An Introduction To Life On Earth

An Introduction To Life On Earth
Chapter 1 An Introduction To Life On Earth Copyright © 2011 Pearson Education Inc.

Chapter 1 At a Glance 1.1 How Do Scientists Study Life?
1.2 Evolution: The Unifying Theory of Biology 1.3 What Are the Characteristics of Living Things? 1.4 How Do Scientists Categorize the Diversity of Life?

How Do Scientists Study Life?
Life can be studied at different levels Atom, molecule, cell Tissue, organ, organ system Mulicellular organism, population, species Community, ecosystem, biosphere

Levels of Organization of Matter
Fig. 1-1

1.1 How Do Scientists Study Life?
Levels of organization All matter is formed of elements An atom is the smallest particle of an element retaining the properties of an element Atoms combine to form molecules Molecules provide the building blocks for cells, the smallest unit of life

The Cell Is the Smallest Unit of Life
Fig. 1-2

Levels of organization (continued) Some forms of life consist of single cells In multicellular forms, cells combine to form tissues Tissues combine to form organs, which can be united as organ systems Multicellular organisms are composed of multiple organ systems

Levels of organization (continued) Organisms of the same type that are capable of interbreeding are called a species A group of organisms of the same species living in a given area is a population Interacting populations make up a community

Levels of organization (continued) A community and its nonliving environment is an ecosystem The entire surface of the Earth, including living and nonliving components, is the biosphere

Scientific principles underlie all scientific inquiry Natural causality is the principle that all events can be traced to natural causes Natural laws apply to every time and place Scientific inquiry is based on the assumption that people perceive natural events in similar ways

Historical approaches to studying life The belief that some events happen through supernatural forces (e.g., the actions of Greek gods) The belief that all events can be traced to natural causes that we can comprehend (natural causality) Corollary: Evidence gathered from nature has not been deliberately distorted to fool us

Natural laws apply to every time and place Natural laws are uniform in space and time This principle is key to understanding biological events (e.g., evolution) that occurred before humans recorded them

Natural laws apply to every time and place (continued) Creationism is contrary to the principle of uniformity-in-time and natural causality Creationists hold that different species were created one at a time by the direct intervention of God, contrary to events we see happening today

People have similar perceptions This is based on the assumption that all human beings perceive natural events in fundamentally the same way Common perception allows us to accept observations of other humans as reliable

People have similar perceptions (continued) Common perception is usually not found in appreciation of art, poetry, and music, nor between cultures or religious beliefs Value systems are subjective Science requires objectively gathered data

Value Systems Differ Fig. 1-3

The scientific method is the basis for scientific inquiry Observation Question Hypothesis Prediction Experiment or Observation Conclusion

The Scientific Method Fig. 1-4

The scientific method Scientific inquiry is a rigorous method for making observations The scientific method for inquiry follows six steps

The scientific method (continued) 1. Observation of a specific phenomenon 2. The observation, in turn, leads to a question 3. The question leads to formulation of a hypothesis, based on previous observations, that is offered as an answer to the question

The scientific method (continued) The hypothesis leads to a prediction, typically expressed in “if…then…” language The prediction is tested by carefully controlled manipulations called experiments The experiments produce results that either support or refute the hypothesis, allowing the development of a conclusion

The scientific method (continued) Scientific experimentation tests the assertion that a single variable causes a particular observation The experiment must rule out the influence of other possible variables on the recorded observations

The scientific method (continued) Controls are incorporated into experiments Controls keep untested variables constant The scientific method is illustrated by experiments by Francesco Redi and Malte Andersson

Author Animation: Redi and Spontaneous Generation 1

The Experiments of Francesco Redi
Fig. E1-1

The Experiments of Malte Andersson
Fig. E1-2

Application of the scientific method to everyday problems Assume you are late for an appointment and hurriedly try to start your car Observation: The car won’t start Question: Why won’t the car start? Hypothesis: The battery is dead Prediction: IF the hypothesis is correct, THEN the car will start if the battery is replaced Experiment: The battery is replaced and the car starts

Application to everyday problems (continued) Premature conclusion: The problem was a dead battery because the car starts when replaced with a different one Recognition of inadequate controls Did you attempt to start the car more than once? Was the battery cable on the original battery loose?

