Second Grade - Science - Lesson 29 - Life Cycles

Background Information for Life Cycles Unit: Plants

All living things pass through life stages as they grow and change. These stages of the life cycle--birth, growth, reproduction and death--can be seen in plants, animals and humans. A fertilized egg cell is the beginning of each generation.

Plants germinate from a fertilized egg cell that has developed into a seed. Curled inside the seed is a tiny plant embryo, complete with shoot and root, plus stored food to provide energy for the plant when it starts to grow. One can imagine that the plant embryo is like a space colonist in suspended animation. Tucked away in its protective capsule, its life support system is designed to click in when conditions are right to sprout. It waits for warm weather, rain and fresh air. The stored food in many seeds is also food for people. Examples of seeds we eat are lima beans, rice, wheat, coconut, corn, peanuts, mustard, coffee among many others.

Unfertilized egg cells never develop into viable seeds. In order for an egg cell to develop, it must be fertilized by sperm cells in pollen. The male part of a flower (stamen) produces pollen--a yellow, powdery dust. Egg cells are inside a female part of the flower called a pistil. There are a number of ways pollen can reach the pistil. Plants that produce great quantities of pollen depend on wind to carry it from stamen to pistil (corn, wheat, grasses, ragweed). Others have evolved brightly-colored petals, scents and nectar to attract insect and animal pollinators such as bees, beetles, bats, hummingbirds and butterflies. Once the pollen has settled (pollination), each grain grows a tube down into the pistil. Sperm travels down each tube to the egg cell inside and fertilization takes place. While the flower withers, the egg cells inside the plant's pistil grow into seeds that hold the embryos of new plants.


Suggested Books for Life Cycles Unit: Plants

Back, Christine. Bean and Plant. Englewood Cliffs: Silver Burdett, 1984.

Bennett, Paul. Pollinating a Flower. New York: Thomson Learning, 1994.

Carle, Eric. The Tiny Seed. New York: Simon & Schuster, 1987.

Cole, Joanna. The Magic School Bus Plants Seeds. New York: Scholastic, 1995.

Heller, Ruth. The Reason for a Flower. New York: Grosset, 1983.

Ladyman, Phyllis. Learning About Flowering Plants. New York: Young Scott Books, 1970. Contains excellent drawings of parts of the flower.

Lauber, Patricia. From Flower to Flower, Animals and Pollination. New York: Crown, 1986. Close-up photographs of bees and other insects visiting flowers and microphotography of pollen grains.

North Carolina Museum of Life and Scienc. Life Cycles, How Things Grow and Change. New York: Scholastic, 1993. Includes a flower model-making activity.

Selsam, Millicent. Play With Seeds. New York: Morrow, 1957. Text is middle school level but seed experiments are classic and well thought out.

Unwin, Mike. Science With Plants. Tulsa: EDC Publishers, 1992.


Second Grade - Science - Lesson 29 - Life Cycles

Teacher Resource

Moore, Jo Ellen & Joy Evans. Animal Life Cycles, Posters and Reproducible Pages. Monterey, CA: Evans-Moor Corp., 1986.

Walker, Colin. Pollination and Germination. Cleveland: Modern Curriculum Press, 1993.

Several good illlustrations of the inside of a seed.


Dissect a seed and look at a plant embryo.

Describe how flowers are pollinated.

Recognize that egg cells must be fertilized by pollen to grow into seeds.


An apple and knife

Seed dissection and sprouting kits for each student: in a sandwich bag- a few lima beans (soaked in water overnight), a handful of peas, kidney beans or lentils, toothpick, damp paper towel, hand lens

A lily (any variety); florists will often donate cut flowers that are beginning to fade. Also available in some supermarkets.

A piece of dark cloth

A dark-colored fuzzy sock


Ask the children: Has anyone ever said to you, "My, how you've grown.I hardly even recognized you, you've gotten so big"? You have changed a lot since you were babies. In what ways have you changed? (taller, stronger, have teeth, grew hair, can walk and talk, can read, accept all answers) . All living things change as they grow. In this new unit we're going to look at how plants and animals change as they go through different stages in their lives, as they go through their life cycles.

Slice the apple in half with a knife to expose the seeds inside. Remind the children that they learned about Johnny Appleseed and how he planted apple seeds out west. The seeds sprouted and grew into trees that bore fruit for the settlers. Take the seeds out of the apple, show them to the children and tell them that Johnny Appleseed saved the seeds from especially good-tasting apples and planted them to grow more trees with good-tasting apples. Draw on the board an apple tree life cycle: an apple to seeds to sprouts to apple tree to apple blossoms back to apple again. Show the children that the cycle is a circle.

Distribute the seed dissection kits. Tell the children that you have soaked the lima bean seeds overnight to soften their coats. Have the children peel off the largest seed's coat and split the seed in half lengthwise along its seam. (The toothpick is a handy tool for this.) Using the hand lens for a close-up look, ask the children to draw the seed and what they see inside it.

