Jim’s Biology Overview and Study Guide

The purpose of this page is to provide a summary of major concepts in the study of living things. Biology is a terminology-intensive course with more details and change than many or all other high school courses. Therefore, this overview is no substitute for attending classes or reading your text. As you review the concepts below, note any statement that was not completely familiar, and then go to your text and other resources for further study.

Overview of Biology

% Scientific Method$
Biologists investigate and understand nature, explain events in nature, and use those explanations to make useful predictions.
A hypothesis should be tested by an experiment in which only one variable is changed (the independent variable) at a time. All the other variables should be kept unchanged, or controlled.
In science, the word theory applies to a well-tested explanation that unifies a broad range of observations.
Most scientists use the System Internationale (metric system) when collecting data and doing experiments.
Compound light microscopes produce images by focusing visible light rays at 40x, 100x or 400x. Electron microscopes produce images by focusing beams of electrons.

% Characteristics of Living Things$
Living things share characteristics including cellular organization, reproduction, heredity through a universal genetic code, growth and development, use of materials and energy, response to their environment, and maintaining an internal stability (homeostasis).
Living organisms can be studied at different levels of organization – molecules, cells, tissues, organs, organ systems, organisms, species, population, community, ecosystem, biome or biosphere.

Overview of Chemistry of Biology

% The Nature of Matter$
The subatomic particles that make up atoms are protons, neutrons, and electrons.
Because they have the same number of protons, all isotopes of an element have the same chemical properties.
The main types of chemical bonds are covalent bonds and ionic bonds.

% Properties of Water$
A water molecule is polar, because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.
Acidic solutions contain higher concentrations of H⁺ ions than pure water and have pH values below 7.
Basic, or alkaline, solutions contain lower concentrations of H⁺ ions than pure water and have pH values above 7.

% Carbon Compounds$
Four groups of carbon compounds found in living things are carbohydrates, lipids, nucleic acids, and proteins.
Living things use carbohydrates as their main source of energy. Plants and some animals also use carbohydrates for structural purposes.
Lipids can be used to store energy. Some lipids are important parts of biological membranes and waterproof coverings.
Nucleic acids store and transmit hereditary, or genetic, information.
Some proteins control the rate of reactions and regulate cell processes. Some proteins build tissues such as bone and muscle. Others transport materials or help to fight disease.

% Chemical Reactions and Enzymes$
Chemical reactions always involve the breaking of bonds in reactants and the formation of new bonds in products.
Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will not occur without a source of energy.
Cells use enzymes to speed up chemical reactions that take place in cells.

Cell Structure and Function

The cell theory states that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from existing cells.
Biologists divide cells into two categories: eukaryotes and prokaryotes. The cells of eukaryotes have a nucleus; the cells of prokaryotes do not.
Cells in multicellular organisms are specialized to perform particular functions within the organism.
The levels of organization in a multicellular organism are individual cells, tissues, organs, and organ systems.

% Cell Structures$
The main function of the cell wall is to provide support and protection for the cell.
The nucleus controls most cell processes and contains the hereditary information of DNA.
The cytoskeleton is a network of protein filaments that helps the cell to maintain its shape. The cytoskeleton is also involved in many forms of cell movement.
The endoplasmic reticulum is the organelle in which components of the cell membrane are assembled and some proteins are modified.
Enzymes in the Golgi apparatus attach carbohydrates and lipids to proteins.
Chloroplasts use the energy from sunlight to make energy-rich food molecules, a process known as photosynthesis.
Mitochondria use the energy from food to make high-energy compounds that the cell can use to power growth, development, and movement.

% Movement Through Membranes$
The cell membrane regulates what enters and leaves the cell and also provides protection and support.
Diffusion causes many substances to move across a cell membrane but does not require the cell to use energy.
Osmosis is the diffusion of water through a selectively permeable membrane.

Photosynthesis

Plants and some other types of organisms are able to use light energy from the sun to produce food.
The characteristics of ATP make it an exceptionally useful molecule that is used by all types of cells as their basic energy source.
The experiments performed by van Helmont, Priestley, Ingenhousz, and other scientists reveal that in the presence of light, plants transform carbon dioxide and water into carbohydrates and release oxygen as a byproduct.
Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into oxygen and high-energy sugars.
In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule found in chloroplasts.
The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle.
The light-dependent reactions produce oxygen gas and convert ADP and NADP⁺ into ATP and NADPH. The light-dependent reactions occur in different areas of the thylakoid, called photosystem I and photosystem II.
The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. The Calvin cycle is also known as the light-independent reactions.

Cell Respiration

% Chemical Pathways$
Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen.
Glycolysis is the process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid, a 3-carbon compound.
Glycolysis captures two pairs of high-energy electrons with the carrier NAD⁺. Because glycolysis does not require oxygen, it supplies chemical energy to cells when oxygen is not available.
The two main types of fermentation are alcoholic fermentation and lactic acid fermentation.
In the absence of oxygen, yeast and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes.
Animals cannot perform alcoholic fermentation, but some cells, such as human muscle cells, can convert glucose into lactic acid. This is called lactic acid fermentation.

% The Krebs Cycle and Electron Transport$
During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.
The electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP into ATP.
The products of photosynthesis are similar to the reactants of cellular respiration. The products of cellular respiration are the reactants of photosynthesis.

