TEXTS FOR HOME—READING

THE SCIENCE OF BIOLOGY

Biology is the science of living organisms. It is

concerned with their nature, functions, reproduction, and

place in their environment. It is a ramifying science,

but it aims to be a precise one. It is ruoted in physics

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and chemistry and many of its interpretations are made

in terms of these sciences and of mathematics. It is bound

closely with geology and meteorology, and applications

of its principles are found in anthropology, psychology,

sociology, agriculture, medicine, industry, and indeed,

in everyday living. Inasmuch as one of its ultimate aims

is thorough understanding of living organisms including

man, biology is entitled to be called the most vital of

. the sciences.

composition of living bodies. Chemical analyses show

that living materials consist of carbon, hydrogen, oxygen,

nitrogen, sulfur, phosphorus,, potassium, iron, ancj

magnesium. In addition, they usually contain sodium, chlorine,

and lesser amounts of such elements as manganese,

copper, iodine and fluorine. Everything can be.identified.

There is no residue of unidentifiable stuff. But the

elements present in living matter are all found in abundance

In mineral deposits, in sea water, or in the atmosphere.

Hence we can conclude that there is nothing peculiar in

the elemental composition of living matter.

But what of the wdy in which these elemental blocks

are put together? We know, for instance, that hydrogen

and oxygen combined in one proportion (H2O) constitute

water, a specific substance; in another (H2O2), hydrogen

peroxide have quite different properties, associated with

their differences in composition. Is living matter

distinguished from nonliving matter by its chemical

organization? With reference to many of chemical compounds

found in living matter the answer to this question is no.

With reference to the sum total of the compounds which

together make up any living body the answer is yes.

A major part* 65 to 90 percent, of every living body

is composed of hydrogen and oxygen combined as water.

Water is an inorganic substance, chemically simple and

obviously not confined to living organisms. The bodies

of plants and animals contain numerous other inorganic

substances—acids, bases, and salts. None of them differ

from the acids, bases, and salts with which the inorganic

chemist works daily in his laboratory.

Other substances, the so-called carbon or organic

compounds; are restricted, in nature, to living bodies or the

products of living bodies. They include the carbohydrates,

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fats, and proteins. All contain carbon, hydrogen* and

oxygen. In.addition, the proteins contain nitrogen and often

suffur and other elements. ^

The carbohydrates are generally considered the

simplest organic substances. Their stru<^ure is adequately

known and many of them can be synthesized. In Tiving

organisms they are important as energy compounds.

Nearly all the energy used by living organisms, plant,

and animal, is light energy derived from the sun. This

light energy is converted to other energy forms by a

process called photosynthesis. It is in carbohydrates

that green plants first store this energy. It is primarily

in carbohydrates that the energy is distributed to,all

parts of the plant, and it is from carbohydrates that much

of the energy used by animals is obtained.\"

Fats resemble carbohydrates in composition but are

chemically more complex and contain more stored energy.

Like the carbohydrates, many fats can be synthesized Fn

the laboratory.

Proteins differ considerably from fats and

carbohydrates. Chemically they are much more complicated than

all except a few carbohydrates and fats. So far no

proteins have been synthesized. Proteins are more closely

xelated to certain of the activities which characterize

the living state than are the carbohydrates and fats.

Proteins have a specific character which the other organic

compouns lack. Whereas the same carbohydrates and fats

are found in thousand's of different kinds of organisms,

among the proteins there is a high degree of specificity.

Each protein tends to be characteristic of only one kind

of organism, sometimes of only certain organs or of

particular stages in development. Hence, the differences

among living things seem to be in some way correlated

with differences in the nature of their proteins.

subdivisions of biology. We shall consider plants and

animals together, both in the discussion of fundamental

biological principles and with respect to their natural

associations with each other. They will be treated

separately when this appears desirable for purposes of

emphasizing basic differences and when the problems of

approach are different.

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Plants and animals are, similar in the their

fundamental composition. They are made up of the same group of

elements combined in essentially the same way. Both are

composed of cells as the fundamental structural units,

but their tissue systems, organ systems, and general

construction are very different. Animals are usually

more complicated than- plants, and with this greater

structural complexity are associated with more highly

developed coordination and greater activity. Plants lack the

power of locomotion; animals have various means of

moving about. The nutritional activity of a plant is

circumscribed by its inability to move; that of an animal is fairly

brqad. This difference is associated with the expenditure of

far more energy by animals and with more intricate

mechanisms for the liberation and use of energy. Partly as

a result of such differences, evolution has brought about

greater diversity among animals, the types of animals

being much widely different than the types of plants.

Biology may be divided in either of two ways,

depending upon whether thfe emphasis is placed on type of

organisms or on processes, structures, and functions.

With the first system there are two principal divisions:

botany, which deals with plants, and zoology, which

deals with animals.

Botany may be subdivided as follows:

Bacteriology — study of bacteria.

Mycology — study of fungi. -

Algology (sometimes called phycology)—study of algae.

Bryology — study of mosses.

Pteridology — study of ferns.

All these branches may be grouped together as

mic botany, the study of plants which do not produce seed.

Study oi the seed plants (actually two groups — the

nosperms, which bear cones, and the angiosperms, which

bear flowers) covers a single field, phanerogamic botany.

Zoology is similarly divided as follows:

Protozoology — study of single-celled animals. ,

Entomology — study of insects. ' •

Ichthyology — study of fishes.

Herpetology — study of amphibians and reptiles.

Ornithology — study of birds.

Mammalogy — study of mammals.

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Anthropology — study of man (with reference to physical

rather than cultural characteristics).

This botany-zoology system grew up naturally as

biological science developed, the emphasis during its early years

being placed on structure and relationships.

As it became more arid more of a precise experimental

science and emphasis was given to finer aspects of

structure and function, another system of classification based

upon the parts or prpcesses studied came into use. In this

system there are such subdivisions as the following:

Cytology — study of cells.

Histology — study of tissues.

Anatomy — study of internal structure as revealed by

dissection.

Morphology — study of gross structure, the organism