Tiktaalik: A Fish Out of Water

In this lesson designed to enhance literacy skills, students learn that transitional fossils provide scientists with evidence to establish how major animal groups are related to one another.

Acid Lake

Add acidity to a healthy lake and see what happens to the plants and animals in this interactive activity adapted from EcoKids.

Adaptation

Students examine some of the behaviors and physical characteristics that enable organisms to live successfully in their environment.

Adaptive Radiation: Darwin's Finches

Finches on the Galapagos Islands have evolved to exploit almost every possible niche. This diagram shows the range of food sources available on the island and the different beak shapes adapted to exploit each of them.

The Advantage of Sex

Why did sex evolve? The likely answers, in this essay for the Evolution Web site by science journalist Matt Ridley, may surprise you.

Agricultural Runoff and the Gulf of Mexico Dead Zone

This video segment adapted from Big River: A King Corn Companion shows how agricultural chemicals from the Midwest that travel downstream in water runoff create a vast marine "dead zone" in the Gulf of Mexico.

Air Quality Index

In this interactive activity adapted from "Air Quality Index: A Guide to Air Quality and Your Health" by the U.S. EPA, learn about common pollutants in the air we breathe, their health effects, and how their levels are reported.

Alaska Native Ways of Knowing

In this media-rich lesson, students prepare classroom science fair projects that demonstrate the application of traditional knowledge to a scientific topic.

All in the Family

In this Evolution Web feature, test your skills at judging who's who on the tree of life while you learn about the tools and methods of cladistics.

Allopatric Speciation

These images from the Smithsonian Institution depict Nancy Knowlton's work with snapping shrimp in Panama. Knowlton found that the closing of the isthmus -- dividing the Pacific Ocean from the Caribbean -- resulted in new species of shrimp.

All Systems Are Go

Test your knowledge of the digestive, respiratory, and other human body systems in this interactive game from Kinetic City. Race the clock to put Arnold's organs back into his body one system at a time.

Alzheimer's Disease

This video segment from the Secret of Life School Video: "Genetic Medicine: Tinkering with Our Genes" explores the potential for gene therapy to cure diseases like Alzheimer's.

Accessibility features: Caption

Amazing Heart Facts

This feature from the NOVA "Cut to the Heart" Web site highlights facts about the heart -- including its size and placement -- and will help you to understand the importance of this wondrous organ in our bodies.

Accessibility features: Alt Text

Amazon Rainforest

This video segment from the Race to Save the Planet teaching module "Saving the Diversity of Life" describes the ecological value of tropical rainforests and explores some of the causes of their destruction.

Accessibility features: Caption, Transcript

American Chestnut Tree

This annotated slideshow adapted from KET's Electronic Field Trip to the Forest illustrates how blight decimated the American chestnut tree and the methods scientists use to identify and pollinate the remaining trees to create blight-resistant trees.

Analyzing an Ecosystem

In this interactive activity adapted from the University of Alberta, identify the living and nonliving things in an ecosystem. Then look further at the living things to identify the producers, the consumers, and examples of mimicry.

Ancient Farmers of the Amazon

This video segment from Evolution: "Evolutionary Arms Race" tells the story of the leafcutter ant and the fungus it farms -- an example of mutually beneficial symbiosis.

Accessibility features: Caption

Anglerfish

This video segment from NOVA: "Animal Imposters" shows the lightning-fast strike of the anglerfish.

Accessibility features: Audio Description, Caption

Animal and Plant Cell

Think you can tell a yam from a yak? Examine these still images of typical plant and animal cells from Biology by Kenneth R. Miller and Joseph Levine. What similarities and differences can you find?

Animal Babies

This interactive slide show illustrates the variety of animal babies that exist on earth -- some completely independent and others deeply reliant on parental care.