Cell Growth and Division

% Cell Growth and Division$
The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cell membrane.
During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again.
Biologists divide the events of mitosis into four phases: prophase, metaphase, anaphase, and telophase.
During prophase in animal cells, the centrioles separate and take up positions on opposite sides of the nucleus.
During metaphase, the chromosomes line up across the center of the cell. Microtubules connect the centromere of each chromosome to the poles of the spindle.
During anaphase, the centromeres that join the sister chromatids split, allowing the sister chromatids to separate and become individual chromosomes.
In telophase, the chromosomes, which were distinct and condensed, begin to disperse into a tangle of dense material.
Cytokinesis is the division of the cytoplasm.

% Regulating the Cell Cycle$
Cyclins regulate the timing of the cell cycle in eukaryotic cells. Checkpoints minimize duplication of errors.
Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, they form masses of cells called tumors that can damage the surrounding tissues.

Genetics Overview

%Mendelian Genetics$
The principle of dominance states that some alleles are dominant and others are recessive.
When each F₁ plant flowers, the two alleles are segregated from each other so that each gamete carries only a single copy of each gene. Therefore, each F₁ plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness.
The principles of probability can be used to predict the outcomes of genetic crosses.
The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.
Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

% Meiosis$
Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells.

% Linkage and Gene Maps$
The chromosomes assort independently; individual genes do not.

DNA and RNA

% DNA$
Avery and other scientists discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation of an organism to the next.
Hershey and Chase concluded that the genetic material of the bacteriophage they used to infect bacteria was DNA, not protein.
Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other.

% Chromosomes and DNA Replication$
During DNA replication, the DNA molecule separates into two strands, then produces two new complementary strands following the rules of base pairing. Each strand of the double helix of DNA serves as a template, or model, for the new strand.

% RNA and Protein Synthesis$
There are three main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA.
During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template on which nucleotides are assembled into a strand of RNA.
During translation, the cell uses information from messenger RNA to produce proteins.

% Mutations$
Gene mutations result from changes in a single gene. Chromosomal mutations involve changes in whole chromosomes.

% Gene Regulation$
The lac genes are turned off by repressors and turned on by the presence of lactose.
Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon.

Genetic Engineering

% Artificial and Sexual Selection$
Humans use selective breeding to pass desired traits on to the next generation of organisms.
Breeders can increase the genetic variation in a population by inducing mutations, which are the ultimate source of genetic variability.

% Manipulating DNA$
Scientists use their knowledge of the structure of DNA and its chemical properties to study and change DNA molecules. Different techniques are used to extract DNA from cells, to cut DNA into smaller pieces, to identify the sequence of bases in a DNA molecule, and to make unlimited copies of DNA.
Knowing the sequence of an organism's DNA allows researchers to study specific genes, to compare them with the genes of other organisms, and to try to discover the functions of different genes and gene combinations.

% Cell Transformation$
During transformation, a cell takes in DNA from outside the cell. This external DNA becomes a part of the cell's DNA.
If transformation is successful, the recombinant DNA is integrated into one of the chromosomes of the cell.

% Applications of Genetic Engineering$
Using the basic techniques of genetic engineering, a gene from one organism can be inserted into cells from another organism. These transformed cells can then be used to grow new organisms.

Human Genome

% Human Heredity$
All egg cells carry a single X chromosome (23X). However, half of all sperm cells carry an X chromosome (23X), and half carry a Y chromosome (23Y). This ensures that just about half of the zygotes will be 46XX (female), and half will be 46XY (male).
In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder.

% Human Chromosomes$
Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive.
Nondisjunction causes gametes to have abnormal numbers of chromosomes, which in turn causes a chromosome number disorder.

% Human Molecular Genetics$
The Human Genome Project is an attempt to sequence all human DNA.
In gene therapy, an absent or faulty gene is replaced by a normal, working gene.

Darwin’s Evolution

% Darwin’s Observations$
During his travels, Charles Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.
Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galápagos.

% Ideas That Shaped Darwin's Thinking$
Hutton and Lyell helped scientists realize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.
Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species.
Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.

% Darwin’s Theories$
In artificial selection, nature provides the variation among different organisms, and humans select those variations that they find useful.
Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species' fitness in its environment.
Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process could be found in the fossil record, the geographical distribution of living species, homologous structures of living organisms, and similarities in early development.

Population Evolution

% Genes and Variation$
Biologists have discovered that there are two main sources of genetic variation: mutations and the genetic shuffling that results from sexual reproduction.
The number of phenotypes produced for a given trait depends on how many genes control the trait.

% Evolution as Genetic Change$
Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution.
Natural selection can affect the distributions of phenotypes in any of three ways: directional selection, stabilizing selection, or disruptive selection.
In small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population.
Five conditions are required to maintain genetic equilibrium from generation to generation: there must be random mating; the population must be very large; and there can be no movement into or out of the population, no mutations, and no natural selection.

% Speciation$
As new species evolve, populations become reproductively isolated from each other.
Speciation in the Galápagos finches occurred by founding of a new population, geographic isolation, changes in the new population's gene pool, reproductive isolation, and ecological competition.

Origin and History of Life on Earth

% The Fossil Record$
The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms have changed over time.
Relative dating allows paleontologists to estimate a fossil's age compared with that of other fossils.
In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.
After Precambrian Time, the basic divisions of the geologic time scale are eras and periods.

