Life, in its simplest form, is a characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased or because they never had such functions. Understanding the intricacies of life requires delving into the realm of biology. conduct.edu.vn offers a complete guide to biology, explaining key ideas such as scientific thinking, chemistry, cell biology, genetics, and more. Gain a deeper understanding of what is life, its many forms, and the processes that sustain it by reading on to learn about biological literacy, the scientific method, and the essential themes that unite the diversified field of biology.
1. Scientific Thinking and Biological Literacy
Scientific thinking is essential in today’s world because it provides a framework for understanding and analyzing information objectively. Biological literacy, the ability to understand and apply biological concepts, is equally important. A beginner’s guide to scientific thinking emphasizes observation, experimentation, and critical analysis.
1.1. Thinking Like a Scientist: The Scientific Method
The scientific method is a systematic approach to understanding the natural world. It involves several key steps:
- Make observations: Observing the natural world is the first step in the scientific method. This involves gathering information through your senses and existing knowledge.
- Formulate a hypothesis: A hypothesis is a testable explanation for an observation. It should be clear, concise, and based on existing knowledge.
- Devise a testable prediction: A prediction is a statement of what will happen if your hypothesis is correct. It should be specific and measurable.
- Conduct a critical experiment: An experiment is a controlled test of your hypothesis. It should be designed to isolate the variable you are testing.
- Draw conclusions and make revisions: Based on the results of your experiment, you can draw conclusions about whether your hypothesis is supported. If the results do not support your hypothesis, you may need to revise it or develop a new one.
1.2. The Importance of Well-Designed Experiments
Well-designed experiments are essential for testing hypotheses effectively. Controlling variables is crucial in making experiments more powerful. By controlling variables, researchers can isolate the effects of a single variable and determine its impact on the outcome. It is also important to watch out for biases during experiments.
1.3. Theories in Science
Hypotheses become theories when they are supported by a large body of evidence and have been tested repeatedly. Theories are broad explanations of natural phenomena that are widely accepted by the scientific community. Scientific thinking can help us make better decisions by providing a framework for evaluating evidence and making informed judgments.
1.4. Data Visualization and Statistics
Visual displays of data can help us understand phenomena by making patterns and trends more apparent. Statistics can help us make decisions by providing a way to quantify the uncertainty in our data. Pseudoscience and anecdotal evidence can obscure the truth by presenting claims that are not supported by scientific evidence.
1.5. Limits of Science
There are limits to what science can do. Science is limited to the natural world and cannot address questions of morality, ethics, or aesthetics. Additionally, science is always subject to revision as new evidence emerges.
1.6. Major Themes in Biology
Important themes unify and connect diverse topics in biology, including:
- Evolution: The process by which populations of organisms change over time.
- Ecology: The study of how organisms interact with each other and their environment.
- Genetics: The study of heredity and the variation of inherited characteristics.
- Cell biology: The study of the structure and function of cells.
2. The Chemistry of Biology: Atoms, Molecules, and Life
Atoms, molecules, and compounds make life possible. Chemistry provides the foundation for understanding the structure and function of biological molecules.
2.1. Atoms: The Building Blocks of Matter
Everything is made of atoms, which are the smallest units of matter that retain the chemical properties of an element. An atom’s electrons determine whether (and how) the atom will bond with other atoms. Atoms can bond together to form molecules and compounds.
2.2. Water: The Elixir of Life
Water has features that enable it to support all life. Hydrogen bonds make water cohesive, allowing it to transport nutrients and waste products. Hydrogen bonds between molecules give water properties critical to life, such as high surface tension and the ability to moderate temperature.
2.3. Acids, Bases, and pH
Living systems are highly sensitive to acidic and basic conditions. The pH of a fluid is a measure of how acidic or basic the solution is. Buffers help maintain a stable pH by neutralizing acids or bases.
3. Molecules of Life: Macromolecules and Their Roles
Macromolecules can store energy and information and serve as building blocks for living organisms. They are the raw materials for life.
