Unit 3 - Natural Selection
Study Guide
1. Identify and describe two sources of natural variation in organisms and one
sources of human influenced variation in organisms (Sexual reproduction and
mutations=natural) (selective breeding: [breed two organisms each with
different desirable traits with the hope that the offspring has both desirable
traits] and genetic engineering [purposely changing the genes of an
organism]=human influenced).
2. Describe how variations in organisms relate to survival.
Some mutations are helpful, some harmful, and some neutral, depending on the
ENVIRONMENT. If the variation is beneficial (helpful) aka an ADAPTATION,
the organism will survive. If it is not helpful, the organism will probably die.
3. Define "mutation" and cite examples of factors that might cause a mutation.
A random change in DNA that can be caused by pollution, smoking,
chemicals, and other environmental factors as well as other unexplained
reasons.
4. Explain why some mutations are passed on to offspring and others are not.
Beneficial mutations have a better chance of passing to offspring because the
organism will most likely survive to reproductive age.
5. Discuss and give examples of mutations that have given rise to a variety of
traits.
Opposable thumbs
6. Describe the process of natural selection.
 Overpopulation causes some of the offspring to die
 The remaining organisms left compete for resources
 Variations cause some organisms to be better adapted
 The better adapted organisms have a better chance surviving
 The survivors may pass these traits on to offspring
7. Explain and give examples of competition.
Competition is when organisms struggle for resources.
8. Identify resources for which organisms compete.
Food, water, shelter, mate
9. Describe and give examples of adaptations for survival including structural,
physiological, and behavioral adaptations.
Structural – body feature such as webbed feet
Physiological – automatic response such a blinking
Behavioral – an action such as growling