Biology: 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 unifying theories in biology, and the processes that underlie biological diversity and function.

Properties of Life

Defining Characteristics of Living Things

All living organisms share several key properties that distinguish them from non-living matter.

• Made of cells: The cell is the basic membrane-bound unit of activity in all living things.

• Can replicate: Living organisms reproduce by replicating their cells, ensuring continuity of life.

• Process information: Organisms respond to environmental information and transmit hereditary information to offspring.

• Evolve: Populations of organisms change over time through evolutionary processes, not individual organisms.

• Require energy: All living things need energy to drive cellular processes and maintain organization.

Example: Bacteria, plants, and animals all consist of cells, can reproduce, process information, evolve, and require energy.

Scientific Theories in Biology

Definition and Importance

A scientific theory is an explanation for a very general class of phenomena or observations, supported by a wide body of evidence. This differs from the everyday use of the word "theory," which may refer to a guess or hypothesis.

• Wide body of evidence: Scientific theories are supported by extensive and reproducible data.

• Predictive power: Theories allow scientists to make predictions about natural phenomena.

Example: The theory of evolution explains the diversity of life based on evidence from genetics, fossils, and comparative anatomy.

Unifying Theories of Biology

Cell Theory

The Cell Theory states that all organisms are made of cells, and all cells come from preexisting cells. The plasma membrane encloses chemicals in solution, allowing cellular processes to occur.

• All organisms are cellular: Both unicellular and multicellular organisms are composed of cells.

• Plasma membrane: Separates the cell from its environment and regulates the movement of substances.

• Cell lineage: All cells trace their ancestry to a common ancestor cell.

Theory of Evolution by Natural Selection

Proposed by Charles Darwin and Alfred Russel Wallace, this theory explains how species change over time.

• Common ancestry: All species are related by descent from a common ancestor.

• Descent with modification: Species change from generation to generation as traits are inherited and modified.

• Natural selection: Certain heritable traits increase an organism's fitness, leading to greater reproductive success. Over generations, adaptive traits become more common in the population.

Example: The evolution of finch beak shapes in response to food availability in the Galápagos Islands.

Chromosome Theory of Inheritance

Developed by Walter Sutton and Theodor Boveri, this theory states that hereditary information is encoded in genes located on chromosomes, which are composed of DNA.

• Genes: Segments of DNA that code for cell products.

• DNA: The hereditary material passed from cell to cell and from parent to offspring.

• Mutations: Changes in DNA sequence can lead to changes in proteins and traits, providing the variation necessary for evolution.

Example: Mutations in DNA can result in new traits, such as antibiotic resistance in bacteria.

Central Dogma of Molecular Biology

Flow of Genetic Information

The Central Dogma describes how genetic information flows within a cell:

• DNA codes for RNA: Messenger RNA (mRNA) is transcribed from DNA.

• RNA codes for protein: mRNA is translated to produce proteins.

• Proteins: Determine the physical traits and functions of cells.

Example: The gene for hemoglobin is transcribed into mRNA and then translated into the hemoglobin protein, which carries oxygen in blood.

Phylogenetic Tree and Classification

Tree of Life and Domains

A phylogenetic tree represents the evolutionary relationships among species. Nodes indicate common ancestors, and branches show how species diverged over time.

• Domains: The major groups of life are Bacteria, Archaea, and Eukarya.

• Molecular phylogeny: Uses DNA sequences to determine relationships between organisms.

Example: DNA sequence comparison can show that fungi are more closely related to animals than to plants.

Taxonomy and Scientific Naming

Taxonomy is the effort to name and classify organisms. Each organism has a unique two-part scientific name: the genus and the species.

• Genus: Capitalized, groups closely related species.

• Species: Lowercase, refers to individuals that regularly breed together.

• Scientific names: Always italicized or underlined, e.g., Homo sapiens.

Example: Canis lupus is the scientific name for the gray wolf.

Energy and Metabolism

Why Living Things Need Energy

All living organisms require energy to drive chemical reactions that sustain life. These reactions transform one form of chemical into another and require energy input.

• Acquiring chemical energy: Organisms obtain energy from their environment and convert it to a usable form, such as adenosine triphosphate (ATP).

• Obtaining molecules: Organisms need molecules to build DNA, RNA, proteins, and other cellular components.

Example: Humans eat food to acquire energy and building blocks for growth and repair.

Review Questions

• What are the properties of life?

• What is Cell Theory?

• Explain Evolution by Natural Selection.

• At what scale does each occur?

• What is an Adaptation?

• Describe the Chromosome Theory of Inheritance.

• What is the Central Dogma?

• Why are mutations important for evolution?

• What does a phylogenetic tree show?

• What are the two reasons all organisms need energy?

Additional info: Some content was inferred and expanded for clarity and completeness, including examples, definitions, and equations.