% Earth's Early History$
Earth's early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.
Miller and Urey's experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth.
The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration.
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms.

% Evolution of Multicellular Life$
Early in the Paleozoic Era, the fossil record became rich with evidence of many types of marine life.
During the Devonian, animals began to invade the land.
The mass extinction at the end of the Paleozoic affected both plants and animals on land and in the seas. As much as 95 percent of the complex life in the oceans disappeared.
Events during the Mesozoic include the increasing dominance of dinosaurs. The Mesozoic is marked by the appearance of flowering plants.
During the Cenozoic, mammals evolved adaptations that allowed them to live in various environments—on land, in water, and even in the air.

% Patterns of Evolution$
Six important patterns of macroevolution are mass extinctions, adaptive radiation, convergent evolution, coevolution, punctuated equilibrium, and changes in developmental genes.

Classification

% Strategies for Understanding Diversity$
To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.
In binomial nomenclature, each species is assigned a two-part scientific name.
Linnaeus's system of classification uses seven taxonomic categories. They are—from smallest to largest—species, genus, family, order, class, phylum, and kingdom.

% Modern Evolutionary Classification$
Organisms are now grouped into categories that represent lines of evolutionary descent.
The genes of many organisms show important similarities at the molecular level. These similarities can be used as criteria for classification.

% Kingdoms and Domains$
The six-kingdom system of classification includes the kingdoms Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.
The three domains are Bacteria, Archaea, and Eukarya.

Bacteria and Viruses

% Prokaryotes$
Archaebacteria lack peptidoglycan, a carbohydrate found in the cell walls of eubacteria, and their membrane lipids are quite different. Also, the DNA sequences of key archaebacterial genes are more like those of eukaryotes than eubacteria.
Prokaryotes are identified by their shapes, the chemical natures of their cell walls, the ways they move, and the ways they obtain energy.

% Bacteria$
Bacteria are vital to maintaining the living world. Some are producers that capture energy by photosynthesis. Others help to break down the nutrients in dead matter and the atmosphere, allowing other organisms to use the nutrients.
Bacteria cause disease in one of two general ways. Some damage the tissues of the infected organism directly by breaking them down for food. Other bacteria release toxins (poisons) that harm the body.

% Viruses$
A typical virus is composed of a core of either DNA or RNA surrounded by a protein coat.
In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst.
In a lysogenic infection, a virus embeds its genome into the DNA of the host cell and is replicated along with the host cell's DNA.

Protists

Protists are eukaryotes that are not members of the kingdoms Plantae, Animalia, or Fungi.

% Animallike Protists: Protozoans$
Animallike protists that swim using flagella are classified in the phylum Zoomastigina and are often referred to as zooflagellates.
Sarcodines are animallike protists that use pseudopods for feeding and movement.
Members of the phylum Ciliophora, known as ciliates, use cilia for feeding and movement.
Members of the phylum Sporozoa do not move on their own and are parasitic.
Some animallike protists cause serious diseases, including malaria and African sleeping sickness.

% Plantlike Protists: Unicellular Algae$
Chlorophyll and accessory pigments allow algae to harvest and use the energy from sunlight.
Euglenophytes are plantlike protists that have two flagella but no cell wall.
About half of dinoflagellates are photosynthetic; the other half live as heterotrophs.
Members of the phylum Chrysophyta are a diverse group of plantlike protists that have gold-colored chloroplasts.
Diatoms produce thin, delicate cell walls rich in silicon (Si)—the main ingredient in glass.

% More Plantlike Protists: Red, Brown, and Green Algae$
Red algae are able to live in great depths due to their efficiency in harvesting light energy. Red algae contain chlorophyll a and reddish accessory pigments called phycobilins.
Brown algae contain chlorophyll a and c, as well as a brown accessory pigment, fucoxanthin.
Green algae share many characteristics with plants, including their photosynthetic pigments and cell wall composition.
The life cycles of most algae include both a diploid and a haploid generation.

% Funguslike Protists$
Funguslike protists lack chlorophyll and absorb nutrients from dead or decaying organic matter. But unlike most true fungi, funguslike protists have centrioles. They also lack the chitin cell walls of true fungi.
Slime molds are funguslike protists that play key roles in recycling organic material.
Oomycetes thrive on dead or decaying organic matter in water and are plant parasites on land.

Fungi

% The Kingdom Fungi$
Fungi are eukaryotic heterotrophs that have cell walls made of chitin.
The bodies of multicellular fungi are composed of many hyphae tangled together into a thick mass called a mycelium.
Most fungi reproduce both asexually and sexually.
Fungi are found in every ecosystem, where they recycle nutrients by breaking down the bodies of other organisms.
Parasitic fungi cause serious plant and animal diseases. A few fungi cause diseases in humans.
Some fungi form symbiotic relationships in which both partners benefit. Two such mutualistic associations, lichens and mycorrhizae, are essential to many ecosystems.

% Classification of Fungi$
Zygomycetes have life cycles that include a zygospore.
The phylum Ascomycota is named for the ascus, a reproductive structure that contains spores.
The phylum Basidiomycota, or club fungi, gets its name from the basidium, a specialized reproductive structure that resembles a club.
Deuteromycota is an extremely varied phylum. It is composed of those fungi that are not placed in other phyla because researchers have never been able to observe a sexual phase in their life cycles.