Ask: What did you find inside the seed? Did you find a baby plant? Tell the children that the baby plant is called a plant embryo. It has a little shoot and a tiny root. The two halves of its seed are stored food that the plant can use to grow. Draw the seed on the board and label the plant embryo, the stored food and the seed coat that keeps the inside of the seed from drying out. BCP DRAFT SCI 59

Second Grade - Science - Lesson 29 - Life Cycles

Ask: Who else eats the stored food in a lima bean seed? (people, animals) What other kinds of seeds do we eat? (peas, lentils, green beans, rice, peanuts-see above list)

Ask: If we give these seeds air and water, what do you think will happen to the plant embryo inside? Tell the children to find out what will happen by placing the seeds on the wet paper towel, folding it in half and slipping it carefully inside the sandwich bag. Remind them not to tip the bag, but to keep it lying flat. Ask: Why do we not want to seal the bag? (We want to let the air get in.) Suggest they check on the seeds daily.

Hand out the flower worksheet. Show the children the lily. Ask two children to come up and help. Have one child spread out the dark cloth on the table and ask the other child to shake the flower gently over the cloth. (If the pollen does not readily shake off, have the child touch the flower to the cloth.) When enough pollen has collected on the dark cloth, ask the first child to hold it up for the class to see. Ask: Where did this yellow dust come from? (the flower) Tell the children that the yellow dust is pollen. Pollen is made by the male part of the flower. There is also a female part of the flower. In the female part there are tiny egg cells. Pollen must mix with those egg cells or the plant's seeds will not form. The egg cells need to be fertilized in order to grow into seeds with plant embryos inside them like the lima bean seeds.

Blow on the lily flower. Ask: How can male pollen get to the female part of a flower? (wind, bees, accept any answer) Tell the children that the wind can blow pollen from one flower to another where it can stick onto the female part just like it stuck to the cloth. Another way flowers spread their pollen to other flowers is by using insect messengers as pollinators.

Put the sock on your hand. Tell the children that bees, butterflies, hummingbirds and even bats visit flowers to drink sweet nectar inside the flower. When they poke inside, (demonstrate with the sock and the lily) the flower dusts them with pollen that sticks to their fuzzy backs, fur or feathers. Then when they fly to another flower and reach inside it, the pollen rubs off on the female part. So these pollinators help the plants to spread their pollen. The pollen fertilizes egg cells. Ask: what do the fertilized egg cells grow to be? (seeds that can grow into plants) Write the names of the pollinators on the board.

Discuss how the color and scent of flowers might also attract pollinators. Ask: Why would farmers put bee hives in their orchards among the apple trees? (to be sure the apple blossoms are pollinated and fruit will grow) What else do the farmers get from the bee hives?

Instruct the children to color the lily worksheet and draw pictures of their favorite pollinators visiting the flower.

Homework Suggestion

What seeds do we eat? Look at home in the kitchen cabinet and the refrigerator and make a list of the seeds we eat. You can also look in magazines or the newspaper and cut out pictures of seed foods.

Optional Activity


Recognize that kernels of corn are seeds.

Observe the way pollen (sperm cells) travels through silks to reach egg cells.


Second Grade - Science - Lesson 29 - Life Cycles


Transparency of corn plant made from drawing (see attached)

For each group of four: an unhusked ear of corn, hand lens, newspaper to cover desk


Display transparency of the corn plant. Ask individual children to come up and point to the parts of the plant--stem, leaf and roots. Point out the tassel on the top. Tell them it is the male part of the plant. It doesn't look like a flower but it is. This is where the pollen is made. When the wind blows through the cornfield, it shakes the tassel and the pollen is blown off. Point to the female part of the plant, the ear. Show the children the silks coming out of the top of the ear. Tell them when the pollen blows around the cornfield, it sticks on the sticky silks. It travels down the silks into the ear of corn and fertilizes the egg cells there so they will grow into big, juicy kernels of corn.

Have runners from each group pick up materials. Tell the children they are going to be detectives and follow the path of the silks to see where they go. Tell them to peel back the layers of the husk until they get to the ear inside, but be careful to leave as many of the silks in place as they can. When they have the ears open, ask: Where do the silks go? Use your hand lens to get a close look. (Each strand of silk goes to a single corn kernel.) Are they attached to the kernels of corn? Do you think this is how the pollen gets down to the egg cells? Tell the children that the cells in the tiny pollen grains are so small, they can move down a tube inside a thread of cornsilk, reach the egg cell and fertilize it so it will grow. Ask: Do you see any little, shriveled corn kernels that have not grown? Why do you think they did not grow? (Pollen did not reach them. They were not fertilized.) Tell the children that this corn came from the supermarket. If this corn were not for eating by people and the farmer was not going to feed it to cows, pigs or other livestock, it would be dried out and saved for seed corn. Then in the spring, the farmer would plant it to grow another field full of corn plants.

