What Is Life? A Guide to Biology with Physiology

Chapter 1
Scientific Thinking
Your best pathway to understanding the world
Science is a process for understanding the world.
1.1 Scientific thinking and biological literacy are essential in the modern world. A beginner’s guide to scientific thinking.
1.2 Thinking like a scientist: how do you use the scientific method?
1.3 Element 1: Make observations.
1.4 Element 2: Formulate a hypothesis.
1.5 Element 3: Devise a testable prediction.
1.6 Element 4: Conduct a critical experiment.
1.7 Element 5: Draw conclusions, make revisions.Well-designed experiments are essential to testing hypotheses.
1.8 Controlling variables makes experiments more powerful.
1.9  This is how we do it: Is arthroscopic surgery for arthritis of the knee beneficial?
1.10  We’ve got to watch out for our biases.
1.11  What are theories? When do hypotheses become theories? Scientific thinking can help us make better decisions.
1.12  Visual displays of data can help us understand phenomena.
1.13  Statistics can help us make decisions.
1.14  Pseudoscience and anecdotal evidence can obscure the truth.
1.15  There are limits to what science can do.What are the major themes in biology?
1.16  Important themes unify and connect diverse topics in biology.

Chapter 2
The Chemistry of Biology: Atoms, molecules, and their roles in supporting life
Atoms, molecules, and compounds make life possible.
2.1  Everything is made of atoms.
2.2  An atom’s electrons determine whether (and how) the atom will bond with other atoms.
2.3  Atoms can bond together to form molecules and compounds.Water has features that enable it to support all life.
2.4  Hydrogen bonds make water cohesive.
2.5  Hydrogen bonds between molecules give water properties critical to life. Living systems are highly sensitive to acidic and basic conditions.
2.6  The pH of a fluid is a measure of how acidic or basic the solution is.
2.7  This is how we do it: Do antacids impair digestion and increase the risk of food allergies?

Chapter 3
Molecules of Life:
Macromolecules can store energy and information and serve as building blocks
Macromolecules are the raw materials for life.
3.1 Carbohydrates, lipids, proteins, and nucleic acids are essential to organisms. Carbohydrates can fuel living machines.
3.2 Carbohydrates include macromolecules that function as fuel.
3.3 Many complex carbohydrates are time-release packets of energy.
3.4 Not all carbohydrates are digestible by humans. Lipids serve several functions.
3.5 Lipids store energy for a rainy day.
3.6 Dietary fats differ in degrees of saturation.
3.7 This is how we do it: How do trans fatty acids affect heart health?
3.8 Cholesterol and phospholipids are used to build sex hormones and membranes. Proteins are building blocks.
3.9 Proteins are bodybuilding macromolecules essential in our diet.
3.10  A protein’s function is influenced by its three-dimensional shape.
3.11  Enzymes are proteins that speed up chemical reactions.
3.12  Enzyme activity is influenced by chemical and physical factors. Nucleic acids encode information on how to build and run a body.
3.13  Nucleic acids are macromolecules that store information.
3.14  DNA holds the genetic information to build an organism.
3.15  RNA is a universal translator, reading DNA and directing protein production.

Chapter 4
Cells
The smallest part of you
What is a cell?
4.1  All organisms are made of cells.
4.2  Prokaryotic cells are structurally simple but extremely diverse.
4.3  Eukaryotic cells have compartments with specialized functions.Cell membranes are gatekeepers.
4.4  Every cell is bordered by a plasma membrane.
4.5  Faulty membranes can cause diseases.
4.6  Membrane surfaces have a “fingerprint” that identifies the cell.
4.7  Connections between cells hold them in place and allow for communication. Molecules move across membranes in several ways.
4.8  Passive transport is the spontaneous diffusion of molecules are spontaneously diffused across a membrane.
4.9  In active transport, cells use energy to transport molecules across the cell a membrane.
4.10  Endocytosis and exocytosis are used for bulk transport of move large particles into and out of cells.
Important landmarks distinguish eukaryotic cells.
4.11 The nucleus is the cell’s genetic control center.
4.12  The cytoskeleton provides support and can generate motion.
4.13  Mitochondria are the cell’s energy converters.
4.14  This is how we do it: Can cells change their composition to adapt to their environment?
4.15  Lysosomes are the cell’s garbage disposals.
4.16   In the endomembrane system, cells build, process, and package molecules, and disarm toxins.
4.17 The cell wall provides additional protection and support for plant cells.
4.18  Vacuoles are multipurpose storage sacs for cells.
4.19 Chloroplasts are the plant cell’s solar power plant.