3.1. Essential Macromolecules
Carbohydrates, lipids, proteins, and nucleic acids are essential to organisms. These macromolecules perform a variety of functions, including providing energy, storing information, and building structures.
3.2. Carbohydrates: Fuels for Life
Carbohydrates include macromolecules that function as fuel. Simple carbohydrates, such as glucose and fructose, provide quick energy. Complex carbohydrates, such as starch and glycogen, are time-release packets of energy. Not all carbohydrates are digestible by humans, such as cellulose, which provides dietary fiber.
3.3. Lipids: Energy Storage and More
Lipids serve several functions, including energy storage, insulation, and hormone production. Lipids store energy for a rainy day. Dietary fats differ in degrees of saturation. Saturated fats are solid at room temperature, while unsaturated fats are liquid. Cholesterol and phospholipids are used to build sex hormones and membranes.
3.4. Proteins: The Building Blocks
Proteins are bodybuilding macromolecules essential in our diet. A protein’s function is influenced by its three-dimensional shape. Enzymes are proteins that speed up chemical reactions. Enzyme activity is influenced by chemical and physical factors, such as temperature and pH.
3.5. Nucleic Acids: Information Storage
Nucleic acids encode information on how to build and run a body. Nucleic acids are macromolecules that store information. DNA holds the genetic information to build an organism. RNA is a universal translator, reading DNA and directing protein production.
4. Cells: The Smallest Units of Life
The cell is the fundamental unit of life. Understanding cell structure and function is essential to understanding biology.
4.1. The Cell Theory
All organisms are made of cells. Cells are the basic units of structure and function in living organisms. All cells arise from pre-existing cells.
4.2. Prokaryotic vs. Eukaryotic Cells
Prokaryotic cells are structurally simple but extremely diverse. They lack a nucleus and other membrane-bound organelles. Eukaryotic cells have compartments with specialized functions, including a nucleus and other organelles.
4.3. Cell Membranes: Gatekeepers
Every cell is bordered by a plasma membrane. The plasma membrane controls what enters and exits the cell. Faulty membranes can cause diseases. Membrane surfaces have a “fingerprint” that identifies the cell. Connections between cells hold them in place and allow for communication.
4.4. Molecular Transport Across Membranes
Molecules move across membranes in several ways. Passive transport is the spontaneous diffusion of molecules across a membrane. In active transport, cells use energy to transport molecules across the cell a membrane. Endocytosis and exocytosis are used for bulk transport of move large particles into and out of cells.
4.5. Eukaryotic Cell Landmarks
Important landmarks distinguish eukaryotic cells. The nucleus is the cell’s genetic control center. The cytoskeleton provides support and can generate motion. Mitochondria are the cell’s energy converters. Lysosomes are the cell’s garbage disposals. In the endomembrane system, cells build, process, and package molecules, and disarm toxins. The cell wall provides additional protection and support for plant cells. Vacuoles are multipurpose storage sacs for cells. Chloroplasts are the plant cell’s solar power plant.
5. Energy Flow: From Sun to Life
Energy flows from the sun and through all life on earth. Understanding energy flow is essential to understanding how ecosystems function.
5.1. Forms of Energy
Energy has two forms: kinetic and potential. Kinetic energy is the energy of motion, while potential energy is stored energy. As energy is captured and converted, the amount of energy available to do work decreases, illustrating the laws of thermodynamics.
5.2. ATP: The Energy Currency of the Cell
ATP molecules are like rechargeable batteries floating around in all living cells. ATP stores energy in its chemical bonds and releases it when the bonds are broken.
5.3. Photosynthesis: Capturing Sunlight
Photosynthesis uses energy from sunlight to make food. It takes place in the chloroplasts of plant cells. Light energy travels in waves. Photons cause electrons in chlorophyll to enter an excited state. The energy of sunlight is captured as chemical energy. The captured energy of sunlight is used to make sugar. We can use plants adapted to water scarcity in the battle against world hunger.
5.4. Cellular Respiration: Extracting Energy
Living organisms extract energy through cellular respiration. Cellular respiration: the big picture. Glycolysis is the universal energy-releasing pathway. The citric acid cycle extracts energy from sugar. ATP is built in the electron transport chain. There are alternative pathways for acquiring energy, such as fermentation. Beer, wine, and spirits are by-products of cellular metabolism in the absence of oxygen.
