SCIENCE 7B LESSON 2

is anything that causes a reaction or change in an organism. A stimulus can be an environmental factor such as temperature.

is an organism’s reaction to a stimulus. For example, some animals respond to cold temperatures by growing extra fur to stay warm, while others respond by moving to warm environments.

A set of actions taken by an organism in response to a stimulus is called a behavior.

is maintaining a stable balance in the body. Organisms’ bodies constantly respond to stimuli to maintain homeostasis.

is a chemical signal produced in one part of an organism that affects cell activity in another part of the organism. Hormones move more slowly than electrical signals.

is the movement of organisms toward or away from an external stimulus. An organism shows positive taxis when it moves toward a stimulus.

the movement of a plant in response to an external stimulus, such as light or gravity.

A deep sleep during which an animal slows down its body processes to save energy

When internal processes slow down during hot, dry weather

is a group of organisms that can reproduce only with one another and not with other organisms. For example, mockingbirds reproduce with other mockingbirds.

is a group of organisms of the same species that live in the same place at the same time

is the differences that occur in individuals within a species. Variation of physical characteristics is partly due to the genetic variation of the individuals within a species or a population

refers to the process by which populations gradually change over time

The practice by which humans breed specific plants or animals for desired traits is called selective breeding,

is the process by which organisms that inherit helpful traits tend to reproduce more successfully than other organisms do.

overproduction, genetic variation, selection, and adaptation

More offspring are usually born than the environment can support.

Remember that selection works only on traits that exist in a population. Individuals with a helpful trait are more likely to survive to reproduce. As a result, the trait is “selected” for becoming more common in the next generation

An inherited trait that improves the survival and reproductive success of an organism

Within a population, there are naturally occurring variations in traits. For example, of the two jaguars to the left, one has a larger jaw than the other. The different jaw sizes result from genetic differences. Genetic differences, or variations, pass from parents to their offspring

The specific place where an organism lives is

The number and variety of plants, animals, and other organisms living in a area

is the science of naming and classifying organisms.

The organization of living things into groups based on their traits