Credits and Acknowledgements: Photography:

Images – Science

• 1:100,000 topo. map, © U.S. Geological Survey

(Grade 5/Unit 1)

• 1:24,000 topo. map, © U.S. Geological Survey

(Grade 5/Unit 1)

• 1:50,000 topo. map, © U.S. Geological Survey

(Grade 5/Unit 1)

• Acorn barnacle, © L.L. Rue IV/Bruce Coleman Inc.

(Grade 4/Unit 2)

• Adult mayfly, © Robert C. Simpson/Visuals Unlimited

(Grade 3/Unit 3)

• Aerial of deranged drainage, © Yann Arthus-Bertrand/Corbis

(Grade 5/Unit 1)

• Aerial of river system, © Getty Images, Inc.

(Grade 5/Unit 1)

• Aerial, estuary #1, © Joy Spurr/Bruce Coleman Inc.

(Grade 5/Unit 2)

• Aerial, estuary #2, © Getty Images, Inc.

(Grade 5/Unit 2)

• Aerial, estuary #3, © Yann Arthus-Bertrand/Corbis

(Grade 5/Unit 2)

• Anemometer, © Terry Gleason/Visuals Unlimited

(Grade 3/Unit 1)

• Anemones, © Phil Degginger/Bruce Coleman Inc.

(Grade 5/Unit 2)

• Angler fish, © IQ3d-visual & written/Bruce Coleman Inc.

(Grade 5/Unit 2)

• Ann Morgan #2, © Courtesy of  Mount Holyoke College Archives and Special Collections

Grade 3/Unit 3)

• Antarctic cod, © Galen Rowell/Corbis

(Grade 4/Unit 1)

• Arctic fox, © Ken Graham/Bruce Coleman Inc.

(Grade 3/Unit 4)

• Atoll with lagoon, © Douglas Peebles/Corbis

(Grade 3/Unit 3)

• Baby birds respond to parent, © Fotopic International/West Stock, Inc.

(Grade 4/Unit 2)

• Baby lynx in rotting stump, © Tom Brakefield/Bruce Coleman Inc.

(Grade 4/Unit 1)

• Bacteria, © SIMKO/Visuals Unlimited

(Grade 4/Unit 1)

• Bacteria (re-use), © SIMKO/Visuals Unlimited

(Grade 4/Unit 1)

• Bamboo for pulp, © Wolfgang Kaehler/Corbis

(Grade 4/Unit 1)

• Barometer project, © K12 Inc.

(Grade 3/Unit 1)

• Bat, © Getty Images, Inc.

(Grade 3/Unit 2)

• Beads of mercury, © Getty Images, Inc.

(Grade 3/Unit 5)

• Beaufort Spinner, © K12 Inc.

(Grade 3/Unit 1)

• Beautiful water shot, © Getty Images, Inc.

(Grade 5/Unit 2)

• Bee pollinating apple blossom, © Getty Images, Inc.

(Grade 4/Unit 1)

• Bee pollinating flower, © Getty Images, Inc.

(Grade 4/Unit 2)

• Bird on a sandy beach, © Windland Rice/Bruce Coleman Inc.

(Grade 5/Unit 2)

• Bison grazing, © Raymond Gehman/Corbis

(Grade 4/Unit 2)

• Blackberry bush, © Bruce Coleman Inc.

(Grade 4/Unit 2)

• Black-footed ferret, © D. Robert & Lorri Franz/Corbis

(Grade 4/Unit 2)

• Bog with moss, © Getty Images, Inc.

(Grade 5/Unit 1)

• Boiling kettle, © David Wrobel/Visuals Unlimited

(Grade 3/Unit 5)

• Boreal forest (taiga), © O. Kosterin/Bruce Coleman Inc.

(Grade 3/Unit 3)

• Boreal forest (taiga), © O. Kosterin/Bruce Coleman Inc.

(Grade 3/Unit 3)

• Boy on rock by water, © Corbis

(Grade 4/Unit 1)

• Brown trout (magnifier tool), © Ken Lucas-Photo/Visuals Unlimited

(Grade 3/Unit 2)

• Cactus in desert, © Gunter Marx/Corbis

(Grade 3/Unit 3)

• Cactus in desert, © Getty Images, Inc.

