Chapter One: Evolution, the Themes of Biology, and Scientific Inquiry

Chapter One: Evolution, the Themes of Biology, and Scientific Inquiry

Characteristics of Life

Living organisms share a set of fundamental characteristics that distinguish them from non-living matter. These features are essential for the maintenance and perpetuation of life.

• Highly organized: Living things exhibit complex and ordered structures, from molecules to entire organisms.

• Adapt over time: Populations of organisms evolve in response to environmental changes.

• Regulated: Organisms maintain stable internal conditions (homeostasis).

• Reproduce: Living things produce offspring, ensuring the continuation of their species.

• Respond to stimuli: Organisms detect and react to environmental changes.

• Grow and develop: Organisms increase in size and undergo developmental changes.

• Acquire energy and materials: Living things obtain and use energy and nutrients to sustain life processes.

Ecosystems and Levels of Biological Organization

Biology studies life at multiple levels, from molecules to the entire biosphere. Understanding these levels helps explain how life is structured and interconnected.

• Biosphere: All life on Earth and the environments they inhabit.

• Ecosystem: Communities of living organisms interacting with each other and their physical environment (e.g., Galveston Bay).

• Community: Different populations of organisms living together in an ecosystem (e.g., fish, plants, mammals).

• Population: All individuals of a single species in a specific area (e.g., all flounder in a forest).

• Organism: An individual living entity.

• Organ: A body part composed of tissues that performs a specific function.

• Tissue: Groups of similar cells performing a particular function.

• Cell: The basic unit of life.

• Organelle: Specialized structures within cells (e.g., nucleus, mitochondria).

• Molecule: Chemical structures consisting of two or more atoms.

The Cell: Basic Unit of Life

The cell is the fundamental unit of structure and function in all living organisms. The Cell Theory states that all living things are composed of cells.

• Prokaryotic cells: Lack a nucleus; found in bacteria and archaea.

• Eukaryotic cells: Have a nucleus and membrane-bound organelles; found in protists, fungi, plants, and animals.

DNA: The Genetic Material

Deoxyribonucleic acid (DNA) is the molecule that stores genetic information in all living organisms.

• Gene: A segment of DNA that codes for a specific protein; the unit of inheritance.

• Structure: DNA is a double helix with nucleotide bases (A, T, C, G) forming the rungs.

• Gene expression: The process by which information from a gene is used to synthesize a functional product (protein): $\text{DNA} \rightarrow \text{mRNA} \rightarrow \text{Amino acids} \rightarrow \text{Protein}$

• Universality: The genetic code is nearly universal among all organisms.

• Genome: The complete set of genes or genetic material present in a cell or organism.

Evolution: Unity and Diversity of Life

Evolution explains both the similarities and differences among living organisms. It is the process by which species change over time.

• Binomial nomenclature: The two-part scientific naming system for species (Genus species), e.g., Homo sapiens.

• Unity: All life shares common features due to descent from a common ancestor.

• Diversity: Adaptations to different environments lead to the variety of life forms.

Domains of Life

All living organisms are classified into three domains based on cellular organization and genetics.

• Archaea: Unicellular prokaryotes; often found in extreme environments (high salt, temperature, or acidity).

• Bacteria: Unicellular prokaryotes; found in diverse environments (soil, water, human body); can be beneficial or harmful.

• Eukarya: Organisms with membrane-bound nuclei; includes protists, fungi, plants, and animals. Eukarya are further divided into four kingdoms.

Charles Darwin and the Theory of Evolution

Charles Darwin's work laid the foundation for evolutionary biology. His book, The Origin of Species (1859), introduced key concepts:

• Descent with modification: Species change over time and give rise to new species.

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

• Variation: Individuals in a population differ in their traits.

• Overproduction: Populations produce more offspring than can survive.

• Adaptation: Species are suited to their environments through inherited traits.

Scientific Inquiry and the Scientific Method

Scientific inquiry involves making observations, forming hypotheses, and testing them through experiments.

• Steps: Accumulate data, formulate a hypothesis, observe and experiment, analyze data, and draw conclusions.

• Types of data:

  • Quantitative data: Numerical measurements (e.g., length, mass).

  • Qualitative data: Descriptions based on observations (e.g., color, texture).

• Inductive reasoning: Drawing general conclusions from many observations.

• Deductive reasoning: Making predictions based on general principles ("if...then" logic).

Variables and Controls in Experiments

Controlled experiments are designed to test the effect of a single variable.

• Independent variable: The factor manipulated by the researcher.

• Dependent variable: The factor being measured or observed.

• Control group: The group that does not receive the experimental treatment, used for comparison.

Science and Social Responsibility

Science seeks to explain the natural world through testable hypotheses, but it does not address ethical or moral questions.

• Science and ethics: Science can lead to technologies with significant social or ecological impacts, but ethical decisions are outside the scope of scientific testing.

• Scientific method: Used to test hypotheses about the natural world, not moral or ethical issues.

Basic Theories of Biology

Several foundational theories underpin all of biology:

• Cell Theory: All organisms are composed of cells.

• Biogenesis: Life arises only from pre-existing life.

• Ecosystem Theory: Organisms interact with each other and their environment in specific locales.

• Evolution: All living things share a common ancestor but are adapted to their environments.

• Gene Theory: Organisms contain coded information (genes) that determines their form, function, and behavior.