Chapter 5
From the sun to you in just two steps
Energy flows from the sun and through all life on earth.
5.1 Can cars run on french fry oil?
5.2 Energy has two forms: kinetic and potential.
5.3 As energy is captured and converted, the amount of energy available to do work decreases.
5.4 ATP molecules are like rechargeable batteries floating around in all living cells. Photosynthesis uses energy from sunlight to make food.
5.5 Where does plant matter come from?
5.6 Photosynthesis takes place in the chloroplasts.
5.7 Light energy travels in waves.
5.8 Photons cause electrons in chlorophyll to enter an excited state.
5.9 The energy of sunlight is captured as chemical energy.
5.10  The captured energy of sunlight is used to make sugar.
5.11  We can use plants adapted to water scarcity in the battle against world hunger. Living organisms extract energy through cellular respiration.
5.12  Cellular respiration: the big picture.
5.13  Glycolysis is the universal energy-releasing pathway.
5.14  The citric acid cycle extracts energy from sugar.
5.15  ATP is built in the electron transport chain.
5.16  This is how we do it: Can we combat jet lag with NADH pills? There are alternative pathways for acquiring energy.
5.17  Beer, wine, and spirits are by-products of cellular metabolism in the absence of oxygen.

Chapter 6
DNA and Gene Expression 
DNA: what is it, and what does it do?
6.1 Knowledge about DNA is helping to increase justice in the world.
6.2 DNA contains instructions for the development and functioning of all living organisms.
6.3 Genes are sections of DNA that contain instructions for making proteins.
6.4 Not all DNA contains instructions for making proteins.
6.5 How do genes work? An overview. Information in DNA directs the production of the molecules that make up an organism.
6.6 In transcription, the information coded in DNA is copied into mRNA.
6.7 In translation, the mRNA copy of the information from DNA is used to build functional molecules.
6.8 Genes are regulated in several ways. Damage to the genetic code has a variety of causes and effects.
6.9 What causes a mutation and what are the consequences?
6.10  This is how we do it: Does sunscreen use reduce skin cancer risk?
6.11  Faulty genes, coding for faulty enzymes, can lead to sickness.

Chapter 7
Biotechnology
Harnessing the genetic code
Living organisms can be manipulated for practical benefits.
7.1 What is biotechnology and what does it promise?
7.2 A few important processes underlie many biotechnology applications.
7.3 CRISPR is a tool with the potential to revolutionize medicine. Biotechnology is producing improvements in agriculture.
7.4 Biotechnology can improve food nutrition and farming practices.
7.5 Rewards, with risks: what are the possible dangers of genetically modified foods?
7.6 This is how we do it: How can we determine whether GMOs are safe? Biotechnology has the potential for improving human health.
7.7 Biotechnology can help treat diseases and produce medicines.
7.8 Gene therapy: biotechnology can help diagnose and prevent genetic diseases, but has had limited success in curing them.
7.9 Cloning offers both opportunities and perils. Biotechnology can improve the criminal justice system.
7.10  The uses (and abuses) of DNA fingerprinting.