Plants

% Introduction to Plants$
Plants are multicellular eukaryotes that have cell walls made of cellulose. They develop from multicellular embryos and carry out photosynthesis using the green pigments chlorophyll a and b.
The lives of plants revolve around the need for sunlight, water and minerals, gas exchange, and the movement of water and nutrients throughout the plant body.
The first plants evolved from an organism much like the multicellular green algae living today.

% Bryophytes$
Bryophytes have life cycles that depend on water for reproduction. Lacking vascular tissue, these plants can draw up water by osmosis only a few centimeters above the ground.
Bryophytes include mosses, liverworts, and hornworts.
In bryophytes, the gametophyte is the dominant, recognizable stage of the life cycle and is the stage that carries out most of the plant's photosynthesis.

% Seedless Vascular Plants$
Both forms of vascular tissue—xylem and phloem—can move fluids throughout the plant body, even against the force of gravity.
Seedless vascular plants include club mosses, horsetails, and ferns.
Ferns and other vascular plants have a life cycle in which the diploid sporophyte is the dominant stage.

% Seed Plants$
Adaptations that allow seed plants to reproduce in areas without water include flowers or cones, the transfer of sperm by pollination, and the protection of embryos in seeds.
Gymnosperms include gnetophytes, cycads, ginkgoes, and conifers.

% Angiosperms—Flowering Plants$
Angiosperms have unique reproductive organs known as flowers. Flowers contain ovaries, which surround and protect the seeds.
Monocots and dicots are named for the number of seed leaves, or cotyledons, in the plant embryo. Monocots have one seed leaf, and dicots have two.
There are three categories of plant life spans: annual, biennial, and perennial.

% Specialized Tissues in Plants$
The three principal organs in seed plants are roots, stems, and leaves.
Plants consist of three tissue systems: dermal tissue, vascular tissue, and ground tissue.
Meristematic tissue is the only plant tissue that produces new cells by mitosis.
Vascular tissue contains several different cell types. Xylem consists of tracheids and vessel elements, and phloem consists of sieve tube elements and companion cells.

% Roots$
The two main types of roots are taproots, found mainly in dicots, and fibrous roots, found mainly in monocots.
A mature root has an outside layer of epidermal cells and a central cylinder of vascular tissue separated by a large area of ground tissue called the cortex.
Roots anchor a plant in the ground and absorb water and dissolved nutrients from the soil.

% Stems$
Stems have three important functions: they produce leaves, branches, and flowers; they hold leaves up in the sunlight; and they transport various substances between roots and leaves.
In monocots, vascular bundles are scattered throughout the stem. In dicots and most gymnosperms, vascular bundles are arranged in a cylinder.
In all seed plants, primary growth of stems is produced by cell divisions in the apical meristem.
In conifers and dicots, secondary growth takes place in lateral meristematic tissues called the vascular cambium and cork cambium.

% Leaves$
The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.
Plants keep their stomata open just enough to allow photosynthesis to take place, but not so much that they lose an excessive amount of water.

% Transport in Plants$
Root pressure, capillary action, and transpiration work together to move water through the xylem tissue of even the largest plant.
When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of water in that same direction. As a result, phloem is able to move nutrients in either direction to meet the nutritional needs of the plant.

% Reproduction With Cones and Flowers$
Reproduction in gymnosperms takes place in cones, which are produced by a mature sporophyte plant.
Flowers are reproductive organs that are composed of four kinds of specialized leaves: sepals, petals, stamens, and carpels.
Reproduction in angiosperms takes place within the flower. Following pollination and fertilization, the seeds develop inside protective structures called fruits.
Most gymnosperms are wind pollinated, whereas most flowering plants are pollinated by animals.

% Seed Development and Germination$
As angiosperm seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds.
Seeds dispersed by animals are typically contained in fleshy, nutritious fruits.
Seeds dispersed by wind or water are typically lightweight, allowing them to be carried in the air or to float on the surface of the water.
Environmental factors such as temperature and moisture can cause a seed to end dormancy and germinate.

% Plant Propagation and Agriculture$
Vegetative reproduction includes the production of new plants from horizontal stems, cuttings, leaves, plantlets, and underground roots.
Horticulturists use plant propagation to make many identical copies of a plant or to produce offspring from seedless plants.
Most of the people of the world depend on a few crop plants, such as wheat, rice, and corn, for the bulk of their food supply.

% Hormones and Plant Growth$
Plant hormones are chemical substances that control a plant's patterns of growth and development and the plant's responses to environmental conditions.
Auxins are produced in the apical meristem and are transported downward into the rest of the plant. They stimulate cell elongation.
Cytokinins are produced in growing roots and in developing fruits and seeds. They stimulate cell division and the growth of lateral buds, and cause dormant seeds to sprout.
Gibberellins produce dramatic increases in size, particularly in stems and fruit.
In response to auxins, fruit tissues release small amounts of the hormone ethylene. Ethylene then stimulates fruits to ripen.

% Plant Responses$
Plant tropisms include gravitropism, phototropism, and thigmotropism. Each of these responses demonstrates the ability of plants to respond effectively to conditions in which they live.
Photoperiodism in plants is responsible for the timing of seasonal activities such as flowering and growth.
As cold weather approaches, deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves off from the rest of the plant.

