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Lecture 2

2.2 Exploring Life

Book Chapters: 1 Campbell7,

• Biologists have named about 1.8 million species
• Estimates of total species range from 10 million to over 200 million

Concept 2.2.1: Biologists explore life across its

great diversity of species

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

Bacteria 4 μm^ 100 μm

0.5 μm

Protists Kingdom Plantae

Archaea Kingdom Fungi Kingdom Animalia

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

Cilia of Paramecium Cilia of windpipe cells

15 μm 5 μm

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

Concept 2.2.2: Evolution accounts for life’s unity

and diversity

• 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

• Natural selection can “edit” a population’s heritable variations
• Natural selection is often evident in adaptations of organisms to their way of life and environment
• Bat wings are an example of adaptation

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]

• 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

Concept 2.2.3: Biologists use various forms of

inquiry to explore life

Discovery Science

• Discovery science describes nature through careful

observation and data analysis

• Inductive reasoning involves generalizing based on

many specific observations

• Data are recorded observations
• Two types of data:
  • Quantitative data: numerical measurements
  • Qualitative data: recorded descriptions

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 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

Biology is a historical science

• Students tend to think that there is one universally applied scientific method, and that all “real science” is hypothesis-driven and experimental. As a result of this misunderstanding, students may discount theories about historical events. Scientists use many different methods to investigate biological questions.
• In contrast to the methods used in experimental sciences, historical narratives, cannot usually be tested by performing controlled experiments. Historical narratives must stand or fall on the basis of whether they can consistently explain evidence gathered from many different sources.

Model Building in Science

• Models are representations of ideas, structures, or processes
• Models may range from lifelike representations to symbolic schematics

From body

From lungs

Right atrium

Left atrium

Right ventricle

Left ventricle

To lungs To body

The Culture of Science

• Science is an intensely social activity

• Both cooperation and competition characterize

scientific culture