Chapter 8
Chromosomes and Cell Division
There are different types of cell division.
8.1 Immortal cells can spell trouble.
8.2 Some chromosomes are circular; others are linear.
8.3 There is a time for everything in the eukaryotic cell cycle.
8.4 Cell division is preceded by chromosome replication. Mitosis replaces worn-out old cells with fresh new duplicates.
8.5 Overview: mitosis leads to duplicate cells.
8.6 The details: mitosis is a four-stage process.
8.7 Cell division out of control may result in cancer. Meiosis generates sperm and eggs and a great deal of variation.
8.8 Overview: sexual reproduction requires special cells made by meiosis.
8.9 The details: Sperm and egg are produced by meiosis.
8.10  Male and female gametes are produced in slightly different ways.
8.11  Crossing over and meiosis are important sources of variation.
8.12  What are the costs and benefits of sexual reproduction? There are sex differences in the chromosomes.
8.13  How is sex determined in humans (and other species)?
8.14  This is how we do it: Can the environment determine the sex of a turtle’s offspring? Deviations from the typical chromosome number lead to problems.
8.15  Down syndrome can be detected before birth.
8.16  Life is possible with too many or too few sex chromosomes.

Chapter 9
Genes and Inheritance
Family resemblance: how traits are inherited 
Why (and how) do offspring resemble their parents?
9.1 Your mother and father each contribute to your genetic makeup.
9.2 Some traits are controlled by a single gene.
9.3 Mendel’s research in the nineteenth century informs our current understanding of genetics.
9.4 Segregation: you have two copies of each gene but each sperm or egg you produce has just one copy.
9.5 Observing an individual’s phenotype is not sufficient to determine its genotype. Tools of genetics highlight a central role for chance.
9.6 Using probability we can make predictions in genetics.
9.7 A test-cross enables us to figure out which alleles an individual carries.
9.8 We use pedigrees to decipher and predict the inheritance patterns of genes. How are genotypes translated into phenotypes?
9.9 The effects of both alleles in a genotype can show up in the phenotype.
9.10  Blood types: Some genes have more than two alleles.
9.11  How are continuously varying traits such as height influenced by genes?
9.12  Sometimes one gene influences multiple traits.
9.13  Sex-linked traits differ in their patterns of expression in males and females.
9.14  This is how we do it: What is the cause of male-pattern baldness?
9.15  Environmental effects: identical twins are not identical. Some genes are linked together.
9.16  Most traits are passed on as independent features.
9.17  Genes on the same chromosome are sometimes inherited together.
 
Chapter 10
Evolution and Natural Selection 
Darwin’s dangerous idea
Evolution is an ongoing process.
10.1  We can see evolution occurring right before our eyes. Darwin journeyed to a new idea.
10.2  Before Darwin, many believed that species had been created all at once and were unchanging.
10.3  Observing living organisms and fossils around the world, Darwin developed a theory of evolution.
Four mechanisms can give rise to evolution.
10.4  Evolution occurs when the allele frequencies in a population change.
10.5  Mechanism 1: Mutation—a direct change in the DNA of an individual—is the ultimate source of all genetic variation.
10.6  Mechanisms 2: Genetic drift is a random change in allele frequencies in a population.
10.7  Mechanism 3: Migration into or out of a population may change allele frequencies.
10.8  Mechanism 4: When three simple conditions are satisfied, evolution by natural selection is occurring.
10.9  A trait does not decrease in frequency simply because it is recessive. Populations of organisms can become adapted to their environments.
10.10 Traits causing some individuals to have more offspring than others become more prevalent in the population.
10.11 Populations can become better matched to their environment through natural selection.
10.12 There are several ways that natural selection can change the traits in a population.
10.13 This is how we do it: Why do zebras have stripes?
10.14 Natural selection can cause the evolution of complex traits and behaviors. The evidence for evolution is overwhelming.
10.15   The fossil record documents the process of natural selection.
10.16   Geographic patterns of species distributions reflect species’ evolutionary histories.
10.17   Comparative anatomy and embryology reveal common evolutionary origins.
10.18   Molecular biology reveals that common genetic sequences link all life forms.
10.19   Experiments and real-world observations reveal evolution in progress.

