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Boundless Biology: 4.1: Studying Cells

Boundless Biology
4.1: Studying Cells
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table of contents
  1. 1: The Study of Life
    1. 1.1: The Science of Biology
      1. 1.1.0: Introduction to the Study of Biology
      2. 1.1.1: Scientific Reasoning
      3. 1.1.2: The Scientific Method
      4. 1.1.3: Basic and Applied Science
      5. 1.1.4: Publishing Scientific Work
      6. 1.1.5: Branches and Subdisciplines of Biology
    2. 1.2: Themes and Concepts of Biology
      1. 1.2.0: Properties of Life
      2. 1.2.1: Levels of Organization of Living Things
      3. 1.2.2: The Diversity of Life
  2. 2: The Chemical Foundation of Life
    1. 2.1: Atoms, Isotopes, Ions, and Molecules
      1. 2.1.0: Overview of Atomic Structure
      2. 2.1.1: Atomic Number and Mass Number
      3. 2.1.2: Isotopes
      4. 2.1.3: The Periodic Table
      5. 2.1.4: Electron Shells and the Bohr Model
      6. 2.1.5: Electron Orbitals
      7. 2.1.6: Chemical Reactions and Molecules
      8. 2.1.7: Ions and Ionic Bonds
      9. 2.1.8: Covalent Bonds and Other Bonds and Interactions
      10. 2.1.9: Hydrogen Bonding and Van der Waals Forces
    2. 2.2: Water
      1. 2.2.0: Water’s Polarity
      2. 2.2.1: Water’s States: Gas, Liquid, and Solid
      3. 2.2.2: Water’s High Heat Capacity
      4. 2.2.3: Water’s Heat of Vaporization
      5. 2.2.4: Water’s Solvent Properties
      6. 2.2.5: Water’s Cohesive and Adhesive Properties
      7. 2.2.6: pH, Buffers, Acids, and Bases
    3. 2.3: Carbon
      1. 2.3.0: The Chemical Basis for Life
      2. 2.3.1: Hydrocarbons
      3. 2.3.2: Organic Isomers
      4. 2.3.3: Organic Enantiomers
      5. 2.3.4: Organic Molecules and Functional Groups
  3. 3: Biological Macromolecules
    1. 3.1: Synthesis of Biological Macromolecules
      1. 3.1.0: Types of Biological Macromolecules
      2. 3.1.1: Dehydration Synthesis
      3. 3.1.2: Hydrolysis
    2. 3.2: Carbohydrates
      1. 3.2.0: Carbohydrate Molecules
      2. 3.2.1: Importance of Carbohydrates
    3. 3.3: Lipids
      1. 3.3.0: Lipid Molecules
      2. 3.3.1: Waxes
      3. 3.3.2: Phospholipids
      4. 3.3.3: Steroids
    4. 3.4: Proteins
      1. 3.4.0: Types and Functions of Proteins
      2. 3.4.1: Amino Acids
      3. 3.4.2: Protein Structure
      4. 3.4.3: Denaturation and Protein Folding
    5. 3.5: Nucleic Acids
      1. 3.5.0: DNA and RNA
      2. 3.5.1: The DNA Double Helix
      3. 3.5.2: DNA Packaging
      4. 3.5.3: Types of RNA
  4. 4: Cell Structure
    1. 4.1: Studying Cells
      1. 4.1.0: Cells as the Basic Unit of Life
      2. 4.1.1: Microscopy
      3. 4.1.2: Cell Theory
      4. 4.1.3: Cell Size
    2. 4.2: Prokaryotic Cells
      1. 4.2.0: Characteristics of Prokaryotic Cells
    3. 4.3: Eukaryotic Cells
      1. 4.3.0: Characteristics of Eukaryotic Cells
      2. 4.3.1: The Plasma Membrane and the Cytoplasm
      3. 4.3.2: The Nucleus and Ribosomes
      4. 4.3.3: Mitochondria
      5. 4.3.4: Comparing Plant and Animal Cells
    4. 4.4: The Endomembrane System and Proteins
      1. 4.4.0: Vesicles and Vacuoles
      2. 4.4.1: The Endoplasmic Reticulum
      3. 4.4.2: The Golgi Apparatus
      4. 4.4.3: Lysosomes
      5. 4.4.4: Peroxisomes
    5. 4.5: The Cytoskeleton
      1. 4.5.0: Microfilaments
      2. 4.5.1: Intermediate Filaments and Microtubules
    6. 4.6: Connections between Cells and Cellular Activities
      1. 4.6.0: Extracellular Matrix of Animal Cells
      2. 4.6.1: Intercellular Junctions
  5. 5: Structure and Function of Plasma Membranes
    1. 5.1: Components and Structure
      1. 5.1.0: Components of Plasma Membranes
      2. 5.1.1: Fluid Mosaic Model
      3. 5.1.2: Membrane Fluidity
    2. 5.2: Passive Transport
      1. 5.2.0: The Role of Passive Transport
      2. 5.2.1: Selective Permeability
      3. 5.2.2: Diffusion
      4. 5.2.3: Facilitated transport
      5. 5.2.4: Osmosis
      6. 5.2.5: Tonicity
      7. 5.2.6: Osmoregulation
    3. 5.3: Active Transport
      1. 5.3.0: Electrochemical Gradient
      2. 5.3.1: Primary Active Transport
      3. 5.3.2: Secondary Active Transport
    4. 5.4: Bulk Transport
      1. 5.4.0: Endocytosis
      2. 5.4.1: Exocytosis
  6. 6: Metabolism
    1. 6.1: Energy and Metabolism
      1. 6.1.0: The Role of Energy and Metabolism
      2. 6.1.1: Types of Energy
      3. 6.1.2: Metabolic Pathways
      4. 6.1.3: Metabolism of Carbohydrates
    2. 6.2: Potential, Kinetic, Free, and Activation Energy
      1. 6.2.0: Free Energy
      2. 6.2.1: The First Law of Thermodynamics
      3. 6.2.2: The Second Law of Thermodynamics
      4. 6.2.3: Activation Energy
    3. 6.3: ATP: Adenosine Triphosphate
      1. 6.3.0: ATP: Adenosine Triphosphate
    4. 6.4: Enzymes
      1. 6.4.0: Enzyme Active Site and Substrate Specificity
      2. 6.4.1: Control of Metabolism Through Enzyme Regulation
  7. 7: Cellular Respiration
    1. 7.1: Energy in Living Systems
      1. 7.1.0: Transforming Chemical Energy
      2. 7.1.1: Electrons and Energy
      3. 7.1.2: ATP in Metabolism
    2. 7.2: Glycolysis
      1. 7.2.0: Importance of Glycolysis
      2. 7.2.1: The Energy-Requiring Steps of Glycolysis
      3. 7.2.2: The Energy-Releasing Steps of Glycolysis
      4. 7.2.3: Outcomes of Glycolysis
    3. 7.3: Oxidation of Pyruvate and the Citric Acid Cycle
      1. 7.3.0: Breakdown of Pyruvate
      2. 7.3.1: Acetyl CoA to CO2
      3. 7.3.2: Citric Acid Cycle
    4. 7.4: Oxidative Phosphorylation
      1. 7.4.0: Electron Transport Chain
      2. 7.4.1: Chemiosmosis and Oxidative Phosphorylation
      3. 7.4.2: ATP Yield
    5. 7.5: Metabolism without Oxygen
      1. 7.5.0: Anaerobic Cellular Respiration
    6. 7.6: Connections of Carbohydrate, Protein, and Lipid Metabolic Pathways
      1. 7.6.0: Connecting Other Sugars to Glucose Metabolism
      2. 7.6.1: Connecting Proteins to Glucose Metabolism
      3. 7.6.2: Connecting Lipids to Glucose Metabolism
    7. 7.7: Regulation of Cellular Respiration
      1. 7.7.0: Regulatory Mechanisms for Cellular Respiration
      2. 7.7.1: Control of Catabolic Pathways
  8. 8: Photosynthesis
    1. 8.1: Overview of Photosynthesis
      1. 8.1.0: The Purpose and Process of Photosynthesis
      2. 8.1.1: Main Structures and Summary of Photosynthesis
      3. 8.1.2: The Two Parts of Photosynthesis
    2. 8.2: The Light-Dependent Reactions of Photosynthesis
      1. 8.2.0: Introduction to Light Energy
      2. 8.2.1: Absorption of Light
      3. 8.2.2: Processes of the Light-Dependent Reactions
    3. 8.3: The Light-Independent Reactions of Photosynthesis
      1. 8.3.0: CAM and C4 Photosynthesis
      2. 8.3.1: The Calvin Cycle
      3. 8.3.2: The Carbon Cycle
  9. 9: Cell Communication
    1. 9.1: Signaling Molecules and Cellular Receptors
      1. 9.1.0: Signaling Molecules and Cellular Receptors
      2. 9.1.1: Forms of Signaling
      3. 9.1.2: Types of Receptors
      4. 9.1.3: Signaling Molecules
    2. 9.2: Propagation of the Cellular Signal
      1. 9.2.0: Binding Initiates a Signaling Pathway
      2. 9.2.1: Methods of Intracellular Signaling