(Grade 4/Unit 1)

• Cactus plant, © Getty Images, Inc.

(Grade 4/Unit 1)

• California condor, © Kenneth W. Fink/Bruce Coleman Inc.

(Grade 4/Unit 2)

• Camouflaged octopus, © Getty Images, Inc.

(Grade 4/Unit 2)

• Child blowing up balloon, © Cheryl A. Ertelt/Visuals Unlimited

(Grade 3/Unit 1)

• Child brushing teeth, © Richard Hutchings/Corbis

(Grade 5/Unit 2)

• Child on pond bank, © Getty Images, Inc.

(Grade 3/Unit 3)

• Child planting tree, © Gary Braasch/Corbis

(Grade 5/Unit 1)

• Cirrus clouds, © Getty Images, Inc.

(Grade 3/Unit 1)

• Clay soil, © D. Yeske/Visuals Unlimited

(Grade 5/Unit 1)

• Clean stream in city, © Steve Raymer/Corbis

(Grade 5/Unit 1)

• Close-up of acacia tree, © Michael & Patricia Fogden/Corbis

(Grade 4/Unit 2)

• Clouds over lake, © Getty Images, Inc.

(Grade 3/Unit 1)

• Coal seam, © Nicholas De Vore/Bruce Coleman Inc.

(Grade 3/Unit 4)

• Coal/rocks, © Getty Images, Inc.

(Grade 4/Unit 1)

• Colored liquids pouring, © Larry Stepanowicz/Visuals Unlimited

(Grade 3/Unit 5)

• Colorful coral reef, © Getty Images, Inc.

(Grade 3/Unit 3)

• Community stream cleanup, © Getty Images, Inc.

• (Grade 5/Unit 1)

• Cool, sunny day, © Getty Images, Inc.

• (Grade 3/Unit 1)

• Coral colony, © Ronald Sefton/Bruce Coleman Inc.

(Grade 3/Unit 3)

• Coral polyp, open, © Colla-V&W/Bruce Coleman Inc.

(Grade 3/Unit 3)

• Coral reef structure-reuse, © Getty Images, Inc.

(Grade 3/Unit 4)

• Cornell-Gilbert mastadon jaw, © Courtesy Cornell News Service
  (Grade 3/Unit 4)

• Crabs on a seashore, © Norman Owen Tomalin/Bruce Coleman Inc.
  (Grade 3/Unit 4)

• Cricket, © Getty Images, Inc.
  (Grade 3/Unit 5)

• Crop-dusting, © Robert P. Carr/Bruce Coleman Inc.
  (Grade 5/Unit 1)

• Cumulonimbus cloud, © M. Dillon/Corbis
  (Grade 3/Unit 1)

• Cumulus clouds, © Getty Images, Inc.
  (Grade 3/Unit 1)

• Dandelions, © Gary W. Carter/Visuals Unlimited
  (Grade 4/Unit 1,4)

• Darwin's finch, C. Parvulus, © John Guistana/Bruce Coleman Inc.
  (Grade 4/Unit 2)

• Darwin's finch, G. magnarostris, © Tui DeRoy/Bruce Coleman Inc.
  (Grade 4/Unit 2)

• Deciduous tree, © Getty Images, Inc.
  (Grade 4/Unit 4)

• Decomposition station, © K12 Inc.
  (Grade 4/Unit 1)

• Deep zone sea star, © Richard Herrmann/Visuals Unlimited
  (Grade 5/Unit 2)

• Deer, © Brenda Davison/Corbis
  (Grade 4/Unit 1)

• Deer eating dandelions, © Gustav W. Verderber/Visuals Unlimited
  (Grade 4/Unit 1)

• Deer eating leaves, © Brenda Davison/Corbis
  (Grade 4/Unit 1)

• Desert, © Getty Images, Inc.
  (Grade 3/Unit 3)

• Dew on spider web, © Getty Images, Inc.
  (Grade 3/Unit 1)