Chapter 11
Evolution and Behavior
Communication, cooperation, and conflict in the animal world
Behaviors, like other traits, can evolve.
11.1  Behavior has adaptive value, just like other traits.
11.2  Some behaviors are innate.
11.3  Some behaviors must be learned (and some are learned more easily than others).
11.4  Complex-appearing behaviors don’t require complex thought to evolve. Cooperation, selfishness, and altruism can be better understood with an evolutionary approach.
11.5  “Kindness” can be explained.
11.6  Apparent altruism toward relatives can evolve through kin selection.
11.7  Apparent altruism toward unrelated individuals can evolve through reciprocal altruism.
11.8  In an “alien” environment, adaptations produced by natural selection may no longer be adaptive.
11.9  Selfish genes win out over group selection. Sexual conflict can result from unequal reproductive investment by males and females.
11.10   Males and females invest differently in reproduction.
11.11   Males and females are vulnerable at different stages of the reproductive exchange.
11.12   Competition and courtship can help males and females secure reproductive success.
11.13   Mate guarding can protect a male’s reproductive investment.
11.14   This is how we do it: When paternity uncertainty seems greater, is paternal care reduced?
11.15   Monogamy versus polygamy: mating behaviors vary across human and animal cultures.
11.16   Sexual dimorphism is an indicator of a population’s mating behavior. Communication and the design of signals evolve.
11.17   Animal communication and language abilities evolve.
11.18   Honest signals reduce deception.

Chapter 12
The Origin and Diversification of Life on Earth
Understanding biodiversity
 Life on earth most likely originated from non-living materials.
12.1 Cells and self-replicating systems evolved together to create the first life.
12.2 This is how we do it: Could life have originated in ice, rather than in a “warm little pond”? Species are the basic units of biodiversity.
12.3 What is a species?
12.4  Species are not always easily defined.
12.5  How do new species arise? Evolutionary trees help us conceptualize and categorize biodiversity.
12.6  The history of life can be imagined as a tree.
12.7  Evolutionary trees show ancestor–descendant relationships.
12.8  Similar structures don’t always reveal common ancestry. Macroevolution gives rise to great diversity.
12.9  Macroevolution is evolution above the species level.
12.10 Adaptive radiations are times of extreme diversification.
12.11 There have been several mass extinctions on earth. An overview of the diversity of life on earth: organisms are divided into three domains.
12.12 All living organisms are classified into one of three groups.
12.13 The bacteria domain has tremendous biological diversity.
12.14 The archaea domain includes many species living in extreme environments.
12.15 The eukarya domain consists of four kingdoms: plants, animals, fungi, and protists.

Chapter 13
Anmal Diversification
Visibility in motion
Animals are just one branch of the eukarya domain.
13.1 What is an animal?
13.2 There are no “higher” or “lower” species.
13.3 Four key distinctions divide the animals.Invertebrates—animals without a backbone—are the most diverse group of animals.
13.4 Sponges are animals that lack tissues and organs.
13.5 Jellyfishes and other cnidarians are among the most poisonous animals in the world.
13.6 Flatworms, roundworms, and segmented worms come in all shapes and sizes.
13.7 Most mollusks live in shells.
13.8 Arthropods are the most diverse group of animals.
13.9 This is how we do it: How many species are there on earth?
13.10 Flight and metamorphosis produced the greatest adaptive radiation ever.
13.11 Echinoderms are vertebrates’ closest invertebrate relatives. The phylum Chordata includes vertebrates--animals with a backbone.
13.12 All vertebrates are members of the phylum Chordata.
13.13 The movement onto land required several adaptations. All terrestrial vertebrates are tetrapods.
13.14 Amphibians live a double life.
13.15 Birds are reptiles in which feathers evolved.
13.16 Mammals are animals that have hair and produce milk.Humans and our closest relatives are primates.
13.17 We are descended from arboreal primates, but our human ancestors left the trees.
13.18  How did we get here? The past 200,000 years of human evolution.

