[Free Registration/Login may be required to access all resource tools.] Reptiles play an important role in the life of humans. In addition to playing an important role in many food chains, which keep the populations of small animals...

[Free Registration/Login may be required to access all resource tools.] Lizards and snakes belong to the largest order of reptiles, Squamata. Lizards are a large group of reptiles, with nearly 5,000 species, living on every continent...

[Free Registration/Login may be required to access all resource tools.] Chimpanzees and humans turn out to be very similar - if you look at their DNA. When scientists determined the entire genetic code of both humans and chimpanzees,...

[Free Registration/Login may be required to access all resource tools.] We breathe because we need oxygen. Breathing also releases carbon dioxide from our bodies into the air. The respiratory system is the body system that brings air...

[Free Registration/Login may be required to access all resource tools.] The structure and function of the eye and how we see.

[Free Registration/Login may be required to access all resource tools.] How heat is transferred in the atmosphere.

[Free Registration/Login may be required to access all resource tools.] Identify the shape and size of the Milky Way and where our solar system is located in the Milky Way.

[Free Registration/Login may be required to access all resource tools.] The signs scientists might see prior to an earthquake occurring.

[Free Registration/Login may be required to access all resource tools.] From a human point of view, a habitat is where you live, go to school, and go to have fun. Your habitat can be altered, and you can easily adapt. Most people live in...

[Free Registration/Login may be required to access all resource tools.] With so many species of bacteria, some are bound to be harmful. Harmful bacteria can make you sick. They can also ruin food and be used to hurt people. Learn more...

[Free Registration/Login may be required to access all resource tools.] What do listening to music and riding a bike have in common? It might surprise you to learn that both activities depend on your ears. The ears do more than just...

[Free Registration/Login may be required to access all resource tools.] Can we survive without bacteria? Could bacteria survive without us? Learn more about helpful bacteria in this learning module produced by CK-12.

[Free Registration/Login may be required to access all resource tools.] The great apes are the members of the biological family Hominidae, which includes four living genera: chimpanzees, gorillas, humans, and orangutans. Learn more about...

[Free Registration/Login may be required to access all resource tools.] Most insects can reproduce quickly within a short period of time, which means they evolve faster and can adjust to environmental changes. Most reproduce by sexual...

[Free Registration/Login may be required to access all resource tools.] Mammals don't typically lay eggs, but monotremes are the exception. All other mammals give birth to live young and belong to one of two categories, the marsupials...

[Free Registration/Login may be required to access all resource tools.] Infectious diseases are diseases that spread from person to person. What can you do to avoid infectious diseases? Eating right and getting plenty of sleep are a good...

[Free Registration/Login may be required to access all resource tools.] Today most people realize that microorganisms, such as bacteria or viruses, are the cause of disease. This concept is known as the germ theory of disease, one of the...

[Free Registration/Login may be required to access all resource tools.] Definition of activation energy and why all chemical reactions require it.

[Free Registration/Login may be required to access all resource tools.] How to write chemical formulae and what they represent about the substance.

[Free Registration/Login may be required to access all resource tools.] Definition of ethics, ethical rules in science, and how science influences ethical decisions.

[Free Registration/Login may be required to access all resource tools.] Scientific notation, why it is used, and converting numbers to and from scientific notation.

[Free Registration/Login may be required to access all resource tools.] Provides a definition of a compound machine with examples and discusses the efficiency and mechanical advantage of compound machines.

[Free Registration/Login may be required to access all resource tools.] Explains what an electrical grid is and the role of power plants, transmission lines, and electric substations.

[Free Registration/Login may be required to access all resource tools.] Overview of electric safety: short circuits, electric safety features, and how to use electricity safely.