| A | B |
|---|
| immune system | the body's primary defense against disease-causing pathogens |
| indicator | a substance that changes color when it encounters certain chemical conditions |
| inorganic | a type of molecule that does not contain both carbon and hydrogen but can contain any other combination of elements |
| limiting factor | any factor in the environment that limits the size of a population |
| lipid | any one of a group of organic compounds that includes oils, fats, and waxes |
| meiosis | the process that results in the production of sex cells (sperm and egg) |
| meniscus | the curved surface at the top of a column of liquid |
| metabolism | all the chemical reactions that occur within the cells of an organism |
| microbe | any microscopic organism |
| micrometer | a unit of length equal to one millionth of a meter |
| mitochondria | pod-shaped organelles that contain enzymes used to extract energy from nutrients |
| mitosis | the process that divides the cell's nucleus into two, each with a complete set of genetic material from the parent cell |
| mutation | any alteration in the sequence of DNA |
| natural selection | the process by which the organisms that are best adapted to a specific environment survive and produce more offspring than organisms that are not as well adapted |
| niche | the specific role played by an organism in its ecosystem |
| nitrogen cycle | the movement of nitrogen from the atmosphere to the soil and organisms and then back to the atmosphere |
| nitrogen fixation | the process by which nitrogen forms compounds that can be used by living things |
| nonrenewable resource | any resource, such as fossil fuels and minerals, that cannot be replaced |
| nucleus | a large structure within a cell that controls the cell's metabolism and stores genetic information, including chromosomes and DNA |
| nucleic acids | large, complex organic molecules that contain the instructions cells need to carry out their life processes |
| nutrient | a substance that provides the body with the materials and energy needed to carry out the basic life of cells |