    3. 9.3: Response to the Cellular Signal
      1. 9.3.0: Termination of the Signal Cascade
      2. 9.3.1: Cell Signaling and Gene Expression
      3. 9.3.2: Cell Signaling and Cellular Metabolism
      4. 9.3.3: Cell Signaling and Cell Growth
      5. 9.3.4: Cell Signaling and Cell Death
    4. 9.4: Signaling in Single-Celled Organisms
      1. 9.4.0: Signaling in Yeast
      2. 9.4.1: Signaling in Bacteria
  10. 10: Cell Reproduction
    1. 10.1: Cell Division
      1. 10.1.0: The Role of the Cell Cycle
      2. 10.1.1: Genomic DNA and Chromosomes
      3. 10.1.2: Eukaryotic Chromosomal Structure and Compaction
    2. 10.2: The Cell Cycle
      1. 10.2.0: Interphase
      2. 10.2.1: The Mitotic Phase and the G0 Phase
    3. 10.3: Control of the Cell Cycle
      1. 10.3.0: Regulation of the Cell Cycle by External Events
      2. 10.3.1: Regulation of the Cell Cycle at Internal Checkpoints
      3. 10.3.2: Regulator Molecules of the Cell Cycle
    4. 10.4: Cancer and the Cell Cycle
      1. 10.4.0: Proto-oncogenes
      2. 10.4.1: Tumor Suppressor Genes
    5. 10.5: Prokaryotic Cell Division
      1. 10.5.0: Binary Fission
  11. 11: Meiosis and Sexual Reproduction
    1. 11.1: The Process of Meiosis
      1. 11.1.0: Introduction to Meiosis
      2. 11.1.1: Meiosis I
      3. 11.1.2: Meiosis II
      4. 11.1.3: Comparing Meiosis and Mitosis
    2. 11.2: Sexual Reproduction
      1. 11.2.0: Advantages and Disadvantages of Sexual Reproduction
      2. 11.2.1: Life Cycles of Sexually Reproducing Organisms
  12. 12: Mendel's Experiments and Heredity
    1. 12.1: Mendel’s Experiments and the Laws of Probability
      1. 12.1.0: Introduction to Mendelian Inheritance
      2. 12.1.1: Mendel’s Model System
      3. 12.1.2: Mendelian Crosses
      4. 12.1.3: Garden Pea Characteristics Revealed the Basics of Heredity
      5. 12.1.4: Rules of Probability for Mendelian Inheritance
    2. 12.2: Patterns of Inheritance
      1. 12.2.0: Genes as the Unit of Heredity
      2. 12.2.1: Phenotypes and Genotypes
      3. 12.2.2: The Punnett Square Approach for a Monohybrid Cross
      4. 12.2.3: Alternatives to Dominance and Recessiveness
      5. 12.2.4: Sex-Linked Traits
      6. 12.2.5: Lethal Inheritance Patterns
    3. 12.3: Laws of Inheritance
      1. 12.3.0: Mendel's Laws of Heredity
      2. 12.3.1: Mendel's Law of Dominance
      3. 12.3.2: Mendel's Law of Segregation
      4. 12.3.3: Mendel's Law of Independent Assortment
      5. 12.3.4: Genetic Linkage and Violation of the Law of Independent Assortment
      6. 12.3.5: Epistasis
  13. 13: Modern Understandings of Inheritance
    1. 13.1: Chromosomal Theory and Genetic Linkage
      1. 13.1.0: Chromosomal Theory of Inheritance
      2. 13.1.1: Genetic Linkage and Distances
      3. 13.1.2: Identification of Chromosomes and Karyotypes
    2. 13.2: Chromosomal Basis of Inherited Disorders
      1. 13.2.0: Disorders in Chromosome Number
      2. 13.2.1: Chromosomal Structural Rearrangements
      3. 13.2.2: X-Inactivation
  14. 14: DNA Structure and Function
    1. 14.1: Historical Basis of Modern Understanding
      1. 14.1.0: Discovery of DNA
      2. 14.1.1: Modern Applications of DNA
    2. 14.2: DNA Structure and Sequencing
      1. 14.2.0: The Structure and Sequence of DNA
      2. 14.2.1: DNA Sequencing Techniques
    3. 14.3: DNA Replication
      1. 14.3.0: Basics of DNA Replication
      2. 14.3.1: DNA Replication in Prokaryotes
      3. 14.3.2: DNA Replication in Eukaryotes
      4. 14.3.3: Telomere Replication
    4. 14.4: DNA Repair
      1. 14.4.0: DNA Repair
  15. 15: Genes and Proteins
    1. 15.1: The Genetic Code
      1. 15.1.0: The Relationship Between Genes and Proteins
      2. 15.1.1: The Central Dogma: DNA Encodes RNA and RNA Encodes Protein
    2. 15.2: Prokaryotic Transcription
      1. 15.2.0: Transcription in Prokaryotes
      2. 15.2.1: Initiation of Transcription in Prokaryotes
      3. 15.2.2: Elongation and Termination in Prokaryotes
    3. 15.3: Eukaryotic Transcription
      1. 15.3.0: Initiation of Transcription in Eukaryotes
      2. 15.3.1: Elongation and Termination in Eukaryotes
    4. 15.4: RNA Processing in Eukaryotes
      1. 15.4.0: mRNA Processing
      2. 15.4.1: Processing of tRNAs and rRNAs
    5. 15.5: Ribosomes and Protein Synthesis
      1. 15.5.0: The Protein Synthesis Machinery
      2. 15.5.1: The Mechanism of Protein Synthesis
      3. 15.5.2: Protein Folding, Modification, and Targeting
  16. 16: Gene Expression
    1. 16.1: Regulation of Gene Expression
      1. 16.1.0: The Process and Purpose of Gene Expression Regulation
      2. 16.1.1: Prokaryotic versus Eukaryotic Gene Expression
    2. 16.2: Prokaryotic Gene Regulation
      1. 16.2.0: The trp Operon: A Repressor Operon
      2. 16.2.1: Catabolite Activator Protein (CAP): An Activator Regulator
      3. 16.2.2: The lac Operon: An Inducer Operon
    3. 16.3: Eukaryotic Gene Regulation
      1. 16.3.0: The Promoter and the Transcription Machinery
      2. 16.3.1: Transcriptional Enhancers and Repressors
      3. 16.3.2: Epigenetic Control: Regulating Access to Genes within the Chromosome
      4. 16.3.3: RNA Splicing
      5. 16.3.4: The Initiation Complex and Translation Rate
      6. 16.3.5: Regulating Protein Activity and Longevity
    4. 16.4: Regulating Gene Expression in Cell Development
      1. 16.4.0: Gene Expression in Stem Cells
      2. 16.4.1: Cellular Differentiation
      3. 16.4.2: Mechanics of Cellular Differentation
      4. 16.4.3: Establishing Body Axes during Development
      5. 16.4.4: Gene Expression for Spatial Positioning
      6. 16.4.5: Cell Migration in Multicellular Organisms
      7. 16.4.6: Programmed Cell Death
    5. 16.5: Cancer and Gene Regulation
      1. 16.5.0: Altered Gene Expression in Cancer
      2. 16.5.1: Epigenetic Alterations in Cancer
      3. 16.5.2: Cancer and Transcriptional Control
      4. 16.5.3: Cancer and Post-Transcriptional Control
      5. 16.5.4: Cancer and Translational Control
  17. 17: Biotechnology and Genomics
    1. 17.1: Biotechnology
      1. 17.1.0: Biotechnology
      2. 17.1.1: Basic Techniques to Manipulate Genetic Material (DNA and RNA)
      3. 17.1.2: Molecular and Cellular Cloning
      4. 17.1.3: Reproductive Cloning
      5. 17.1.4: Genetic Engineering
      6. 17.1.5: Genetically Modified Organisms (GMOs)
      7. 17.1.6: Biotechnology in Medicine
      8. 17.1.7: Production of Vaccines, Antibiotics, and Hormones
    2. 17.2: Mapping Genomes
      1. 17.2.0: Genetic Maps
      2. 17.2.1: Physical Maps and Integration with Genetic Maps
    3. 17.3: Whole-Genome Sequencing
      1. 17.3.0: Strategies Used in Sequencing Projects
      2. 17.3.1: Use of Whole-Genome Sequences of Model Organisms
      3. 17.3.2: Uses of Genome Sequences
    4. 17.4: Applying Genomics
      1. 17.4.0: Predicting Disease Risk at the Individual Level
      2. 17.4.1: Pharmacogenomics, Toxicogenomics, and Metagenomics
      3. 17.4.2: Genomics and Biofuels
    5. 17.5: Genomics and Proteomics
      1. 17.5.0: Genomics and Proteomics
      2. 17.5.1: Basic Techniques in Protein Analysis
