Chapter 1: Biology – The Study of Life (General Biology Study Notes)

Biology: The Study of Life

Introduction

Biology is the scientific study of life and living organisms. This chapter introduces the foundational concepts that define life, the major themes in biology, and the scientific methods used to study living systems.

What Does It Mean to Say That Something is Alive?

Five Fundamental Characteristics of Living Organisms

• Cells: All organisms are composed of one or more membrane-bound cells, which are the basic units of life.

• Replication: All organisms are capable of reproduction, either sexually or asexually.

• Information: All organisms process hereditary information encoded in genes (DNA) and respond to information from their environment.

• Energy: All organisms acquire and use energy to maintain internal order and sustain life processes.

• Evolution: Populations of organisms are continually evolving, leading to diversity and adaptation.

Example: Humans, plants, and bacteria all meet these criteria, while non-living things like rocks do not.

Theories in Biology

Definition of Theory

• A theory is an explanation for a broad class of phenomena or observations that is supported by a wide body of evidence.

• This differs from the everyday use of "theory," which often means speculation or guess.

Major Theories in Modern Biology

• Cell Theory: Addresses what organisms are made of and where they come from.

• Theory of Evolution by Natural Selection: Explains how organisms are related and how they change over time.

• Chromosome Theory of Inheritance: Describes how hereditary information is transmitted from one generation to the next.

Life is Cellular and Replicates Through Cell Division

Historical Discoveries

• Robert Hooke (1665): Used a 30x microscope to observe small compartments in cork, which he called "cells."

• Anton van Leeuwenhoek: Developed a 300x microscope and observed single-celled organisms, which he termed "animalcules."

• By the 1800s, it was established that all organisms are made of cells.

Cell Theory

• All organisms are made up of cells.

• All cells come from preexisting cells.

• Cells are highly organized compartments separated from their environment by a membrane.

Levels of Biological Organization

• Biological systems are organized in a hierarchy from molecules to the biosphere.

• Levels include: molecules, organelles, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystems, and biosphere.

Scientific Method and Hypothesis Testing

Key Terms

• Hypothesis: A testable statement that explains something observed.

• Experiment: A procedure to test the effect of a single, well-defined factor on a phenomenon.

• Prediction: A measurable or observable result that must be correct if the hypothesis is valid.

Example: Pasteur's Experiment

• Tested whether cells arise from preexisting cells or by spontaneous generation.

• Used two flasks with nutrient broth, one with a swan neck (open to air) and one without.

• Result: Only the open flask developed life, supporting the "all-cells-from-cells" hypothesis.

Life Processes Information and Requires Energy

Chromosome Theory of Inheritance

• Hereditary information is encoded in genes located on chromosomes.

• Chromosomes are made of DNA (deoxyribonucleic acid).

Structure of DNA

• DNA is a double helix composed of four building blocks: A (adenine), T (thymine), C (cytosine), and G (guanine).

• Base pairing: A pairs with T, C pairs with G.

• This structure allows DNA to be copied accurately.

The Central Dogma of Molecular Biology

• Describes the flow of genetic information in cells:

$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

• RNA: Molecules that carry out specialized functions; messenger RNA (mRNA) is read to make proteins.

• Proteins: Perform crucial tasks in cells, including structural roles and catalyzing chemical reactions.

Genetic Variation and Evolution

• DNA is copied to pass genetic information to offspring.

• Mutations (changes in DNA sequence) can lead to changes in proteins and heritable variation.

Energy and Metabolism

• Organisms require energy for chemical reactions and to build cellular components.

• Energy is often stored and transferred in the form of adenosine triphosphate (ATP).

• Organisms acquire energy in different ways, such as photosynthesis (plants) or consuming other organisms (animals).

Life Evolves

Evolution and Natural Selection

• Evolution: Change in the characteristics of a population over time.

• Population: A group of individuals of the same species living in the same area at the same time.

• Natural Selection: The process by which individuals with certain heritable traits produce more offspring than others, leading to changes in the population.

Conditions for Natural Selection

• Individuals must vary in heritable characteristics.

• Certain traits must increase reproductive success in a particular environment.

Fitness and Adaptation

• Fitness: The ability of an individual to produce surviving offspring.

• Adaptation: A trait that increases fitness in a particular environment.

• Example: Galapagos finches with small, pointed beaks had higher fitness when small seeds were abundant, leading to an increase in this trait in the population.

The Tree of Life and Classification

Phylogeny and the Tree of Life

• The "tree of life" depicts evolutionary relationships among species, with a single ancestral species at its base.

• Phylogeny: The actual genealogical relationships among all organisms.

• Genetic variation is analyzed by comparing DNA or RNA sequences; fewer differences indicate closer relationships.

Major Domains of Life

• Three major domains: Bacteria, Archaea, and Eukarya.

• Bacteria and Archaea are prokaryotes (lack a nucleus); Eukarya are eukaryotes (have a nucleus).

Taxonomy and Classification

• Taxonomy: The discipline of naming and classifying organisms.

• Taxon: A named group of organisms.

• Domain: The most inclusive taxonomic category, followed by kingdom, phylum, class, order, family, genus, and species.

• Binomial Nomenclature: Each species is given a two-part scientific name (genus and species), e.g., Homo sapiens.

Taxonomic Category	Description
Domain	Most inclusive; Bacteria, Archaea, Eukarya
Kingdom	Major groups within domains
Phylum	Groups of related classes
Class	Groups of related orders
Order	Groups of related families
Family	Groups of related genera
Genus	Groups of related species
Species	Least inclusive; individuals that can breed together

Doing Biology: The Scientific Process

Nature of Science

• Science involves asking questions that can be answered by collecting data and making measurements.

• Scientists formulate hypotheses and seek evidence to support or refute them.

Hypothesis Testing and Experimental Design

• State the hypothesis and list its predictions.

• Design observational or experimental studies to test predictions.

• Include control groups, keep conditions constant, repeat tests, and use large sample sizes for reliability.

Example: Giraffe Neck Length

• Food Competition Hypothesis: Giraffes evolved long necks to reach food high in trees.

• Tested by observing feeding behavior; evidence did not support this hypothesis.

• Sexual Competition Hypothesis: Long-necked males win more fights and father more offspring; evidence supports this hypothesis.

Example: Ant Navigation Experiment

• Tested whether desert ants use stride length and step number to navigate back to their nest (pedometer hypothesis).

• Ants with shortened legs stopped short, typical ants returned to the nest, and ants with lengthened legs overshot the nest.

• Conclusion: Ants use stride length and step number to calculate distance.

Additional info: These notes summarize the foundational concepts of biology, including the characteristics of life, major biological theories, the scientific method, and the classification of living organisms. They are suitable for introductory college-level biology courses.