Science of Biology

The Scientific Study Of Life

Biosphere

EcosystemFlorida coast

CommunityAll organisms onthe Florida coast

PopulationGroup of brown

pelicans

OrganismBrown pelican

Organ systemNervous system

OrganBrain

TissueNervous tissue

CellNerve cell

OrganelleNucleus Molecule

DNA

AtomNucleus

Brain

Spinal cord

Nerve

Biology• Nature is not neatly packaged into the

individual life sciences.

• Organisms and their environment are natural systems to which the basic concepts of chemistry and physics apply.

• Biology is a multidisciplinary science, drawing on the insights from other sciences.

What is Life?• Life resists a simple, one-sentence

definition, yet we can recognize life by what living things do.

• All organisms share a common set of features or properties

Properties of Life• Form high degree of ordered structures• Regulate internal conditions

Properties of Life• Harvest and use energy• Reproduce and evolve

Properties of Life• Grow and develop

• Respond to environmental stimuli

Organizational Hierarchy• Life can be

organized into a hierarchy of structural levels.

• At each successive level additional emergent properties appear.

Fig. 2.1

Biosphere

EcosystemFlorida coast

CommunityAll organisms onthe Florida coast

PopulationGroup of brown

pelicans

OrganismBrown pelican

Organ systemNervous system

OrganBrain

TissueNervous tissue

CellNerve cell

OrganelleNucleus Molecule

DNA

AtomNucleus

Brain

Spinal cord

Nerve

The hierarchy of Life• Organ systems• Organs• Tissues• Cells• Organelles• Molecules

Biologists investigate the full spectrum of life, from the biosphere to the biochemical reactions within a cell.

Emergent Properties• Life’s basic characteristic is a high degree of

order• Biological organization is based on a hierarchy

of structural levels, each building on the levels below

• Novel properties emerge at each step upward • Emergent properties result from interactions

between components• Emergent properties reflect importance of

structural arrangement and organization

Reductionism• The complex organization of life presents a

dilemma to scientists seeking to understand biological processes.• We cannot fully explain a higher level of organization

by breaking it down into parts.• At the same time, it is futile to try to analyze something

a complex as an organism or cell without taking it apart.

• Reductionism - Reducing complex systems to simpler components, is a powerful strategy in biology.

• Reductionism is balanced by the longer-range objective of understanding emergent properties.

Unity and Diversity• Biology can be viewed as having two

dimensions:• A “vertical” dimension covering the size scale

from atoms to the biosphere• A “horizontal” dimension that stretches across

the diversity of life.• The latter includes not only present day organisms

but those throughout life’s history.

Diversity - Hallmark Of Life• At present, biologists have identified and

named about 1.5 million species.• This includes over 280,000 plants, almost

50,000 vertebrates, and over 750,000 insects.• Thousands of newly identified species are

added each year.

• Estimates of the total diversity of life range from about 5 million to over 30 million species.

Unity• Underlying the diversity of life

is a striking unity, especially at the lower levels of organization.

• The universal genetic language of DNA unites prokaryotes, like bacteria, with eukaryotes, like humans.

• Among eukaryotes, unity is evident in many details of cell structure.

Fig. 1.12

Unity and Diversity• Evolution is the key to understanding biological diversity• The evolutionary connections among all organisms

explain the unity and diversity of life• Descent with modification accounts for both the unity

and diversity of life.• In many cases, features shared by two species are due to their

descent from a common ancestor.• Differences are due to modifications by natural selection

modifying the ancestral equipment in different environments.

• Evolution is the core theme of biology - a unifying thread that ties biology together.

Evolution• Can explain the unity and diversity

of life

• Charles Darwin synthesized the theory of evolution by natural selection, his book on evolution presented two important concepts.

• Species evolved from ancestors, and there was modification in the process or, as Darwin stated, “descent with modification.”

• Natural selection occurs as heritable variations are exposed to environmental factors that favor the reproductive success of some individuals over others.