      3. 17.5.2: Cancer Proteomics
  18. 18: Evolution and the Origin of Species
    1. 18.1: Understanding Evolution
      1. 18.1.0: What is Evolution?
      2. 18.1.1: Charles Darwin and Natural Selection
      3. 18.1.2: The Galapagos Finches and Natural Selection
      4. 18.1.3: Processes and Patterns of Evolution
      5. 18.1.4: Evidence of Evolution
      6. 18.1.5: Misconceptions of Evolution
    2. 18.2: Formation of New Species
      1. 18.2.0: The Biological Species Concept
      2. 18.2.1: Reproductive Isolation
      3. 18.2.2: Speciation
      4. 18.2.3: Allopatric Speciation
      5. 18.2.4: Sympatric Speciation
    3. 18.3: Hybrid Zones and Rates of Speciation
      1. 18.3.0: Hybrid Zones
      2. 18.3.1: Varying Rates of Speciation
    4. 18.4: Evolution of Genomes
      1. 18.4.0: Genomic Similiarities between Distant Species
      2. 18.4.1: Genome Evolution
      3. 18.4.2: Whole-Genome Duplication
      4. 18.4.3: Gene Duplications and Divergence
      5. 18.4.4: Noncoding DNA
      6. 18.4.5: Variations in Size and Number of Genes
    5. 18.5: Evidence of Evolution
      1. 18.5.0: The Fossil Record as Evidence for Evolution
      2. 18.5.1: Fossil Formation
      3. 18.5.2: Gaps in the Fossil Record
      4. 18.5.3: Carbon Dating and Estimating Fossil Age
      5. 18.5.4: The Fossil Record and the Evolution of the Modern Horse
      6. 18.5.5: Homologous Structures
      7. 18.5.6: Convergent Evolution
      8. 18.5.7: Vestigial Structures
      9. 18.5.8: Biogeography and the Distribution of Species
  19. 19: The Evolution of Populations
    1. 19.1: Population Evolution
      1. 19.1.0: Defining Population Evolution
      2. 19.1.1: Population Genetics
      3. 19.1.2: Hardy-Weinberg Principle of Equilibrium
    2. 19.2: Population Genetics
      1. 19.2.0: Genetic Variation
      2. 19.2.1: Genetic Drift
      3. 19.2.2: Gene Flow and Mutation
      4. 19.2.3: Nonrandom Mating and Environmental Variance
    3. 19.3: Adaptive Evolution
      1. 19.3.0: Natural Selection and Adaptive Evolution
      2. 19.3.1: Stabilizing, Directional, and Diversifying Selection
      3. 19.3.2: Frequency-Dependent Selection
      4. 19.3.3: Sexual Selection
      5. 19.3.4: No Perfect Organism
  20. 20: Phylogenies and the History of Life
    1. 20.1: Organizing Life on Earth
      1. 20.1.0: Phylogenetic Trees
      2. 20.1.1: Limitations of Phylogenetic Trees
      3. 20.1.2: The Levels of Classification
    2. 20.2: Determining Evolutionary Relationships
      1. 20.2.0: Distinguishing between Similar Traits
      2. 20.2.1: Building Phylogenetic Trees
    3. 20.3: Perspectives on the Phylogenetic Tree
      1. 20.3.0: Limitations to the Classic Model of Phylogenetic Trees
      2. 20.3.1: Horizontal Gene Transfer
      3. 20.3.2: Endosymbiotic Theory and the Evolution of Eukaryotes
      4. 20.3.3: Web, Network, and Ring of Life Models
  21. 21: Viruses
    1. 21.1: Viral Evolution, Morphology, and Classification
      1. 21.1.0: Discovery and Detection of Viruses
      2. 21.1.1: Evolution of Viruses
      3. 21.1.2: Viral Morphology
      4. 21.1.3: Virus Classification
    2. 21.2: Virus Infections and Hosts
      1. 21.2.0: Steps of Virus Infections
      2. 21.2.1: The Lytic and Lysogenic Cycles of Bacteriophages
      3. 21.2.2: Animal Viruses
      4. 21.2.3: Plant Viruses
    3. 21.3: Prevention and Treatment of Viral Infections
      1. 21.3.0: Vaccines and Immunity
      2. 21.3.1: Vaccines and Anti-Viral Drugs for Treatment
    4. 21.4: Prions and Viroids
      1. 21.4.0: Prions and Viroids
  22. 22: Prokaryotes: Bacteria and Archaea
    1. 22.1: Prokaryotic Diversity
      1. 22.1.0: Classification of Prokaryotes
      2. 22.1.1: The Origins of Archaea and Bacteria
      3. 22.1.2: Extremophiles and Biofilms
    2. 22.2: Structure of Prokaryotes
      1. 22.2.0: Basic Structures of Prokaryotic Cells
      2. 22.2.1: Prokaryotic Reproduction
    3. 22.3: Prokaryotic Metabolism
      1. 22.3.0: Energy and Nutrient Requirements for Prokaryotes
      2. 22.3.1: The Role of Prokaryotes in Ecosystems
    4. 22.4: Bacterial Diseases in Humans
      1. 22.4.0: History of Bacterial Diseases
      2. 22.4.1: Biofilms and Disease
      3. 22.4.2: Antibiotics: Are We Facing a Crisis?
      4. 22.4.3: Bacterial Foodborne Diseases
    5. 22.5: Beneficial Prokaryotes
      1. 22.5.0: Symbiosis between Bacteria and Eukaryotes
      2. 22.5.1: Early Biotechnology: Cheese, Bread, Wine, Beer, and Yogurt
      3. 22.5.2: Prokaryotes and Environmental Bioremediation
  23. 23: Protists
    1. 23.1: Eukaryotic Origins
      1. 23.1.0: Early Eukaryotes
      2. 23.1.1: Characteristics of Eukaryotic DNA
      3. 23.1.2: Endosymbiosis and the Evolution of Eukaryotes
      4. 23.1.3: The Evolution of Mitochondria
      5. 23.1.4: The Evolution of Plastids
    2. 23.2: Characteristics of Protists
      1. 23.2.0: Cell Structure, Metabolism, and Motility
      2. 23.2.1: Protist Life Cycles and Habitats
    3. 23.3: Groups of Protists
      1. 23.3.0: Excavata
      2. 23.3.1: Chromalveolata: Alveolates
      3. 23.3.2: Chromalveolata: Stramenopiles
      4. 23.3.3: Rhizaria
      5. 23.3.4: Archaeplastida
      6. 23.3.5: Amoebozoa and Opisthokonta
    4. 23.4: Ecology of Protists
      1. 23.4.0: Protists as Primary Producers, Food Sources, and Symbionts
      2. 23.4.1: Protists as Human Pathogens
      3. 23.4.2: Protists as Plant Pathogens
  24. 24: Fungi
    1. 24.1: Characteristics of Fungi
      1. 24.1.0: Characteristics of Fungi
      2. 24.1.1: Fungi Cell Structure and Function
      3. 24.1.2: Fungi Reproduction
    2. 24.2: Ecology of Fungi
      1. 24.2.0: Fungi Habitat, Decomposition, and Recycling
      2. 24.2.1: Mutualistic Relationships with Fungi and Fungivores
    3. 24.3: Classifications of Fungi
      1. 24.3.0: Chytridiomycota: The Chytrids
      2. 24.3.1: Zygomycota: The Conjugated Fungi
      3. 24.3.2: Ascomycota: The Sac Fungi
      4. 24.3.3: Basidiomycota: The Club Fungi
      5. 24.3.4: Deuteromycota: The Imperfect Fungi
      6. 24.3.5: Glomeromycota
    4. 24.4: Fungal Parasites and Pathogens
      1. 24.4.0: Fungi as Plant, Animal, and Human Pathogens
    5. 24.5: Importance of Fungi in Human Life
      1. 24.5.0: Importance of Fungi in Human Life
  25. 25: Seedless Plants
    1. 25.1: Early Plant Life
      1. 25.1.0: Early Plant Life
      2. 25.1.1: Evolution of Land Plants
      3. 25.1.2: Plant Adaptations to Life on Land
      4. 25.1.3: Sporophytes and Gametophytes in Seedless Plants
      5. 25.1.4: Structural Adaptations for Land in Seedless Plants
      6. 25.1.5: The Major Divisions of Land Plants
    2. 25.2: Green Algae: Precursors of Land Plants
      1. 25.2.0: Streptophytes and Reproduction of Green Algae
      2. 25.2.1: Charales
    3. 25.3: Bryophytes
      1. 25.3.0: Bryophytes
      2. 25.3.1: Liverworts and Hornworts
      3. 25.3.2: Mosses
    4. 25.4: Seedless Vascular Plants
      1. 25.4.0: Seedless Vascular Plants
      2. 25.4.1: Vascular Tissue: Xylem and Phloem
      3. 25.4.2: The Evolution of Roots in Seedless Plants
