Viewed as a whole.

Physiology — study of functions and processes.

Genetics — study of heredity and variation.

Pathology— study of aberrant conditions and diseases and

their effects.

Evolution — study of origin and changes in species.

Paleontology — study of fossil organisms.

Taxonomy — classification of organisms.

Ecology — study of organism-environment interrelations.

Psychology (experimental psychology) — study s of the

animal mind.

Examples of more specialized fields that fall within this

same general classification are:

Embryology — study of individual development.

Endocrinology — study of the endocrine gland system in

animals.

Parasitology — study of parasitism.

As the emphasis on these finer studies increased, biology

as an exact science has become more dependent on the

other exact sciences for interpretation of its data and their

significance. Biochemistry, a division of chemistry, deals

with the chemistry of living organisms and their products,

biophysics has as its subject matter the physics involved

in the structure, development and functioning of living

organisms. Biometrics fs a special field of mathematics

concerned with the analysis of biological data.

We must recognize that any classification of biology

or any other science into branches or subsciences is purely

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arbitrary and has value only in providing for the

presentation of facts. It is impossible to obtain a true idea of

plants and their significance without a parallel

consideration of animals. It is equally impossible to study structure

effectively without at the same time studying function,

or to study distribution without studying inheritance.

We shall consider what have come to be recognized as

main principles concerning the organization of functioning,

distribution, and interrelation of living organism. In doing

this we shall break down the whole subject and deal

with specific groups or processes when doing so will

lend clarity to the presentation.

Basic life functions

The characteristic organization of living creatures is

inseparable from those functions that are the

distinguishing marks of life. One of the most significant of these

is photosynthesis, the process by which green plants, with

adequate light, manufacture carbohydrates. These

carbohydrates, important as energy sources, are the initial

sources of the organic substances from which most living

organisms are built. Plants store them or convert them

into other chemical compounds. Animals derive^- their

building materials and their energy directly or indirectly

from plants. Although photosynthesis is a function of

green plants — indeed, of only certain cells in these

plants — it is one of the most important of all biological

processes.

A universal life process is respiration, by which the

energy in chemical compounds is released for use in the

activities of protoplasm — in the maintenance of cells and

tissues, in the formation of new cells and tissues, and in

the processes involved in their breakdown.

AH organisms are characterized by growth and

reproduction. Growth may be defined in a general way as a

simple increase in mass, but the growth of an organism

usually includes increase in the number and size of the

cell units and progressive development of the various

parts of the organism. Growth ceases and the individual

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is said to be mature. All organisms can reproduce and thus

increase their number — reproduction, which is essential

to the perpetuation of each type of organism, usually takes

place during maturity.

Irritability — the capacity to react to stimuli — is

characteristic of all living organisms. Upon this capacity

to react to such stimuli as light, temperature, contact

and specific chemicals rests the ability of the organism

to adjust itself to its environment.

To define the nature of living material we must

consider not only the functions and characteristics of living

things, but also the environment in which the organisms

exist. No plant or animal can live apart from this

environment or even far out of adjustment with it.

L i v i n g Organisms And Their

Environment — An organism's surroundings and all the factors

which influence it constitute its environment. The complex

relations between organisms and their environment can

be seen in a very brief consideration of food supply.

The green plants are at the base of the system of food

relations in the organic world. They take from their

surroundings only simple inorganic .materials — water, carbon

dioxide, oxygen, inorganic nitrogen, and various mineral

salts. From these simple substances plants build

carbohydrates, fats, and proteins. With the exception of a few

bacteria and molds, all other organisms depend upon the

green plants for their food supply. Herbivorous animals

consume plants directly. Carnivorous animals eat other

animals which may in turn be herbivorous. Some are

omnivorous; that is, they eat both plants and other

animals. The types of plants in a particular environment

determine to a large extent what kinds of animals can

inhabit that environment. As we shall see later, the

presence of a particular organism in a given environment

may influence all the others found there. The basic

physical and chemical factors in the environment are also of

the utmost importance.

Oxygen is an absolute requirement for most organisms;

it is likewise abundant in most surroundings. Land-dwel-

Land-dwelling species obtain oxygen from the air; most aquatic

species utilize the oxygen dissolved in water; If as

sometimes happens in experimental or otherwise limited

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ronments, the oxygen supply of organisms is cut off the

organisms will die.

Quite as important as oxygen is water which is a

universal component of protoplasm. It provides the essential

medium for the chemical processes of life and the transport

of materials. The amount of water available determines

what types of organisms will occur in an environment,

how fast they will grow, and the rate of many of their

basic life processes.

Carbon dioxide in the environment is essential for

photosynthesis. If either carbon dioxide or inorganic

nitrogen is absent or deficient, the growth of photosynthetic

plants is limited or prevented. This, in turn, affects the

animal population.

Equally important are, such physical factors as light,

temperature, and gravity. __

Light furnishes, through photosynthesis, virtually all

the energy of the Organic world. Furthermore, it has many

direct influences, such as those on the growth patterns

and flowering habits of plants and the migratory and sex

cycles of some animals.