Vaccination, 1017, 1020

Vaccine, 588–589, 593

Vacuoles, 198

Valence electrons, 36

Valves, 950

Van der Waals forces, 38

Van Leeuwenhoek, Anton, 190

Variation, 419–420, 457–458, 460, 462–463, 482–486. See also Natural selection

Vascular tissue of plants, 641, 643–644, 665–666, 680

• vascular bundles, 675

• vascular cambium, 677–679

• vascular cylinder, 670, 672–673

Vas deferens, 989

Vectors, 1013

Vegetables, 704

Vegetative reproduction, 702–703

Veins, human, 952

Veins, leaf, 680

Venter, Craig, 349

Ventricle, 792–793, 949–951

Venus' flytrap, 712

Vertebrae, 731

Vertebrates, 731, 757, 789–790. See also Chordates; Invertebrates

• brains of, 811

• cephalization in, 740

• circulatory systems of, 734, 792–793

• homologous structures in, 469

• limb formation in, 743

• muscular systems of, 816–818

• nervous systems of, 809

• sense organs, 813

• skeletons of, 733, 815–818

Vesicles, 198

Vessel elements, 666

Vestigial structures, 469

Villi, 880

Viral sexually transmitted diseases (STDs), 994

Virchow, Rudolf, 191

Viruses, 574–579

• bacterial, 340–341

• and cells, 579

• discovery of, 574

• diseases caused by, 588–589, 994, 1010–1011

• and medication, 1021

• structure and composition of, 575

• viral infections, 576–578

Visible spectrum, 230

Vision, 912–913

Vitamin D production, 935

Vitamin K deficiency, 881

Vitamins, 871

Vitreous humor, 912

Viviparous species, 822

Vocal cords, 964

Wallace, Alfred Russel, 459, 460

Water

• adhesion, 686

• atomic composition of, 36

• capillary action, 686

• cohesion, 686

• cycle, 81

• dehydration, 189, 869

• and human body, 869, 986

• intoxication, 221

• molecules of, 37, 40–41

• osmosis, 210–211, 218, 672, 795

• and photosynthesis, 240

• and plants, 635, 641, 672–673, 685–687

• properties of, 40–43

• quality and pollution, 156, 160–162

• and seed germination, 706

• solutions and suspensions, 42

• and spread of disease, 1012–1013

Water mold, 608–609, 613

Watershed, 162

Water-soluble vitamins, 871

Water transport in plants, 666, 685–686

Watson, James, 349–350, 362

Weather, 96

West Nile virus, 588, 1013

Wetlands, 119, 156

Wheat rust, 622

White blood cells, 955

White matter, 902

White muscle, 933

Wildlife photographer, 105

Wilmut, Ian, 427

Wilting, 683

Wind

• and heat transport, 98

• pollination, 700

Wood, 678–679

Woodland, 113

Woody plants, 653

Worms

• earthworms, 755, 792

• flatworms, 755, 783, 794, 796, 810, 812

• marine, 755

• parasitic, 820, 1011

• roundworms, 755, 783, 810

• tapeworms, 104

X chromosomes, 393–396, 401

X-ray diffraction, 346

Xylem, 643, 666

Y chromosomes, 393–395, 434

Yeasts, 192, 214, 263, 278, 424, 585, 619, 623

Yolk sac, 825

Zoo curator, 736

Zoonosis, 1013

Zooplankton, 76, 117

Zygote, 325, 637, 739, 995–996