      4. 25.4.3: Ferns and Other Seedless Vascular Plants
      5. 25.4.4: The Importance of Seedless Vascular Plants
  26. 26: Seed Plants
    1. 26.1: Evolution of Seed Plants
      1. 26.1.0: The Evolution of Seed Plants and Adaptations for Land
      2. 26.1.1: Evolution of Gymnosperms
      3. 26.1.2: Evolution of Angiosperms
    2. 26.2: Gymnosperms
      1. 26.2.0: Characteristics of Gymnosperms
      2. 26.2.1: Life Cycle of a Conifer
      3. 26.2.2: Diversity of Gymnosperms
    3. 26.3: Angiosperms
      1. 26.3.0: Angiosperm Flowers
      2. 26.3.1: Angsiosperm Fruit
      3. 26.3.2: The Life Cycle of an Angiosperm
      4. 26.3.3: Diversity of Angiosperms
    4. 26.4: The Role of Seed Plants
      1. 26.4.0: Herbivory and Pollination
      2. 26.4.1: The Importance of Seed Plants in Human Life
      3. 26.4.2: Biodiversity of Plants
  27. 27: Introduction to Animal Diversity
    1. 27.1: Features of the Animal Kingdom
      1. 27.1.0: Characteristics of the Animal Kingdom
      2. 27.1.1: Complex Tissue Structure
      3. 27.1.2: Animal Reproduction and Development
    2. 27.2: Features Used to Classify Animals
      1. 27.2.0: Animal Characterization Based on Body Symmetry
      2. 27.2.1: Animal Characterization Based on Features of Embryological Development
    3. 27.3: Animal Phylogeny
      1. 27.3.0: Constructing an Animal Phylogenetic Tree
      2. 27.3.1: Molecular Analyses and Modern Phylogenetic Trees
    4. 27.4: The Evolutionary History of the Animal Kingdom
      1. 27.4.0: Pre-Cambrian Animal Life
      2. 27.4.1: The Cambrian Explosion of Animal Life
      3. 27.4.2: Post-Cambrian Evolution and Mass Extinctions
  28. 28: Invertebrates
    1. 28.1: Phylum Porifera
      1. 28.1.0: Phylum Porifera
      2. 28.1.1: Morphology of Sponges
      3. 28.1.2: Physiological Processes in Sponges
    2. 28.2: Phylum Cnidaria
      1. 28.2.0: Phylum Cnidaria
      2. 28.2.1: Class Anthozoa
      3. 28.2.2: Class Scyphozoa
      4. 28.2.3: Class Cubozoa and Class Hydrozoa
    3. 28.3: Superphylum Lophotrochozoa
      1. 28.3.0: Superphylum Lophotrochozoa
      2. 28.3.1: Phylum Platyhelminthes
      3. 28.3.2: Phylum Rotifera
      4. 28.3.3: Phylum Nemertea
      5. 28.3.4: Phylum Mollusca
      6. 28.3.5: Classification of Phylum Mollusca
      7. 28.3.6: Phylum Annelida
    4. 28.4: Superphylum Ecdysozoa
      1. 28.4.0: Superphylum Ecdysozoa
      2. 28.4.1: Phylum Nematoda
      3. 28.4.2: Phylum Arthropoda
      4. 28.4.3: Subphyla of Arthropoda
    5. 28.5: Superphylum Deuterostomia
      1. 28.5.0: Phylum Echinodermata
      2. 28.5.1: Classes of Echinoderms
      3. 28.5.2: Phylum Chordata
  29. 29: Vertebrates
    1. 29.1: Chordates
      1. 29.1.0: Characteristics of Chordata
      2. 29.1.1: Chordates and the Evolution of Vertebrates
      3. 29.1.2: The Evolution of Craniata and Vertebrata
      4. 29.1.3: Characteristics of Vertebrates
    2. 29.2: Fishes
      1. 29.2.0: Agnathans: Jawless Fishes
      2. 29.2.1: Gnathostomes: Jawed Fishes
    3. 29.3: Amphibians
      1. 29.3.0: Characteristics and Evolution of Amphibians
      2. 29.3.1: Modern Amphibians
    4. 29.4: Reptiles
      1. 29.4.0: Characteristics of Amniotes
      2. 29.4.1: Evolution of Amniotes
      3. 29.4.2: Characteristics of Reptiles
      4. 29.4.3: Evolution of Reptiles
      5. 29.4.4: Modern Reptiles
    5. 29.5: Birds
      1. 29.5.0: Characteristics of Birds
      2. 29.5.1: Evolution of Birds
    6. 29.6: Mammals
      1. 29.6.0: Characteristics of Mammals
      2. 29.6.1: Evolution of Mammals
      3. 29.6.2: Living Mammals
    7. 29.7: The Evolution of Primates
      1. 29.7.0: Characteristics and Evolution of Primates
      2. 29.7.1: Early Human Evolution
      3. 29.7.2: Early Hominins
      4. 29.7.3: Genus Homo
  30. 30: Plant Form and Physiology
    1. 30.1: The Plant Body
      1. 30.1.0: Plant Tissues and Organ Systems
    2. 30.2: Stems
      1. 30.2.0: Functions of Stems
      2. 30.2.1: Stem Anatomy
      3. 30.2.2: Primary and Secondary Growth in Stems
      4. 30.2.3: Stem Modifications
    3. 30.3: Roots
      1. 30.3.0: Types of Root Systems and Zones of Growth
      2. 30.3.1: Root Modifications
    4. 30.4: Leaves
      1. 30.4.0: Leaf Structure and Arrangment
      2. 30.4.1: Types of Leaf Forms
      3. 30.4.2: Leaf Structure, Function, and Adaptation
    5. 30.5: Plant Development
      1. 30.5.0: Meristems
      2. 30.5.1: Genetic Control of Flowers
    6. 30.6: Transport of Water and Solutes in Plants
      1. 30.6.0: Water and Solute Potential
      2. 30.6.1: Pressure, Gravity, and Matric Potential
      3. 30.6.2: Movement of Water and Minerals in the Xylem
      4. 30.6.3: Transportation of Photosynthates in the Phloem
    7. 30.7: Plant Sensory Systems and Responses
      1. 30.7.0: Plant Responses to Light
      2. 30.7.1: The Phytochrome System and Red Light Response
      3. 30.7.2: Blue Light Response
      4. 30.7.3: Plant Responses to Gravity
      5. 30.7.4: Auxins, Cytokinins, and Gibberellins
      6. 30.7.5: Abscisic Acid, Ethylene, and Nontraditional Hormones
      7. 30.7.6: Plant Responses to Wind and Touch
    8. 30.8: Plant Defense Mechanisms
      1. 30.8.0: Plant Defenses Against Herbivores
      2. 30.8.1: Plant Defenses Against Pathogens
  31. 31: Soil and Plant Nutrition
    1. 31.1: Nutritional Requirements of Plants
      1. 31.1.0: Plant Nutrition
      2. 31.1.1: The Chemical Composition of Plants
      3. 31.1.2: Essential Nutrients for Plants
    2. 31.2: The Soil
      1. 31.2.0: Soil Composition
      2. 31.2.1: Soil Formation
      3. 31.2.2: Physical Properties of Soil
    3. 31.3: Nutritional Adaptations of Plants
      1. 31.3.0: Nitrogen Fixation: Root and Bacteria Interactions
      2. 31.3.1: Mycorrhizae: The Symbiotic Relationship between Fungi and Roots
      3. 31.3.2: Nutrients from Other Sources
  32. 32: Plant Reproduction
    1. 32.1: Plant Reproductive Development and Structure
      1. 32.1.0: Plant Reproductive Development and Structure
      2. 32.1.1: Sexual Reproduction in Gymnosperms
      3. 32.1.2: Sexual Reproduction in Angiosperms
    2. 32.2: Pollination and Fertilization
      1. 32.2.0: Pollination and Fertilization
      2. 32.2.1: Pollination by Insects
      3. 32.2.2: Pollination by Bats, Birds, Wind, and Water
      4. 32.2.3: Double Fertilization in Plants
      5. 32.2.4: Development of the Seed
      6. 32.2.5: Development of Fruit and Fruit Types
      7. 32.2.6: Fruit and Seed Dispersal
    3. 32.3: Asexual Reproduction
      1. 32.3.0: Asexual Reproduction in Plants
      2. 32.3.1: Natural and Artificial Methods of Asexual Reproduction in Plants
      3. 32.3.2: Plant Life Spans
  33. 33: The Animal Body: Basic Form and Function
    1. 33.1: Animal Form and Function
      1. 33.1.0: Characteristics of the Animal Body
      2. 33.1.1: Body Plans
      3. 33.1.2: Limits on Animal Size and Shape
      4. 33.1.3: Limiting Effects of Diffusion on Size and Development
      5. 33.1.4: Animal Bioenergetics
      6. 33.1.5: Animal Body Planes and Cavities
    2. 33.2: Animal Primary Tissues
      1. 33.2.0: Epithelial Tissues
