Cycles in Nature


Change Through the Seasons

The series of stages in the growth and development of a plant or animal is called its life cycle. A seed germinates, sprouting roots, stems, and leaves, and eventually forms a flower in which new seeds develop. A butterfly emerges from its pupa case, drinks the sweet nectar of flowers, finds a mate and lays its eggs; the next generation will soon hatch out as caterpillars, ready for the next phase of their life cycle. These events repeat year after year in a pattern of ongoing change.

The life cycles of living organisms are closely tied to the seasonal cycles of the earth. Many animals – frogs, turtles, chipmunks, bats – lie dormant in winter when days are short and food is scarce, while they become active in the months when sunlight and food abound. A tree stands bare of leaves through winter’s snows, but the warmth of spring sunlight encourages the buds to open and leaves to unfurl. Insects emerge to feed on the young leaves, and birds migrate northward to dine on the emerging insects. Particular stages of life cycles are often timed to coincide with specific seasonal events. During the first warm rain of springtime, salamanders migrate to ponds to mate and lay eggs. On the forest floor, early spring flowers quickly bloom and go to seed before the trees leaf out and shade them.

Animal and plant life cycles are often closely linked, each performing important services for the other. Goldenrods, willows, and many other plants provide food and homes for gall-making insects during certain stages of their lives, and many flowers depend on bees and other insects for pollination. Squirrels burying acorns in the fall are helping to plant the next generation of oak trees.

In these units we’ll meet different plants and animals, learning about their life cycles or key phases that occur in different seasons. In Insect Life Cycles we learn how insects go through distinct stages as they develop, undergoing metamorphosis as they change from young to adult. An important part of the life cycle of seed-bearing plants is the dispersal of the seeds. In Traveling Seeds we examine the anatomy of seeds and the structures that help them to disperse – by wind or water, aided by animals, or by mechanical means.

Winter is a challenging time in the lives of animals, with cold weather, snow, ice, and a shortage of food. Animals cope with winter in a variety of ways, from migration to hibernation. In Birds On the Wing we consider why some birds stay while others migrate. We’ll learn about the different challenges faced by each and how they prepare. In Winter Ways we compare the strategies of a variety of animals, from insects to snakes, frogs to hares, for surviving this critical period of their lives.


Trees must survive the winter as well and be ready to put out leaves when springtime comes. In Winter Trees we take a close look at twigs. Here we see buds that formed in the summer and that contain the beginnings of next spring’s leaves, stems, and flowers – a tree’s way of preparing for the next growth phase of its life cycle. In Maple Sugaring, we’ll learn how maples wake up from their winter dormancy, drawing water up from the ground and delivering sweet sap to their branches, a process we exploit to produce syrup.

The life cycles of some organisms are intimately connected to another species. In Galls Galore we meet a variety of plant galls and the gall-makers, often insects, that cause them to form. We’ll discover how each gall-maker requires a specific plant to complete its life cycle.

Reproduction is an essential part of every life cycle, and for many birds, song ushers in this chapter of their lives. In Songbird Songs we’ll listen for male birds singing and learn to recognize their songs as they advertise for mates and defend territories. Flowers are the reproductive structures of certain plants. In Flower to Fruit we’ll consider the important connection between flowers and their insect pollinators. We’ll dissect flowers to see how they produce pollen and eggs and attract pollinators. Because dandelions flower and go to seed over a short period of time, we can find all the stages of this part of their life cycle together. In Dandelion Flower to Seed we’ll study the complete cycle of development of the flower, from bud to blossom to puffy seed head. We’ll end by sending some dandelion seeds on their way to start the next generation.

As we study the animals and plants in our neighborhoods, we’ll consider how their life cycles are interconnected with other species and linked with the seasons. Children will observe firsthand the changes in plants and animals throughout the year.

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Next Generation Science Standards and Common Core State Standards

The units and activities in CYCLES support the three Dimensions of the Next Generation Science Standards. Together, the lessons in this concept give children opportunities to engage in the Science and Engineering Practices (Dimension I) and to reflect on the Cross-cutting Concepts (Dimension II) as identified in the Next Generation Science Standards.

The monthly topics also address Disciplinary Core Ideas (Dimension III) in Physical Sciences

(PS1: Matter and Its Interactions, PS4: Waves and Their Applications in Technologies for Information Transfer), Life Sciences (LS1: From Molecules to Organisms: Structures and Processes, LS2: Ecosystems: Interactions, Energy, and Dynamics, LS3: Heredity: Inheritance and Variation of Traits, LS4: Biological Evolution: Unity and Diversity) and Earth and Space Sciences (ESS2: Earth’s Systems). The specific Disciplinary Core Ideas that each lesson addresses are outlined in detail on the “Teacher Resources” page and the “Unit Summary” that accompany each unit.

In addition, each lesson supports aspects of both the English Language Arts and Math Common Core State Standards, including Reading for Informational Texts, Speaking and Listening, and Writing, as well as Counting, Operations, Measurement and Data.


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