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Biology is the study of living things. There are five major principles governing biology today: cell theory, genetic change and variation (also called evolution), gene theory, homeostasis, and energy.

Bi*ol"o*gy, n. Etym: [Gr. life + -logy: cf. F. biologie.]

Defn: The science of life; that branch of knowledge which treats of living matter as distinct from matter which is not living; the study of living tissue. It has to do with the origin, structure, development, function, and distribution of animals and plants.


Biology and You

Biology at Work Today: What is killing the frogs, Testing an idea

The Scientific Process: The six stages of a scientific investigation

Properties of Life: Living things share certain properties

Addressing Real-World Problems: Protecting our earth, Feeding a growing population, Defeating diseases, What you can contribute

Scientific Method: Experimental method, Correlation studies

It's a Fact: When a scientific fact is not a fact, Scientific "facts" are open for discussion

Fundamental Concepts of Biology

Changes: Adaptions, Energy, Natural selection

Limitations of Science

Biological subjects are divided into specialized fields. These fields are called disciplines. The major disciplines of biology are: Acarology, Aerobiology, Anatomy, Arachnology, Astrobiology, Biochemistry, Bionics, Biogeography, Bioinformatics, Biological Psychiatry, Biomechanics, Biomedical Research, Biophysics, Biotechnology, Botany, Cell Biology, Chorology, Cladistics, Carcinology, Cryptozoology, Cytology, Cytopathology, Developmental Biology, Ecology, Epidemiology, Ethology, Endocrinology, Entomology, Freshwater Biology, Genetics, Herpetology, Histology, Human Biology, Ichthyology, Immunology, Lichenology, Malacology, Mammalogy, Marine Biology, Matrix biology, Medicine, Microbiology, Molecular Biology, Morphology, Mycology, Myrmecology, Nematology, Neuroscience, Oncology, Ontogeny, Abiogenesis, Ornithology, Paleontology, Parasitology, Pathology, Photobiology, Phycology, Physiology, Plant Pathology, Population biology, Reproductive Biology, Scatology, Structural Biology, Systems Biology, Sociobiology, Taxonomy, Toxicology, Virology, and Zoology.

Principles of Cell Biology - The Unity of Life

Basic Chemistry

Chemical Elements and Atoms

Bonds Between Atoms

Molecules and Compounds

Movement of Molecules

Chemical Reactions


Dissociation of the pH Scale

Isotopes - Chemical Tools for Biology

Biological Chemistry

Structure of Organic Molecules: Carbon skeletons, Functional groups, Building biological polymers

Lipids: Fatty acids, Fats and oils, Phospholipids, Steroids


Nucleic Acids

Proteins: Protein structure, denatured proteins (gelatin and pineapple)

Enzymes: Enzyme-substrate complexes, Factors that effect enzyme activity


The Nature of the Cell

Cells - The Smallest Units of Life: How cells were discovered, Formation of the cell theory, A short history of cells, Cells must be small

The Chemistry of Living Cells: Atoms are the cell's smallest components, Atoms chemically react to form compounds, Water is a major compound of cells, Acids and bases affect the cell's environment

Chemically Building Blocks of Cells: Cells use carbohydrates to store energy and provide support, Lipids store energy and are a component of cell membranes, Many cellular activities involve proteins, Nucleic acids contain the cell's hereditary information, ATP is the cell's fuel

The Interior of the Cell: Microscopes reveal cell structure, Internal membranes transport materials within the cell, The nucleus directs all activities and stores DNA, Specialized organelles act as cellular powerhouses, Biochemical factories of the cell, Protein fibers provide an interior framework, Diversity and themes in biology

Cells and Their Environment

Structure of the Plasma Membrane: A lipid bilayer is the foundation of the membrane, proteins are embedded within the bilayer

Roles of the Plasma Membrane

Moving Materials In and Out of Cells: Passive processes do not use energy, Active processes expend energy

How Small Uncharged Molecules Cross Membranes: Diffusion, Osmosis, Cells as osmotic systems

Transport by Membrane Proteins: Channel proteins, Facilitated diffusion, Active transport

Membrane Transport of Large Particles

Membrane Attachments Between Cells

How Cells Communicate: Direct and indirect communication, Receptors receive information

Energy and Metabolism

Energy and Living Things: Energy takes many forms, Energy can be transformed, Energy tends to become disorganized, Energy flows through living systems, Energy is carried by electrons