% Plant Adaptations$
To take in sufficient oxygen, many aquatic plants have tissues with large air-filled spaces through which oxygen can diffuse.
Plant adaptations to a desert climate include extensive roots, reduced leaves, and thick stems that can store water.
Plants that have specialized features for obtaining nutrients include carnivorous plants and parasites.
Many plants defend themselves against insect attack by manufacturing compounds that have powerful effects on animals.

Animalia

% Introduction to the Animal Kingdom$
An animal is a multicellular, eukaryotic heterotroph whose cells lack cell walls.
Animals are specialized to carry out the following essential functions: feeding, respiration, circulation, excretion, response, movement, and reproduction.
In general, complex animals tend to have high levels of cell specialization and internal organization, bilateral body symmetry, cephalization, and a body cavity.

Sponges

Sponges are classified as animals because they are multicellular, heterotrophic, have no cell walls, and contain a few specialized cells.
The movement of water through a sponge provides a simple mechanism for feeding, respiration, circulation, and excretion.

% Cnidarians$
Cnidarians are soft-bodied, carnivorous animals that have stinging tentacles (cnidocytes with nematocysts) arranged in circles around their mouth. They are the simplest animals to have body symmetry and specialized tissues.
Cnidarians typically have a life cycle that includes two different-looking stages, a polyp and a medusa.
Cnidarians include jellyfishes, hydras and their relatives, sea anemones, and corals.

% Flatworms$
Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization.
Turbellarians are free-living marine or freshwater flatworms.
Flukes are parasitic flatworms that usually infect the internal organs of their hosts.
Tapeworms are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts.

% Roundworms$
Roundworms are unsegmented worms that have pseudocoeloms and digestive systems with two openings—a mouth and an anus.
Parasitic roundworms include trichinosis-causing worms, filarial worms, ascarid worms, and hookworms.

% Annelids$
Annelids are worms with segmented bodies. They have a true coelom that is completely lined with mesoderm.
Oligochaetes are annelids that typically have only a few setae and live in soil or fresh water.
Leeches are typically external parasites that suck the blood and body fluids of their host.
Polychaetes are marine annelids that have paired, paddlelike appendages tipped with setae.

% Mollusks$
Mollusks are soft-bodied animals that usually have an internal or external shell.
The typical mollusk body plan has four parts: foot, mantle, shell, and visceral mass.
Gastropods are shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side.
Bivalves have two shells that are held together by one or two powerful muscles.
Cephalopods are typically soft-bodied mollusks in which the head is attached to a single foot. The foot is divided into tentacles or arms.

% Arthropods$
Arthropods have a segmented body, a tough exoskeleton, and jointed appendages.
In many groups of arthropods, continuing evolution has led to fewer body segments and highly specialized appendages for feeding, movement, and other functions.
When they outgrow their exoskeletons, arthropods undergo periods of molting.

% Classification of Arthropods$
Arthropods are classified based on the number and structure of their body segments and appendages, particularly their mouthparts.
Crustaceans typically have two pairs of branched antennae, two or three body sections, and chewing mouthparts called mandibles.
Chelicerates have mouthparts called chelicerae and two body sections, and most have four pairs of walking legs.
Uniramians have jaws, one pair of antennae, and unbranched appendages.
Insects have a body divided into three parts—head, thorax, and abdomen. Three pairs of legs are attached to the thorax.
The growth and development of insects usually involve metamorphosis, which is a process of changing shape and form. Insects undergo either incomplete metamorphosis or complete metamorphosis.
Ants, bees, termites, and some of their relatives form complex associations called societies.

% Echinoderms$
Echinoderms are characterized by spiny skin, five-part radial symmetry, an internal skeleton, a water vascular system, and suction-cup-like structures called tube feet.
The water vascular system carries out many essential body functions in echinoderms, including respiration, circulation, and movement.
Classes of echinoderms include sea lilies and feather stars, sea stars, brittle stars, sea urchins and sand dollars, and sea cucumbers.

Comparing Invertebrates

% Invertebrate Evolution$
As animals became larger and more complex, specialized cells joined together to form tissues, organs, and organ systems that work together to carry out complex functions.
All invertebrates except sponges exhibit some type of body symmetry—either radial symmetry or bilateral symmetry.
Invertebrates with cephalization can respond to the environment more quickly and in more sophisticated ways than can simpler invertebrates.
Most invertebrates with bilateral symmetry also have segmented bodies. Over the course of evolution, different segments have often become specialized for specific functions.
Most animal phyla have a true coelom that is lined completely with mesoderm.
Worms, arthropods, and mollusks are protostomes, and echinoderms are deuterostomes.

% Form and Function in Invertebrates$
The simplest animals break down food primarily through intracellular digestion, whereas more complex animals use extracellular digestion.
Respiratory organs have large surface areas that are in contact with the air or water. In order for diffusion to occur, these respiratory surfaces must be kept moist.
Most complex animals move fluid through their bodies using one or more hearts and an open or closed circulatory system.
Most animals have an excretory system that rids the body of metabolic wastes and controls the amount of water in their tissues.
Invertebrates show three trends in the evolution of the nervous system: centralization, cephalization, and specialization.
Invertebrates have one of three main kinds of skeletal systems: hydrostatic skeletons, exoskeletons, and endoskeletons.
Most invertebrates reproduce sexually during at least part of their life cycle. Depending on environmental conditions, however, many invertebrates may also reproduce asexually.