6. DNA and Gene Expression: The Blueprint of Life
DNA contains the instructions for building and operating living organisms. Knowledge about DNA is helping to increase justice in the world.
6.1. DNA Structure and Function
DNA contains instructions for the development and functioning of all living organisms. Genes are sections of DNA that contain instructions for making proteins. Not all DNA contains instructions for making proteins. How do genes work? An overview.
6.2. Gene Expression: From DNA to Protein
Information in DNA directs the production of the molecules that make up an organism. In transcription, the information coded in DNA is copied into mRNA. In translation, the mRNA copy of the information from DNA is used to build functional molecules. Genes are regulated in several ways.
6.3. Mutations and Their Consequences
Damage to the genetic code has a variety of causes and effects. What causes a mutation and what are the consequences? Faulty genes, coding for faulty enzymes, can lead to sickness.
7. Biotechnology: Harnessing the Genetic Code
Living organisms can be manipulated for practical benefits through biotechnology.
7.1. Applications of Biotechnology
What is biotechnology and what does it promise? A few important processes underlie many biotechnology applications. CRISPR is a tool with the potential to revolutionize medicine.
7.2. Biotechnology in Agriculture
Biotechnology is producing improvements in agriculture. Biotechnology can improve food nutrition and farming practices. Rewards, with risks: what are the possible dangers of genetically modified foods?
7.3. Biotechnology and Human Health
Biotechnology has the potential for improving human health. Biotechnology can help treat diseases and produce medicines. Gene therapy: biotechnology can help diagnose and prevent genetic diseases, but has had limited success in curing them. Cloning offers both opportunities and perils. Biotechnology can improve the criminal justice system through the uses (and abuses) of DNA fingerprinting.
8. Chromosomes and Cell Division: The Circle of Life
There are different types of cell division, each with its own purpose and mechanism.
8.1. Chromosome Structure
Some chromosomes are circular; others are linear. There is a time for everything in the eukaryotic cell cycle. Cell division is preceded by chromosome replication.
8.2. Mitosis: Cell Duplication
Mitosis replaces worn-out old cells with fresh new duplicates. Overview: mitosis leads to duplicate cells. The details: mitosis is a four-stage process. Cell division out of control may result in cancer.
8.3. Meiosis: Generating Genetic Variation
Meiosis generates sperm and eggs and a great deal of variation. Overview: sexual reproduction requires special cells made by meiosis. The details: Sperm and egg are produced by meiosis. Male and female gametes are produced in slightly different ways. Crossing over and meiosis are important sources of variation. What are the costs and benefits of sexual reproduction?
8.4. Sex Chromosomes and Determination
There are sex differences in the chromosomes. How is sex determined in humans (and other species)? Deviations from the typical chromosome number lead to problems. Down syndrome can be detected before birth. Life is possible with too many or too few sex chromosomes.
9. Genes and Inheritance: Family Resemblance
Why (and how) do offspring resemble their parents? Understanding the principles of inheritance is essential to understanding genetics.
9.1. Genetic Contributions
Your mother and father each contribute to your genetic makeup. Some traits are controlled by a single gene. Mendel’s research in the nineteenth century informs our current understanding of genetics.
9.2. Mendel’s Laws
Segregation: you have two copies of each gene but each sperm or egg you produce has just one copy. Observing an individual’s phenotype is not sufficient to determine its genotype. Tools of genetics highlight a central role for chance.
9.3. Genetic Probability
Using probability we can make predictions in genetics. A test-cross enables us to figure out which alleles an individual carries. We use pedigrees to decipher and predict the inheritance patterns of genes.
9.4. Genotype to Phenotype
How are genotypes translated into phenotypes? The effects of both alleles in a genotype can show up in the phenotype. Blood types: Some genes have more than two alleles. How are continuously varying traits such as height influenced by genes? Sometimes one gene influences multiple traits. Sex-linked traits differ in their patterns of expression in males and females.