Energy and Chemical Reactions: Chemical reactions absorb or release energy, Starting chemical reactions requires energy, Enzymes catalyze chemical reactions in cells

Metabolism: Life processes are driven by energy, ATP supplies energy for metabolism, Coenzymes help transport energy, Enzymes direct metabolism in cells

Photosynthesis and Cellular Respiration

How Energy Cycles: Photosynthesis and cellular respiration form a cycle, Energy is stored in carbon compounds, Energy flows through food chains

How Photosynthesis Works: Plants are specialized for photosynthesis, Light energy is packaged in photons, Photosynthetic pigments absorb photons, Light energy is converted into chemical energy, Chemical energy is stored in organic molecules, Environment affects the rate of photosynthesis

How Cellular Respiration Works: Glucose is split during glycosis, Making more ATP requires oxygen, Fermentation occurs in the absence of oxygen, Many fuels are used for cellular respiration, cells control the rate of cellular respiration

Cell Reproduction

Chromosomes: Chromosome structure, Chromosomes affect development, Chromosomes determine gender

Mitosis and Cell Division: Bacteria simply split, Eukaryotic cells undergo nuclear division, What happens during mitosis and cell division, Stages of mitosis

Meiosis: What happens during meiosis, Meiosis I separates homologues, Meiosis II separates chromatids, The importance of crossing-over

Principles of Genetics

Mendel and Heredity

Fundamentals of Genetics: The beginnings of genetics, Mendel studied the garden pea, Mendel proposed a Theory of Heredity, Mendel's theory became Laws of Heredity

Analyzing Heredity: Interpreting Mendel's model, Patterns of heredity can be complex

Human Genetics: Mutations cause genetic disorders, Tracking traits in families, Identifying and treating people at risk

DNA: The Genetic Material

Identifying the Genetic Material: The genetic material - protein or DNA, Griffith demonstrates transformation, Hershey and Chase show that genes are made of DNA, DNA stores genetic information

The Structure of DNA: Nucleotides are the building blocks of DNA, The DNA molecule is a double helix, How DNA is coppied

The Structure of a Gene: Genes in Eukaryotes are often interrupted, Some genes exist in many copies, Some genes can jump to new locations, Some genes protect cells from mutation

Gene Expression

From Genes to Proteins: The path of genetic information, Transcription - making RNA, The genetic code, Translation - making proteins, RNA and protein synthesis

Regulation Gene Expression: Gene regulation in Prokaryotes, Gene regulation in Eukaryotes, Reproduction of eukaryotic cells

Genes, Mutation, and Cancer: Mutations are changes in DNA, Mutations can cause cancer

Gene Technology

Note: This section has not been revised to include the negative role genetic modification plays on the environment.

What is genetic engineering: The basics of genetic engineering, Cleaving DNA, Producing recombinant DNA, Cloning cells, Screening cells, Identifying sequences in DNA

The New Medicine: Making of genetically engineered drugs, making of genetically engineered vaccines, curing genetic disorders

The New Agriculture: Transporting genes into plants, Making crops resistant to herbicides and insects, Developing crops that need no fertilizer, Improving livestock production

Principles of Life

The Origin of Life

The Mystery of Life's Origin: There are several ideas about the origin of life, Life's basic chemicals can form spontaneously, Proteins can be assembled by RNA, Microspheres might have led to cells, origin of heredity remains a mystery

Evaluating the Spontaneous Origin Hypothesis: Is earth old enough? Is life too complex to have arisen naturally? Does spontaneous origin violate the Second Law of Thermodynamics? Can proteins assemble spontaneously?

Is There Life on Other Worlds: Life reflects the nature of the planet, Life probably exists elsewhere, Scientists are listening for other life forms

The Evolution Issue

Similarity of some fossilized animals and plants to those which currently exist

Gene pools: Some traits may be magnified where the gene pool is limited, The gene pool can contribute to characteristics that vary from group to group

Survival of the fittest:

Genetic variation can cause one group to survive while another dies off due to climatic or area-specific issues, such as disease. Nature does not nurture weakness. Only the strongest and healthiest creatures survive in the wild. This does not pertain as much to the survival of one species over the survival of another species, but to the survival of one organism over another organism of the same species. Medicine, however, has contributed greatly to the survival and betterment of the weaker members of various species.