• Dino skeleton and scientists, © Reuters New Media Inc./Corbis
  (Grade 3/Unit 4)

• Doorway, © Jeff Greenberg/Visuals Unlimited
  (Grade 3/Unit 5)

• Doppler radar, © Gene Rhoden/Visuals Unlimited
  (Grade3/Unit 1)

• Duck with ducklings, © Getty Images, Inc.
  (Grade 4/Unit 2)

• Duckling, © Lindsey P. Martin/Corbis
  (Grade 4/Unit 1)

• Dungeness crab, © Ted Streshinsky/Corbis
  (Grade 4/Unit 2)

• Earth with water colored, © NASA
  (Grade 5/Unit 1)

• Earthworm/soil, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Earthworms, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Echidna, © Erwin & Peggy Bauer/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Electromagnet, © Leslie Garland Picture Library/Alamy

(Grade 4/Unit 7)

• Elephant profile, © Bruce Aiken/Bruce Coleman Inc.
  (Grade 3/Unit 4)

• Evaporated lemonade, © K12 Inc.
  (Grade 4/Unit 3)

• Evenly mixed pile of laundry, © K12 Inc.
  (Grade 4/Unit 3)

• Everglades with alligators, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Expansive view of ocean, © Robert Holmes/Corbis
  (Grade 3/Unit 3)

• Exposed dinosaur fossils, © James L. Amos/Corbis
  (Grade 3/Unit 4)

• Family picnic, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Feather, © Jerome Wexler/Visuals Unlimited
  (Grade 3/Unit 5)

• Field and factory, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Fiji crested iguana, © John Giustina/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Fiji crested iguana, © John Giustina/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Filtering sand from water, © K12 Inc.
  (Grade 4/Unit 3)

• Fishing trawler, © Jeffrey L. Rotman/Corbis
  (Grade 4/Unit 2)

• Flowers in clumped distribution, © Getty Images, Inc.
  (Grade 4/Unit 2)

• Fossil fish school, © James L. Amos/Corbis
  (Grade 3/Unit 4)

• Fossil shrimp, © Kevin Schafer/Corbis
  (Grade 3/Unit 4)

• Fossil starfish, © Kevin Schafer/Corbis
  (Grade 3/Unit 4)

• Fox chasing rabbit in snow, © Tom Brakefield/Corbis
  (Grade 4/Unit 1)

• Fragile reef, © Lawson Wood/Corbis
  (Grade 3/Unit 3)

• Fringe reef, © Paul A. Souders/Corbis
  (Grade 3/Unit 3)

• Frog, © Getty Images, Inc.
  (Grade 3/Unit 2;Grade 4/Unit 1)

• Frog eggs, © G.L. Twiest/Visuals Unlimited
  (Grade 3/Unit 2)

• Gannet colony, © Getty Images, Inc.
  (Grade 4/Unit 2)

• Garden with veggies and weeds, © Lynda Richardson/Corbis
  (Grade 4/Unit 2)

• Gases rising from volcano, © Marty Snyderman/Visuals Unlimited
  (Grade 3/Unit 5)

• Geese on a pond, © Iain Davidson/Alamy Images
  (Grade 3/Unit 3)

• Giraffe eating leaves, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Glacial landscape, © John Corbett/Corbis
  (Grade 3/Unit 4)

• Glacier-sculpted valley, © David Muench/Corbis
  (Grade 3/Unit 4)

• Glass of soda, © Corbis
  (Grade 4/Unit 3)

• Golden Gate Bridge, © Hal Beral/Visuals Unlimited
  (Grade 3/Unit 5)

• Graduated cylinders with liquid, © Larry Stepanowicz/Visuals Unlimited
  (Grade 3/Unit 5)

• Grass, closeup, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Grasshopper, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Grasslands, © John Shaw/Bruce Coleman Inc.
  (Grade 3/Unit 3)

• Grasslands, © Michele Burgess/Corbis
  (Grade 3/Unit 3)

• Great Barrier Reef, © Robert Holmes/Corbis
  (Grade 3/Unit 3)

• Great white shark, © Ron & Val Taylor/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Gypsum rock, © Ken Lucas/Visuals Unlimited
  (Grade 3/Unit 4)

