Chapter One:

Exploring Life

Biology is the scientific study of life Biologists are moving closer to

understanding: How a single cell develops into an organism How plants convert sunlight to chemical

energy How the human mind works How living things interact in communities How life’s diversity evolved from the first

microbes

What is Biology

Life’s basic characteristic is a high degree of order

Each level of biological organization has emergent properties

Video: Seahorse CamouflageVideo: Seahorse Camouflage

Concept 1.1: Biologists explore life from the microscopic to the global scale

The study of life extends from molecules and cells to the entire living planet

Biological organization is based on a hierarchy of structural levels

A Hierarchy of Biological Organization

1. Biosphere: all environments on Earth2. Ecosystem: all living and nonliving things

in a particular area3. Community: all organisms in an ecosystem4. Population: all individuals of a species

in a particular area5. Organism: an individual living thing

A Hierarchy of Biological Organization (continued)

6. Organ and organ systems: specialized body parts made up of tissues

7. Tissue: a group of similar cells8. Cell: life’s fundamental unit of structure

and function9. Organelle: a structural component of a cell10. Molecule: a chemical structure consisting of

atoms

Ecosystems

The biosphere

Organisms

Populations

Communities

Cells

Organelles

Molecules

Tissues

Organs and organ systems

Cell1 µm

Atoms

10 µm

50 µm

A Closer Look at Ecosystems

Each organism interacts with its environment Both organism and environment affect each other

Ecosystem Dynamics

The dynamics of an ecosystem include two major processes: Cycling of nutrients, in which materials

acquired by plants eventually return to the soil

The flow of energy from sunlight to producers to consumers

Energy Conversion

Activities of life require work Work depends on sources of energy Energy exchange between an organism and

environment often involves energy transformations

In transformations, some energy is lost as heat

Energy flows through an ecosystem, usually entering as light and exiting as heat

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Sunlight

Ecosystem

Heat

Heat

Chemicalenergy

Consumers(including animals)

Producers(plants and otherphotosynthetic

organisms)

A Closer Look at Cells

The cell is the lowest level of organization that can perform all activities of life

The ability of cells to divide is the basis of all reproduction, growth, and repair of multicellular organisms

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25 µm

The Cell’s Heritable Information

Cells contain DNA, the heritable information that directs the cell’s activities

DNA is the substance of genes Genes are the units of inheritance that transmit

information from parents to offspring

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Sperm cell

NucleicontainingDNA

Egg cell

Fertilized eggwith DNA fromboth parents

Embryo’s cells With copies of inherited DNA

Offspring with traits inherited from both parents

Each DNA molecule is made up of two long chains arranged in a double helix

Each link of a chain is one of four kinds of chemical building blocks called nucleotides

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DNA double helix Single strand of DNA

Nucleotide

Cell

Nucleus DNA

Two Main Forms of Cells Characteristics shared by all cells:

Enclosed by a membrane Use DNA as genetic information

Two main forms of cells: Eukaryotic: divided into organelles; DNA in

nucleus Prokaryotic: lack organelles; DNA not

separated in a nucleus

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Membrane

Cytoplasm

EUKARYOTIC CELL PROKARYOTIC CELL

DNA(no nucleus)

Membrane

1 µm

Organelles

Nucleus (contains DNA)

Concept 1.2: Biological systems are much more than the sum of their parts

A system is a combination of components that form a more complex organization

Cells, organisms, and ecosystems are some examples of biological systems

The Emergent Properties of Systems

Emergent properties result from arrangements and interactions within systems

New properties emerge with each step upward in the hierarchy of biological order

The Power and Limitations of Reductionism

Reductionism is reducing complex systems to simpler components that are easier to study

The studies of DNA structure and the Human Genome Project are examples of reductionism

Systems Biology

Systems biology seeks to create models of the dynamic behavior of whole biological systems

An example is a systems map of interactions between proteins in a fruit fly cell

Such models may predict how a change in one part of a system will affect the rest of the system

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CELL

Nucleus

Cytoplasm

Outer membraneand cell surface

Systems biology uses three key research developments: High-throughput technology: methods to

generate large data sets rapidly Bioinformatics: using computers and

software to process and integrate large data sets

Interdisciplinary research teams

Feedback Regulation in Biological Systems

Regulatory systems ensure a dynamic balance in living systems

Chemical processes are catalyzed (accelerated) by enzymes

Many biological processes are self-regulating: the product regulates the process itself

In negative feedback, the accumulation of a product slows down the process itself