Principles of Ecology

Distribution of Organisms


How Populations Grow: What a population is, How a population grows, Two strategies of population growth, The rapidly growing human population

How Populations Change: Unchanging populations, Applying the Hardy-Weinberg principle, Five forces cause populations to change

How Natural Selection Shapes Populations: Selection against unfavorable recessive alleles is slow, many genes have more than one common allele, Selection on traits controlled by more than one gene


An Introduction to Ecosystems: Living things are interdependent, The inhabitants of an ecosystem, The things that determine the boundaries of an ecosystem, Natural changes in ecosystems, An example of ecological succession - Glacier Bay

Energy Flows Through Ecosystems: The path of energy - who eats whom in the ecosystem, Energy transfers between trophic levels are insufficient, Energy loss limits the number of trophic levels in an ecosystem

Materials Cycle Within Ecosystems: Materials cycle between organisms and the nonliving environment, The water cycle is driven by the sun, The carbon cycle is linked to the flow of energy, The nitrogen and phosphorus cycles

Biological Communities

How Organisms Interact in Communities: Interacting species change in response to one another, Changing in opposition - predators and prey, competition - common use of scarce resources, Changing in cooperation

How Competition Shapes Communities: Each species in a community plays a unique role, A closer look at niches, Demonstrating competition in nature, The outcome of competition, Predation can lessen competition among prey

The Influence of Physical Environment: The causes of climate, Solar heating drives the circulation of the earth's atmosphere, Why it rains where it does, Patterns of circulation in the ocean

Major Biological Communities: Marine communities, Freshwater communities, Terrestrial communities

Human Impact on the Environment

Human Ecology

Global Change: Burning high-sulphur coal creates acidic precipitation, Destruction of the ozone layer, Real causes of global warming

Ecosystem Damage: Pollution, Consuming nonreplaceable resources, The core problem is not population growth

Solving Environmental Problems: Reducing pollution, How to solve environmental problems, What you can contribute

Exploring Diversity

Overview of Diversity


Origin of Eukaryotes: Prokaryotes - the oldest organisms, The first eukaryotes - a new kind of cell, The origin of Mitosis is unknown

Variations in Reproduction: Single-gender reproduction is primitive and prevalent, Male and female has advantages, Eukaryotes have life cycles

Multicellularity: Multicellularity allows for specialization, Colonies and aggragates are not truly multicellular, Multicellularity appears in four scientific kingdoms, Multicellularity requires cell specialization and coordination

Classification of Living Things: Living things can be classified in many different ways. Although scientists and writers throughout the centuries (such as Aristotle) have developed many different methods of classifying living things, Carl Linnaeus formulated the original framework for the organizational system most commonly used by scientists, which bears the name of Linnaean taxonomy in his honor. Linnaean taxonomy assigns organisms two-word names. Scientific names are universal, All organisms are classified in a hierarchy (kingdom, phylum, class, order, family, genus, species), Recognizing a species, Reconstructing theories of origin, How to construct a Cladogram, considering the weight of a character

Viruses and Bacteria

Viruses: Is a virus a living organism, viruses are made of protein and nucleic acid, Viruses reproduce inside living cells, Viruses take over a cell's machinery, Origins of viruses

Bacteria: Bacteria differ in cell wall structure, Comparing bacteria with eukaryotic cells, Grouping bacteria according to how they obtain energy

Bacteria and Viruses as Pathenogens: Diseases caused by bacteria, Diseases caused by viruses


Characteristics of Protists: Protists were the first Eukaryotes, Some protists can reproduce as male and female

Protist Diversity: Protists that move using cytoplasmic extensions, Diatoms have double shells, Some algae are multicellular, some protists move with Flagella, Protists that use cilia to swim, Protistan molds are not fungi, Some protists form resistant spores

Protists and Human Health: Plasmodius causes malaria


Characteristics of Fungi: Fungi are classified in their own kingdom, Fungi are well suited for absorbing nutrients, How fungi reproduce

Fungal Diversity: Fungi that form Zygosporangia, Fungi that form sacs of spores, Fungi that form clublike structures, Fungi in which there seems to be only single-gender reproduction

Fungal Associations: Lichens - fungi and photsynthetic partners, Mycorrhizae - fungi and roots

Exploring Plants

Overview of Plants

Vascular Plants: Mosses have simple vascular tissue, Vascular plants are characterized by several several features

Seeds: Gynmosperms are the simplest seed plants, Most living gymnosperms are conifers, What makes a seed

Flowers: What makes a flower, Double fertilization provides large food reserves in seeds, Fruits enable efficient seed dispersal