Vertebrates

% Chordates$
A chordate is an animal that has, for at least some stage of its life, a dorsal, hollow nerve cord; a notochord; pharyngeal pouches; and a tail that extends beyond the anus.
The two groups of nonvertebrate chordates are tunicates and lancelets.

% Fishes$
Fishes are aquatic vertebrates that are characterized by paired fins, scales, and gills.
The evolution of jaws and the evolution of paired fins were important developments during the rise of fishes.
Fishes' adaptations to aquatic life include various modes of feeding, specialized structures for gas exchange, and paired fins for locomotion.
On the basis of their basic internal structure, all living fishes can be classified into one of three groups: jawless fishes, cartilaginous fishes, and bony fishes.

% Amphibians$
An amphibian is a vertebrate that, with some exceptions, lays eggs in water, lives in water as a larva and on land as an adult, breathes with lungs as an adult, has moist skin that contains mucus glands, and lacks scales and claws.
Early amphibians evolved several adaptations that helped them live at least part of their lives out of water. Bones in the limbs and limb girdles of amphibians became stronger, permitting more efficient movement. A set of lungs and breathing tubes enabled them to breathe air. Their sternum formed a bony shield that supports and protects the internal organs, especially the lungs.
The three groups of living amphibians are salamanders, frogs and toads, and caecilians.

% Reptiles$
A reptile is a vertebrate that has scaly skin, lungs, and eggs with several membranes.
Well-developed lungs; a double-loop circulatory system; an efficient excretory system; strong limbs; internal fertilization; and shelled, terrestrial eggs are the main adaptations that have contributed to the success of reptiles on land.
The four surviving orders of reptiles are lizards and snakes, crocodilians, turtles and tortoises, and the tuatara.

% Birds$
Birds are reptilelike animals that maintain a constant internal body temperature. They have an outer covering of feathers, two legs that are covered with scales and are used for walking or perching, and front limbs modified into wings.
Birds have a number of adaptations that enable them to fly. These adaptations include highly efficient digestive, respiratory, and circulatory systems; aerodynamic feathers and wings; and strong chest muscles.

% Introduction to the Mammals$
In addition to having hair and the ability to nourish their young with milk, all mammals breathe air and are endotherms that generate their body heat internally.
The first true mammals appeared during the late Triassic Period, about 220 million years ago.
The ability of mammals to regulate their body heat from within is an example of homeostasis.
As mammals evolved to eat foods other than insects, the form and function of their jaws and teeth became adapted to their diets.
The kidneys of mammals help maintain homeostasis by excreting or retaining excess liquid.

% Diversity of Mammals$
The three groups of living mammals are the monotremes, the marsupials, and the placentals. Marsupials bear live young that complete their development in a pouch. Monotremes lay eggs. In placental mammals, nutrients, oxygen, carbon dioxide, and wastes are exchanged between embryo and mother through the placenta.
Similar ecological opportunities on the different continents have produced some striking examples of convergent evolution in mammals.

% Primates and Human Origins$
In general, primates have binocular vision, a well-developed cerebrum, fingers and toes, and arms that rotate in their joints.
Primates that evolved from two of the earliest ancestral branches look very little like typical monkeys and are called prosimians. Members of the more familiar primate group that includes monkeys, apes, and humans are called anthropoids.
Today, most paleontologists agree that the hominid fossil record includes at least five genera—Ardipithecus, Australopithecus, Paranthropus, Kenyanthropus, and Homo—and as many as 16 separate hominid species. This diverse group of fossils covers roughly 4.5 million years.

% Chordate Evolution$
The chordate family tree has its roots in ancestors that vertebrates share with tunicates and lancelets.
Over the course of evolution, the appearance of new adaptations—such as jaws and paired appendages—has launched adaptive radiation in chordate groups.

% Controlling Body Temperature$
The control of body temperature is important for maintaining homeostasis in many vertebrates, particularly in habitats where temperature varies widely with time of day and with season.
Most fishes, amphibians, and reptiles are ectotherms—organisms that obtain heat from outside their bodies. Birds and mammals are endotherms, which means they can generate heat inside their bodies.

% Form and Function in Chordates$
The digestive systems of vertebrates have organs that are well adapted for different feeding habits.
Aquatic chordates—such as tunicates, fishes, and amphibian larvae—use gills for respiration. Land vertebrates, including adult amphibians, reptiles, birds, and mammals, use lungs.
During the course of chordate evolution, the heart developed chambers and partitions that help separate the blood traveling in the circulatory system.
Nonvertebrate chordates have a relatively simple nervous system with a mass of nerve cells that form a brain. Vertebrates have a more complex brain with distinct regions, each with a different function.
Muscular and skeletal systems support a vertebrate's body and make it possible to control movement.

% Elements of Behavior$
When an animal responds to a stimulus, body systems—including the sense organs, nervous system, and muscles—interact to produce the resultant behavior.
Innate behaviors appear in fully functional form the first time they are performed, even though the animal may have had no previous experience with the stimuli to which it responds.
The four major types of learning are habituation, classical conditioning, operant conditioning, and insight learning.

