Evolution and Themes in Biology

Opening Questions in Biology

Biology is the study of life, seeking to answer fundamental questions about living organisms and their processes.

• What is the study of life? Biology explores the structure, function, growth, origin, evolution, and distribution of living organisms.

• What is science? Science is a systematic enterprise that builds and organizes knowledge through testable explanations and predictions.

• How is science done? Science uses observation, experimentation, and reasoning to understand natural phenomena.

Five Unifying Themes of Biology

Biology reveals five major themes that help organize our understanding of life:

• Organization

• Information

• Evolution

• Energy and Matter

• Interactions

Theme 1: New Properties Emerge at Successive Levels of Biological Organization

Complex properties result from the arrangement and interactions of parts as complexity increases.

• Example: Hydrogen and oxygen combine to make water; parts of a bicycle work together to allow movement.

Biosphere: Complexity of Life on Earth

• Reductionist approach: Studies simpler components of living systems.

• Systems biology: Studies interactions among parts of a system, focusing on emergent properties.

• Emergent properties: New characteristics arise at each level of organization.

Structure and Function

The structure of an organism or its parts often determines its function.

• Example: The shape of a bird's wing enables flight.

Cell Theory

• All living organisms are made from cells.

• Cells are the fundamental unit of life.

Theme 2: Life Processes Involve the Expression and Transmission of Genetic Information

• DNA: Deoxyribonucleic acid contains genetic material inherited from parents.

• Chromosomes: Long DNA molecules consisting of thousands of genes.

• Gene expression: DNA is transcribed to RNA and translated to proteins.

Gene Expression Example

• Crystallin protein: Found in the eye lens, produced by gene expression.

Energy and Interactions in Ecosystems

Energy Flow in Ecosystems

Energy flows through ecosystems, enabling life processes.

• Producers: Make their own energy (e.g., plants via photosynthesis).

• Consumers: Obtain energy by eating other organisms.

• Heat loss: Energy is lost as heat during energy transformations.

Theme 4: From Molecules to Ecosystems, Interactions Are Important

• Interactions occur at all levels: molecules, cells, organisms, and ecosystems.

• Interactions can be beneficial, neutral, or harmful.

Theme 5: Interactions with Environment

• Organisms interact with other organisms and their physical environment.

Evolution: The Core Theme of Biology

Unity and Diversity of Life

Evolution explains both the unity and diversity of life.

• All living organisms are modified descendants of common ancestors.

• "Nothing in biology makes sense except in the light of evolution." — Theodosius Dobzhansky

Diversity of Life

• About 1.8 million species have been identified.

• Classified into three domains:

• Natural selection: Drives evolution by favoring traits that enhance survival and reproduction.

How Science Works

Scientific Inquiry

Science seeks information and explanations of natural phenomena.

• Involves making observations, forming hypotheses, and testing them.

• Data can be:

  • Quantitative: Numerical measurements

  • Qualitative: Descriptions

• Inductive reasoning: Generalizations from observations

• Deductive reasoning: Predictions from general premises

Forming and Testing Hypotheses

• Hypothesis: Explanation based on observations and assumptions, can be tested.

• Controlled experiment: Compares an experimental group with a control group.

• Variables:

  • Independent variable: Manipulated by researcher

  • Dependent variable: Measured in response

Scientific Theory

• Broader in scope than a hypothesis

• Supported by a large body of evidence

Science and Society

• Science is collaborative and builds on previous work.

• Results are communicated through publications and presentations.

Chemistry of Life

Elements and Compounds

Elements are pure substances; compounds are combinations of elements.

• Chemical bonding: Atoms combine to form molecules via bonds.

Matter

• Anything that takes up space and has mass.

• Organisms are composed of matter.

Atomic Structure and Isotopes

• Atoms consist of protons, neutrons, and electrons.

• Atomic number: Number of protons

• Mass number: Protons + neutrons

• Isotopes: Atoms of the same element with different numbers of neutrons

Chemical Bonds

• Atoms interact to complete their valence shells.

• Types of bonds:

  • Covalent bonds: Atoms share electrons

  • Ionic bonds: Atoms transfer electrons

  • Hydrogen bonds: Attraction between partial charges

Covalent Bonds

• Single, double, or triple bonds depending on shared electron pairs

• Nonpolar: Electrons shared equally (e.g., H2, CH4)

• Polar: Electrons shared unequally (e.g., H2O)

Ionic Bonds

• Form between oppositely charged ions

• Example: NaCl (sodium chloride)

Hydrogen Bonds

• Attraction between a hydrogen atom carrying a partial positive charge and an electronegative atom (e.g., oxygen, nitrogen)

• Important for water's properties

Water as a Polar Molecule

• One end has a partial positive charge, the other a partial negative charge

• Polarity allows water molecules to form hydrogen bonds

Emergent Properties of Water

• Moderation of temperature

• Expansion upon freezing

• Excellent solvent

Cohesion and Adhesion

• Cohesion: Water molecules stick together via hydrogen bonds

• Adhesion: Water molecules stick to other substances

• Contribute to water transport in plants

Moderation of Temperature

• Water absorbs heat when hydrogen bonds break

• Water releases heat when hydrogen bonds form

• Specific heat: Amount of heat needed to change temperature

• Heat of vaporization: Heat required for water to evaporate

Ice Floats

• Hydrogen bonds keep water molecules far enough apart to make ice less dense than liquid water

Solvent Properties of Water

• Water is a versatile solvent

Acids and Bases

• Water can dissociate into H+ and OH-

• Acids: Proton donors

• Bases: Proton acceptors

Carbon: The Backbone of Life

• Can form 4 covalent bonds

• Can bond with many different elements (e.g., hydrogen, oxygen, nitrogen)

• Can form single, double, and triple bonds

• Allows for molecular diversity

• Example: Urea molecule (organic compound) with carbon forming covalent bonds with oxygen, nitrogen, and hydrogen.

Additional info: The structure of urea demonstrates carbon's ability to form four covalent bonds, contributing to the diversity of organic molecules essential for life.