Ask:Why do you think the farmer will not tell secrets in a cornfield? There are too many ears listening.

Possible Guest Speakers

A local florist or gardener might bring flowers or plants to the classroom. Forced-bloomed amaryllis and paperwhites have impressive flowers with obvious stamens and pistils.

For a speaker from Cooperative Extension Service of the University of Maryland, Urban Gardening Program call Amanda Self at 396-1888.

Possible Field Trips

Cylburn Arboretum Mansion (Horticultural Division of Bureau of Parks) offers tours of their greenhouses for school groups as well as tours of the Conservatory at Druid Hill Park. To arrange a tour of the greenhouses, call Ms. Kief at 396-7839. For a tour of the Conservatory, call 396-0180.


Second Grade - Science - Lesson 30 - Life Cycles

Background Information for Life Cycles Unit:

Egg to Chick to Chicken to Egg

A chicken egg is like a seed. The shell allows air to pass through thousands of tiny holes but keeps the contents of the egg from drying out. Inside the egg is a chicken embryo (a small white dot on the yellow yolk) and stored food (yolk) plus water and minerals (the white) that the embryo needs while it is growing and developing. The egg provides protection, air, water and food for the growing embryo. The hen provides the warmth the egg needs (incubation) by sitting on it for 21 days. Inside the egg, a web of blood vessels spreads over the yolk and supplies the embryo with nourishment from it. The embryo's heart forms first, then the eye, wings and legs. Finally the beak and feathers form. When fully developed, the chick uses a special egg tooth on its beak to peck through the membrane and shell surrounding it. The newly hatched chick is still wet and needs to dry out. In a few hours it is running around and pecking at grain. In six months it will be full grown and laying eggs or mating with hens.

An egg from the super market will never develop into a chick because it has not been fertilized. The egg farmer keeps the rooster separated from the hens so they cannot mate. A farmer raising chickens, however, keeps the rooster with the hens. The rooster mates with a hen, fertilizing an egg cell with sperm, which then travels down an oviduct, is covered with shell in the hen's uterus and is then laid. All birds hatch from eggs; eggs come in a variety of colors and sizes. Birds that nest on the ground tend to have eggs that are brown speckled to blend in with the surroundings so they will not be seen by egg-eating predators. Birds that nest in holes in trees, such as woodpecker, tend to have light-colored eggs, perhaps so they can see them in the dim light of the nest cavity. The largest bird egg in the world is an ostrich's egg. It is the size of a large grapefruit or about 20 times the size of a chicken egg. The smallest, the hummingbird's, is the size of a jellybean.

The nestling period for baby birds varies. Some baby ducks are fed by their parents for only two days before they leave the nest and take to the water. Penguins, on the other hand, are fed fish by their parents for ten weeks before they leave them.


Suggested Books

Back, Christine. Chicken and Egg. Morristown, NJ: Silver Burdett, 1986.

Bailey, Jill. The Life Cycle of a Duck. New York: Bookwright, 1989.

Burton, Robert. Egg, A Photographic Story of Hatching. New York: Dorling Kindersley, from their eggs. Also illustrates all four stages of caterpillar and ladybug metamorphosis.

Burton, Jane. Chester the Chick. New York: Random House, 1988. Follows the life of a chick from hatch to maturity and egg laying.

Cole, Joanna. A Chick Hatches. New York: Morrow, 1987.

Fowler, Allan. The Chicken or the Egg? Chicago: Childrens Press (Rookie Read-About Science series), 1993.

Heller, Ruth. Chickens Aren't the Only Ones. New York: Grosset, 1981. Illustrates in a lively and colorful way the variety of animals and insects that hatch from eggs.

Jenkins, Priscilla. A Nest Full of Eggs. New York: HarperCollins (Let's Read and Find Out Science series), 1995. Highlights life cycle of robins from their arrival in spring and includes other facts about birds and their nesting habits.


Second Grade - Science - Lesson 30 - Life Cycles

McCavley, Jane. Baby Birds and How They Grow. Washington, D.C.: National Geographic, 1983.

Molleson, Diane. How Ducklings Grow. New York: Scholastic, 1993.

Selsam, Millicent. Egg to Chick. New York: Harper (A Science I Can Read Book),1970. Offers a clear explanation of fertilization with easy-to-understand illustrations of how eggs are formed.

Selsam, Millicent. All About Eggs. Reading: Addison Wesley, 1980.

Watts, Barrie. Birds' Nests. Morristown, NJ: Silver Burdett, 1986. Photostory of a bird's nest building, hatching and care of young.

Weiss, Nicki. An Egg is An Egg. New York: Putnam's, 1990.

