[Free Registration/Login may be required to access all resource tools.] How do birds reproduce? We know that chickens lay eggs. But how do they do that? Learn more about bird reproduction in this learning module produced by CK-12.

[Free Registration/Login may be required to access all resource tools.] Cancer is a disease that causes cells to divide out of control. Normally, the body has systems that prevent cells from dividing out of control. But in the case of...

[Free Registration/Login may be required to access all resource tools.] Has this ever happened to you? A student sitting next to you in class has a cold. The other student is coughing and sneezing, but you feel fine. Two days later, you...

[Free Registration/Login may be required to access all resource tools.] Why is animal communication important? Without it, animals would not be able to live together in groups. Animals that live in groups with other members of their...

[Free Registration/Login may be required to access all resource tools.] A pedigree is a chart that shows the inheritance of a trait over several generations. A pedigree is commonly created for families, and it outlines the inheritance...

[Free Registration/Login may be required to access all resource tools.] A population is a group of organisms of the same species, all living in the same area and interacting with each other. Since they live together in one area, members...

[Free Registration/Login may be required to access all resource tools.] A terrestrial biome is an area of land with a similar climate that includes similar communities of plants and animals. Different terrestrial biomes are usually...

[Free Registration/Login may be required to access all resource tools.] The mRNA, which is transcribed from the DNA in the nucleus, carries the directions for the protein-making process. mRNA tells the ribosome how to create a specific...

[Free Registration/Login may be required to access all resource tools.] Carbon is one of the most common elements found in living organisms. Chains of carbon molecules form the backbones of many molecules, such as carbohydrates,...

[Free Registration/Login may be required to access all resource tools.] A person's genome is all of his or her genetic information. In other words, the human genome is all the information that makes us human. Learn more about the human...

[Free Registration/Login may be required to access all resource tools.] What does the word "communication" make you think of? Talking on a cell phone? Texting? Writing? Those are just a few of the ways in which human beings communicate....

[Free Registration/Login may be required to access all resource tools.] DNA is located in the nucleus. Proteins are made on ribosomes in the cytoplasm. Remember that information in a gene is converted into mRNA, which carries the...

[Free Registration/Login may be required to access all resource tools.] Problems can occur with red blood cells, white blood cells, platelets, and other parts of the blood. Many blood disorders are genetic, meaning they are inherited...

[Free Registration/Login may be required to access all resource tools.] Sometimes understanding how common a gene is within a population is necessary. Or, more specifically, you may want to know how common a certain form of that gene is...

[Free Registration/Login may be required to access all resource tools.] Like water and carbon, nitrogen is also repeatedly recycled through the biosphere. This process is called the nitrogen cycle. Learn more about the nitrogen cycle in...

[Free Registration/Login may be required to access all resource tools.] Sometimes, the urinary system is called the excretory system. But the urinary system is only one part of the excretory system. Recall that the excretory system is...

[Free Registration/Login may be required to access all resource tools.] Recombinant DNA is the combination of DNA from two different sources. For example, it is possible to place a human gene into bacterial DNA. Recombinant DNA...

[Free Registration/Login may be required to access all resource tools.] Just about all human behaviors are learned. Learned behavior is behavior that occurs only after experience or practice. Learned behavior has an advantage over innate...

[Free Registration/Login may be required to access all resource tools.] Another exception to Mendel's rules is polygenic inheritance, which occurs when a trait is controlled by more than one gene. This means that each dominant allele...

[Free Registration/Login may be required to access all resource tools.] Natural selection acts on the phenotype (traits or characteristics) of an individual. On the other hand, natural selection does not act on the underlying genotype...

[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.] 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.] Are you on the basketball team? Are you a cheerleader? Do you play an instrument in the band? Your niche would be your role or place in the school. Organisms also...

[Free Registration/Login may be required to access all resource tools.] During active transport, molecules move from an area of low concentration to an area of high concentration. This is the opposite of diffusion, and these molecules...