• Hawk eating snake, © Joe McDonald/Corbis
  (Grade 4/Unit 1)

• Hermit crab, © ViRGili-V&W/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Hikers referring to topo. map, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Hostas, © Eric Crichton/Corbis
  (Grade 4/Unit 1)

• Housefly, © Clive Druett; Papilio/Corbis
  (Grade 4/Unit 1)

• Hunting dog on point, © Dale C. Spartas/Corbis
  (Grade 4/Unit 2)

• Hygroclimograph, © John D. Cunningham/Visuals Unlimited
  (Grade 3/Unit 1)

• Hygrometer project, © K12 Inc.
  (Grade 3/Unit 1)

• Ice core drilling, © Morton Beebe/Corbis
  (Grade 3/Unit 4)

• Ice core with scale, © Roger Ressmeyer/Corbis
  (Grade 3/Unit 4)

• Igneous/Meta rock (basalt), © Albert J. Copley/Visuals Unlimited
  (Grade 5/Unit 1)

• Insect eating leaf, © Peter Johnson/Corbis
  (Grade 4/Unit 2)

• Insects eating dead leaves, © Eric & David Hosking/Corbis
  (Grade 4/Unit 1)

• Inside bee hive with queen, © Carlos Sanz-V&W/Bruce Coleman Inc.
  (Grade 4/Unit 2)

• Irrigation, © David Frazier/Corbis
  (Grade 5/Unit 2)

• Japanese cranes courting, © Steve Kaufman/Corbis
  (Grade 4/Unit 2)

• Jellyfish in ocean, © NOAA
  (Grade 4/Unit 1)

• Kangaroo, © Al Franklin/Corbis
  (Grade 3/Unit 2)

• Killer whale, © Amos Nachoum/Corbis
  (Grade 4/Unit 2)

• Kingfisher eating fish, © Jeremy Woodhouse/Corbis
  (Grade 4/Unit 1)

• Kirtland warbler, © Ron Austing; Frank Lane Picture Agency/Corbis
  (Grade 4/Unit 2)

• Lake landscape, © Getty Images, Inc.
  (Grade 3/Unit 3)

• Lake with minimal surroundings, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Lamprey, © Hans Reinhard/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Large herd of reindeer, © Getty Images, Inc.
  (Grade 4/Unit 2)

• Large spectacular wetland, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Leaves, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Leech, © Anthony Bannister/Corbis
  (Grade 4/Unit 2)

• Lesson Opener: barnacle, © George D. Lepp/Corbis
  (Grade 4/Unit 2)

• Lesson Opener: bison, © Raymond Gehman/Corbis
  (Grade 4/Unit 2)

• Lesson Opener: city stream, © Steve Raymer/Corbis
  (Grade 5/Unit 1)

• Lesson Opener: coral reef, © Getty Images, Inc.
  (Grade 3/Unit 3)

• Lesson Opener: crashing wave, © Getty Images, Inc.
  (Grade 5/Unit 2)

• Lesson Opener: cylinders, © Larry Stepanowicz/Visuals Unlimited
  (Grade 3/Unit 5)

• Lesson Opener: deciduous tree, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Lesson Opener: estuary, © Yann Arthus-Bertrand/Corbis
  (Grade 5/Unit 2)

• Lesson Opener: forest, © Mark Taylor/Bruce Coleman Inc.
  (Grade 3/Unit 4)

• Lesson Opener: gannets, © Getty Images, Inc.
  (Grade 4/Unit 2)

• Lesson Opener: high tide, © Tim Hauf Photography/Visuals Unlimited
  (Grade 5/Unit 2)

• Lesson Opener: hikers with map, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Lesson Opener: hot spring, © Joe McDonald/Visuals Unlimited
  (Grade 3/Unit 5)

• Lesson Opener: leech, © Anthony Bannister/Corbis
  (Grade 4/Unit 2)

• Lesson Opener: melting ice, © Getty Images, Inc.
  (Grade 3/Unit 5)

• Lesson Opener: mountain goats, © W. Wayne Lockwood, M.D./Corbis
  (Grade 4/Unit 2)

