Foundations of Life and Evolution: General Biology Study Notes

1.1 The Study of Life Reveals Common Themes

Properties of Life

Living systems share a set of core properties that distinguish them from non-living matter. These properties are essential for the definition and study of life in biology.

• Order: Organisms exhibit complex organization at both macroscopic and microscopic levels.

• Evolutionary Adaptation: Heritable traits that enhance survival and reproduction become more common in populations over generations due to natural selection.

• Regulation: Organisms maintain stable internal conditions (homeostasis), such as body temperature and pH.

• Energy Processing: Living things obtain and use energy to power activities and chemical reactions (e.g., photosynthesis, cellular respiration).

• Growth and Development: Organisms grow and develop according to instructions coded in their DNA.

• Response to the Environment: Organisms detect and respond to environmental stimuli (e.g., sweating, leaves turning toward sunlight).

• Reproduction: Organisms reproduce sexually or asexually, ensuring the continuation of their species.

Are Viruses Living?

Viruses lack metabolic enzymes and protein-making equipment. They are obligate intracellular parasites—they can only replicate within a host cell and do not meet all criteria for life.

Biology: The Science of Life

• Definition: The scientific study of life and living things.

• Themes of Study:

  • Organization

  • Information

  • Energy and Matter

  • Interactions

  • Evolution

Organization: Properties at Levels

Biological systems are organized in a hierarchy, from the largest to the smallest units:

• Biosphere → Ecosystems → Communities → Populations → Organisms → Organs → Tissues → Cells → Organelles → Molecules

Emergent Properties

Emergent properties arise at each level of biological organization due to the arrangement and interactions of parts as complexity increases. For example, a functioning cell emerges from the interactions of its molecular components.

The Cell: Fundamental Unit of Life

• The smallest unit that can perform all activities required for life.

• All cells are enclosed by a membrane.

• Two main types: Eukaryotic and Prokaryotic.

Domain	Eukaryotes	Prokaryotes
Examples	Eukarya	Bacteria, Archaea
Nucleus and other compartments	Yes, contains both	No (contains neither)
"X" Celled	Single or multicellular	Always singular

Information: Expression and Transmission of Genetic Information

• Chromosomes: Structures containing genetic material (DNA).

• DNA: Deoxyribonucleic acid, the molecule of heredity. DNA is passed on by:

  • Mitosis: Replication and splitting of a cell, producing identical cells.

  • Meiosis: Formation of gametes (sex cells) with half the genetic material.

• Nucleotides: DNA is a double helix composed of four nucleotides:

  • Adenine (A) – Purine, double H bond

  • Thymine (T) – Pyrimidine, double H bond

  • Cytosine (C) – Pyrimidine, triple H bond

  • Guanine (G) – Purine, triple H bond

• Gene: A segment of DNA that codes for a specific protein or function.

• Ribonucleic Acid (RNA): Acts as a messenger between DNA and ribosomes for protein synthesis.

• Proteome: The set of proteins expressed by a genome.

• Central Dogma: The flow of genetic information:

  • Transcription: DNA → RNA

  • Translation: RNA → Protein

Gene Expression: The process of DNA replication, transcription, and translation to create cellular components.

Energy and Matter: Transfer and Transformation

• Energy flows through ecosystems, usually entering as light and exiting as heat.

• Photosynthesis transforms light energy into chemical energy (glucose).

• Cellular respiration and other metabolic processes convert chemical energy for use by organisms.

• Chemicals and nutrients are recycled: producers → consumers → decomposers → environment.

Interactions: From Molecules to Ecosystems

• Feedback Regulation: The output or product of a process regulates that process.

  • Negative feedback: Reduces the initial stimulus (e.g., insulin lowers blood glucose).

  • Positive feedback: Speeds up its own production (e.g., blood clotting).

1.2 The Core Theme: Evolution

Evolution: The Unifying Theory of Biology

• Definition: The scientific explanation for the unity and diversity of organisms, and their adaptation to environments.

• Occurs over time in populations via natural selection.

Phylogenetic (Evolutionary) Trees

These diagrams represent hypotheses about the evolutionary relationships among organisms, based on genetic and morphological data.

Phenotypes and Selective Pressure

• Phenotype: Observable traits of an organism, influenced by genetic variation.

• Populations experience selective pressure from the environment, favoring some traits over others.

Theory of Natural Selection

• Adaptive Radiation: The diversification of a group of organisms into forms filling different ecological niches.

• Key observations:

  • Populations can produce more offspring than the environment can support.

  • Individuals vary in heritable traits.

  • Favorable traits increase in frequency over generations.

Three Domains of Life

• Bacteria: Single-celled prokaryotes, most diverse and widespread.

• Archaea: Single-celled prokaryotes, often found in extreme environments.

• Eukarya: Includes four kingdoms:

  • Plantae

  • Animalia

  • Fungi

  • Protists

Classification: Linnaean System

• Organisms are grouped by resemblance (morphology, DNA sequence).

• Binomial nomenclature: Genus species

• Hierarchy: Kingdom, Phylum, Class, Order, Family, Genus, Species

1.3 Science is the Process of Inquiry

Scientific Process

1. Make observations

2. Form a question based on observations

3. Form a hypothesis (testable explanation)

4. Conduct experiments under controlled conditions

5. Collect data and analyze results

6. Report findings

Definitions and Differences

• Science: A way of knowing; an approach to understanding the natural world.

• Inquiry: The search for information and explanations.

• Inductive Reasoning: Deriving generalizations from many observations.

• Deductive Reasoning: Making specific predictions from general premises.

• Theory: A broad explanation supported by a large body of evidence.

Variables and Controls in Experiments

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

• Variables:

  • Independent: Manipulated by researchers

  • Dependent: Measured outcome, affected by the independent variable

• Correlation does not mean causation.

22.1 Darwinian Revolution

Endless Forms Most Beautiful

• Charles Darwin explained:

  • Organisms are suited to their environments

  • Unity and diversity of life

• Descent with modification: Modern species are modified descendants of ancestral species.

• Evolution is both pattern (observed change) and process (mechanism: natural selection).

Early Ideologies

• Aristotle: Species are unchanging; classified by increasing complexity (Scala Naturae).

• Carolus Linnaeus: Classified species by similarities; developed binomial nomenclature.

Fossils and the History of Life

• Fossils: Remains or traces of organisms found in sedimentary rock layers (strata).

• Georges Cuvier: Each stratum represents a catastrophic event leading to extinction.

• James Hutton: Earth's features result from gradual processes over time.

Additional info:

• Some diagrams and images referenced in the notes (e.g., labeled diagrams, cycle images) are not included here but are commonly found in standard biology textbooks.

• Further details on the Central Dogma, gene expression, and feedback regulation can be found in molecular biology chapters.