Darwin’s Observations• Individual Variation - Individuals in a population

of any species vary in many heritable traits• Differential reproductive success –

• Any population can potentially produce far more offspring than the environment can support

• This creates a struggle for existence among variant members of a population.

• Darwin inferred that those individuals with traits best suited to the local environment will generally leave more surviving, fertile offspring

Natural Selection

• Natural selection is an editing mechanism

• Occurs when populations or organisms, having inherited variations, are exposed to environmental factors that favor the reproductive success of some individuals over others

Struggle for Existence• Struggle for existence: A population produces

many more offspring than can survive long enough to reproduce. This idea was based on Thomas Malthus’s Essay on the Principle of Population – populations tend to increase faster than their food supply.

• This leads to competition and is of great consequence in differential reproductive success

Natural Selection

• Natural selection, by its cumulative effects over vast spans of time, can produce new species from ancestral species.• For example, a population may be fragmented

into several isolated populations in different environments.

• What began as one species could gradually diversify into many species.

• Each isolated population would adapt over many generations to different environmental problems

Finches Of The Galapagos Islands• Diversified after an initial colonization from the mainland to exploit

different food sources on different islands.

Descent With Modification

• Descent with modification accounts for both the unity and diversity of life.• In many cases, features shared by two species

are due to their descent from a common ancestor.

• Differences are due to modifications by natural selection modifying the ancestral equipment in different environments.

• Evolution is the core theme of biology - a unifying thread that ties biology together.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Adaptation• The product of natural

selection is adaptation, the collection of favorable modifications in a population over time.

• All organisms have adaptations that have evolved by means of natural selection

The Process Of Science

• Scientists use two main approaches to learn about nature• Discovery Science - Scientists describe some

aspect of the world and use inductive reasoning to draw general conclusions

• Hypothesis-Based Science - Scientists attempt to explain observations by testing hypotheses

The Process Of Science• There are no absolute truths in science• All that we understand about nature

comes from our ability to observe the world around us.

• Scientists do not “believe” in something• Instead scientists have levels of

confidence in explanations for natural phenomena.

Scientific Theory• Broad in scope, generates hypotheses,

supported by massive body of evidence. Theories constantly challenged through testing of the specific, falsifiable hypotheses they generate.• Einstein’s Theory of General Relativity• Darwin’s Theory of Evolution• Lemaître’s Big Bang Theory of the Universe

Hypothesis-based Science

• Hypothesis-based science involves:• Observations, questions, hypotheses as tentative

answers to questions

• Deductions leading to predictions, and then tests of predictions to see if a hypothesis is falsifiable

What is a hypothesis?• A hypothesis is a tentative or educated guess at

an answer to a problem or question that is being asked.

• A good hypothesis makes predictions that can be tested.

• Part of the process of hypothesis-based science uses deductive reasoning, which flows from a general premise to a specific premise.

• The important aspect of this process is that the deduction can be tested.

Hypothesis-based Science• A Case Study from Every day Life

• Deductive reasoning is used in testing hypotheses as follows

Observations

Question

Hypothesis # 1:Dead batteries

Hypothesis # 2:Burnt-out bulb

Prediction:Replacing batterieswill fix problem

Prediction:Replacing bulbwill fix problem

Test prediction Test prediction

Test falsifies hypothesis Test does not falsify hypothesis

Hypothesis-based Science

• Two important qualities of the hypothesis-based science illustrated in the flashlight example

• A hypothesis must be testable.• A hypothesis must be falsifiable

• If a hypothesis is correct, and we test it, then we can expect a particular outcome

Key Steps in the Scientific Method

• Make observations, may come from others or results of earlier tests

• Ask questions about aspects of the observations: How? Why? When?

• Generate hypotheses; explanations of the phenomena, phrased in such a way as to be testable.

• Derive predictions; logical, testable outcomes of the hypotheses• Developed by the use of deductive reasoning• Predictions take the form of if (statement of hypothesis) is true,

then (predictions).• Test the predictions; performed to determine if the

predictions are supported (fail to falsify) or falsified• A hypothesis becomes credible when repeated attempts

to disprove it fail