[Free Registration/Login may be required to access all resource tools.] The process of cell division in eukaryotic cells is carefully controlled. The cell cycle is the life cycle of a cell, with cell division at the end of the cycle....

[Free Registration/Login may be required to access all resource tools.] DNA contains the instructions to create proteins, but it does not make proteins itself. DNA is located in the nucleus, which it never leaves, while proteins are made...

[Free Registration/Login may be required to access all resource tools.] Puberty is the stage of life when a child becomes sexually mature. Puberty lasts from about 12 to 18 years of age in boys and from about 10 to 16 years of age in...

[Free Registration/Login may be required to access all resource tools.] When a baby girl is born, her ovaries contain all of the eggs they will ever produce. But these eggs are not fully developed. They develop only after she starts...

[Free Registration/Login may be required to access all resource tools.] This comprehensive lesson by CK-12 explains how scientists learn about the past by examining and dating fossils.

[Free Registration/Login may be required to access all resource tools.] How does the food you eat provide energy? Through the process of cellular respiration, the energy in food is changed into energy that can be used by the body's...

[Free Registration/Login may be required to access all resource tools.] Scientists used to think that fungi were members of the plant kingdom. They thought this because fungi had several similarities to plants. However, there are a...

[Free Registration/Login may be required to access all resource tools.] Arthropods might seem a little scary, but they are actually performing important roles in the environment. Arthropods are important to the ecosystem and to humans in...

[Free Registration/Login may be required to access all resource tools.] Recall that air pollution is due to chemical substances and particles released into the air mainly by human actions. When most people think of air pollution, they...

[Free Registration/Login may be required to access all resource tools.] Birds aren't the only creatures that have feathers. One type of echinoderm, the feather star, has feathery arms. These animals don't fly or even move much at all....

[Free Registration/Login may be required to access all resource tools.] Vertebrates are animals with backbones. These include fish, amphibians, reptiles, birds, and mammals. Learn more about vertebrate characteristics in this learning...

[Free Registration/Login may be required to access all resource tools.] There are many risk factors that can cause a person to develop cardiovascular disease. A risk factor is anything that is linked to an increased chance of developing...

[Free Registration/Login may be required to access all resource tools.] Your cardiovascular system has many jobs. At times the cardiovascular system can work like a pump, a heating system, or even a postal carrier. To do these tasks,...

[Free Registration/Login may be required to access all resource tools.] Many insects are considered to be pests by humans. However, insects are also very important for numerous reasons. Learn more about the importance of insects in this...

[Free Registration/Login may be required to access all resource tools.] Mammals play many important roles in ecosystems, and they also benefit people. Learn more about the importance of mammals in this learning module produced by CK-12.

[Free Registration/Login may be required to access all resource tools.] The first year after birth is called infancy. Infancy is a period when the baby grows very fast. During infancy, the baby doubles in length and triples in weight....

[Free Registration/Login may be required to access all resource tools.] A scrape is a break in the skin that may let pathogens enter the body. If bacteria enter through the scrape, they could cause an infection. These bacteria would then...

[Free Registration/Login may be required to access all resource tools.] Activities that challenge your brain, such as working on a Sudoku puzzle, are good for the health of your nervous system. Just like you need to work out your body to...

[Free Registration/Login may be required to access all resource tools.] The central nervous system (CNS) is the largest part of the nervous system. It includes the brain and the spinal cord. The bony skull protects the brain. The spinal...

[Free Registration/Login may be required to access all resource tools.] Many chemical reactions are going on constantly inside your body. In fact, there are probably thousands of chemical reactions occurring every second in every one of...

[Free Registration/Login may be required to access all resource tools.] Mollusks are important in a variety of ways; they are used as food, for decoration, in jewelry, and in scientific studies. They are even used as roadbed material and...

[Free Registration/Login may be required to access all resource tools.] Animals are also often identified as being either invertebrates or vertebrates. These are terms based on the skeletons of the animals. Vertebrates have a backbone...

[Free Registration/Login may be required to access all resource tools.] A cardiovascular disease (CVD) is any disease that affects the cardiovascular system. But the term is usually used to describe diseases that are linked to...

[Free Registration/Login may be required to access all resource tools.] How do you define a living thing? What do mushrooms, daisies, cats, and bacteria have in common? All of these are living things, or organisms. It might seem hard to...