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Send all inquiries to: Glencoe/McGraw-Hill 8787 Orion Place Columbus, OH 43240-4027 ISBN-13: 978-0-07-874599-7 ISBN-10: 0-07-874599-3 Printed in the United States of America 1 2 3 4 5 6 7 8 9 10 024 11 10 09 08 07 06 Table of Contents To the Student . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vii Dinah Zike’s Foldables™ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii Chapter 1 The Study of Life 1.1 Introduction to Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 The Nature of Science. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Methods of Science. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Chapter 2 Principles of Ecology 2.1 Organisms and Their Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2 Flow of Energy in an Ecosystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.3 Cycling of Matter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Chapter 3 Communities, Biomes, and Ecosystems 3.1 Community Ecology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.2 Terrestrial Biomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.3 Aquatic Ecosystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Chapter 4 Population Ecology 4.1 Population Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.2 Human Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Chapter 5 Biodiversity and Conservation 5.1 Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 5.2 Threats to Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 c. 5.3 Conserving Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 n es, I Chapter 6 Chemistry in Biology ni pa 6.1 Atoms, Elements, and Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 m Co 6.2 Chemical Reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 w-Hill 6.3 Water and Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 a Gr 6.4 The Building Blocks of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 c M The Chapter 7 Cellular Structure and Function n of 7.1 Cell Discovery and Theory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 o visi 7.2 The Plasma Membrane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 di w-Hill, a 77..34 SCterluluctlaurr eTsr aannsdp Oorrtg.a .n .e .l l.e .s .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 7850 a Gr Mc Chapter 8 Cellular Energy / oe 8.1 How Organisms Obtain Energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 c n Gle 8.2 Photosynthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 ht © 8.3 Cellular Respiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 g pyri Chapter 9 Cellular Reproduction o C 9.1 Cellular Growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 9.2 Mitosis and Cytokinesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 9.3 Cell Cycle Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 iii Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 10.2 Mendelian Genetics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 10.3 Gene Linkage and Polyploidy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Chapter 11 Complex Inheritance and Human Heredity 11.1 Basic Patterns of Human Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 11.2 Complex Patterns of Inheritance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 11.3 Chromosomes and Human Heredity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Chapter 12 Molecular Genetics 12.1 DNA: The Genetic Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 12.2 Replication of DNA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 12.3 DNA, RNA, and Protein. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 12.4 Gene Regulation and Mutations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Chapter 13 Genetics and Biotechnology 13.1 Applied Genetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 13.2 DNA Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 13.3 The Human Genome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Chapter 14 The History of Life 14.1 Fossil Evidence of Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 14.2 The Origin of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Chapter 15 Evolution 15.1 Darwin’s Theory of Natural Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 15.2 Evidence of Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 15.3 Shaping Evolutionary Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 C Chapter 16 Primate Evolution op 16.1 Primates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 yrigh t © 16.2 Hominoids to Hominins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 G le 16.3 Human Ancestry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 nc o e / Chapter 17 Organizing Life’s Diversity Mc G 17.1 The History of Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 raw -H 17.2 Modern Classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 ill, a 17.3 Domains and Kingdoms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 div is io Chapter 18 Bacteria and Viruses n o 18.1 Bacteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 f Th e 18.2 Viruses and Prions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 Mc G ra Chapter 19 Protists w-H 19.1 Introduction to Protists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 ill C o m 19.2 Protozoans—Animal-like Protists. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 pa n 19.3 Algae—Plantlike Protists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 ies 19.4 Funguslike Protists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 , Inc . Chapter 20 Fungi 20.1 Introduction to Fungi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 20.2 Diversity of Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 20.3 Ecology of Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 iv Chapter 21 Introduction to Plants 21.1 Plant Evolution and Adaptations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 21.2 Nonvascular Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 21.3 Seedless Vascular Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 21.4 Vascular Seed Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 Chapter 22 Plant Structure and Function 22.1 Plant Cells and Tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 22.2 Roots, Stems, and Leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 22.3 Plant Hormones and Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Chapter 23 Reproduction in Plants 23.1 Introduction to Plant Reproduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 23.2 Flowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 23.3 Flowering Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 Chapter 24 Introduction to Animals 24.1 Animal Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 24.2 Animal Body Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 24.3 Sponges and Cnidarians. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Chapter 25 Worms and Mollusks 25.1 Flatworms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 25.2 Roundworms and Rotifers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 25.3 Mollusks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 25.4 Segmented Worms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 Chapter 26 Arthropods 26.1 Arthropod Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 26.2 Arthropod Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 c. s, In 26.3 Insects and Their Relatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 e pani Chapter 27 Echinoderms and Invertebrate Chordates m Co 27.1 Echinoderm Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 w-Hill 27.2 Invertebrate Chordates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 a McGr Chapter 28 Fishes and Amphibians he 28.1 Fishes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 T n of 28.2 Diversity of Today’s Fishes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 o visi 28.3 Amphibians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 di Hill, a Chapter 29 Reptiles and Birds w- 29.1 Reptiles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 a cGr 29.2 Birds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350 M / e co Chapter 30 Mammals n e © Gl 30.1 Mammalian Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 ht 30.2 Diversity of Mammals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362 g Copyri Chapter 31 Animal Behavior 31.1 Basic Behaviors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 31.2 Ecological Behaviors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 v Chapter 32 Integumentary, Skeletal, and Muscular Systems 32.1 The Integumentary System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 32.2 The Skeletal System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 32.3 The Muscular System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382 Chapter 33 Nervous System 33.1 Structure of the Nervous System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385 33.2 Organization of the Nervous System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 33.3 The Senses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392 33.4 Effects of Drugs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 Chapter 34 Circulatory, Respiratory, and Excretory Systems 34.1 Circulatory System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 34.2 Respiratory System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 34.3 Excretory System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 Chapter 35 Digestive and Endocrine Systems 35.1 The Digestive System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 35.2 Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414 35.3 The Endocrine System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 Chapter 36 Human Reproduction and Development 36.1 Reproductive Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 36.2 Human Development Before Birth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 36.3 Birth, Growth, and Aging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 Chapter 37 Immune System 37.1 Infectious Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 37.2 The Immune System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 37.3 Noninfectious Disorders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 Co p yrig h t © G le n c o e / M c G ra w -H ill, a d iv is io n o f T h e M c G ra w -H ill C o m p a n ie s , In c . vi To the Student Reading Essentials for Biology takes the stress out of reading, learning, and understanding biology. This book covers important concepts in biology, offers ideas for how to learn the information, and helps you review what you have learned. Understanding biology concepts will help you improve your critical- thinking skills, solve problems effectively, and make useful decisions. The chapters of Reading Essentials for Biology include the following elements. • B efore You Read sparks your interest in what you will learn and relates it to your world. The Main Idea and What You’ll Learn statements help focus on the most important concepts in the section. • R ead to Learn describes important biology concepts with words and graphics. Next to the text you can find a variety of study tips and ideas for organizing and learning information: • S tudy Coach and Mark the Text offer tips for getting the main ideas out of the text. • F oldables™ Study Organizers help you divide the information into smaller, easier-to-remember concepts. • R eading Checks ask questions about key concepts. The questions are placed so you know whether you understand the material. • T hink It Over elements help you consider the material in-depth, giving you an opportunity to use your critical-thinking skills. c. • P icture This questions relate to the illustrations used with the text. n s, I The questions will help get you actively involved in illustrating the e ni pa important concepts. m o C • A pplying Math reinforces the connection between math and science. Hill w- a Gr c M e h T of n o si vi di a Hill, w- a Gr c M / e o c n e Gl © ht g pyri o C vii Dinah Zike’s FoldablesTM A Foldable is a 3-D, interactive graphic organizer. By using Foldables, you can quickly organize and retain information. Every chapter in Reading Essentials for Biology includes a Foldable that can be used to organize important ideas in the chapter. Later, the Foldable can be used as a study guide for main ideas and key points in the chapter. 