What Is a Life Cycle?

Author: Jennifer Hernandez

Overview: [This is the first in a series of three lessons concerning life cycles] The purpose of this lesson is to introduce the students to the concept of a life cycle and to the concept that abiotic environmental conditions can affect the development of organisms. Students will work in groups of four for the entire lesson. The first part of the lesson is an exercise that introduces the students to life cycles of several different organisms. Each group is provided with a set of photos. Each photo set includes the following: five photos of adult organisms (butterfly, kangaroo, penguin, frog, and plant) and photos of each stage of the life cycle for that organism. The students are given five minutes to place each life cycle photo with the correct adult photo and in order from youngest to oldest. The second portion of the lesson involves the use of a fruit fly station to introduce the effects of temperature on the development of organisms.

Lesson Concepts:

  • All organisms go through stages of development.
  • Environmental conditions such as water, temperature, and light affect the development of organisms.

Grade span: 7th grade


  • Photo set (eight sets needed per class plus one set for instructor)
  • Stopwatch (12 total)
  • 12 vials of fruit flies with all life stages
  • Worksheets
  • Hand lens
  • Ice

Time: About 45 minutes

Grouping: Groups of four students

Vocabulary: life cycle, stage, marsupial, mammal, fetus, egg, larva, pupa


  1. Divide the students into groups of four (5 minutes).
  2. Provide each group with a set of life cycle photos. Instruct the students to leave the cards turned over until you give the signal to begin. Students have five minutes to group the photos so that the life cycle stages match the picture of the adult organism. They should arrange the photos from youngest to oldest. (8 minutes: 3 for directions, 5 for activity)
  3. Discuss the life cycle of each organism providing terms for the stages. I recommend asking a group to describe the order of photos for a specific organism. The stages can be listed as a flow chart on the board (see below). The insect life cycle can be drawn in the traditional circle that is often depicted in text books. (10 minutes)

    Mammal: fetus › juvenile › adult
    Bird: egg › chick › adult
    Amphibian: egg › larva › adult
    Plant: seed › seedling › flowering plant
    Insect life cycle

  4. Provide instructions for the fruit fly station. Students will observe the flies and fill out the first table with their observations. One student from each group will then retrieve some ice. The flies are placed on the ice; two minutes will result in 50% of the adults becoming inactive, five minutes will subdue all the flies. Students make observations and fill out the second table while the flies are on ice. (5 minutes)
  5. Work at station. (10 minutes)
  6. Discussion (5 minutes) — The important points for discussion are:
       • Student observations
       • How can we test the statements regarding the effect of temperature on the fruit flies?
       • How might temperature, light, etc. affect the development of the hornworms?