      2. 33.2.1: Connective Tissues: Loose, Fibrous, and Cartilage
      3. 33.2.2: Connective Tissues: Bone, Adipose, and Blood
      4. 33.2.3: Muscle Tissues and Nervous Tissues
    3. 33.3: Homeostasis
      1. 33.3.0: Homeostatic Process
      2. 33.3.1: Control of Homeostasis
      3. 33.3.2: Homeostasis: Thermoregulation
      4. 33.3.3: Heat Conservation and Dissipation
  34. 34: Animal Nutrition and the Digestive System
    1. 34.1: Digestive Systems
      1. 34.1.0: Digestive Systems
      2. 34.1.1: Herbivores, Omnivores, and Carnivores
      3. 34.1.2: Invertebrate Digestive Systems
      4. 34.1.3: Vertebrate Digestive Systems
      5. 34.1.4: Digestive System: Mouth and Stomach
      6. 34.1.5: Digestive System: Small and Large Intestines
    2. 34.2: Nutrition and Energy Production
      1. 34.2.0: Food Requirements and Essential Nutrients
      2. 34.2.1: Food Energy and ATP
    3. 34.3: Digestive System Processes
      1. 34.3.0: Ingestion
      2. 34.3.1: Digestion and Absorption
      3. 34.3.2: Elimination
    4. 34.4: Digestive System Regulation
      1. 34.4.0: Neural Responses to Food
      2. 34.4.1: Hormonal Responses to Food
  35. 35: The Nervous System
    1. 35.1: Neurons and Glial Cells
      1. 35.1.0: Neurons and Glial Cells
      2. 35.1.1: Neurons
      3. 35.1.2: Glia
    2. 35.2: How Neurons Communicate
      1. 35.2.0: Nerve Impulse Transmission within a Neuron: Resting Potential
      2. 35.2.1: Nerve Impulse Transmission within a Neuron: Action Potential
      3. 35.2.2: Synaptic Transmission
      4. 35.2.3: Signal Summation
      5. 35.2.4: Synaptic Plasticity
    3. 35.3: The Nervous System
      1. 35.3.0: The Nervous System
    4. 35.4: The Central Nervous System
      1. 35.4.0: Brain: Cerebral Cortex and Brain Lobes
      2. 35.4.1: Brain: Midbrain and Brain Stem
      3. 35.4.2: Spinal Cord
    5. 35.5: The Peripheral Nervous System
      1. 35.5.0: Autonomic Nervous System
      2. 35.5.1: Sensory-Somatic Nervous System
    6. 35.6: Nervous System Disorders
      1. 35.6.0: Neurodegenerative Disorders
      2. 35.6.1: Neurodevelopmental Disorders: Autism and ADHD
      3. 35.6.2: Neurodevelopmental Disorders: Mental Illnesses
      4. 35.6.3: Other Neurological Disorders
  36. 36: Sensory Systems
    1. 36.1: Sensory Processes
      1. 36.1.0: Reception
      2. 36.1.1: Transduction and Perception
    2. 36.2: Somatosensation
      1. 36.2.0: Somatosensory Receptors
      2. 36.2.1: Integration of Signals from Mechanoreceptors
      3. 36.2.2: Thermoreception
    3. 36.3: Taste and Smell
      1. 36.3.0: Tastes and Odors
      2. 36.3.1: Reception and Transduction
    4. 36.4: Hearing and Vestibular Sensation
      1. 36.4.0: Sound
      2. 36.4.1: Reception of Sound
      3. 36.4.2: Transduction of Sound
      4. 36.4.3: The Vestibular System
      5. 36.4.4: Balance and Determining Equilibrium
    5. 36.5: Vision
      1. 36.5.0: Light
      2. 36.5.1: Anatomy of the Eye
      3. 36.5.2: Transduction of Light
      4. 36.5.3: Visual Processing
  37. 37: The Endocrine System
    1. 37.1: Types of Hormones
      1. 37.1.0: Hormone Functions
      2. 37.1.1: Lipid-Derived, Amino Acid-Derived, and Peptide Hormones
    2. 37.2: How Hormones Work
      1. 37.2.0: How Hormones Work
      2. 37.2.1: Intracellular Hormone Receptors
      3. 37.2.2: Plasma Membrane Hormone Receptors
    3. 37.3: Regulation of Body Processes
      1. 37.3.0: Hormonal Regulation of the Excretory System
      2. 37.3.1: Hormonal Regulation of the Reproductive System
      3. 37.3.2: Hormonal Regulation of Metabolism
      4. 37.3.3: Hormonal Control of Blood Calcium Levels
      5. 37.3.4: Hormonal Regulation of Growth
      6. 37.3.5: Hormonal Regulation of Stress
    4. 37.4: Regulation of Hormone Production
      1. 37.4.0: Humoral, Hormonal, and Neural Stimuli
    5. 37.5: Endocrine Glands
      1. 37.5.0: Hypothalamic-Pituitary Axis
      2. 37.5.1: Thyroid Gland
      3. 37.5.2: Parathyroid Glands
      4. 37.5.3: Adrenal Glands
      5. 37.5.4: Pancreas
      6. 37.5.5: Pineal Gland and Gonads
      7. 37.5.6: Organs with Secondary Endocrine Functions
  38. 38: The Musculoskeletal System
    1. 38.1: Types of Skeletal Systems
      1. 38.1.0: Functions of the Musculoskeletal System
      2. 38.1.1: Types of Skeletal Systems
      3. 38.1.2: Human Axial Skeleton
      4. 38.1.3: Human Appendicular Skeleton
    2. 38.2: Bone
      1. 38.2.0: Bone
      2. 38.2.1: Cell Types in Bones
      3. 38.2.2: Bone Development
      4. 38.2.3: Growth of Bone
      5. 38.2.4: Bone Remodeling and Repair
    3. 38.3: Joints and Skeletal Movement
      1. 38.3.0: Classification of Joints on the Basis of Structure and Function
      2. 38.3.1: Movement at Synovial Joints
      3. 38.3.2: Types of Synovial Joints
      4. 38.3.3: Bone and Joint Disorders
    4. 38.4: Muscle Contraction and Locomotion
      1. 38.4.0: Structure and Function of the Muscular System
      2. 38.4.1: Skeletal Muscle Fibers
      3. 38.4.2: Sliding Filament Model of Contraction
      4. 38.4.3: ATP and Muscle Contraction
      5. 38.4.4: Regulatory Proteins
      6. 38.4.5: Excitation–Contraction Coupling
      7. 38.4.6: Control of Muscle Tension
  39. 39: The Respiratory System
    1. 39.1: Systems of Gas Exchange
      1. 39.1.0: The Respiratory System and Direct Diffusion
      2. 39.1.1: Skin, Gills, and Tracheal Systems
      3. 39.1.2: Amphibian and Bird Respiratory Systems
      4. 39.1.3: Mammalian Systems and Protective Mechanisms
    2. 39.2: Gas Exchange across Respiratory Surfaces
      1. 39.2.0: Gas Pressure and Respiration
      2. 39.2.1: Basic Principles of Gas Exchange
      3. 39.2.2: Lung Volumes and Capacities
      4. 39.2.3: Gas Exchange across the Alveoli
    3. 39.3: Breathing
      1. 39.3.0: The Mechanics of Human Breathing
      2. 39.3.1: Types of Breathing
      3. 39.3.2: The Work of Breathing
      4. 39.3.3: Dead Space: V/Q Mismatch
    4. 39.4: Transport of Gases in Human Bodily Fluids
      1. 39.4.0: Transport of Oxygen in the Blood
      2. 39.4.1: Transport of Carbon Dioxide in the Blood
  40. 40: The Circulatory System
    1. 40.1: Overview of the Circulatory System
      1. 40.1.0: The Role of the Circulatory System
      2. 40.1.1: Open and Closed Circulatory Systems
      3. 40.1.2: Types of Circulatory Systems in Animals
    2. 40.2: Components of the Blood
      1. 40.2.0: The Role of Blood in the Body
      2. 40.2.1: Red Blood Cells
      3. 40.2.2: White Blood Cells
      4. 40.2.3: Platelets and Coagulation Factors
      5. 40.2.4: Plasma and Serum
    3. 40.3: Mammalian Heart and Blood Vessels
      1. 40.3.0: Structures of the Heart
      2. 40.3.1: Arteries, Veins, and Capillaries
      3. 40.3.2: The Cardiac Cycle
    4. 40.4: Blood Flow and Blood Pressure Regulation
      1. 40.4.0: Blood Flow Through the Body
      2. 40.4.1: Blood Pressure
  41. 41: Osmotic Regulation and the Excretory System
    1. 41.1: Osmoregulation and Osmotic Balance
      1. 41.1.0: Introduction to Osmoregulation
      2. 41.1.1: Transport of Electrolytes across Cell Membranes