• Lesson Opener: musk oxen, © Brian A. Vikander/Corbis
  (Grade 3/Unit 4)

• Lesson Opener: panda, © Warren Jacobi/Corbis
  (Grade 4/Unit 1)

• Lesson Opener: river system, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Lesson Opener: rusty nail, © Getty Images, Inc
  (Grade 4/Unit 3)

• Lesson Opener: sea ice, © Getty Images, Inc.
  (Grade 5/Unit 2)

• Lesson Opener: sea otter, © Jeff Foott/Bruce Coleman Inc.
  (Grade 4/Unit 2)

• Lesson Opener: sea urchins, © Ron Sefton/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Lesson Opener: steep hillside, © Yann Arthus-Bertrand/Corbis
  (Grade 5/Unit 1)

• Lesson Opener: tick, © Joe McDonald/Corbis
  (Grade 4/Unit 2)

• Lesson Opener: tree rings, © Doug Wilson/Corbis
  (Grade 4/Unit 4)

• Lesson Opener: trilobytes, © Kevin Schafer/Corbis
  (Grade 3/Unit 4)

• Lesson Opener: wetland, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Limestone fossils, © Joe McDonald/Bruce Coleman Inc.
  (Grade 3/Unit 4)

• Lion with cub, © Joe McDonald/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Liter bottle, © K12 Inc.
  (Grade 3/Unit 5)

• Lush coniferous forest, © Mark Taylor/Bruce Coleman Inc.
  (Grade 3/Unit 4)

• Mammal running (cheetah), © Corbis
  (Grade 3/Unit 2)

• Mammoth hunt illustration, © Gianni Dagli Orti/Corbis
  (Grade 3/Unit 4)

• Mammoth illustration, © Jonathan Blair/Corbis
  (Grade 3/Unit 4)

• Mangrove seed germinating, © William Webber/Visuals Unlimited
  (Grade 5/Unit 2)

• Mangrove tree, © Ivan Polunin/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Marine ecosystem (coral reef), © Getty Images, Inc.
  (Grade 3/Unit 3)

• Marlin, © Tony Arruza/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Marsh with reeds, sawgrass, © Wendell Metzen/Bruce Coleman Inc.
  (Grade 5/Unit 1)

• Mayfly nymph, © Science Pictures Limited/Corbis
  (Grade 3/Unit 3)

• Melting ice and water drops, © Getty Images, Inc.
  (Grade 3/Unit 5)

• Melting ice cream, © Getty Images, Inc.
  (Grade 3/Unit 5)

• Metered man, © Bettmann/Corbis
  (Grade 3/Unit 5)

• Microscopic bacteria, © SIMKO/Visuals Unlimited
  (Grade 4/Unit 1)

• Mistletoe on a tree, © Frank Blackburn/Corbis
  (Grade 4/Unit 2)

• Mold on lemon, © Danilo Donadoni/Bruce Coleman Inc.
  (Grade 4/Unit 1)

• Mom with children, © Getty Images, Inc.
  (Grade 3/Unit 2)

• Mother predator teaching cubs, © Joe McDonald/Corbis
  (Grade 4/Unit 2)

• Mountain goats fighting, © W. Wayne Lockwood, M.D./Corbis
  (Grade 4/Unit 2)

• Mouse, © E.R. Degginger/Bruce Coleman Inc.
  (Grade 4/Unit 1)

• Mushrooms on stump, © Link/Visuals Unlimited
  (Grade 4/Unit 1)

• Musk oxen herd on tundra, © Brian A. Vikander/Corbis
  (Grade 3/Unit 4)

• Musk oxen in defense circle, © Erwin & Peggy Bauer/Bruce Coleman Inc.
  (Grade 4/Unit 2)

• Nile region from Space, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Nile River scene, © Mark Karrass/Corbis
  (Grade 5/Unit 1)

• Nixon, © Hulton-Archive/Getty Images, Inc.
  (Grade 5/Unit 1)

• Ocean at high tide, © Tim Hauf Photography/Visuals Unlimited
  (Grade 5/Unit 2)