Chapter 14
Plant and Fungi Diversification
Where did all the plants and fungi come from?
Plants face multiple challenges.
14.1  What is a plant?
14.2  Colonizing land brought new opportunities and new challenges.
14.3  Non-vascular plants lack vessels for transporting nutrients and water.
14.4  The evolution of vascular tissue made large plants possible. The evolution of the seed opened new worlds to plants.
14.5  What is a seed?
14.6  With the evolution of the seed, gymnosperms became the dominant plants.
14.7 Conifers include the tallest and longest-living trees. Flowering plants are the most diverse plants.
14.8  Angiosperms are the dominant plants today.
14.9  A flower is nothing without a pollinator.
14.10 Angiosperms improve seeds with double fertilization. Plants and animals have a love-hate relationship.
14.11 Flowering plants use fruits to entice animals to disperse their seeds.
14.12 Unable to escape, plants must resist predation in other ways. Fungi and plants are partners but not close relatives.
14.13 Fungi are more closely related to animals than they are to plants.
14.14 Fungi have some structures in common but are incredibly diverse.
14.15 Most plants have fungal symbionts.
14.16 This is how we do it: Can beneficial fungi save our chocolate?

Chapter 15
Microbe Diversification   
Bacteria, archaea, protists, and viruses: the unseen world
There are microbes in all three domains.
15.1  Not all microbes are closely related evolutionarily.
15.2  Microbes are the simplest but most successful organisms on earth. Bacteria may be the most diverse of all organisms.
15.3  What are bacteria?
15.4  Metabolic diversity among the bacteria is extreme. Bacteria can hurt or help human health.
15.5  Many bacteria are beneficial to humans.
15.6  This is how we do it: Are bacteria thriving on our office desks?
15.7  Only a small percentage of microbial species cause diseases, but they kill millions of people.
15.8  Bacteria’s resistance to drugs can evolve quickly. Archaea define a prokaryotic domain distinct from bacteria.
15.9  Archaea are profoundly different from bacteria.
15.10 Archaea thrive in habitats too extreme for most other organisms. Most protists are single-celled eukaryotes.
15.11 The first eukaryotes were protists.
15.12 There are animal-like protists, fungus-like protists, and plant-like protists.
15.13 Some protists are very harmful to human health. At the border between living and non-living, viruses do not fit into any domain.
15.14 Viruses are not exactly living organisms.
15.15 Viruses infect a wide range of organisms and are responsible for many diseases.
15.16 HIV illustrates the difficulty of controlling infectious viruses.

Chapter 16
Population Ecology
Planet at capacity: patterns of population growth
Population ecology is the study of how populations interact with their environments.
16.1  What is ecology?
16.2  Populations can grow quickly for a while, but not forever.
16.3  A population’s growth is limited by its environment.
16.4  Some populations cycle between large and small.
16.5  Maximum sustainable yield is useful but nearly impossible to implement. A life history is like a species summary.
16.6 Life histories are shaped by natural selection.
16.7 There are trade-offs between growth, reproduction, and longevity.
16.8 This is how we do it: Rapid growth comes at a cost.
16.9 Populations can be depicted in life tables and survivorship curves. Ecology influences the evolution of aging in a population.
16.10 Things fall apart: what is aging and why does it occur?
16.11 What determines the average longevity in different species?
16.12 Can we slow down the process of aging? The human population is growing rapidly.
16.13 Age pyramids reveal much about a population.
16.14 Demographic transitions often occur as less developed countries become more developed.
16.15 Human population growth: how high can it go?

Chapter 17
Ecosystems and Communities
Organisms and their environments
Ecosystems have living and non-living components.
17.1 What are ecosystems?
17.2 Biomes are the world’s largest ecosystems, each determined by temperature and rainfall. Interacting physical forces create climate and weather patterns.
17.3 Global air circulation patterns create deserts and rain forests.
17.4 Local topography influences the climate and weather.
17.5 Ocean currents influence the climate and weather. Energy and chemicals flow within ecosystems.
17.6 Energy flows from producers to consumers.
17.7 Energy pyramids reveal the inefficiency of food chains.
17.8 Essential chemicals cycle through ecosystems. Species interactions influence the structure of communities.
17.9 A species’ role in a community is defined as its niche.
17.10 Interacting species evolve together.
17.11 Competition can be hard to see, yet it influences community structure.
17.12 Predation produces adaptation in both predators and their prey.
17.13 Parasitism is a form of predation.
17.14 Not all species interactions are negative.
17.15 This is how we do it: Investigating ants, plants, and the unintended consequences of environmental intervention. Communities can change or remain stable over time.
17.16 Primary succession and secondary succession describe how communities can change over time.
17.17 Some species have greater influence than others within a community.

