PART I INTRODUCTION TO LIVING ANIMALS

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PART I INTRODUCTION TO LIVING ANIMALS

1 Life: Biological Principles and the Science of Zoology

• The Origin and Chemistry of Life
• Cells as Units of Life
• Cellular Metabolism

CHAPTER 1 LIFE: BIOLOGICAL PRINCIPLES

AND THE SCIENCE OF ZOOLOGY

CHAPTER OUTLINE

The Uses of Principles

• Underlying Principles Central to Understanding Zoology
• Laws of physics and chemistry underlie some zoology principles.
• Principles of genetics and evolution guide much zoological study.
• Principles learned from one animal group can be applied to others.
• Some science methods specify how to conduct solid research.
• Zoology, the Study of Animal Life (Figure 1.1)
• Zoologists studying many dimensions base research upon a long history of work.
• Two central principles are evolution and the chromosomal theory of inheritance.

1.1. Fundamental Properties of Life

• Historical Continuity of Life
• Properties exhibited by life today are different from those at its origin.
• Change over time, or evolution, has generated many unique living properties.
• Definitions based on complex replicative processes would exclude non-life, but also early forms

from which cellular life descended.

• We should not force life into a simple definition, yet we can readily recognize life from a

nonliving world.

• General Properties of Living Systems
• Chemical Uniqueness (Figure 1.2)
• Macromolecules in organisms are far more complex than molecules in nonliving matter.
• They obey the same physical laws as nonliving molecules but are more complex.
• Nucleic acids, proteins, carbohydrates and lipids are common molecules in life.
• Their general structure evolved early; thus the common amino acid subunits of proteins are

found throughout life.

• They provide both a unity based on living ancestry and a potential for diversity.
• Complexity and Hierarchical Organization (Figures 1.3, 1.4; Table 1.1)
• Life has an ascending order of complexity: macromolecules, cells, organisms, populations and

species.

• Each of these levels has an internal structure: macromolecules form ribosomes and

membranes, etc. and cells form tissues.

• Each level has unique abilities and requirements; cells can replicate but are not independent in

a multi-cellular organism.

• New characteristics that appear at the next level of organization are emergent properties.
• Because of the interactions of the components, we must study all levels directly as well as

together.

• Diversity of emergent properties at higher levels is a result of evolution (i.e., lower levels

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Chapter01 - Life: Biological Principles and The Science of Zoology

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• Reproduction (Figure 1.5)
• Life comes from previous life but had to arise from nonliving matter at least once.
• Genes replicate genes, cells divide to produce new cells and organisms produce new

organisms sexually or asexually.

• Reproduction is not necessary of individuals, but is necessary for a lineage to survive.
• Reproduction is a combination of contradictory processes of copying traits, but with variation.
• If heredity were perfect, life would never change; if it were wildly variable, life would lack

stability.

• Possession of a Genetic Program (Figure 1.6)
• Nucleic acids encode structures of protein molecules.
• DNA stores genetic information in animals.
• Sequences of nucleotide bases (A, C, G and T) code for the order of amino acids in a protein.
• The genetic code is correspondence between bases in DNA and the eventual sequence of

amino acids in a protein.

• This genetic code was established early in evolution and has undergone little change.
• The genetic code in animal mitochondrial DNA is slightly different from nuclear and bacterial

DNA.

• Changes in mitochondrial DNA (it contains fewer proteins) are less likely to disrupt cell

functions.

• Metabolism (Figure 1.7)
• Living organisms maintain themselves by acquiring nutrients from the environment.
• Breakdown of nutrients provides both energy and molecular components for cells.
• Metabolism is the range of essential chemical processes.
• Metabolism involves constructive (anabolic) and destructive (catabolic) reactions.
• In animal cells most metabolic pathways occur in specific cellular organelles.
• The study of complex metabolic functions, from the biochemical to the organismal, is

physiology.

• Development (Figure 1.8)
• Development describes characteristic changes an organism undergoes from origin to adult.
• It involves changes in size and shape, and differentiation within the organism.
• Some animals have uniquely different embryonic, juvenile and adult forms.
• The transformation from stage to stage is metamorphosis.
• In animals, early stages of development are often more similar among organisms of different

species than are later developmental stages.

• Environmental Interaction (Figure 1.9)
• Ecology is the study of an organism's interaction with the environment.
• Organisms respond to stimuli in the environment, a property called irritability.
• We cannot separate life and its evolutionary lineage from the environment.
• Movement
• Energy extracted from environment permits living systems to initiate controlled movements

that are essential for reproduction, growth, response to stimuli, and development.

• Animals are adapted for locomotion which has led to dispersal of entire populations from one

geographic location to another over time.

• Movement of nonliving matter is controlled by external forces and thus is dissimilar to

purposeful movements exhibited by living systems.

• Life Obeys Physical Laws
• Vitalism is the belief that life requires more than basic laws of physics; biological research has

found no basis for vitalism.

• All aspects of life require energy.
• First Law of Thermodynamics (the law of conservation of energy): Energy cannot be

created or destroyed; but energy can be transformed from one form to another.

• In animals, chemical energy in food is converted to chemical energy in cells and then

converted to mechanical energy of muscle contraction.