• Ocean at low tide, © Tim Hauf Photography/Visuals Unlimited
  (Grade 4/Unit 2)

• Orange tree, © PictureNet/Corbis
  (Grade 4/Unit 1)

• Panda eating bamboo, © Warren Jacobi/Corbis
  (Grade 4/Unit 1)

• Penguins, © Image Life/Corbis
  (Grade 3/Unit 2)

• People walking in the rain, © Steve Estvanik/Corbis
  (Grade 3/Unit 1)

• Periwinkle, © John D. Cunningham/Visuals Unlimited
  (Grade 5/Unit 2)

• Petrified forest in winter, © David Muench/Corbis
  (Grade 3/Unit 4)

• Pile of laundry, © K12 Inc.
  (Grade 4/Unit 3)

• Poison ivy, © Getty Images, Inc.
  (Grade 4/Unit 2)

• Polar bear, © Tom Brakefield/Bruce Coleman Inc.
  (Grade 3/Units 2,3)

• Political map, © John Henry Williams/Bruce Coleman Inc.
  (Grade 5/Unit 1)

• Pond, © Getty Images, Inc.
  (Grade 3/Unit 2)

• Pond, © Getty Images, Inc.
  (Grade 3/Unit 3)

• Pond, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Pond with ducks, © Steve Alden/West Stock, Inc.
  (Grade 5/Unit 1)

• Pond, wide shot, © John Shaw/Bruce Coleman Inc.
  (Grade 3/Unit 3)

• Porcelain vase, © Getty Images, Inc.
  (Grade 3/Unit 5)

• Prairie dog, © Getty Images, Inc.
  (Grade 3/Unit 3)

• Prairie dog on alert, © Getty Images, Inc.
  (Grade 4/Unit 2)

• Prairie rattlesnake, © W. Perry Conway/Corbis
  (Grade 4/Unit 1)

• Precambrian fossils, © Phil Degginger/Bruce Coleman Inc.
  (Grade 3/Unit 4)

• Project photo #1, © K12 Inc.
  (Grade 5/Unit 2)

• Project photo #2, © K12 Inc.
  (Grade 5/Unit 2)

• Project photo #3, © K12 Inc.
  (Grade 5/Unit 2)

• Project photo #4, © K12 Inc.
  (Grade 5/Unit 2)

• Provence cricket, © Dennis Johnson; Papilio/Corbis
  (Grade 4/Unit 1)

• Python hatchlings, © J. McDonald/Visuals Unlimited
  (Grade 3/Unit 2)

• Quart container, © K12 Inc.
  (Grade 3/Unit 5)

• Red fox eating mouse, © Tom Brakefield/Corbis
  (Grade 4/Unit 1)

• Red-eared turtle, © Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Red-tailed hawk, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Redwood trees, © Jim Zuckerman/Corbis
  (Grade 5/Unit 2)

• Redwood/ferns, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Reptile sunning (lizard), © Getty Images, Inc.
  (Grade 3/Unit 2)

• Reservoir and dam, © Mark N. Boulton/Bruce Coleman Inc.
  (Grade 5/Unit 1)

• Reservoir with dam, © Mark N. Boulton/Bruce Coleman Inc.
  (Grade 5/Unit 1)

• Reuse pond, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Reuse reservoir and dam, © Mark N. Boulton/Bruce Coleman Inc.
  (Grade 5/Unit 1)

• Riptide warning sign, © Arthur Gurmankin & Mary Morina/Visuals Unlimited
  (Grade 5/Unit 2)

• Road map, © Washington State Government
  (Grade 5/Unit 1)

• Robin at nest with eggs, © Tom Silver/Corbis
  (Grade 3/Unit 2)

• Robin chicks, © Jeff Foott/Bruce Coleman Inc.
  (Grade 4/Unit 1)

• Robin with catepillars, © Rolf Kopfle/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Rolling waves in open ocean, © Getty Images, Inc.
  (Grade 5/Unit 2)

• Salt marsh, © Getty Images, Inc.
  (Grade 5/Unit 2)

• Sample study plot, © Galen Rowell/Corbis
  (Grade 4/Unit 2)