% Patterns of Behavior$
Many animals respond to periodic changes in the environment with daily or seasonal cycles of behavior.
To pass along its genes to the next generation, any animal that reproduces sexually needs to locate and mate with another member of its species at least once. Courtship behavior helps many animals identify healthy mates.
Usually, members of a society are related to one another. Related individuals share a large proportion of each other's genes. Therefore, helping a relative survive increases the chance that the genes an individual shares with that relative will be passed along to the next generation of offspring.
Animals may use visual, sound, touch, or chemical signals to communicate with one another.

% Human Body Systems$
The eleven organ systems of the human body work together to maintain homeostasis.

% The Nervous System$
The nervous system controls and coordinates functions throughout the body and responds to internal and external stimuli.
A nerve impulse begins when a neuron is stimulated by another neuron or by its environment.

% Divisions of the Nervous System
The central nervous system relays messages, processes information, and analyzes information.
The sensory division of the peripheral nervous system transmits impulses from sense organs to the central nervous system. The motor division transmits impulses from the central nervous system to the muscles or glands.

% The Senses$
There are five general categories of sensory receptors: pain receptors, thermoreceptors, mechanoreceptors, chemoreceptors, and photoreceptors.

% Drugs and the Nervous System$
Stimulants increase heart rate, blood pressure, and breathing rate. In addition, stimulants increase the release of neurotransmitters at some synapses in the brain.
Depressants slow down heart rate and breathing rate, lower blood pressure, relax muscles, and relieve tension.
Cocaine causes the sudden release of a neurotransmitter in the brain called dopamine.
Opiates mimic natural chemicals in the brain known as endorphins, which normally help to overcome sensations of pain.
Alcohol is a depressant, and even small amounts of alcohol slow down the rate at which the nervous system functions.

% The Skeletal System$
The human skeleton supports the body, protects internal organs, provides for movement, stores mineral reserves, and provides a site for blood cell formation.
Bones are a solid network of living cells and protein fibers that are surrounded by deposits of calcium salts.
Depending on its type of movement, a joint is classified immovable, slightly movable, or freely movable.

% The Muscular System$
There are three different types of muscle tissue: skeletal muscle, smooth muscle, and cardiac muscle.
A muscle fiber contracts when the thin filaments in the muscle fiber slide over the thick filaments.
The energy for muscle contraction is supplied by ATP.

% The Integumentary System$
The integumentary system serves as a barrier against infection and injury, helps to regulate body temperature, removes waste products from the body, and provides protection against ultraviolet radiation from the sun.

% The Circulatory System$
The human circulatory system consists of the heart, a series of blood vessels, and the blood that flows through them.
As the blood flows through the circulatory system, it moves through three types of blood vessels—arteries, capillaries, and veins.

% Blood and the Lymphatic System$
Red blood cells transport oxygen.
White blood cells attack foreign substances or organisms.
Blood clotting is made possible by plasma proteins and cell fragments called platelets.
A network of vessels called the lymphatic system collects the fluid that is lost by the blood and returns it to the circulatory system.

% The Respiratory System$
The respiratory system consists of the nose, pharynx, larynx, trachea, bronchi, and lungs.
Smoking can cause such respiratory diseases as chronic bronchitis, emphysema, and lung cancer.

% Food and Nutrition$
The nutrients that the body needs are water, carbohydrates, fats, proteins, vitamins, and minerals.
Every cell in the human body needs water because many of the body's processes, including chemical reactions, take place in water.

% The Process of Digestion$
The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Several accessory structures, including the salivary glands, the pancreas, and the liver, add secretions to the digestive system.
The function of each organ of the digestive system is to help convert foods into simpler molecules that can be absorbed and used by the cells of the body.

% The Excretory System$
Together, the skin, lungs, and kidneys—along with their associated organs—make up the excretory system.
The kidneys play an important role in maintaining homeostasis. They regulate the water content of the blood and, therefore, blood volume; maintain blood pH; and remove waste products from the blood.

% The Endocrine System$
The endocrine system is made up of glands that release their products into the bloodstream. These products broadcast messages throughout the body.
Like most systems of the body, the endocrine system is regulated by feedback mechanisms that function to maintain homeostasis.

% Human Endocrine Glands$
The pituitary gland secretes nine hormones that directly regulate many body functions and control the actions of several other endocrine glands.
The hypothalamus controls the secretions of the pituitary gland.
The thyroid gland has the major role in regulating the body's metabolism.
Hormones from the thyroid gland and the parathyroid glands maintain homeostasis in blood calcium levels.
The adrenal glands help the body prepare for and deal with stress.
Insulin and glucagon released from the pancreas help to keep the level of glucose in the blood stable.
The gonads serve two important functions: the production of gametes and the secretion of sex hormones.

% The Reproductive System$
The main structures of the male reproductive system are the testes, the epididymis, the vas deferens, the urethra, and the penis. These structures work together to produce and deliver sperm.
The main structures of the female reproductive system are the ovaries, the Fallopian tubes, the uterus, and the vagina. In addition to producing eggs, the female reproductive system prepares the female's body to nourish a developing embryo.
The menstrual cycle has four phases: follicular phase, ovulation, luteal phase, and menstruation.

