Building on the life cycle concept introduced in Lesson 24, learners investigate the remarkable variety of ways different organisms develop. The lesson focuses on metamorphosis, the dramatic physical transformation that many animals undergo, and distinguishes between complete metamorphosis, with four distinct stages, and incomplete metamorphosis, with three. Students also examine variation within a species, discovering that individuals of the same kind can look and behave very differently at different life stages, and explore how environmental conditions can influence life cycle timing.

Key Ideas

• Metamorphosis is a dramatic change in body form that occurs during an organism's life cycle. It allows the same species to occupy different ecological roles at different stages.
• Variation within a species means individuals of the same kind can look very different depending on their life stage, sex, or environment.
• Life cycle timing is not always fixed. Temperature, day length, and food availability can speed up or slow down development in many organisms.

Vocabulary

• Metamorphosis: A dramatic change in body form that some animals undergo during their life cycle.
• Larva: The immature, worm-like stage of an insect that undergoes complete metamorphosis. Examples include caterpillars and grubs.
• Pupa: The resting, transformation stage of complete metamorphosis, during which the larva reorganizes into the adult form.
• Variation: Differences among individuals of the same species in appearance, behavior, or development.

Discussion

• Why might a caterpillar and a butterfly look so different even though they are the same species?
• How does metamorphosis help an organism survive? Why might it be useful for different life stages to have different bodies or diets?
• What are some other examples of animals that look very different at different stages of their life cycle?
• Why might temperature, daylight, or food availability change how quickly an organism grows or develops?
• If two animals of the same species look different, how could you figure out whether the difference is because of their age, sex, or environment?