[Free Registration/Login may be required to access all resource tools.] Do you ever wonder why some birds are big like ostriches and some birds are small like robins? Or why a lion has a mane while a leopard has spots? In the 19th...

[Free Registration/Login may be required to access all resource tools.] Even though two different species may not look similar, they may have similar internal structures that suggest they have a common ancestor. That means both evolved...

[Free Registration/Login may be required to access all resource tools.] Imagine you open a gallon of milk, and you suddenly smell a foul odor. Your sense of smell has informed you that the milk has spoiled. So you pour the spoiled milk...

[Free Registration/Login may be required to access all resource tools.] An organism goes extinct when all of the members of a species die out and no more members remain. Extinctions are part of natural selection. Species often go extinct...

[Free Registration/Login may be required to access all resource tools.] Many animal behaviors are ways that animals act naturally. They are not learned behaviors. Cats are natural-born hunters. They don't need to learn how to hunt....

[Free Registration/Login may be required to access all resource tools.] Many animal behaviors change in a regular way. They go through cycles. Some cycles of behavior repeat each year. Other cycles of behavior repeat every day. Learn...

[Free Registration/Login may be required to access all resource tools.] When an herbivore eats a plant, the energy in the plant tissues is used by the herbivore. Every time energy is transferred from one organism to another, there is a...

[Free Registration/Login may be required to access all resource tools.] Ecology is the study of how living organisms interact with each other and with their environment. Organisms interact with each other through various mechanisms, one...

[Free Registration/Login may be required to access all resource tools.] Energy must constantly flow through an ecosystem for the system to remain stable. What exactly does this mean? Essentially, it means that organisms must eat other...

[Free Registration/Login may be required to access all resource tools.] It might sound good to you to have a condition where you feel no pain. But actually this type of condition would be very dangerous. What would happen if you strained...

[Free Registration/Login may be required to access all resource tools.] Ecosystems are "dynamic." This means that ecosystems change over time. Both natural forces and human actions cause ecosystems to change. Learn more about succession...

[Free Registration/Login may be required to access all resource tools.] The theory of evolution by natural selection means that the inherited traits of a population change over time. Inherited traits are features that are passed from one...

[Free Registration/Login may be required to access all resource tools.] Fossils are the preserved remains of animals, plants, and other organisms from the distant past. By studying fossils, evidence for evolution is revealed....

[Free Registration/Login may be required to access all resource tools.] This is a science text for Grade 3. It has sections on physical science, earth science, and life science. Each of those is broken down into 3 to 5 topics.

[Free Registration/Login may be required to access all resource tools.] This is a science text for Grade 4. It has sections on physical science, earth science, and life science. Each of those is broken down into eleven or twelve topics.

[Free Registration/Login may be required to access all resource tools.] This is a science text for Grade 5. It has sections on physical science, earth science, and life science. The first two are broken down into eleven topics each, and...

This is a complete, full-year Algebra 1 course with interactivity included in every lesson. Some lessons include videos, and all include interactives and inline questions that offer instant, per-answer feedback. Every lesson also has...

A complete CCSS Grade 8 Mathematics course that includes interactives in every lesson, plus videos, hands-on activities, and questions with immediate feedback. Every lesson also has specifically chosen 'Related Modalities' that teach the...

A complete CCSS Grade 7 Mathematics course that includes interactives in every lesson, plus videos, hands-on activities, and questions with immediate feedback. Every lesson also has specifically chosen 'Related Modalities' that teach the...

[Free Registration/Login may be required to access all resource tools.] Students investigate diffraction of light and the interference patterns that are produced through constructive and destructive interference of the waves. Students...

[Free Registration/Login may be required to access all resource tools.] In this module, students will explore the concept of gravity, and be able to use it to perform calculations using constant acceleration.

[Free Registration/Login may be required to access all resource tools.] Students will study how energy flows through an ecosystem and learn about photoautotrophs and chemoautotrophs, the role of decomposers, and of consumers.

[Free Registration/Login may be required to access all resource tools.] Students solve problems dealing with simple harmonic motion using a mass on a string.

[Free Registration/Login may be required to access all resource tools.] Students explain the ray model of light, describe the law of reflection, and investigate how images are formed from flat mirrors.