In positive feedback (less common), the product speeds up its own production

Animation: Negative Feedback Animation: Positive Feedback

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Enzyme 1

A A

BB

C C

DD

D

DD

D

D

D

DDD

Enzyme 2

Enzyme 3

Negativefeedback

Enzyme 1

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W

Enzyme 4

W

XX

Y Y

ZZ

ZZ

Z ZZ

ZZ Z

Enzyme 5

Enzyme 6

Positivefeedback

Enzyme 4

Enzyme 6

Enzyme 5

Z

Z Z Z

Z

Z

Z

ZZ

Concept 1.3: Biologists explore life across its great diversity of species

Biologists have named about 1.8 million species

Estimates of total species range from 10 million to over 200 million

Grouping Species: The Basic Idea

Taxonomy is the branch of biology that names and classifies species into a hierarchical order

Kingdoms and domains are the broadest units of classification

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Ursidae

Ursus

Carnivora

Mammalia

Chordata

Animalia

Eukarya

Species Genus Family Order Class Phylum Kingdom DomainUrsusamericanus(Americanblack bear)

The Three Domains of Life

At the highest level, life is classified into three domains: Bacteria (prokaryotes) Archaea (prokaryotes) Eukarya (eukaryotes)

Eukaryotes include protists and the kingdoms Plantae, Fungi, and Animalia

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Bacteria 4 µm 100 µm

0.5 µm

Kingdom PlantaeProtists

Kingdom AnimaliaKingdom FungiArchaea

Unity in the Diversity of Life

Underlying life’s diversity is a striking unity, especially at lower levels of organization

In eukaryotes, unity is evident in details of cell structure

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Cilia of windpipe cellsCilia of Paramecium

15 µm 5 µm

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Cilia of windpipe cellsCilia of Paramecium

Cross section of cilium,as viewed with anelectron microscope

0.1 µm

Concept 1.4: Evolution accounts for life’s unity and diversity

The history of life is a saga of a changing Earth billions of years old

The evolutionary view of life came into sharp focus in 1859, when Charles Darwin published On the Origin of Species by Natural Selection

“Darwinism” became almost synonymous with the concept of evolution

The Origin of Species articulated two main points: Descent with modification (the view that

contemporary species arose from a succession of ancestors)

Natural selection (a proposed mechanism for descent with modification)

• Some examples of descent with modification are unity and diversity in the orchid family

Natural Selection

Darwin inferred natural selection by connecting two observations: Observation: Individual variation in heritable

traits Observation: Overpopulation and

competition Inference: Unequal reproductive success Inference: Evolutionary adaptation

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Evolution of adaptationsin the population

Differences inreproductive success

Overproductionand competition

Populationof organisms

Hereditaryvariations

Natural selection can “edit” a population’s heritable variations

An example is the effect of birds preying on a beetle population

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Population with varied inherited traits

Elimination of individuals with certain traits

Reproduction of survivors

Increasing frequency of traits that enhancesurvival and reproductive success

Natural selection is often evident in adaptations of organisms to their way of life and environment

Bat wings are an example of adaptation

Video: Soaring HawkVideo: Soaring Hawk

The Tree of Life

• Many related organisms have similar features adapted for specific ways of life

Such kinships connect life’s unity and diversity to descent with modification

Natural selection eventually produces new species from ancestral species

Biologists often show evolutionary relationships in a treelike diagram

[Videos on slide following the figure]

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Largeground finch

Large cactusground finch

Sharp-beakedground finch

Geospizamagnirostris

Geospizaconirostris

Mediumground finch

Geospizafuliginosa

Smallground finch

Woodpecker finch

Camarhynchuspsittacula

Large tree finch

Medium tree finch

Cactusground finch

Geospizadifficilis

Cactus flowereaters

Geospizascandens

Seed eater

Ground finches

Seed eaters

Tree finches

Common ancestor fromSouth American mainland

Insect eaters Bud eater

Warbler finches

Mangrove finchGeospiza

fortis

Cactospizapallida Small

tree finch

Camarhynchuspauper

Camarhynchusparvulus

Greenwarblerfinch

Graywarblerfinch

Certhideaolivacea

Certhideafusca

Vegetarianfinch

Platyspizacrassirostris

Cactospizaheliobates

Video: Albatross Courtship RitualVideo: Albatross Courtship Ritual

Video: Blue-footed Boobies Courtship RitualVideo: Blue-footed Boobies Courtship Ritual