Application to everyday problems (continued) Establishing a control Reinstall your old battery, check for tight cables, and now try to start the car If the car still fails to start on the old battery, the only variable in this investigation now is the effectiveness of the battery

Application to everyday problems (continued) Making a better conclusion, based on controlled experiments Your battery was probably dead

Limitations of the scientific method One can never be sure all untested variables are controlled Conclusions based on the experimental data must remain tentative

Author Animation: Hypothesis Formation and Testing

Communication is crucial to science Results of experimentation must be communicated thoroughly and accurately to other scientists for repetition Repetition by other scientists add verification that findings can be used as the basis for further studies

Science is a human endeavor Human personality traits are part of “real science” Scientists, like other people, may be driven by pride, ambition, or fear Scientists sometimes make mistakes Accidents, lucky guesses, intellectual powers, and controversies with others contribute strongly to scientific advances

Science is a human endeavor (continued) In the 1920s, bacteriologist Alexander Fleming grew bacteria in cultures One of the bacterial cultures became contaminated with a mold Fleming nearly destroyed the culture when he noticed the mold (Penicillium) inhibited bacterial growth in the culture

Science Is a human endeavor (continued) Fleming hypothesized that the mold produced an antibacterial substance Further tests using broth from pure Penicillium cultures lead to the discovery of the first antibiotic, penicillin

Penicillin Kills Bacteria
Fig. 1-5

Science is a human endeavor (continued) Fleming continued beyond a lucky “accident” with further scientific investigation to a great discovery “Chance favors the prepared mind” Louis Pasteur

Scientific theories have been thoroughly tested A scientific theory differs in definition from that of everyday usage Many people use the word theory to mean hypothesis, or an “educated guess”

Scientific theories have been thoroughly tested (continued) A scientific theory is a general explanation for important natural phenomena It is extensively and reproducibly tested It is more like a principle or natural law (e.g., the atomic, gravitational, and cell theories) If compelling evidence arises, a theory may be modified

Scientific theories have been thoroughly tested (continued) New scientific evidence may prompt radical revision of existing theory For example, the discovery of prions

The discovery of prions Before 1980, all known infectious diseases contained DNA or RNA In 1982, Stanley Prusiner showed that the infectious sheep disease scrapie is caused by a protein (a “protein infectious particle,” or prion)

The discovery of prions (continued) Prions have since been shown to cause “mad cow disease” and diseases in humans The willingness of scientists to revise accepted belief in light of new data was critical to understanding and expanding the study of prions

Science is based on reasoning Inductive reasoning is used in the development of scientific theories A generalization is created from many observations For example, the cell theory (that all living things are made of one or more cells) arises from many observations that all indicate a cellular basis for life

Science is based on reasoning (continued) Deductive reasoning is the process of generating hypotheses based on a well-supported generalization (such as a theory) For example, based on the cell theory, any newly discovered organism would be expected to be composed of cells

1.2 Evolution: The Unifying Theory of Biology
Evolution is the process by which modern organisms descended, with modifications, from preexisting forms of life

Abundant evidence has been found to support evolutionary theory since Charles Darwin and Alfred Wallace proposed it in the mid-1800s Those who see evolution as “just a theory” don’t understand the scientific definition of a theory

Evolution explains how diverse forms of life originated through changes in their genetic makeup Modern organisms descended with modification from preexisting life-forms “Nothing in biology makes sense, except in the light of evolution” Theodosius Dobzhansky

Darwin and Wallace formulated the basis of our modern understanding of evolution Evolution arises as a consequence of three natural processes

Three natural processes underlie evolution Genetic variation among members of a population due to differences in their DNA Inheritance of those variations by offspring of parents carrying the variation Natural selection of individuals whose survival and enhanced reproduction are due to the favorable variations they carry

Genetic variability Genetic variation arises from segments of DNA Changes in genes (mutations) alter the informational content Mutations arise from a number of sources Mutations can occur from irradiation Mutations occasionally arise from copying mistakes in DNA during cellular reproduction

DNA Model Fig. 1-6

Genetic variability (continued) Effects of mutation No effect (harmless) A decrease in the organism’s ability to function Death of the organism An increase in an organism’s ability to survive and reproduce (rare) Mutations occurring over millions of years and passed through many generations cause members of a species to be slightly different

Natural selection Organisms that best meet environmental challenges leave the most offspring Natural selection preserves genes that help organisms flourish

Natural selection (continued) Adaptations are structures, physiological process, or behaviors that aid in survival and reproduction Adaptations that are good for one environment may be poor in another

Natural selection (continued) Species that cannot adapt to environmental change go extinct; for example, the dinosaurs

A Fossil Triceratops Fig. 1-7

Natural selection (continued) The many different habitats (environments) in an area coupled with evolutionary adaptive processes produce species variety, or biodiversity Humans are responsible for accelerating the rate of environmental change (and therefore, the rate of extinction of species)

1.3 What Are The Characteristics of Living Things?
Living things are complex, organized, and composed of cells Living things maintain relatively constant internal conditions through homeostasis Living things respond to stimuli Living thing acquire and use materials and energy