• It takes a constant input of usable energy from food to maintain organismal complexity
• Second Law of Thermodynamics: Physical systems tend to proceed toward a state of greater

disorder, or entropy. 2 / 4

Chapter01 - Life: Biological Principles and The Science of Zoology

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• Energy obtained and stored by plants is released in many ways and eventually lost as heat.
• The process of evolution does not violate the second law; complexity is achieved by perpetual

use and dissipation of energy flowing into the biosphere from the sun.

• Physiologists study survival, growth, reproduction, etc. from an energetic perspective.

1.2. Zoology as a Part of Biology (Figure 1.10)

• Characteristics of Animals
• Animals are a branch of the evolutionary tree of life.
• Animals are part of a large limb of eukaryotes, organisms that include fungi and plants, with

nuclei in cells.

• Animals are unique in nutrition; they eat other organisms and therefore need to capture food.
• Animals lack: photosynthesis, the cell walls found in plants, and the absorptive hyphae of fungi.
• Species of Euglena are examples of unicellular eukaryotes that combine properties of animals and

plants.

1.3. Principles of Science

• Nature of Science
• Science is a way of asking about the natural world to obtain precise answers.
• Asking questions about nature is ancient; modern science is about 200 years old.
• Science is separate from activities such as art and religion.
• The trial over creation science provided a definition of science.
• Science is guided by natural law.
• Science has to be explanatory by reference to natural law.
• Science is testable against the observable world.
• Science conclusions are tentative; they are not necessarily the final word.
• Science is falsifiable.
• Science is neutral regarding religion and does not favor one religious position over another.
• The reappearance of “creation-science” in the guise of “intelligent-design theory” may force

further defense of the teaching of science.

• Scientific Method (Figure 1.11)
• Criteria for science form a hypothetico-deductive method.
• Hypotheses are based on prior observations of nature or derived from theories based on nature.
• The scientific method may be summarized in a series of steps: (1) Observation (2) Question (3)

Hypothesis (4) Empirical test (5) Conclusions (6) Publication.

• Testable predictions are made based on hypotheses.
• A hypothesis powerful in explaining a wide variety of related phenomena becomes a theory.
• Falsification of a specific hypothesis does not necessarily lead to rejection of a theory as a whole.
• The most useful theories explain the largest array of different natural phenomena.
• Scientific meaning of “theory” is not the same as common usage of theory as “mere speculation.”
• Powerful theories that guide extensive research are called paradigms.
• Replacement of paradigms is a process known as a scientific revolution; the evolutionary

paradigm has guided biology research for over 160 years.

• Experimental Versus Comparative Methods
• Hypotheses can be divided into those that seek to understand proximate versus ultimate causes.
• Studies that explore proximate causes are experimental sciences using experimental methods that:
• Predict the results of an experimental treatment based on tentative explanation.
• If the explanation is correct, then the predicted outcome should occur.
• If a different result occurs, our explanation is incorrect or incomplete.
• Controls are repetitions of an experiment procedure that lack the treatment.
• The sub-fields of molecular biology, cell biology, endocrinology, developmental biology and

community ecology rely heavily on experimental scientific methods.

• Ultimate causes are addressed by questions involving long-term time spans.
• Evolutionary sciences address ultimate causes.
• Evolutionary questions are often explored using a comparative method.
• Patterns of modern similarities are used to establish hypotheses on evolutionary origins.
• Sub-fields include comparative biochemistry, molecular evolution, comparative cell biology,

comparative anatomy, comparative physiology and phylogenetic systematics.

1.4. Theories of Evolution and Heredity (Figure 1.12) 3 / 4

Chapter01 - Life: Biological Principles and The Science of Zoology

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• Darwin’s Theory of Evolution
• Ernst Mayr describes five central theories of “Darwinism.”
• Perpetual change: changes across generations are a fact documented in the fossil record.
• Common descent: branching lineages form a phylogeny that is confirmed by expanding

research on morphological and molecular similarities. (Figure 1.13)

• Multiplication of species: splitting and transforming species produces new species.
• Gradualism: small incremental changes over long periods of time cause gradual evolution in

most cases. (Figure 1.14)

• Natural selection: based on variability in a population, the inheritance of that variation, and

different survival of those variants, explains adaptation. (Figure 1.15)

• Darwin lacked a correct theory of heredity and assumed the theory of blending inheritance was

correct; Mendel’s theory of particulate inheritance became well known only in the very early 1900s.

• Darwin’s theory, as modified by the incorporation of genetics, is called “neo-Darwinism.”
• Mendelian Heredity and the Chromosomal Theory of Inheritance (Figure 1.16)
• Chromosomal inheritance is the foundation for genetics and evolution, as laid down by Mendel.
• Genetic Approach (Figure 1.17)
• Mendel’s technique involved crossing true-breeding populations.
• Production of F1 hybrids and F2 generations showed lack of blending, and masking of

recessive traits by dominant traits.

• Traits assorted independently unless on the same chromosome.
• Expanded research, especially with fruit flies, clarified genetic mechanisms.
• Contributions of Cell Biology (Figures 1.18, 1.19)
• Improvements in microscopes allowed observation of sperm and location of germ cell line.
• Discovery of chromosome pairs in body cells and single sets in germ cells clarified mode of

heredity.

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