Plant Structure and Function

The Vascular Plant Body: Three tissue systems make up the vascular plant body, Vascular plants are organized into leaves, stems, and roots

Transport in Vascular Plants: Transpiration pulls water up a plant, Guard cells regulate the rate of transpiration, sugar is pushed through a plant, Nutrition in vascular plants

Plant Growth and Development

How Plants Grow and Develop: Reproduction in flowering plants, Growth and development begin as a seed forms, Growth continues as a seed germinates, Apical meristems produce primary growth, Lateral meristems produce secondary growth, Plant development is continuous and "reversible", How long a plant lives

Regulating Growth and Development: Nutrients are needed for plant growth, Hormones control plant growth and development, Plant growth responds to environmental factors

Plants in Our Lives

Plants as Food: Most plants serve as food, Cereals are the most important sources of food, Many other plants supply important foods

Other Uses of Plants: Wood is the most valuable plant product besides food, Many medicines are obtained from plants, Fibers and rubber come from plants

Exploring the Animal World

Muscles and Skeletons

Animal Nutrition, Digestion, and Excretion

Gas Exchange in Animals

Transport and Temperature Regulation

Defenses Against Disease

Nervous Systems

Sense Organs

Animal Hormones and Chemical Regulation

Reproduction and Development

Animal Behavior

Exploring Invertebrates

Overview of Invertebrates

Tissues and Asymmetry: Some general features of animals, Sponges - the simplest animals, Cnidarians - radically symmetric animals

The Body Cavity: Flatworms - worms with solid bodies, Roundworms - nematodes, Mollusks - animals with three-part bodies

Four Innovations in Body Plan: Annelids - segmented worms, Arthropods - walking animals, Echinoderms - animals with a five-part body plan, Chordates - animals with a notochord

Simple Invertebrates

Sponges: Sponges are filter feeders, Sponges have simple skeletons of varied composition, Single-gender and male-female reproduction occur in sponges

Cnidarians: Three classes of cnidarians, Hydrozoans are found in fresh and salt water, Scyphozoans are marine jellyfish, Anthozoans are marine polyps

Kinds of Simple Worms: Flatworms have a solid body, Ribbon worms have a digestive tube with two openings, Roundworms are the simplest animals with a body cavity, Most rotifers are microscopic

Mollusks and Annelids

Mollusks: Characteristics of mollusks, Organ systems of mollusks, Mollusk diversity

Annelids: Characteristics of annelids, Organ systems of annelids, Annelid diversity

Arthropods and Echinoderms

Features of Arthropods: The body plan and characteristics of arthropods, Arthropods shed their exoskeletons to grow

Arthropod Diversity: Arachnids have eight legs, Most crustaceans are aquatic, Most uniramians live on land and can fly

Echinoderms and Invertebrate Chordates: Echinoderm larvae and adults have different body plans, All echinoderms share four major characteristics, Echinoderms are a diverse group, Invertebrate chordates

Exploring Vertebrates

Overview of Vertebrates

Challenge of Obtaining Oxygen: Fishes use gills to get oxygen from water, Amphibians use lungs to get oxygen from air, Lung surface area increases in reptiles and mammals, Birds have the most efficient lungs

Heart: The chordate heart is a simple pump, Fishes have hearts with chambers, Amphibians have a pulonary vein, The heart is divided in terrestrial vertebrates

Challenge of Retaining Water: Fishes use kidneys to balance water and salt, Excretions are concentrated in terrestrial vertebrates, Reptiles have watertight skin, Reptiles have watertight eggs

Development: Fishes reproduce externally, Amphibians are still tied to water, Reptiles, birds, and mammals reproduce internally, Mammals nourish their young

Fishes and Amphibians

Diversity of Fishes: Jawless fishes, Sharks and bony fishes

Characteristics of Fishes: General characteristics of fishes, Additional characteristics of bony fishes

Diversity of Amphibians: Frogs and toads, Newts and efts, Salamanders, Caecilians

Characteristics of Amphibians: General characteristics of amphibians, Frogs and toads are tailless, Salamanders have tails, Caecilians are legless


History of Reptiles: Dinosaurs - the Triassic, Jurassic, and Cretaceous Periods

Characteristics and Diversity of Living Reptiles: Key characteristics of living reptiles, Turtles and tortoises, Tuataras live only in New Zealand, Lizards and snakes, Crocodiles and alligators


Characteristics and Diversity of Birds: Main characteristics of birds, The major orders of birds