• Sandstone block, © Hubert Stadler/Corbis
  (Grade 3/Unit 4)

• Sandy soil, © Larry Stepanowicz/Visuals Unlimited
  (Grade 5/Unit 1)

• Sea dragon, © Kike Calvo-V&W/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Sea ice, © Getty Images, Inc.
  (Grade 5/Unit 2)

• Sea otter eating sea urchin, © Jeff Foott/Bruce Coleman Inc.
  (Grade 4/Unit 2)

• Sea star, © Villoch-V&W/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Sea urchin (crop), © Ron Sefton/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Sedimentary rock (sandstone), © A.J. Copley/Visuals Unlimited
  (Grade 5/Unit 1)

• Sedimentary rock formation, © Wolfgang Kaehler/Corbis
  (Grade 3/Unit 4)

• Seeing-eye dog at work, © Reuters NewMedia Inc./Corbis
  (Grade 4/Unit 2)

• Skate, © John Giustina/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Skunk, © W. Perry Conway/Corbis
  (Grade 4/Unit 2)

• Sky with cumulous clouds, © Getty Images, Inc.
  (Grade 3/Unit 5)

• Smoking factory, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Snake eating frog eggs, © Michael & Patricia Fogden/Corbis
  (Grade 3/Unit 3)

• Snake with fangs showing, © Daniel J. Lyons/Bruce Coleman Inc.
  (Grade 4/Unit 2)

• Sorting laundry, © K12 Inc.
  (Grade 4/Unit 3)

• Sprinkler , © Getty Images, Inc.
  (Grade 5/Unit 2)

• Squirrel (full body mammal), © Curt & Cary Given/West Stock, Inc.
  (Grade 3/Unit 2)

• Star barnacle, © Norman Owen Tomalin/Bruce Coleman Inc.
  (Grade 4/Unit 2)

• Starfish , © Bob & Clara Calhoun/Bruce Coleman Inc.
  (Grade 3/Unit 3)

• Starfish opening mussel, © Richard Mariscal/Bruce Coleman Inc.
  (Grade 3/Unit 3)

• Steep hillside, parallel drainage, © Yann Arthus-Bertrand/Corbis
  (Grade 5/Unit 1)

• Steep mountain valley, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Stinging nettle, © Ken Wilson/Corbis
  (Grade 4/Unit 2)

• Stingray, © Colla-V&W/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Stormpipe drainage, © Ed Boettcher/Corbis
  (Grade 5/Unit 1)

• Stratus clouds, © Charles O'Rear/Corbis
  (Grade 3/Unit 1)

• Sun, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Sun on black background, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Swamp with bald cypress, © Larry Mulvehill/Corbis
  (Grade 5/Unit 1)

• Swamp with birds, © Peter Davey/Bruce Coleman Inc.
  (Grade 5/Unit 1)

• Swimming pool, © Jeff Greenberg/Visuals Unlimited
  (Grade 3/Unit 5)

• Tadpole, © Jane Burton/Bruce Coleman Inc.
  (Grade 3/Unit 2)

• Tapeworm, © Wally Eberhart/Visuals Unlimited
  (Grade 4/Unit 2)

• Temperate deciduous forest, © Getty Images, Inc.
  (Grade 3/Unit 3)

• Termite mound, © Chris Hellier/Corbis
  (Grade 4/Unit 2)

• Thanksgiving dinner, © Corbis
  (Grade 4/Unit 1)

• Thermometer, © David Newman/Visuals Unlimited
  (Grade 3/Unit 1)

• Three Gorges before damming, © Keren Su/Corbis
  (Grade 5/Unit 1)

• Three Gorges dam construction, © Liu Ligun/Corbis
  (Grade 5/Unit 1)

• Tick, © Joe McDonald/Corbis
  (Grade 4/Unit 2)

• Tidal electric plant, © Danilo G. Donadoni/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Tide pool with sea stars, © Ron Sefton/Bruce Coleman Inc.
  (Grade 5/Unit 2)

• Topo. map with symbols, © U.S. Geological Service
  (Grade 5/Unit 1)

• Topographic map, © U.S. Geological Service
  (Grade 5/Unit 1)

