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 fundamental characteristics that define life, the major theories that form the foundation of biological science, and the evolutionary relationships among organisms.

1.1 What Does It Mean to Say That Something is Alive?

Five Fundamental Characteristics of Life

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

• Replication: All organisms have the ability to reproduce, ensuring the continuation of their species.

• Information: Organisms process hereditary information encoded in genes and respond to environmental information.

• Energy: All organisms acquire and utilize energy to maintain life processes.

• Evolution: Populations of organisms are continually evolving, leading to the diversity of life.

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 guesswork.

Three Foundational Theories

• Cell Theory: Addresses what organisms are made of and their origins.

• 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.

1.2 Life is Cellular and Replicates through Cell Division

Discovery of Cells

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

• Anton van Leeuwenhoek: Improved the microscope and observed single-celled organisms ("animalcules").

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

Cell Theory

• All organisms are made up of cells.

• All cells come from preexisting cells ("all-cells-from-cells").

• This theory challenged the idea of spontaneous generation (the belief that organisms could arise spontaneously under certain conditions).

Louis Pasteur’s Experiment

• Tested whether cells arise spontaneously or from preexisting cells using nutrient broth in flasks.

• Only flasks exposed to air (and thus to preexisting cells) developed new cells, supporting the all-cells-from-cells hypothesis.

Cell Division and Chemical Evolution

• Cells replicate to sustain life, and all cells in multicellular organisms share a common lineage.

• Evidence suggests life originated from non-life through chemical evolution early in Earth's history.

1.3 Life Processes Information and Requires Energy

Chromosome Theory of Inheritance

• Proposed by Sutton and Boveri: Hereditary information is encoded in genes located on chromosomes.

• Chromosomes are composed of deoxyribonucleic acid (DNA), which is the hereditary material.

• Genes are segments of DNA that code for cell products.

Structure of DNA

• James Watson and Francis Crick proposed that DNA is a double-stranded helix.

The Central Dogma

• Describes the flow of genetic information in cells:

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

• DNA is transcribed into RNA, which is then translated into proteins.

Genetic Variation and Mutation

• DNA is copied accurately, but mistakes (mutations) can occur.

• Mutations may change proteins, leading to heritable variations and contributing to the diversity of life.

Energy and Nutritional Needs

• Chemical reactions in cells require energy.

• Organisms need:

  • Chemical energy (often in the form of adenosine triphosphate (ATP)).

  • Molecules that serve as building blocks for DNA, RNA, proteins, etc.

• The way organisms acquire energy is central to the diversification of life.

1.4 Life Evolves

Evolution and Common Ancestry

• Evolution is the change in characteristics of a population over time.

• Darwin and Wallace proposed that species are related by common ancestry and can be modified across generations ("descent with modification").

Natural Selection

• Explains how evolution occurs.

• Two conditions for natural selection:

  1. Individuals vary in heritable characteristics.

  2. Certain heritable traits help individuals reproduce more successfully in specific environments.

• Natural selection acts on individuals, but evolutionary change occurs in populations.

• Speciation occurs when populations diverge to form new species.

Fitness and Adaptation

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

• Adaptation: A trait that increases an individual's fitness in a particular environment.

• Example: On the Galápagos Islands, finches with small, pointed beaks had higher fitness when small, soft seeds were abundant. This adaptation increased their population frequency.

1.5 The Tree of Life Depicts Evolutionary History

Phylogeny and the Tree of Life

• The tree of life is a family tree that describes genealogical relationships among species, tracing back to a single ancestral species.

• Phylogeny refers to the actual genealogical relationships among all organisms.

Analyzing Genetic Variation

• Biologists compare DNA and RNA sequences to determine evolutionary relationships.

• Fewer sequence differences indicate a closer relationship.

• Example: Green algae DNA is more similar to land plant DNA than to brown algae DNA, indicating a closer relationship.

Phylogenetic Tree

• Shows relationships between species based on genetic data.

• Branches sharing a recent common ancestor represent closely related species.

• Branches without a recent common ancestor represent more distantly related species.

Major Groups of Life

• The tree of life indicates three major groups:

  • Eukaryotes (have a nucleus): Eukarya

  • Prokaryotes (lack a nucleus): Bacteria and Archaea

Summary Table: Major Theories and Concepts

Theory/Concept	Main Idea	Key Contributors
Cell Theory	All organisms are made of cells; all cells come from preexisting cells	Hooke, van Leeuwenhoek, Pasteur
Theory of Evolution by Natural Selection	Species are related by common ancestry and change over time	Darwin, Wallace
Chromosome Theory of Inheritance	Genetic information is encoded in genes on chromosomes	Sutton, Boveri