      3. 41.1.2: Concept of Osmolality and Milliequivalent
      4. 41.1.3: Osmoregulators and Osmoconformers
    2. 41.2: Nitrogenous Wastes
      1. 41.2.0: Nitrogenous Waste in Terrestrial Animals: The Urea Cycle
      2. 41.2.1: Nitrogenous Waste in Birds and Reptiles: Uric Acid
    3. 41.3: Excretion Systems
      1. 41.3.0: Contractile Vacuoles in Microorganisms
      2. 41.3.1: Flame Cells of Planaria and Nephridia of Worms
      3. 41.3.2: Malpighian Tubules of Insects
    4. 41.4: Human Osmoregulatory and Excretory Systems
      1. 41.4.0: Kidney Structure
      2. 41.4.1: Nephron: The Functional Unit of the Kidney
      3. 41.4.2: Kidney Function and Physiology
    5. 41.5: Hormonal Control of Osmoregulatory Functions
      1. 41.5.0: Epinephrine and Norepinephrine
      2. 41.5.1: Other Hormonal Controls for Osmoregulation
  42. 42: The Immune System
    1. 42.1: Innate Immune Response
      1. 42.1.0: Innate Immune Response
      2. 42.1.1: Physical and Chemical Barriers
      3. 42.1.2: Pathogen Recognition
      4. 42.1.3: Natural Killer Cells
      5. 42.1.4: The Complement System
    2. 42.2: Adaptive Immune Response
      1. 42.2.0: Antigen-presenting Cells: B and T cells
      2. 42.2.1: Humoral Immune Response
      3. 42.2.2: Cell-Mediated Immunity
      4. 42.2.3: Cytotoxic T Lymphocytes and Mucosal Surfaces
      5. 42.2.4: Immunological Memory
      6. 42.2.5: Regulating Immune Tolerance
    3. 42.3: Antibodies
      1. 42.3.0: Antibody Structure
      2. 42.3.1: Antibody Functions
    4. 42.4: Disruptions in the Immune System
      1. 42.4.0: Immunodeficiency
      2. 42.4.1: Hypersensitivities
  43. 43: Animal Reproduction and Development
    1. 43.1: Reproduction Methods
      1. 43.1.0: Methods of Reproducing
      2. 43.1.1: Types of Sexual and Asexual Reproduction
      3. 43.1.2: Sex Determination
    2. 43.2: Fertilization
      1. 43.2.0: External and Internal Fertilization
      2. 43.2.1: The Evolution of Reproduction
    3. 43.3: Human Reproductive Anatomy and Gametogenesis
      1. 43.3.0: Male Reproductive Anatomy
      2. 43.3.1: Female Reproductive Anatomy
      3. 43.3.2: Gametogenesis (Spermatogenesis and Oogenesis)
    4. 43.4: Hormonal Control of Human Reproduction
      1. 43.4.0: Male Hormones
      2. 43.4.1: Female Hormones
    5. 43.5: Fertilization and Early Embryonic Development
      1. 43.5.0: Fertilization
      2. 43.5.1: Cleavage, the Blastula Stage, and Gastrulation
    6. 43.6: Organogenesis and Vertebrate Formation
      1. 43.6.0: Organogenesis
      2. 43.6.1: Vertebrate Axis Formation
    7. 43.7: Human Pregnancy and Birth
      1. 43.7.0: Human Gestation
      2. 43.7.1: Labor and Birth
      3. 43.7.2: Contraception and Birth Control
      4. 43.7.3: Infertility
  44. 44: Ecology and the Biosphere
    1. 44.1: The Scope of Ecology
      1. 44.1.0: Introduction to Ecology
      2. 44.1.1: Organismal Ecology and Population Ecology
      3. 44.1.2: Community Ecology and Ecosystem Ecology
    2. 44.2: Biogeography
      1. 44.2.0: Biogeography
      2. 44.2.1: Energy Sources
      3. 44.2.2: Temperature and Water
      4. 44.2.3: Inorganic Nutrients and Other Factors
      5. 44.2.4: Abiotic Factors Influencing Plant Growth
    3. 44.3: Terrestrial Biomes
      1. 44.3.0: What constitutes a biome?
      2. 44.3.1: Tropical Wet Forest and Savannas
      3. 44.3.2: Subtropical Deserts and Chaparral
      4. 44.3.3: Temperate Grasslands
      5. 44.3.4: Temperate Forests
      6. 44.3.5: Boreal Forests and Arctic Tundra
    4. 44.4: Aquatic Biomes
      1. 44.4.0: Abiotic Factors Influencing Aquatic Biomes
      2. 44.4.1: Marine Biomes
      3. 44.4.2: Estuaries: Where the Ocean Meets Fresh Water
      4. 44.4.3: Freshwater Biomes
    5. 44.5: Climate and the Effects of Global Climate Change
      1. 44.5.0: Climate and Weather
      2. 44.5.1: Causes of Global Climate Change
      3. 44.5.2: Evidence of Global Climate Change
      4. 44.5.3: Past and Present Effects of Climate Change
  45. 45: Population and Community Ecology
    1. 45.1: Population Demography
      1. 45.1.0: Population Demography
      2. 45.1.1: Population Size and Density
      3. 45.1.2: Species Distribution
      4. 45.1.3: The Study of Population Dynamics
    2. 45.2: Environmental Limits to Population Growth
      1. 45.2.0: Exponential Population Growth
      2. 45.2.1: Logistic Population Growth
      3. 45.2.2: Density-Dependent and Density-Independent Population Regulation
    3. 45.3: Life History Patterns
      1. 45.3.0: Life History Patterns and Energy Budgets
      2. 45.3.1: Theories of Life History
    4. 45.4: Human Population Growth
      1. 45.4.0: Human Population Growth
      2. 45.4.1: Overcoming Density-Dependent Regulation
      3. 45.4.2: Age Structure, Population Growth, and Economic Development
    5. 45.5: Community Ecology
      1. 45.5.0: The Role of Species within Communities
      2. 45.5.1: Predation, Herbivory, and the Competitive Exclusion Principle
      3. 45.5.2: Symbiosis
      4. 45.5.3: Ecological Succession
    6. 45.6: Innate Animal Behavior
      1. 45.6.0: Introduction to Animal Behavior
      2. 45.6.1: Movement and Migration
      3. 45.6.2: Animal Communication and Living in Groups
      4. 45.6.3: Altruism and Populations
      5. 45.6.4: Mating Systems and Sexual Selection
    7. 45.7: Learned Animal Behavior
      1. 45.7.0: Simple Learned Behaviors
      2. 45.7.1: Conditioned Behavior
      3. 45.7.2: Cognitive Learning and Sociobiology
  46. 46: Ecosystems
    1. 46.1: Ecology of Ecosystems
      1. 46.1.0: Ecosystem Dynamics
      2. 46.1.1: Food Chains and Food Webs
      3. 46.1.2: Studying Ecosystem Dynamics
      4. 46.1.3: Modeling Ecosystem Dynamics
    2. 46.2: Energy Flow through Ecosystems
      1. 46.2.0: Strategies for Acquiring Energy
      2. 46.2.1: Productivity within Trophic Levels
      3. 46.2.2: Transfer of Energy between Trophic Levels
      4. 46.2.3: Ecological Pyramids
      5. 46.2.4: Biological Magnification
    3. 46.3: Biogeochemical Cycles
      1. 46.3.0: Biogeochemical Cycles
      2. 46.3.1: The Water (Hydrologic) Cycle
      3. 46.3.2: The Carbon Cycle
      4. 46.3.3: The Nitrogen Cycle
      5. 46.3.4: The Phosphorus Cycle
      6. 46.3.5: The Sulfur Cycle
  47. 47: Conservation Biology and Biodiversity
    1. 47.1: The Biodiversity Crisis
      1. 47.1.0: Loss of Biodiversity
      2. 47.1.1: Types of Biodiversity
      3. 47.1.2: Biodiversity Change through Geological Time
      4. 47.1.3: The Pleistocene Extinction
      5. 47.1.4: Present-Time Extinctions
    2. 47.2: The Importance of Biodiversity to Human Life
      1. 47.2.0: Human Health and Biodiversity
      2. 47.2.1: Agricultural Diversity
      3. 47.2.2: Managing Fisheries
    3. 47.3: Threats to Biodiversity
      1. 47.3.0: Habitat Loss and Sustainability
      2. 47.3.1: Overharvesting
      3. 47.3.2: Exotic Species
      4. 47.3.3: Climate Change and Biodiversity
    4. 47.4: Preserving Biodiversity
      1. 47.4.0: Measuring Biodiversity
      2. 47.4.1: Changing Human Behavior in Response to Biodiversity Loss
      3. 47.4.2: Ecological Restoration

