Biology and the Tree of Life

Fundamental Characteristics of Life

Biology is the study of living organisms and their interactions with the environment. To define life, biologists identify several key characteristics shared by all living things.

• Cellular Organization: All living things are composed of one or more cells.

• Metabolism: Living organisms carry out chemical reactions to obtain and use energy.

• Homeostasis: The ability to maintain a stable internal environment.

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

• Reproduction: The ability to produce new organisms, either sexually or asexually.

• Response to Stimuli: Organisms respond to environmental changes.

• Evolutionary Adaptation: Populations evolve over generations through natural selection.

Unifying Ideas of Biology: The cell theory, gene theory, evolution, and homeostasis are central concepts that unify the study of biology.

Nature of Science: Science is a systematic way of knowing based on evidence, observation, and experimentation.

• Scientific Method: Involves making observations, forming hypotheses, conducting experiments, and drawing conclusions.

• Hypothesis: A testable explanation for an observation.

• Theory: A well-supported explanation of natural phenomena, such as the theory of evolution.

Linnaean Hierarchy: A system of classifying organisms into nested groups: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Taxonomy: The science of naming, describing, and classifying organisms.

Evolution by Natural Selection: Darwin's theory that organisms better adapted to their environment tend to survive and produce more offspring.

• Spontaneous Generation: The disproven idea that living things can arise from nonliving matter. Pasteur's experiments showed that life comes from pre-existing life.

Evolution and Natural Selection

Major Theories and Evidence

Evolution explains the diversity of life through gradual change in populations over time. Several theories have been proposed:

• Typological Thinking: Species are unchanging types; variation is ignored.

• Lamarckian Evolution: Organisms change during their lifetime and pass those changes to offspring (disproven).

• Darwinian Evolution: Populations change over generations due to natural selection.

Evidence for Evolution:

• Fossil record

• Homologous structures

• Vestigial traits

• Biogeography

• Molecular evidence (DNA, proteins)

Natural Selection: The process by which individuals with advantageous traits survive and reproduce more successfully.

• Darwin's Postulates: Variation exists, traits are heritable, more offspring are produced than survive, and survival is non-random.

• Artificial Selection: Humans select for desirable traits in plants and animals.

Common Misconceptions: Natural selection acts on individuals, but only populations evolve. It does not lead to perfection or goal-directed change.

Acclimation vs. Adaptation: Acclimation is a short-term physiological change; adaptation is a genetic change in a population over generations.

Phylogenies and the History of Life

Fossil Record and Major Events

The fossil record provides evidence for the history of life and major evolutionary transitions.

• Fossilization: The process by which remains are preserved in sedimentary rock.

• Biases: Not all organisms are equally likely to fossilize (abundance, tissue, habitat, temporal, and taxonomic biases).

• Major Extinctions: Mass extinction events, such as the Permian and Cretaceous extinctions, have shaped the diversity of life.

• Adaptive Radiation: Rapid evolution of many species from a common ancestor, often after mass extinction events.

Phylogenetic Trees: Diagrams that show evolutionary relationships among species.

• Monophyletic Group (Clade): Includes an ancestor and all its descendants.

• Paraphyletic Group: Includes an ancestor and some, but not all, descendants.

• Polyphyletic Group: Does not include the most recent common ancestor.

• Principle of Parsimony: The simplest explanation (fewest evolutionary changes) is preferred.

• Homology: Similarity due to shared ancestry.

• Analogy (Homoplasy): Similarity due to convergent evolution, not common ancestry.

• Synapomorphy: A shared derived trait that defines a clade.

Prokaryotes: Bacteria and Archaea

Diversity, Structure, and Metabolism

Prokaryotes are unicellular organisms without a nucleus, including Bacteria and Archaea. They are the most diverse and abundant organisms on Earth.

• Prokaryotic Cell Structure: Lack membrane-bound organelles; have cell wall, plasma membrane, ribosomes, and sometimes flagella or pili.

• Endospore: A resistant, dormant structure formed by some bacteria for survival in harsh conditions.

• Metabolism: Prokaryotes can be autotrophic (photosynthetic or chemosynthetic) or heterotrophic.

• Extremophiles: Organisms that thrive in extreme environments (e.g., high temperature, salinity, acidity).

• Genetic Variation: Achieved through mutation, conjugation, transformation, and transduction.

• Antibiotic Resistance: The ability of bacteria to survive and multiply in the presence of antibiotics.

• Role in Ecosystems: Nitrogen fixation, decomposition, bioremediation, and symbiosis with other organisms.

Classification: Based on cell wall structure (Gram-positive vs. Gram-negative), metabolism, and genetic analysis.

Domains of Life: Bacteria, Archaea, and Eukarya. Each domain has unique characteristics but shares some similarities.

Lab 1: Scientific Literature

Understanding Scientific Papers

Scientific literature includes primary, secondary, tertiary, and popular sources. Understanding the structure of a scientific paper is essential for interpreting research.

• Primary Literature: Original research articles presenting new data.

• Secondary Literature: Reviews and summaries of primary research.

• Tertiary Literature: Encyclopedias, textbooks, and databases.

• Peer Review: The process by which scientific work is evaluated by experts before publication.

• Sections of a Scientific Paper: Introduction, Materials and Methods, Results, Discussion, Figures, and Figure Legends.

• Hypothesis/Main Question: Usually found in the introduction or abstract.

Lab 2: Microscopy and Microbes

Microscope Structure and Use

Microscopes are essential tools for studying cells and microorganisms. There are several types of microscopes, each with unique applications.

• Main Parts: Ocular lens (eyepiece), objective lenses, stage, condenser, light source, focus knobs.

• Types of Microscopy: Light microscopy, confocal microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM).

• Magnification: Always start with the lowest magnification and increase as needed.

• Image Orientation: Images may appear inverted or reversed under the microscope.

• Micrographs: Images produced by microscopes; can be distinguished by their appearance and the type of microscope used.

• Light vs. Electron Microscopy: Light microscopes use visible light; electron microscopes use electron beams for much higher resolution.

Key Terms and Concepts Table

The following table summarizes some of the most important terms and their definitions or associations for this exam:

Formulas and Equations

• Binomial Nomenclature: Genus species (e.g., Homo sapiens)

• Hardy-Weinberg Equation:

• Exponential Growth (Bacteria):

Additional info: The Hardy-Weinberg equation and exponential growth formula are foundational for understanding population genetics and microbial growth, respectively.