9.5. Environmental Effects
Environmental effects: identical twins are not identical. Some genes are linked together. Most traits are passed on as independent features. Genes on the same chromosome are sometimes inherited together.
10. Evolution and Natural Selection: Darwin’s Dangerous Idea
Evolution is an ongoing process. Understanding evolution is essential to understanding the diversity of life.
10.1. Evidence of Evolution
We can see evolution occurring right before our eyes. Darwin journeyed to a new idea. Before Darwin, many believed that species had been created all at once and were unchanging. Observing living organisms and fossils around the world, Darwin developed a theory of evolution.
10.2. Mechanisms of Evolution
Four mechanisms can give rise to evolution. Evolution occurs when the allele frequencies in a population change. Mechanism 1: Mutation—a direct change in the DNA of an individual—is the ultimate source of all genetic variation. Mechanism 2: Genetic drift is a random change in allele frequencies in a population. Mechanism 3: Migration into or out of a population may change allele frequencies. Mechanism 4: When three simple conditions are satisfied, evolution by natural selection is occurring. A trait does not decrease in frequency simply because it is recessive.
10.3. Adaptation
Populations of organisms can become adapted to their environments. Traits causing some individuals to have more offspring than others become more prevalent in the population. Populations can become better matched to their environment through natural selection. There are several ways that natural selection can change the traits in a population.
10.4. Evidence for Evolution
The evidence for evolution is overwhelming. The fossil record documents the process of natural selection. Geographic patterns of species distributions reflect species’ evolutionary histories. Comparative anatomy and embryology reveal common evolutionary origins. Molecular biology reveals that common genetic sequences link all life forms. Experiments and real-world observations reveal evolution in progress.
11. Evolution and Behavior: Communication, Cooperation, and Conflict
Behaviors, like other traits, can evolve. Understanding the evolutionary basis of behavior can provide insights into animal interactions.
11.1. Adaptive Behavior
Behavior has adaptive value, just like other traits. Some behaviors are innate. Some behaviors must be learned (and some are learned more easily than others). Complex-appearing behaviors don’t require complex thought to evolve.
11.2. Cooperation, Selfishness, and Altruism
Cooperation, selfishness, and altruism can be better understood with an evolutionary approach. “Kindness” can be explained. Apparent altruism toward relatives can evolve through kin selection. Apparent altruism toward unrelated individuals can evolve through reciprocal altruism. In an “alien” environment, adaptations produced by natural selection may no longer be adaptive. Selfish genes win out over group selection.
11.3. Sexual Conflict
Sexual conflict can result from unequal reproductive investment by males and females. Males and females invest differently in reproduction. Males and females are vulnerable at different stages of the reproductive exchange. Competition and courtship can help males and females secure reproductive success. Mate guarding can protect a male’s reproductive investment.
11.4. Mating Behaviors
Monogamy versus polygamy: mating behaviors vary across human and animal cultures. Sexual dimorphism is an indicator of a population’s mating behavior.
11.5. Animal Communication
Communication and the design of signals evolve. Animal communication and language abilities evolve. Honest signals reduce deception.
12. The Origin and Diversification of Life on Earth
Life on earth most likely originated from non-living materials. Understanding the origin and diversification of life is essential to understanding biodiversity.
12.1. Origin of Life
Cells and self-replicating systems evolved together to create the first life. Species are the basic units of biodiversity. What is a species? Species are not always easily defined. How do new species arise?
12.2. Evolutionary Trees
Evolutionary trees help us conceptualize and categorize biodiversity. The history of life can be imagined as a tree. Evolutionary trees show ancestor–descendant relationships. Similar structures don’t always reveal common ancestry.
12.3. Macroevolution
Macroevolution gives rise to great diversity. Macroevolution is evolution above the species level. Adaptive radiations are times of extreme diversification. There have been several mass extinctions on earth.
12.4. Domains of Life
An overview of the diversity of life on earth: organisms are divided into three domains. All living organisms are classified into one of three groups. The bacteria domain has tremendous biological diversity. The archaea domain includes many species living in extreme environments. The eukarya domain consists of four kingdoms: plants, animals, fungi, and protists.