Living things grow Living things reproduce themselves Living things, collectively, have the capacity to evolve

Defining life The dictionary definition of life is “the quality that distinguishes a vital and functioning being from a dead body” Living things are more than the sum of their parts; life is difficult to define The complexity and ordered interactions of parts in living things gives rise to certain properties

What Are The Characteristics of Living Things?
Living things are composed of cells Living things are both complex and organized Fig. 1-8

Living things are composed of cells (continued) The cell theory states that the cell is the basic unit of life A single cell has an elaborate internal structure

Living things are composed of cells (continued) All cells contain: Genes that provide information to control the life of the cell Organelles, which are small, specialized structures that perform specific functions A plasma membrane that encloses the fluid cytoplasm and organelles from the outside world

Homeostasis Organisms must maintain relatively constant internal conditions, or homeostasis For example, many organisms regulate body temperature

Homeostasis (continued) Homeostatic mechanisms include: Sweating in hot weather or dousing oneself with cool water Metabolizing more food, basking in the sun, or turning up the thermostat in cold weather Organisms still grow and change while maintaining homeostasis

Living Things Maintain Homeostasis
Fig. 1-9

Living things respond to stimuli Organisms sense and respond to internal and external environmental stimuli Sensory organs in animals can detect and respond to external stimuli like light, sound, chemicals, etc. Internal stimuli in animals are perceived by stretch, temperature, pain, and chemical receptors Plants and bacteria respond to stimuli as well (e.g., plants grow toward the light, and bacteria move toward available nutrients in a medium)

Living things acquire materials Materials and energy are required for the organism to maintain organization, to grow, and to reproduce

Living things acquire materials (continued) Important materials (nutrients) are acquired from air, water, soil, or other living things Nutrients are incorporated into the bodies of organisms Nutrients are continuously recycled among living and nonliving things

The Flow of Energy and the Recycling of Nutrients
Fig. 1-10

Living things acquire materials (continued) Organisms obtain energy in two ways Plants and some single-celled organisms capture sunlight in photosynthesis Other organisms consume energy-rich molecules in the bodies of other organisms All energy that sustains life comes directly or indirectly from the sun

Living things grow Every organism becomes larger over time Plants, birds, and mammals grow by producing more cells to increase their mass Bacteria grow by enlarging their cells; they also divide to make more individuals Growth involves the conversion of acquired materials to molecules of the organism’s body

Living things reproduce themselves Organisms give rise to offspring of the same type The parent’s genetic material (DNA) is passed on to the offspring, creating continuity of life

Living things have the capacity to evolve The genetic composition of a whole species changes over many generations Mutations and variable offspring allow a species to evolve

1.4 How Do Scientists Categorize the Diversity of Life?
Scientists generally categorize organisms into three major groups, or domains Bacteria Archaea Eukarya

The Domains and Kingdoms of Life
Fig. 1-11

Categorizing life The domain Eukarya contains four subdivisions, or kingdoms Fungi Plantae Animalia The “protists”

Categorizing life (continued) There are exceptions to any simple set of rules used to distinguish the domains and kingdoms, but three characteristics are particularly useful Cell type The number of cells in each organism Energy acquisition

Table 1-1

The domains Bacteria and Archaea consist of prokaryotic cells The domain Eukarya is composed of eukaryotic cells

Two cell types are seen among all living things: prokaryotic and eukaryotic cells Cell types are named after presence or absence of a nucleus The nucleus is a membrane-enclosed sac containing the cell’s genetic material

Prokaryotic and eukaryotic cells (continued) Prokaryotic (“before nucleus” in Greek) They are only 1–2 micrometers in diameter They lack organelles or a nucleus This cell type is found in the domains Bacteria and Archaea

Prokaryotic and eukaryotic cells (continued) Eukaryotic (“true nucleus” in Greek) They are larger than prokaryotic cells They contain a variety of organelles, including a nucleus This cell type is found only among members of the domain Eukarya

Unicellular vs. multicellular Unicellular (single-celled) organisms are found in: Bacteria Archaea

Unicellular vs. multicellular Multicellular (many-celled) organisms are found in Eukarya, within the kingdoms: Fungi Plantae Animalia

Members of different kingdoms have different ways organisms acquire energy Autotrophs (“self-feeding”) Photosynthetic organisms that capture sunlight and store it in sugar and fats Includes plants, some bacteria, and some protists

Ways organisms acquire energy (continued) Heterotrophs (“other-feeding”) Organisms that acquire energy through ingesting molecules in the bodies of other organisms Includes many archaeans, bacteria, protists, fungi, and animals The size of the food eaten varies from individual food molecules to ingestion and digestion of whole chunks

An Introduction To Life On Earth

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