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C o p yrig h t © G le n c o e / M c G ra w -H ill, a d iv is io n o f T h e M c G ra w -H ill C o m p a n ie s , In c . viii The Study of Life (cid:99)(cid:104)(cid:97)(cid:112)(cid:116)(cid:101)(cid:114) 1 Introduction to Biology section ●1 Before You Read (cid:45)(cid:33)(cid:41)(cid:46)(cid:0)(cid:0)(cid:41)(cid:68)(cid:69)(cid:65) All living thin gs share the What does it mean to be alive? On the lines below, list characteristics of life. characteristics that you think living things have. Then read What You’ll Learn the section to learn what you have in common with other ■ the defi nition of biology living things. ■ possible benefi ts from studying biology ■ characteristics of living things Read to Learn (cid:51)(cid:84)(cid:85)(cid:68)(cid:89)(cid:0)(cid:35)(cid:79)(cid:65)(cid:67)(cid:72) The Science of Life Make Flash Cards Make a fl ash card for each key term in Biology is the science of life. In biology, you will learn the this section. Write the term on origins and history of life and once-living things. You will also one side of the card. Write the c. s, In learn structures, functions, and interactions of living things. defi nition on the other side. Use e the fl ash cards to review what ni a p you have learned. m Co What do biologists do? Hill aw- Biologists make discoveries and look for explanations by Gr Mc performing laboratory and fi eld studies. Some biologists e Th study animals in their natural environment. For example, Jane of n Goodall’s observations helped scientists know how best to o si divi protect chimpanzees. a Hill, Other biologists research diseases to develop new medicines. aw- Many biologists work to develop new technology. Technology Gr /Mc is the application of scientifi c knowledge to solve human needs Summarize Information e co and to extend human capabilities. For example, Dr. Charles Make an eight-tab Foldable from n e Gl Drew developed methods to separate blood plasma for a sheet of paper. Label the tabs © ht transfusions. His research led to blood banks. with the question heads in this pyrig Some biologists study genetic engineering of plants. They section. As you read, summarize Co the answers under the tabs. try to develop plants that can grow in poor soils and resist insects and disease. Environmental biologists try to protect apnroimteaclts t ahnedm p.lants from extinction by developing ways to What dobiologists do? Reading Essentials Chapter 1 The Study of Life 1 Picture This The Characteristics of Life 1. Highlight each From many observations, biologists concluded that all characteristic of life in the living things have certain characteristics. The characteristics of table as you read about life are listed in the table below. An organism is anything that it in the section. Use the has or once had all these characteristics. descriptions in the table to review what you have learned. Characteristic of Life Description Made of one or The cell is the basic unit of life. Some organisms have one cell only. Others have more cells many cells. Displays organization The organization of a biological system begins with atoms and molecules. Each organized structure in an organism has a specifi c function. For example, an anteater’s snout is long because it functions as a container for the long tongue. Grows and develops Growth results in an increase in mass. Development results in different abilities. For example, a tadpole grows larger and develops into an adult frog. Reproduces Organisms reproduce and pass on traits to the next generation. Reproduction must occur for a species to continue to exist. Responds to stimuli Reactions to stimuli from inside and outside the body are called responses. For example, a cheetah responds to the need for food by chasing a gazelle. The gazelle responds by running away. Requires energy Energy is needed for life processes. Many organisms get energy by taking in food. Other organisms make their own food. c. Maintains homeostasis Homeostasis is the process that keeps conditions inside the bodies of all organisms n stable. For example, humans perspire when hot to lower body temperature. es, I ni a p m Adaptations evolve Adaptations are inherited changes that occur over time and help the species o C over time survive. Hill w- a Gr c What determines a cell’s structure? M e h T Cells are the basic units of structure and function in of n all living things. Some organisms, such as bacteria, are sio vi unicellular—they have just one cell. Humans and plants are a di multicellular—they have many cells. The structure of a cell is Hill, w- a related to its function. For example, each cell in a tree’s roots Gr c M has a structure that enables it to take in water from soil. / e o c n 2. Sequence the levels of How are living things organized? © Gle organization, from least Living things display organization. This means they are ht g complex to most complex. arranged in an orderly way. Each cell is made up of atoms and pyri o C molecules. Tissues are groups of specialized cells that work together. Tissues are organized into organs, which perform functions such as digestion. Organ systems work together to support an organism. 2 Chapter 1 The Study of Life Reading Essentials