13. Animal Diversification: Visibility in Motion
Animals are just one branch of the eukarya domain. Understanding the diversity of animals requires understanding their evolutionary history.
13.1. Defining Animals
What is an animal? There are no “higher” or “lower” species. Four key distinctions divide the animals.
13.2. Invertebrates
Invertebrates—animals without a backbone—are the most diverse group of animals. Sponges are animals that lack tissues and organs. Jellyfishes and other cnidarians are among the most poisonous animals in the world. Flatworms, roundworms, and segmented worms come in all shapes and sizes. Most mollusks live in shells. Arthropods are the most diverse group of animals. Flight and metamorphosis produced the greatest adaptive radiation ever. Echinoderms are vertebrates’ closest invertebrate relatives.
13.3. Vertebrates
The phylum Chordata includes vertebrates–animals with a backbone. All vertebrates are members of the phylum Chordata. The movement onto land required several adaptations. All terrestrial vertebrates are tetrapods. Amphibians live a double life. Birds are reptiles in which feathers evolved. Mammals are animals that have hair and produce milk.
13.4. Primates and Human Evolution
Humans and our closest relatives are primates. We are descended from arboreal primates, but our human ancestors left the trees. How did we get here? The past 200,000 years of human evolution.
14. Plant and Fungi Diversification: Where Did They Come From?
Where did all the plants and fungi come from? Understanding the diversification of plants and fungi requires understanding their adaptations to different environments.
14.1. Plant Challenges
Plants face multiple challenges. What is a plant? Colonizing land brought new opportunities and new challenges. Non-vascular plants lack vessels for transporting nutrients and water. The evolution of vascular tissue made large plants possible.
14.2. Seed Evolution
The evolution of the seed opened new worlds to plants. What is a seed? With the evolution of the seed, gymnosperms became the dominant plants. Conifers include the tallest and longest-living trees.
14.3. Flowering Plants
Flowering plants are the most diverse plants. Angiosperms are the dominant plants today. A flower is nothing without a pollinator. Angiosperms improve seeds with double fertilization. Plants and animals have a love-hate relationship. Flowering plants use fruits to entice animals to disperse their seeds. Unable to escape, plants must resist predation in other ways.
14.4. Fungi
Fungi and plants are partners but not close relatives. Fungi are more closely related to animals than they are to plants. Fungi have some structures in common but are incredibly diverse. Most plants have fungal symbionts.
15. Microbe Diversification: The Unseen World
Bacteria, archaea, protists, and viruses: the unseen world. Understanding the diversity of microbes requires understanding their unique characteristics.
15.1. Microbial Diversity
There are microbes in all three domains. Not all microbes are closely related evolutionarily. Microbes are the simplest but most successful organisms on earth.
15.2. Bacteria
What are bacteria? Metabolic diversity among the bacteria is extreme. Bacteria can hurt or help human health. Many bacteria are beneficial to humans. Only a small percentage of microbial species cause diseases, but they kill millions of people. Bacteria’s resistance to drugs can evolve quickly.
15.3. Archaea
Archaea define a prokaryotic domain distinct from bacteria. Archaea are profoundly different from bacteria. Archaea thrive in habitats too extreme for most other organisms.
15.4. Protists
Most protists are single-celled eukaryotes. The first eukaryotes were protists. There are animal-like protists, fungus-like protists, and plant-like protists. Some protists are very harmful to human health.
15.5. Viruses
At the border between living and non-living, viruses do not fit into any domain. Viruses are not exactly living organisms. Viruses infect a wide range of organisms and are responsible for many diseases. HIV illustrates the difficulty of controlling infectious viruses.
16. Population Ecology: Planet at Capacity
Planet at capacity: patterns of population growth. Understanding population ecology requires understanding how populations interact with their environments.
16.1. Ecology
What is ecology? Populations can grow quickly for a while, but not forever. A population’s growth is limited by its environment. Some populations cycle between large and small. Maximum sustainable yield is useful but nearly impossible to implement.