4.1: Studying Cells

4.1.1: Cells as the Basic Unit of Life

A cell is the smallest unit of a living thing and is the basic building block of all organisms.

Learning Objective

State the general characteristics of a cell

Key Points

  • A living thing can be composed of either one cell or many cells.
  • There are two broad categories of cells: prokaryotic and eukaryotic cells.
  • Cells can be highly specialized with specific functions and characteristics.

Key Terms

prokaryotic

Small cells in the domains Bacteria and Archaea that do not contain a membrane-bound nucleus or other membrane-bound organelles.

eukaryotic

Having complex cells in which the genetic material is contained within membrane-bound nuclei.

cell

The basic unit of a living organism, consisting of a quantity of protoplasm surrounded by a cell membrane, which is able to synthesize proteins and replicate itself.

Close your eyes and picture a brick wall. What is the basic building block of that wall? A single brick, of course. Like a brick wall, your body is composed of basic building blocks, and the building blocks of your body are cells.

Cells as Building Blocks

A cell is the smallest unit of a living thing. A living thing, whether made of one cell (like bacteria) or many cells (like a human), is called an organism. Thus, cells are the basic building blocks of all organisms. Several cells of one kind that interconnect with each other and perform a shared function form tissues; several tissues combine to form an organ (your stomach, heart, or brain); and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems that function together form an organism (like a human being). There are many types of cells all grouped into one of two broad categories: prokaryotic and eukaryotic. For example, both animal and plant cells are classified as eukaryotic cells, whereas bacterial cells are classified as prokaryotic.

Types of Specialized Cells

Your body has many kinds of cells, each specialized for a specific purpose. Just as a home is made from a variety of building materials, the human body is constructed from many cell types. For example, epithelial cells protect the surface of the body and cover the organs and body cavities within. Bone cells help to support and protect the body. Cells of the immune system fight invading bacteria. Additionally, blood and blood cells carry nutrients and oxygen throughout the body while removing carbon dioxide. Each of these cell types plays a vital role during the growth, development, and day-to-day maintenance of the body. In spite of their enormous variety, however, cells from all organisms—even ones as diverse as bacteria, onion, and human—share certain fundamental characteristics.

Various Cell Types

Various Cell Types

(a) Nasal sinus cells (viewed with a light microscope), (b) onion cells (viewed with a light microscope), and (c) Vibrio tasmaniensis bacterial cells (seen through a scanning electron microscope) are from very different organisms, yet all share certain characteristics of basic cell structure.

4.1.2: Microscopy

Microscopes allow for magnification and visualization of cells and cellular components that cannot be seen with the naked eye.

Learning Objective

Compare and contrast light and electron microscopy.

Key Points

  • Light microscopes allow for magnification of an object approximately up to 400-1000 times depending on whether the high power or oil immersion objective is used.
  • Light microscopes use visible light which passes and bends through the lens system.
  • Electron microscopes use a beam of electrons, opposed to visible light, for magnification.
  • Electron microscopes allow for higher magnification in comparison to a light microscope thus, allowing for visualization of cell internal structures.

Key Terms

electron

The subatomic particle having a negative charge and orbiting the nucleus; the flow of electrons in a conductor constitutes electricity.

resolution

The degree of fineness with which an image can be recorded or produced, often expressed as the number of pixels per unit of length (typically an inch).

Microscopy

Cells vary in size. With few exceptions, individual cells cannot be seen with the naked eye, so scientists use microscopes (micro- = "small"; -scope = "to look at") to study them. A microscope is an instrument that magnifies an object. Most photographs of cells are taken with a microscope; these images can also be called micrographs.

The optics of a microscope's lenses change the orientation of the image that the user sees. A specimen that is right-side up and facing right on the microscope slide will appear upside-down and facing left when viewed through a microscope, and vice versa. Similarly, if the slide is moved left while looking through the microscope, it will appear to move right, and if moved down, it will seem to move up. This occurs because microscopes use two sets of lenses to magnify the image. Because of the manner by which light travels through the lenses, this system of two lenses produces an inverted image (binocular, or dissecting microscopes, work in a similar manner, but they include an additional magnification system that makes the final image appear to be upright).

Light Microscopes

To give you a sense of cell size, a typical human red blood cell is about eight millionths of a meter or eight micrometers (abbreviated as eight μm) in diameter; the head of a pin of is about two thousandths of a meter (two mm) in diameter. That means about 250 red blood cells could fit on the head of a pin.

Most student microscopes are classified as light microscopes . Visible light passes and is bent through the lens system to enable the user to see the specimen. Light microscopes are advantageous for viewing living organisms, but since individual cells are generally transparent, their components are not distinguishable unless they are colored with special stains. Staining, however, usually kills the cells.

Light and Electron Microscopes

Light and Electron Microscopes

(a) Most light microscopes used in a college biology lab can magnify cells up to approximately 400 times and have a resolution of about 200 nanometers. (b) Electron microscopes provide a much higher magnification, 100,000x, and a have a resolution of 50 picometers.

Light microscopes, commonly used in undergraduate college laboratories, magnify up to approximately 400 times. Two parameters that are important in microscopy are magnification and resolving power. Magnification is the process of enlarging an object in appearance. Resolving power is the ability of a microscope to distinguish two adjacent structures as separate: the higher the resolution, the better the clarity and detail of the image. When oil immersion lenses are used for the study of small objects, magnification is usually increased to 1,000 times. In order to gain a better understanding of cellular structure and function, scientists typically use electron microscopes.

Electron Microscopes

In contrast to light microscopes, electron microscopes use a beam of electrons instead of a beam of light. Not only does this allow for higher magnification and, thus, more detail, it also provides higher resolving power. The method used to prepare the specimen for viewing with an electron microscope kills the specimen. Electrons have short wavelengths (shorter than photons) that move best in a vacuum, so living cells cannot be viewed with an electron microscope.

In a scanning electron microscope, a beam of electrons moves back and forth across a cell's surface, creating details of cell surface characteristics. In a transmission electron microscope, the electron beam penetrates the cell and provides details of a cell's internal structures. As you might imagine, electron microscopes are significantly more bulky and expensive than light microscopes.

4.1.3: Cell Theory

Cell theory states that living things are composed of one or more cells, that the cell is the basic unit of life, and that cells arise from existing cells.

Learning Objective

Identify the components of cell theory

Key Points

  • The cell theory describes the basic properties of all cells.
  • The three scientists that contributed to the development of cell theory are Matthias Schleiden, Theodor Schwann, and Rudolf Virchow.
  • A component of the cell theory is that all living things are composed of one or more cells.
  • A component of the cell theory is that the cell is the basic unit of life.
  • A component of the cell theory is that all new cells arise from existing cells.

Key Term

cell theory

The scientific theory that all living organisms are made of cells as the smallest functional unit.