Chapter 18
Conservation and Biodiversity
Human influences on the environment 
Biodiversity is valuable in many ways.
18.1  Biodiversity has intrinsic and extrinsic value.
18.2  This is how we do it: When 200,000 tons of methane disappears, how do you find it?
18.3  Biodiversity occurs at multiple levels.
18.4  Where does the greatest biodiversity occur? Extinction reduces biodiversity.
18.5  There are multiple causes of extinction.
18.6  We are in the midst of a mass extinction.Human activities can damage the environment.
18.7  The effects of some ecosystem disturbances are reversible and others are not.
18.8 Human activities can damage the environment: 1. Introduced non-native
18.9 Human activities can damage the environment: 2. Acid rain.18.10 Human activities can damage the environment: 3. Greenhouse gas releases.
18.11 Human activities can damage the environment: 4. Tropical deforestation.We can develop strategies for effective conservation.
18.12 Reversal of ozone layer depletion is a success story.
18.13 We must prioritize which species should be preserved.
18.14 There are multiple effective strategies for preserving biodiversity.
 
Chapter 19
Plant Structure and Nutrient Transport
How plants function, and why we need them
Plants are a diverse group of organisms with multiple pathways to evolutionary success.
19.1  Older, taller, bigger: plants are extremely diverse.
19.2  Monocots and eudicots are the two major groups of flowering plants.
19.3  The plant body is organized into three basic tissue types. Most plants have common structural features.
19.4  Roots anchor the plant and take up water and minerals.
19.5  Stems are the backbone of the plant.
19.6  Leaves feed the plant.
19.7  Several structures help plants resist water loss. Plants harness sunlight and obtain usable chemical elements from the environment.
19.8  Four factors are necessary for plant growth.
19.9  Nutrients cycle from soil to organisms and back again.
19.10 Plants acquire essential nitrogen with the help of bacteria.
19.11 This is how we do it: Carnivorous plants can consume prey and undergo photosynthesis. Plants transport water, sugar, and minerals through vascular tissue.
19.12 Plants take up water and minerals through their roots.
19.13 Water and minerals are distributed through the xylem.
19.14 Sugar and other nutrients are distributed through the phloem.

Chapter 20
Growth, Reproduction, and Environmental Responses in Plants
Problem solving with flowers, wood, and hormones
Plants can reproduce sexually and asexually.
20.1  Plant evolution has given rise to two methods of reproduction.
20.2  Many plants can reproduce asexually when necessary.
20.3  Plants can reproduce sexually, even though they cannot move.
20.4 Most plants can avoid self-fertilization. Pollination, fertilization, and seed dispersal often depend on help from other organisms.
20.5  Pollen grains and embryo sacs contain the plant gametes.
20.6  Plants need help getting the male gamete to the female gamete for fertilization.
20.7  This is how we do it: Does it matter how much nectar a flower produces?
20.8  Fertilization occurs after pollination.
20.9  Ovules develop into seeds, and ovaries into fruits. Plants have two types of growth, usually enabling lifelong increases in length and thickness.
20.10 How do seeds germinate and grow?
20.11 Plants grow differently from animals.
20.12 Primary plant growth occurs at the apical meristems.
20.13 Secondary growth produces wood. Hormones regulate growth and development.
20.14  Hormones help plants respond to their environments.
20.15 Gibberellins and auxins stimulate growth.
20.16 Other plant hormones regulate flowering, fruit ripening, and responses to stress. External cues trigger internal responses.
20.17 Tropisms influence plants’ direction of growth.
20.18 Plants have internal biological clocks.
20.19 With photoperiodism and dormancy, plants prepare for winter.