% Fertilization and Development$
The process of a sperm joining with an egg is called fertilization.
The placenta is the embryo's organ of respiration, nourishment, and excretion.

% Infectious Disease$
Some diseases are inherited. Others are caused by materials in the environment. Still others are produced by organisms such as bacteria and fungi.
Some infectious diseases are spread from one person to another through coughing, sneezing, or physical contact. Other infectious diseases are spread through contaminated water or food. Still others are spread by infected animals.

% The Immune System$
Your body's most important nonspecific defense is the skin.
The inflammatory response is a nonspecific defense reaction to tissue damage caused by injury or infection.
Once the body has been exposed to a pathogen, millions of memory B and T cells remain capable of producing specific antibodies to that pathogen.

% Immune System Disorders$
When the immune system makes a mistake and attacks the body's own cells, it produces an autoimmune disease.

% Cancer$
Cancers begin when something goes wrong with the controls that normally regulate cell growth and division.
Treatments for cancer fall into three general categories: surgery, radiation therapy, and drug therapy.

Ecology

% Overview$
To understand the various relationships within the biosphere, ecologists ask questions about events and organisms that range in complexity from a single individual to a population, community, ecosystem, or biome, or to the entire biosphere.
Scientists conduct modern ecological research according to three basic approaches: observing, experimenting, and modeling. All of these approaches rely on the application of scientific methods to guide ecological inquiry.

% Energy Flow$
Sunlight is the main energy source for life on Earth. In a few ecosystems, some organisms rely on the energy stored in inorganic chemical compounds.
Energy flows through an ecosystem in one direction, from the sun or inorganic compounds to autotrophs (producers) and then to various heterotrophs (consumers).
Only about 10 percent of the energy available within one trophic level is transferred to organisms at the next trophic level.

% Cycles of Matter$
Unlike the one-way flow of energy, matter is recycled within and between ecosystems.
Every living organism needs nutrients to build tissues and carry out essential life functions. Like water, nutrients are passed between organisms and the environment through biogeochemical cycles.

% The Role of Climate$
Carbon dioxide, methane, water vapor, and a few other atmospheric gases trap heat energy and maintain Earth's temperature range.
As a result of differences in latitude and thus the angle of heating, Earth has three main climate zones: polar, temperate, and tropical.

% What Shapes an Ecosystem?$
Together, biotic and abiotic factors determine the survival and growth of an organism and the productivity of the ecosystem in which the organism lives.
Community interactions, such as competition, predation, and various forms of symbiosis, can powerfully affect an ecosystem.
Ecosystems are constantly changing in response to natural and human disturbances. As an ecosystem changes, older inhabitants gradually die out and new organisms move in, causing further changes in the community.

% Land Biomes$
The world's major land biomes include tropical rain forest, tropical dry forest, tropical savanna, temperate grassland, desert, temperate woodland and shrubland, temperate forest, northwestern coniferous forest, boreal forest, and tundra. Each of these biomes is defined by a unique set of abiotic factors—particularly climate—and has a characteristic ecological community.

% Aquatic Ecosystems$
Aquatic ecosystems are determined primarily by the depth, flow, temperature, and chemistry of the overlying water.
Freshwater ecosystems can be divided into two main types: flowing-water ecosystems and standing-water ecosystems.
In addition to the division between the photic and aphotic zones, marine biologists also divide the ocean into zones based on the depth and distance from shore: the intertidal zone, coastal ocean, and the open ocean.

Population Ecology

% How Populations Grow$
Three important characteristics of a population are its geographic distribution, density, and growth rate.
Three factors affect population size: the number of births, the number of deaths, and the number of individuals that enter or leave the population.
Under ideal conditions and with unlimited resources, a population will continue to grow in a pattern called exponential growth. As resources are used up and population growth slows or stops, the population exhibits logistic growth.

% Limits to Growth$
Density-dependent limiting factors include competition, predation, parasitism, and disease.
Unusual weather, natural disasters, seasonal cycles, and certain human activities—such as damming rivers and clear-cutting forests—are all examples of density-independent limiting factors.

% Human Population Growth$
Like the populations of many other living organisms, the size of the human population tends to increase with time.
The characteristics of populations, and the social and economic factors that affect them, explain why some countries have high population growth rates while populations of other countries grow slowly or not at all.

Human Impact

% A Changing Landscape$
Among the human activities that have transformed the biosphere are hunting and gathering, agriculture, industry, and urban development.

% Renewable and Nonrenewable Resources$
Regardless of whether they are held in common, environmental resources can be classified into two types: renewable and nonrenewable.
Human activities affect the supply and the quality of renewable resources, including resources such as land, forests, ocean resources, air, and water.

% Biodiversity$
Biodiversity is one of Earth's greatest natural resources. Many species have provided us with foods, industrial products, and medicines—including painkillers, antibiotics, heart drugs, antidepressants, and anticancer drugs.
Human activity can reduce biodiversity by altering habitats, hunting species to extinction, introducing toxic compounds into food webs, and introducing foreign species to new environments.
Today, conservation efforts focus on protecting entire ecosystems as well as single species. Protecting an ecosystem will ensure that the natural habitats and interactions of many different species will be preserved at the same time.

% Charting a Course for the Future$
Many biologists are concerned about the biological effects of two types of global change: the thinning, or depletion, of the ozone layer and global warming.