16.2. Life Histories
A life history is like a species summary. Life histories are shaped by natural selection. There are trade-offs between growth, reproduction, and longevity. Populations can be depicted in life tables and survivorship curves.
16.3. Aging
Ecology influences the evolution of aging in a population. Things fall apart: what is aging and why does it occur? What determines the average longevity in different species? Can we slow down the process of aging?
16.4. Human Population
The human population is growing rapidly. Age pyramids reveal much about a population. Demographic transitions often occur as less developed countries become more developed. Human population growth: how high can it go?
17. Ecosystems and Communities: Organisms and Their Environments
Ecosystems have living and non-living components. Understanding ecosystems and communities requires understanding the interactions between organisms and their environments.
17.1. Ecosystem Components
What are ecosystems? Biomes are the world’s largest ecosystems, each determined by temperature and rainfall. Interacting physical forces create climate and weather patterns. Global air circulation patterns create deserts and rain forests. Local topography influences the climate and weather. Ocean currents influence the climate and weather.
17.2. Energy and Chemicals
Energy and chemicals flow within ecosystems. Energy flows from producers to consumers. Energy pyramids reveal the inefficiency of food chains. Essential chemicals cycle through ecosystems.
17.3. Species Interactions
Species interactions influence the structure of communities. A species’ role in a community is defined as its niche. Interacting species evolve together. Competition can be hard to see, yet it influences community structure. Predation produces adaptation in both predators and their prey. Parasitism is a form of predation. Not all species interactions are negative.
17.4. Community Change
Communities can change or remain stable over time. Primary succession and secondary succession describe how communities can change over time. Some species have greater influence than others within a community.
18. Conservation and Biodiversity: Human Influences
Human influences on the environment threaten biodiversity. Understanding conservation and biodiversity requires understanding the impact of human activities on the environment.
18.1. Biodiversity Value
Biodiversity is valuable in many ways. Biodiversity has intrinsic and extrinsic value. Biodiversity occurs at multiple levels. Where does the greatest biodiversity occur?
18.2. Extinction
Extinction reduces biodiversity. There are multiple causes of extinction. We are in the midst of a mass extinction.
18.3. Human Impacts
Human activities can damage the environment. The effects of some ecosystem disturbances are reversible and others are not. Human activities can damage the environment: 1. Introduced non-native species. 2. Acid rain. 3. Greenhouse gas releases. 4. Tropical deforestation.
18.4. Conservation Strategies
We can develop strategies for effective conservation. Reversal of ozone layer depletion is a success story. We must prioritize which species should be preserved. There are multiple effective strategies for preserving biodiversity.
19. Plant Structure and Nutrient Transport: Function and Need
How plants function, and why we need them. Understanding plant structure and nutrient transport requires understanding their adaptations to terrestrial life.
19.1. Plant Diversity
Older, taller, bigger: plants are extremely diverse. Monocots and eudicots are the two major groups of flowering plants. The plant body is organized into three basic tissue types.
19.2. Plant Structures
Most plants have common structural features. Roots anchor the plant and take up water and minerals. Stems are the backbone of the plant. Leaves feed the plant. Several structures help plants resist water loss.
19.3. Plant Growth Factors
Plants harness sunlight and obtain usable chemical elements from the environment. Four factors are necessary for plant growth. Nutrients cycle from soil to organisms and back again. Plants acquire essential nitrogen with the help of bacteria.
19.4. Nutrient Transport
Plants transport water, sugar, and minerals through vascular tissue. Plants take up water and minerals through their roots. Water and minerals are distributed through the xylem. Sugar and other nutrients are distributed through the phloem.
20. Growth, Reproduction, and Environmental Responses in Plants
Problem solving with flowers, wood, and hormones. Understanding plant growth, reproduction, and environmental responses requires understanding their unique strategies.
20.1. Reproduction
Plant evolution has given rise to two methods of reproduction. Many plants can reproduce asexually when necessary. Plants can reproduce sexually, even though they cannot move. Most plants can avoid self-fertilization.