Video: GalapVideo: Galapáágos Islands Overviewgos Islands Overview

Video Galapágos Marine Iguanagos Marine Iguana

Video: Galapágos Sea LionVideo: Galapágos Sea Lion

Video: Galapágos TortoiseVideo: Galapágos Tortoise

Concept 1.5: Biologists use various forms of inquiry to explore life

Inquiry is a search for information and explanation, often focusing on specific questions

The process of science blends two main processes of scientific inquiry: Discovery science: describing nature Hypothesis-based science: explaining nature

Discovery Science

Discovery science describes nature through careful observation and data analysis

Examples of discovery science: understanding cell structure expanding databases of genomes

Types of Data

Data are recorded observations Two types of data:

Quantitative data: numerical measurements Qualitative data: recorded descriptions

Induction in Discovery Science

Inductive reasoning involves generalizing based on many specific observations

Hypothesis-Based Science

In science, inquiry usually involves proposing and testing hypotheses

Hypotheses are hypothetical explanations

The Role of Hypotheses in Inquiry

In science, a hypothesis is a tentative answer to a well-framed question

A hypothesis is an explanation on trial, making a prediction that can be tested

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Hypothesis #1:Dead batteries

Hypothesis #2:Burnt-out bulb

Observations

Question

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Hypothesis #1:Dead batteries

Hypothesis #2:Burnt-out bulb

Test prediction

Test falsifies hypothesis

Prediction:Replacing batterieswill fix problem

Prediction:Replacing bulbwill fix problem

Test prediction

Test does not falsify hypothesis

Deduction: The “If…then” Logic of Hypothesis-Based Science

In deductive reasoning, the logic flows from the general to the specific

If a hypothesis is correct, then we can expect a particular outcome

A Closer Look at Hypotheses in Scientific Inquiry

A scientific hypothesis must have two important qualities: It must be testable It must be falsifiable

The Myth of the Scientific Method The scientific method is an idealized

process of inquiry Very few scientific inquiries adhere

rigidly to the “textbook” scientific method

In mimicry, a harmless species resembles a harmful species

An example of mimicry is a stinging honeybee and a nonstinging mimic, a flower fly

A Case Study in Scientific Inquiry: Investigating Mimicry in Snake

Populations

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Flower fly (nonstinging)

Honeybee (stinging)

This case study examines king snakes’ mimicry of poisonous coral snakes

The hypothesis states that mimics benefit when predators mistake them for harmful species

The mimicry hypothesis predicts that predators in non–coral snake areas will attack king snakes more frequently than will predators that live where coral snakes are present

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Scarlet king snake

Eastern coralsnake

Scarlet king snake

Key

Range of scarlet king snake

NorthCarolina

Range of easterncoral snake

SouthCarolina

Field Experiments with Artificial Snakes

To test this mimicry hypothesis, researchers made hundreds of artificial snakes: An experimental group resembling king snakes A control group resembling plain brown snakes

• Equal numbers of both types were placed at field sites, including areas without coral snakes

• After four weeks, the scientists retrieved the artificial snakes and counted bite or claw marks

• The data fit the predictions of the mimicry hypothesis

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(a) Artificial king snake

(b) Artificial brown snake that has been attacked

In areas where coral snakes were present, most attacks were on brown artificial snakes.

In areas where coral snakeswere absent, most attacks

were on artificial king snakes.

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% of attacks onartificial king snakes

% of attacks onbrown artificial snakes

Field site withartificial snakes

83%

NorthCarolina

SouthCarolina

17%

16%

84%

Key

Designing Controlled Experiments

Scientists do not control the experimental environment by keeping all variables constant

Researchers usually “control” unwanted variables by using control groups to cancel their effects

Limitations of Science

The limitations of science are set by its naturalism Science seeks natural causes for natural

phenomena Science cannot support or falsify

supernatural explanations, which are outside the bounds of science

Theories in Science

A scientific theory is much broader than a hypothesis

A scientific theory is: broad in scope general enough to generate new

hypotheses supported by a large body of evidence

Model Building in Science

Models are representations of ideas, structures, or processes

Models may range from lifelike representations to symbolic schematics

LE 1-30Frombody

Fromlungs

Rightatrium

Leftatrium

Rightventricle

Leftventricle

To lungs To body

The Culture of Science

Science is an intensely social activity Both cooperation and competition

characterize scientific culture

Science, Technology, and Society

The goal of science is to understand natural phenomena

Technology applies scientific knowledge for some specific purpose

Concept 1.6: A set of themes connects the concepts of biology

Biology is the science most connected to the humanities and social sciences

Underlying themes provide a framework for understanding biology