Chapter 21
Introduction to Animal Physiology
Principles of animal organization and function
Animal body structures reflect their functions.
21.1  Animal organ systems are built from four tissue types with distinct functions.
21.2  Connective tissue provides support.
21.3  Epithelial tissue covers and protects most inner and outer surfaces of the body.
21.4  Muscle tissue enables movement.
21.5  Nervous tissue transmits information.
21.6  Each organ system performs a coordinated set of related body functions. Animals maintain a steady internal environment.
21.7  Animal bodies function best within a narrow range of internal conditions.
21.8  Animals regulate their internal environment through homeostasis. How does homeostasis work?
21.9  Negative and positive feedback systems influence homeostasis.
21.10 Animals employ various mechanisms to regulate body temperature.
21.11 This is how we do it: Why do we yawn?
21.12 Animals regulate their water balance within a narrow range.
21.13 In humans, the kidneys regulate water balance.

Chapter 22
Circulation and Respiration
Transporting fuel, raw materials, and gases into, out of, and around the body
The circulatory system is the chief route of distribution in animals.
22.1  What is a circulatory system, and why is one needed?
22.2  Circulatory systems can be open or closed.
22.3  Vertebrates have several different types of closed circulatory systems. The human circulatory system consists of a heart, blood vessels, and blood.
22.4  Blood flows through the four chambers of the human heart.
22.5  Electrical activity in the heart generates the heartbeat.
22.6  Blood flows out of and back to the heart in blood vessels.
22.7  This is how we do it: Does thinking make your head heavier?
22.8  Blood is a mixture of cells and fluid.
22.9  Blood pressure is a key measure of heart health.
22.10 Cardiovascular disease is a leading cause of death in the United States.
22.11 The lymphatic system plays a supporting role in circulation. The respiratory system enables gas exchange in animals.
22.12 Oxygen and carbon dioxide must get into and out of the circulatory system.
22.13 Oxygen is transported while bound to hemoglobin.
22.14 Gas exchange takes place in the gills of aquatic vertebrates.
22.15 Gas exchange takes place in the lungs of terrestrial vertebrates.
22.16 Muscles control the flow of air into and out of the lungs.
22.17 Birds have unusually efficient respiratory systems.
22.18 Adaptation or acclimation to low-oxygen conditions at high elevation improves oxygen delivery.

Chapter 23
Nutrition and Digestion
At rest and at play: optimizing human physiological functioning
Food provides the raw materials for growth and the fuel to make it happen.
23.1  Why do organisms need food?
23.2  Animals have a variety of diets.
23.3  Calories count: organisms need sufficient energy. Nutrients are grouped into six categories.
23.4  Water is an essential nutrient.
23.5  Proteins in food are broken down to build proteins in the body.
23.6  Carbohydrates and fats provide bodies with energy and more.
23.7  Vitamins and minerals are necessary for good health.We extract energy and nutrients from food.
23.8  We convert food into nutrients in four steps.
23.9  Ingestion is the first step in the breakdown of food.
23.10 Digestion dismantles food into usable parts.
23.11 Absorption moves nutrients from your gut to your cells.
23.12 Elimination removes unusable materials from your body.
23.13 Some animals have alternative means for processing their food.What we eat profoundly affects our health.
23.14 What constitutes a healthy diet?
23.15 This is how we do it: Does human judgment depend on blood sugar?
23.16 Obesity can result from too much of a good thing.
23.17 Weight-loss diets are a losing proposition.
23.18 Diabetes is caused by the body’s inability to regulate blood sugar effectively.

Chapter 24
Nervous and Motor Systems
Actions, reactions, sensations, and addictions: meet your nervous system
What is the nervous system?
24.1 Why do we need a nervous system?
24.2  Neurons are the building blocks of all nervous systems.
24.3  The vertebrate nervous system consists of the peripheral and central nervous systems. How do neurons work?
24.4 Dendrites receive external stimuli.
24.5  The action potential propagates a signal down the axon.
24.6  At the synapse, a neuron interacts with another cell.
24.7 There are many types of neurotransmitters. Our senses detect and transmit stimuli.
24.8  Sensory receptors are our windows to the world around us.
24.9  Taste: an action potential serves up a taste sensation to the brain.
24.10 Smell: receptors in the nose detect airborne chemicals.
24.11 Vision: seeing is the perception of light by the brain.
24.12 Hearing: sound waves are collected by the ears and stimulate auditory neurons.
24.13 Touch: the brain perceives pressure, temperature, and pain. The muscular and skeletal systems enable movement.
24.14 Muscles generate force through contraction.
24.15 The skeletal system functions in support, movement, and protection. The brain is organized into distinct structures dedicated to specific functions.
24.16  The brain has several distinct regions.
24.17  Specific brain areas are involved in the processes of learning, language, and memory.
24.18  This is how we do it: Can intense cognitive training induce brain growth? Drugs can hijack pleasure pathways.
24.19  Our nervous system can be tricked by chemicals.
24.20  A brain slows down when it needs sleep. Caffeine wakes it up.
24.21  Alcohol interferes with many different neurotransmitters.