20.2. Pollination and Fertilization
Pollination, fertilization, and seed dispersal often depend on help from other organisms. Pollen grains and embryo sacs contain the plant gametes. Plants need help getting the male gamete to the female gamete for fertilization. Fertilization occurs after pollination. Ovules develop into seeds, and ovaries into fruits.
20.3. Plant Growth
Plants have two types of growth, usually enabling lifelong increases in length and thickness. How do seeds germinate and grow? Plants grow differently from animals. Primary plant growth occurs at the apical meristems. Secondary growth produces wood.
20.4. Hormonal Regulation
Hormones regulate growth and development. Hormones help plants respond to their environments. Gibberellins and auxins stimulate growth. Other plant hormones regulate flowering, fruit ripening, and responses to stress.
20.5. Environmental Cues
External cues trigger internal responses. Tropisms influence plants’ direction of growth. Plants have internal biological clocks. With photoperiodism and dormancy, plants prepare for winter.
21. Introduction to Animal Physiology: Organization and Function
Principles of animal organization and function. Understanding animal physiology requires understanding the relationship between structure and function.
21.1. Animal Tissues
Animal body structures reflect their functions. Animal organ systems are built from four tissue types with distinct functions. Connective tissue provides support. Epithelial tissue covers and protects most inner and outer surfaces of the body. Muscle tissue enables movement. Nervous tissue transmits information.
21.2. Organ Systems
Each organ system performs a coordinated set of related body functions. Animals maintain a steady internal environment. Animal bodies function best within a narrow range of internal conditions. Animals regulate their internal environment through homeostasis.
21.3. Homeostasis
How does homeostasis work? Negative and positive feedback systems influence homeostasis. Animals employ various mechanisms to regulate body temperature. Animals regulate their water balance within a narrow range.
21.4. Human Water Balance
In humans, the kidneys regulate water balance.
22. Circulation and Respiration: Transporting Life’s Essentials
Transporting fuel, raw materials, and gases into, out of, and around the body. Understanding circulation and respiration requires understanding how animals transport essential materials.
22.1. Circulatory Systems
The circulatory system is the chief route of distribution in animals. What is a circulatory system, and why is one needed? Circulatory systems can be open or closed. Vertebrates have several different types of closed circulatory systems.
22.2. Human Circulation
The human circulatory system consists of a heart, blood vessels, and blood. Blood flows through the four chambers of the human heart. Electrical activity in the heart generates the heartbeat. Blood flows out of and back to the heart in blood vessels. Blood is a mixture of cells and fluid. Blood pressure is a key measure of heart health. Cardiovascular disease is a leading cause of death in the United States. The lymphatic system plays a supporting role in circulation.
22.3. Respiratory Systems
The respiratory system enables gas exchange in animals. Oxygen and carbon dioxide must get into and out of the circulatory system. Oxygen is transported while bound to hemoglobin. Gas exchange takes place in the gills of aquatic vertebrates. Gas exchange takes place in the lungs of terrestrial vertebrates. Muscles control the flow of air into and out of the lungs. Birds have unusually efficient respiratory systems. Adaptation or acclimation to low-oxygen conditions at high elevation improves oxygen delivery.
23. Nutrition and Digestion: Fueling Life’s Processes
At rest and at play: optimizing human physiological functioning. Understanding nutrition and digestion requires understanding how animals obtain and process food.
23.1. Food Needs
Food provides the raw materials for growth and the fuel to make it happen. Why do organisms need food? Animals have a variety of diets. Calories count: organisms need sufficient energy.
23.2. Essential Nutrients
Nutrients are grouped into six categories. Water is an essential nutrient. Proteins in food are broken down to build proteins in the body. Carbohydrates and fats provide bodies with energy and more. Vitamins and minerals are necessary for good health.
23.3. Digestive Processes
We extract energy and nutrients from food. We convert food into nutrients in four steps. Ingestion is the first step in the breakdown of food. Digestion dismantles food into usable parts. Absorption moves nutrients from your gut to your cells. Elimination removes unusable materials from your body. Some animals have alternative means for processing their food.