• Tortoise, © Getty Images, Inc.
  (Grade 3/Unit 2)

• Tractor plowing field/seagulls, © Gunter Marx/Corbis
  (Grade 4/Unit 2)

• Tree rings, © Doug Wilson/Corbis
  (Grade 3/Unit 4)

• Trees in random distribution, © Getty Images, Inc.
  (Grade 4/Unit 2)

• Trilobyte cluster, © Kevin Schafer/Corbis
  (Grade 3/Unit 4)

• Tropical fish, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Tropical rainforest, © Mark Taylor-Warren Photographic/Bruce Coleman Inc.
  (Grade 3/Unit 3)

• Tsunami damage, © NOAA
  (Grade 5/Unit 2)

• Tundra, © John Swedbe/Bruce Coleman Inc.
  (Grade 3/Unit 3)

• Turkey vulture eating opposum, © Arthur Morris/Visuals Unlimited
  (Grade 4/Unit 1)

• Unevenly mixed laundry, © K12 Inc.
  (Grade 4/Unit 3)

• Unit Opener: colored liquids, © Larry Stepanowicz/Visuals Unlimited
  (Grade 3/Unit 5)

• Unit Opener: dino fossils, © James L. Amos/Corbis
  (Grade 3/Unit 4)

• Unit Opener: insects eating, © Peter Johnson/Corbis
  (Grade 4/Unit 2)

• ,Unit Opener: tidal electric plant, © Danilo G. Donadoni/Bruce Coleman Inc.

• Unit Opener: waves, © Getty Images, Inc.
  (Grade 5/Unit 2)

• Very flat land, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Warm thunderstorm, © Mark Karrass/Corbis
  (Grade 3/Unit 1)

• Water pollution, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Water pouring from faucet, © Gregg Otto/Visuals Unlimited
  (Grade 3/Unit 5)

• Water recreation scene, © Getty Images, Inc.
  (Grade 5/Unit 1)

• Water striders, © Gary Zahm/Bruce Coleman Inc.
  (Grade 3/Unit 3)

• Watering hole, © Michael Fogden/Bruce Coleman Inc.
  (Grade 4/Unit 1)

• Waves crashing on rocks, © Getty Images, Inc.
  (Grade 5/Unit 2)

• Waves eroding seashore house, © James R. Mccullagh/Visuals Unlimited
  (Grade 5/Unit 2)

• Waves gently lapping, © Getty Images, Inc.
  (Grade 5/Unit 2)

• Waxy coating experiment, © K12 Inc.
  (Grade 3/Unit 3)

• Weather balloon, © NOAA
  (Grade 3/Unit 1)

• Weather radar - Doppler, © NOAA
  (Grade 3/Unit 1)

• Weather satellite, © Science VU/NASA/NOAA
  (Grade 3/Unit 1)

• Weather vane, © Terry Gleason/Visuals Unlimited
  (Grade 3/Unit 1)

• Wetland being destroyed, © Marc Epstein/Visuals Unlimited
  (Grade 5/Unit 1)

• Wetland being restored, © Marc Epstein/Visuals Unlimited
  (Grade 5/Unit 1)

• Whale jumping, © Getty Images, Inc.
  (Grade 4/Unit 1)

• Whale with barnacles, © George D. Lepp/Corbis
  (Grade 4/Unit 2)

• White wolf in snow, © Getty Images, Inc.
  (Grade 3/Unit 3)

• Wolf eating deer, © Joe McDonald/Visuals Unlimited
  (Grade 4/Unit 1)

• Wolf eating deer, © Joe McDonald/Visuals Unlimited
  (Grade 4/Unit 1)

• Wolf eating deer, © D. Robert & Lorri Franz/Corbis
  (Grade 4/Unit 2)

• Wooden toy block, © Getty Images, Inc.
  (Grade 3/Unit 5)

• Yellowstone hot spring in winter, © Joe McDonald/Visuals Unlimited
  (Grade 3/Unit 5)

• Young rabbit, © Erwin & Peggy Bauer/Bruce Coleman Inc.
  (Grade 4/Unit 1)