Metabolism 2

Metabolic reactions
occur continuously in every living
organism. (a) Relationships of some
metabolic activities. Some of the
nutrients provided by proper nutrition are used to synthesize needed
materials and cell parts; other nutrients are used as fuel for cellular
respiration, a process that captures
energy stored in food. This energy
is needed for synthesis and for
other forms of cellular work. Cellular respiration also requires oxygen,
which is provided by the process of
gas exchange. Wastes from the @115
such as carbon dioxide and water
must be excreted from the body.
(b) Like most organisms

Metabolism

In all living organisms chemical reactions take place that are essential to
nutrition, growth and repair of cells, and conversion of energy into usable
forms. The sum of all the chemical activities of the organism is called metabolism. Metabolic reactions occur continuously in every living organism
(Figure 1-3); when they cease, the organism dies.
Each individual cell of an organism constantly takes in new substances,
alters them chemically in a variety of ways, and builds new cellular

Specific Organization

The cell theory, one of the fundamental concepts of biology, states that all
living things are composed of basic units called cells and of cell products.
Although organisms (living things) vary greatly in size and appearance, all
(except the viruses‘) are composed of these small building blocks. Some of
the simplest organisms, such as bacteria, are unicellular; that is, they consist of a single cell. In contrast, the body of a human or an oak tree is made
of billions of cells. In such complex multicellular organisms the processes
of the entire organism depend on the coordinated functions of the constituent cells

WHAT IS LIFE?

It is relatively easy to determine that a human being, an oak tree, and a
grasshopper are living whereas rocks are not. Yet it remains difficult to
define life. At one time it was believed that a living system could be distinguished from a nonliving system by its possession of a special ”vital force."
Now, after centuries of searching, we understand that there is no single
substance or force that is unique to living things. Perhaps the best we can
do toward defining life is to list the features that living things have in
common. When we do this, we find that the characteristics that distinguish
most living things from nonliving things include a precise kind of organization, a variety of chemical reactions we term metabolism, the ability to
maintain an appropriate internal environment even when the external environment changes (a process referred to as homeostasis), movement, responsiveness, growth, reproduction, and adaptation to Environmental
change. We consider each of these characteristics in the following section

Sea cucumber

.................................This sea cucumber is composed of millions of cells that are organized to perform specialized functions


discover a cure for cancer. Or perhaps you will choose to enter an applied
field of biology such as dentistry, medicine, or veterinary medicine. Even if
you are not planning a career in one of the biological sciences, learning
about this exciting science will enable you to better understand yourself
your environment, and the organisms with which you share your planet
As you become biologically literate you will increase your understanding of
the impact biology continues to have on life and society.
In this first chapter we examine some of our everyday assumptions
about living things, and start to formulate a structure for Organizing our
knowledge. First, as we begin our study of living things we need t develop a deeper understanding of what life is

A View Of life 3

A View Of life 2

During the past century biology, the study of life, has undergone
rapid change and has had a significant impact on the way we live. We
are now able to produce vaccines‘ and antibiotics, transplant hearts, and
manipulate genes. Biologists today are working on such vital projects as
increasing world food supply, improving environmental quality, identity-
satisfactorily contribute them health and longevity, and conquering killers
like cancer, heart disease, and AIDS. Biologists also continue their interest
in the study of interrelationships of the diverse forms of living things that
inhabit our planet. These scientists have enhanced our awareness of the
exquisite complexity that characterless all living things, and have helped
us better appreciate our own impact on other living t-hings and on the
environment

A View Of life 1

Modern biology examines the world of in all its details and interactions. An organism's ability to reproduce itself essential to the continuity of life. DNA, the hereditary material of life, is shown in (a) a computer
drawn simulation of the colored plastic space~filling molecular models used by
biologists. The balls represent the different atoms that make up DNA:
dark blue, carbon; , oxygen; white, hydrogen; blue, nitrogen; yellow, phospho-
rus. (b) A genetically engineered Escherichia coli bacterium (magnified 68,000
times). its hereditary material has been modified so that the bacterium produces
large quantities of the hormone human insulin. Individuals with the disease
diabetes mellitus have insufficient amounts of this hormone, which is necessary
for the normal metabolism of sugar. Since the bacterium itself has no use for
the insulin, and has no way of excreting it, instead the hormone accumulates in
an “inclusion bod)/’ within the bacterial cell. The insulin can be harvested by
destroying the bacterium. (c) An angelfish guarding a section of coral reef. BiolOgists are concerned with the physical characteristics of the fish, how its body
functions, its behavior, and its interaction with other living things in its environment, (d) Biologists also study the effects of human activities on the envi
ronment. Because human populations are expanding rapidly in the world’s
tropical areas, rainforests are being cleared to provide more land for agriculture.
Unfortunately, tropical soils are infertile and can produce crops for only a few
years. The cleared areas of rain forests may never recover from this destruction,
and many species of plants and animals may become extinct as a result.