Key Mammal Characteristics: Hair is a unique mammalian feature, Nurturing and care of young, Mammals have diverse, specialized teeth, Maintaining a high body temperature, Three forms of reproduction

Mammalian Diversity: Monotremes are egg-laying mammals, Marsupials are pouched mammals, Most mammals are placental mammals

Exploring Human Biology

Overview of the Human Body

The Human Body Plan: Supporting the body, Collecting and evaluating information, Transporting oxygen and nutrients, protecting the heart, lungs, and digestive organs, Obtaining nutrients from food, Maintaining a relatively constant temperature

How the Body Is Organized: Epithelial tissue is protective tissue, Connective tissue supports and defends the body, Nerve tissue conducts signals rapidly, Muscle tissue permits movement, Organs and organ systems

Homeostasis: Why homeostasis is critical, The feedback of information, Homeostasis in action, The body's signaling system

Skeleton, Muscles, and Skin

The Skeletal System: The human skeleton is mainly bone, Osteoperosis results from bone loss, The human skeleton has two main parts, Joints fasten bones together

The Muscular System: Muscles make the skeleton move, Myrosin and actin cause muscle fibers to shorten, Exercise increases muscle size and efficiency

The Skin: The skin is composed of three layers, Skin disorders are common

Circulatory and Respiratory Systems

The Circulatory System: The circulatory system transports materials and distributes heat, Components of the circulatory system, blood has liquid and solid components, surface proteins on red blood cells determine blood type

The Heart: The heart pumps blood in two separate loops, Tracing the path of blood through the heart, A wave of contraction spreads over the heart, Cardiovascular functions can be monitored, Heart and blood vessel disorders kill many Americans

The Respiratory System: The respiratory system is a network of tubes and air sacs, Inhalation and exhalation are caused by pressure changes, Breathing exchanges oxygen and carbon dioxide, The brain controls breathing, The respiratory diseases limit lung function

Digestive and Excretory Systems

Diet - What We Need to Eat and Why: Energy-rich compounds are used to make ATP, Other components serve as raw materials

Digestion: Food molecules are broken down by enzymes, The digestive journey begins in the mouth, Proteins are dismantled in the stomach, Digestion and absorption occur in the small intestine, Solids are compacted in the large intestine, How nutrients are delivered to cells

Excretion: Carbon dioxide, nitrogen compounds, and water are excreted, The kidneys regulate plasma composition, Kidneys are composed of tiny blood filters, Liquid waste leave the body through a system of tubes, Kidney failure is life threatening

The Body's Defenses

Defending Against Infection: Skin and mucous membranes - the first line of defense, Counterattacks - the second line of defense

The Immune System: The Key players in the immune system, Killer T cells attack infected body cells, B cells attack invading microbes, The benefits and downsides of vaccinations

Malfunctions and Failures of the Immune System: When the body attacks its own tissues, Allergy - attacking a harmless substance, The surface proteins of influenza viruses evolve rapidly, AIDS - immune system collapse

Nervous System

Neurons and Nerve Impulses: Neurons transmit electrical signals, A reversal in voltage triggers an impulse

Architecture in the Nervous System: The nervous system has two divisions, The central nervous system directs and coordinates information, The peripheral nervous system shuttles information, The autonomic nervous system keeps the body functioning

The Sense Organs: Receptors in the ear sense equilibrium and sound, Photoreceptors in the eye sense light, Receptors throughout the body sense its internal condition, Taste and smell are chemical senses

Drugs and the Nervous System: Psychoactive drugs affect the nervous system, Addiction is due to a change in receptor protein numbers, Narcotics quickly produce addiction, Dangerous social drugs

Hormones and the Endocrine System

Hormones: Hormones have advantages over nerve signals, Endocrine glands produce most hormones, Non-endocrine chemical signals also regulate cell activities, The hypothalamus initiates most chemical signals

How Hormones Work: Peptide hormones remain outside cells, Steroid hormones work inside cells, One hormone works inside the nucleus

The Body's Endocrine Glands: The pituitary gland regulates other endocrine glands, The thyroid gland regulates metabolic rate, Parathyroid glands regulate blood calcium, The adrenals are two glands in one, The pancreas regulates blood sugar, Other organs and glands produce hormones

Development of the Human

God made man in His own image; male and female He created them.

Human development: The embryo forms during early development, The fetus grows rapidly until birth

Media in category "Biology"

The following 46 files are in this category, out of 46 total.

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