23.4. Healthy Diets
What we eat profoundly affects our health. What constitutes a healthy diet? Obesity can result from too much of a good thing. Weight-loss diets are a losing proposition. Diabetes is caused by the body’s inability to regulate blood sugar effectively.
24. Nervous and Motor Systems: Actions, Reactions, and Sensations
Actions, reactions, sensations, and addictions: meet your nervous system. Understanding nervous and motor systems requires understanding how animals sense and respond to their environment.
24.1. Nervous System
What is the nervous system? Why do we need a nervous system? Neurons are the building blocks of all nervous systems. The vertebrate nervous system consists of the peripheral and central nervous systems.
24.2. Neuron Function
How do neurons work? Dendrites receive external stimuli. The action potential propagates a signal down the axon. At the synapse, a neuron interacts with another cell. There are many types of neurotransmitters.
24.3. Sensory Systems
Our senses detect and transmit stimuli. Sensory receptors are our windows to the world around us. Taste: an action potential serves up a taste sensation to the brain. Smell: receptors in the nose detect airborne chemicals. Vision: seeing is the perception of light by the brain. Hearing: sound waves are collected by the ears and stimulate auditory neurons. Touch: the brain perceives pressure, temperature, and pain.
24.4. Muscular and Skeletal Systems
The muscular and skeletal systems enable movement. Muscles generate force through contraction. The skeletal system functions in support, movement, and protection.
24.5. Brain Organization
The brain is organized into distinct structures dedicated to specific functions. The brain has several distinct regions. Specific brain areas are involved in the processes of learning, language, and memory.
24.6. Drugs and Addiction
Drugs can hijack pleasure pathways. Our nervous system can be tricked by chemicals. A brain slows down when it needs sleep. Caffeine wakes it up. Alcohol interferes with many different neurotransmitters.
25. Hormones: Master Regulators of Life
Mood, emotions, growth, and more: hormones as master regulators. Understanding hormones requires understanding their role in regulating cell functions.
25.1. Hormone Function
Hormones are chemical messengers regulating cell functions. The “cuddle” chemical: oxytocin increases trust and enhances pair bonding. Hormones travel through the circulatory system to influence cells elsewhere in the body. Hormones can regulate target tissues in different ways.
25.2. Hormone Production
Hormones are produced in glands throughout the body. The hypothalamus controls secretions of the pituitary. Other endocrine glands also produce and secrete hormones.
25.3. Hormone Influence
Hormones influence nearly every facet of an organism. Hormones can affect physique and physical performance. Hormones can affect mood. Hormones can affect behavior. Hormones can affect cognitive performance. Hormones can affect health and longevity.
25.4. Environmental Disruptors
Environmental contaminants can disrupt normal hormone functioning. Chemicals in the environment can mimic or block hormones, with disastrous results.
26. Reproduction and Development: From Two Parents to One
How do animals reproduce? Understanding reproduction and development requires understanding the processes that create new individuals.
26.1. Reproductive Strategies
Reproductive options (and ethical issues) are on the rise. There are costs and benefits to having a partner: sexual versus asexual reproduction. Fertilization can occur inside or outside a female’s body.
26.2. Reproductive Systems
Male and female reproductive systems have important similarities and differences. Sperm are made in the testes. There is unseen conflict among sperm cells. Eggs are made in the ovaries (and the process can take decades). Hormones direct the process of ovulation and the preparation for gestation.
26.3. Fertilization and STDs
Sex can lead to fertilization, but it can also spread sexually transmitted diseases. In fertilization, two cells become one. Numerous strategies can help prevent fertilization. Sexually transmitted diseases reveal battles between microbes and humans.
26.4. Human Development
Human development occurs in specific stages. Early embryonic development occurs during cleavage, gastrulation, and neurulation. There are three stages of pregnancy. Pregnancy culminates in childbirth and the start of lactation.
26.5. Reproductive Technology
Reproductive technology has benefits and dangers. Assisted reproductive technologies are promising and perilous.
27. Immunity and Health: The Body’s Defenses
How the body defends and maintains itself. Understanding immunity and health requires understanding how animals protect
