of carbon, which is the most basic component of organic
matter and divides them into autotrophs and heterotrophs
• The source of energy, which divides them into photosynthetic and
chemosynthetic organisms
DOI: 10.1201/b14609-2