Cell Theory

The microscopes we use today are far more complex than those used in the 1600s by Antony van Leeuwenhoek, a Dutch shopkeeper who had great skill in crafting lenses. Despite the limitations of his now-ancient lenses, van Leeuwenhoek observed the movements of protista (a type of single-celled organism) and sperm, which he collectively termed "animalcules. "

In a 1665 publication called Micrographia, experimental scientist Robert Hooke coined the term "cell" for the box-like structures he observed when viewing cork tissue through a lens. In the 1670s, van Leeuwenhoek discovered bacteria and protozoa. Later advances in lenses, microscope construction, and staining techniques enabled other scientists to see some components inside cells.

Structure of an Animal Cell

Structure of an Animal Cell

The cell is the basic unit of life and the study of the cell led to the development of the cell theory.

By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory. The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells. Rudolf Virchow later made important contributions to this theory.

Schleiden and Schwann proposed spontaneous generation as the method for cell origination, but spontaneous generation (also called abiogenesis) was later disproven. Rudolf Virchow famously stated "Omnis cellula e cellula"... "All cells only arise from pre-existing cells. "The parts of the theory that did not have to do with the origin of cells, however, held up to scientific scrutiny and are widely agreed upon by the scientific community today. The generally accepted portions of the modern Cell Theory are as follows:

  1. The cell is the fundamental unit of structure and function in living things.
  2. All organisms are made up of one or more cells.
  3. Cells arise from other cells through cellular division.

The expanded version of the cell theory can also include:

  • Cells carry genetic material passed to daughter cells during cellular division
  • All cells are essentially the same in chemical composition
  • Energy flow (metabolism and biochemistry) occurs within cells

4.1.4: Cell Size

Cell size is limited in accordance with the ratio of cell surface area to volume.

Learning Objective

Describe the factors limiting cell size and the adaptations cells make to overcome the surface area to volume issue

Key Points

  • As a cell grows, its volume increases much more rapidly than its surface area. Since the surface of the cell is what allows the entry of oxygen, large cells cannot get as much oxygen as they would need to support themselves.
  • As animals increase in size they require specialized organs that effectively increase the surface area available for exchange processes.

Key Term

surface area

The total area on the surface of an object.

At 0.1 to 5.0 μm in diameter, prokaryotic cells are significantly smaller than eukaryotic cells, which have diameters ranging from 10 to 100 μm. The small size of prokaryotes allows ions and organic molecules that enter them to quickly diffuse to other parts of the cell. Similarly, any wastes produced within a prokaryotic cell can quickly diffuse out. This is not the case in eukaryotic cells, which have developed different structural adaptations to enhance intracellular transport.

Relative Size of Atoms to Humans

Relative Size of Atoms to Humans

This figure shows relative sizes on a logarithmic scale (recall that each unit of increase in a logarithmic scale represents a 10-fold increase in the quantity being measured).

In general, small size is necessary for all cells, whether prokaryotic or eukaryotic. Consider the area and volume of a typical cell. Not all cells are spherical in shape, but most tend to approximate a sphere. The formula for the surface area of a sphere is 4πr2, while the formula for its volume is 4πr3/3. As the radius of a cell increases, its surface area increases as the square of its radius, but its volume increases as the cube of its radius (much more rapidly). 

Therefore, as a cell increases in size, its surface area-to-volume ratio decreases. This same principle would apply if the cell had the shape of a cube (below). If the cell grows too large, the plasma membrane will not have sufficient surface area to support the rate of diffusion required for the increased volume. In other words, as a cell grows, it becomes less efficient. One way to become more efficient is to divide; another way is to develop organelles that perform specific tasks. These adaptations lead to the development of more sophisticated cells called eukaryotic cells.

Surface Area to Volume Ratios

Surface Area to Volume Ratios

Notice that as a cell increases in size, its surface area-to-volume ratio decreases. When there is insufficient surface area to support a cell’s increasing volume, a cell will either divide or die. The cell on the left has a volume of 1 mm3 and a surface area of 6 mm2, with a surface area-to-volume ratio of 6 to 1, whereas the cell on the right has a volume of 8 mm3 and a surface area of 24 mm2, with a surface area-to-volume ratio of 3 to 1.

Smaller single-celled organisms have a high surface area to volume ratio, which allows them to rely on oxygen and material diffusing into the cell (and wastes diffusing out) in order to survive. The higher the surface area to volume ratio they have, the more effective this process can be. Larger animals require specialized organs (lungs, kidneys, intestines, etc.) that effectively increase the surface area available for exchange processes, and a circulatory system to move material and heat energy between the surface and the core of the organism.

Increased volume can lead to biological problems. King Kong, the fictional giant gorilla, would have insufficient lung surface area to meet his oxygen needs, and could not survive. For small organisms with their high surface area to volume ratio, friction and fluid dynamics (wind, water flow) are relatively much more important, and gravity much less important, than for large animals.

However, increased surface area can cause problems as well. More contact with the environment through the surface of a cell or an organ (relative to its volume) increases loss of water and dissolved substances. High surface area to volume ratios also present problems of temperature control in unfavorable environments.

Attributions

  • Cells as the Basic Unit of Life
    • "OpenStax College, Biology. October 16, 2013." http://openstaxcollege.org/textbooks/biology. OpenStax CNX CC BY-SA 3.0.
    • "eukaryotic." http://en.wiktionary.org/wiki/eukaryotic. Wiktionary CC BY-SA 3.0.
    • "prokaryotic." http://en.wiktionary.org/wiki/prokaryotic. Wiktionary CC BY-SA 3.0.
    • "Robert Bear and David Rintoul, Introduction to Cells. October 23, 2013." http://cnx.org/content/m47170/latest/. OpenStax CNX CC BY 3.0.
    • "cell." http://en.wiktionary.org/wiki/cell. Wiktionary CC BY-SA 3.0.
    • "OpenStax College, Biology. October 16, 2013." http://cnx.org/content/m44404/latest/?collection=col11448/latest. OpenStax CNX CC BY 3.0.
    • "OpenStax College, Introduction. October 16, 2013." http://cnx.org/content/m44404/latest/Figure_04_00_00.jpg. OpenStax CNX CC BY 3.0.
  • Microscopy
    • "Boundless." http://www.boundless.com/. Boundless Learning CC BY-SA 3.0.
    • "electron." http://en.wiktionary.org/wiki/electron. Wiktionary CC BY-SA 3.0.
    • "resolution." http://en.wiktionary.org/wiki/resolution. Wiktionary CC BY-SA 3.0.
    • "OpenStax College, Biology. October 16, 2013." http://cnx.org/content/m44405/latest/?collection=col11448/latest. OpenStax CNX CC BY 3.0.
    • "OpenStax College, Studying Cells. October 16, 2013." http://cnx.org/content/m44405/latest/Figure_04_01_01ab_new.jpg. OpenStax CNX CC BY 3.0.
  • Cell Theory
    • "Boundless." http://www.boundless.com/. Boundless Learning CC BY-SA 3.0.
    • "OpenStax College, Biology. October 16, 2013." http://cnx.org/content/m44405/latest/?collection=col11448/latest. OpenStax CNX CC BY 3.0.
    • "cell theory." http://en.wiktionary.org/wiki/cell_theory. Wiktionary CC BY-SA 3.0.
    • "General Biology/Cells/Cell Structure." http://en.wikibooks.org/wiki/General_Biology/Cells/Cell_Structure%23Cell_Theory. Wikibooks CC BY-SA 3.0.
    • "Diagram of an animal cell in three dimensions." http://commons.wikimedia.org/wiki/File:Diagram_of_an_animal_cell_in_three_dimensions.png. Wikimedia Public domain.
  • Cell Size
    • "Surface Area to Volume Ratios." https://en.wikipedia.org/wiki/Surface-area-to-volume_ratio. Wikipedia CC BY-SA 3.0.
    • "Surface area." https://en.wiktionary.org/wiki/surface_area. Wiktionary CC BY-SA 3.0.
    • "Cell Size." http://cnx.org/contents/GFy_h8cu@9.87:pOpVdIwp@11/Prokaryotic-Cells. OpenStax CNX CC BY-SA 3.0.
    • "cells.jpg." http://cnx.org/contents/GFy_h8cu@9.87:pOpVdIwp@11/Prokaryotic-Cells. OpenStax CNX CC BY-SA 3.0.
    • "Figure_04_02_02.jpg." http://cnx.org/contents/GFy_h8cu@9.87:pOpVdIwp@11/Prokaryotic-Cells. OpenStax CNX CC BY-SA 3.0.

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