Chapter 25
Hormones
Mood, emotions, growth, and more: hormones as master regulators
Hormones are chemical messengers regulating cell functions.
25.1   The “cuddle” chemical: oxytocin increases trust and enhances pair bonding.
25.2   Hormones travel through the circulatory system to influence cells elsewhere in the body.
25.3   Hormones can regulate target tissues in different ways. Hormones are produced in glands throughout the body.
25.4   The hypothalamus controls secretions of the pituitary.
25.5   Other endocrine glands also produce and secrete hormones. Hormones influence nearly every facet of an organism.
25.6   Hormones can affect physique and physical performance.
25.7   Hormones can affect mood.
25.8   Hormones can affect behavior.
25.9   Hormones can affect cognitive performance.
25.10 Hormones can affect health and longevity. Environmental contaminants can disrupt normal hormone functioning.
25.11 Chemicals in the environment can mimic or block hormones, with disastrous results.
25.12 This is how we do it: Would you like your receipt? (Maybe not.)

Chapter 26
Reproduction and Development
From two parents to one embryo to one baby
How do animals reproduce?
26.1  Reproductive options (and ethical issues) are on the rise.
26.2  There are costs and benefits to having a partner: sexual versus asexual reproduction.
26.3  Fertilization can occur inside or outside a female’s body. Male and female reproductive systems have important similarities and differences.
26.4  Sperm are made in the testes.
26.5  There is unseen conflict among sperm cells.
26.6  This is how we do it: Can males increase sperm investment in response to the presence of another male?
26.7  Eggs are made in the ovaries (and the process can take decades).
26.8  Hormones direct the process of ovulation and the preparation for gestation. Sex can lead to fertilization, but it can also spread sexually transmitted diseases.
26.9  In fertilization, two cells become one.
26.10 Numerous strategies can help prevent fertilization.
26.11 Sexually transmitted diseases reveal battles between microbes and humans. Human development occurs in specific stages.
26.12 Early embryonic development occurs during cleavage, gastrulation, and neurulation.
26.13 There are three stages of pregnancy.
26.14 Pregnancy culminates in childbirth and the start of lactation. Reproductive technology has benefits and dangers.
26.15 Assisted reproductive technologies are promising and perilous.

Chapter 27
Immunity and Health
How the body defends and maintains itself
Your body has different ways to protect you against disease-causing invaders.
27.1  Three lines of defense prevent and fight pathogen attacks.
27.2  External barriers prevent pathogens from entering your body.
27.3  The non-specific division of the immune system recognizes and fights pathogens and signals for additional defenses.
27.4  The non-specific system responds to infection with the inflammatory response and with fever.
Specific immunity develops after exposure to pathogens.
27.5  The specific division of the immune system forms a memory of specific pathogens.
27.6  The structure of antibodies reflects their function.
27.7  Lymphocytes fight pathogens on two fronts.
27.8  Clonal selection helps in fighting infection now and later.
27.9  This is how we do it: Does contact with dogs make kids healthier?
27.10 Cytotoxic T cells and helper T cells serve different functions. Malfunction of the immune system causes disease.
27.11 Autoimmune diseases occur when the body turns against its own tissues.
27.12 AIDS is an immune deficiency disease.
27.13 Allergies are an inappropriate immune response to a harmless substance.