Wood, A. J. Egg! Boston: Little, Brown, 1993. Unfold the pages to reveal twelve different eggs from butterfly to crocodile.

Teacher Resource

Ranger Rick's NatureScope: Birds, Birds, Birds. Washington, D.C.: National Wildlife Federation, 1985.

Maryland Dept. of Natural Resources. Out of the Egg. 30 min. video. MD: (Scales and Tales Production),1994. Ranger Bill Trautman of Scales and Tales and three children explore Patapsco State Park and discover a number of animals that hatch from eggs including owls, ducks, snakes, and turtles.


Look at the contents of an unfertilized chicken egg and compare it to a seed.

Recognize that a chicken egg cell must be fertilized by sperm from a rooster in order to develop into a chicken.

Discuss the life cycle of the chicken and other birds.

Design camouflage for an egg.


As a student activity

For each group of four (Note: This can also be a teacher demonstration.): 2 raw eggs, hand lens, plastic dish or pie tin, pencil, ruler, wet paper towel, worksheet (see attached)

Some or all of the following: shredded newspaper, colored tissue paper, yarn and string, dried grass and weeds, dryer fluff, cellophane, hair or fur, tiny twigs, feathers


Review with the children what they learned about seeds. Ask: What is inside a seed? (Inside a seed is a plant embryo, food for the baby plant and a protective coat on the outside.) Check the contents of some of the sandwich bags from Lesson 29 to confirm that the embryos have sprouted and roots and shoots are growing.

Hold up a chicken egg and ask: What do you think is inside this?(accept all answers) Today we are going to find out how an egg is like a seed. Divide the children into work groups and assign jobs of runner, reader, recorder, and reporter. Have runners collect supplies. (It is


Second Grade - Science - Lesson 30 - Life Cycles

probably best to distribute eggs to each group yourself after the children are settled to avoid egg accidents.) Tell them to save one of the eggs for another experiment. When they have finished their worksheets, ask the reporters to read the groups' findings. Ask one or two children to come up to the board and draw what they saw inside of the egg.

Remind the children that we want to answer the question: How is an egg like a seed?

Hold up an egg and tap on the shell. Tell them the outside of a seed, the seed coat, protected the embryo inside and kept it from drying out. Ask: Was the chicken egg wet inside? Do you think the shell kept it from drying out? Tell the children that there are really thousands of tiny holes too small to see in the egg shell that let air in, but the egg shell does keep the insides from drying out. Point to the yolk of the egg drawing on the board. Ask: What do you think the yellow part is? (Some children will say it is the chicken embryo because it is yellow and a chick is yellow.) Tell the children that the yellow is the food supply for the chicken embryo to use while it is growing inside the egg. Ask: What do you think the clear part is? Tell them that it is water and minerals the chick embryo needs to grow. Just as they found inside the seed, there is a supply of food for the growing baby.

Tell them your next question is a trick question. Ask: Where is the chick embryo? Tell the children that the reason it is a trick question is that there is no embryo in the eggs. That is because they were not fertilized. For a baby chick to form and grow inside the egg, the hen must mate with a rooster, a male chicken. The rooster puts sperm inside the hen's body to fertilize the egg cells there. Then the hen lays eggs with shells around them and embryos inside. Remember the egg cells in the flower had to be fertilized with male pollen to grow into seeds, and the chicken egg has to be fertilized with sperm from a rooster before it can hold a baby chick embryo. Tell them that all the eggs we buy in the supermarket like the ones they are looking at, were not fertilized.

Show the children pictures of a chick developing inside an egg (see suggested books list for illustrations and photos). Tell them that when the little chick is fully formed with wings, feet, feathers, beak, and crowded tight in the shell, it is ready to hatch. It must use a tiny tooth on the end of its beak called an egg tooth to peck through the hard shell and come out. It is hard work and the chick might take a long time doing it.

Tell the children to imagine they are tiny chicks and not big, strong children.Tell them to use the tip of a pencil like an egg tooth and using baby chick strength, try to peck-peck through the shells of their second eggs. (Remind them to hold the egg over the dish.) When they are finished ask: Do you think the chick would be tired after getting out of its shell? (Note to the teacher: Clean up should include wiping hands thoroughly with wet paper towel.)

Tell the children that all birds hatch from eggs. Brainstorm with the children the different kinds of birds and make a list on the board. (Don't forget to include parrots, penguins, owls, vultures, ostriches, peacocks, orioles and even dinosaurs!) Tell the children that eggs come in many different sizes and colors. There are blue eggs like the robin's, speckled eggs, brown eggs, green eggs, yellow, orange, pink, even black eggs. An ostrich's egg is as big as a grapefruit. A tiny hummingbird's egg is the size of a jelly bean.

Tell the children that birds build their nests in all kinds of places: on sandy beaches, up in trees, on rocks, in bushes, in holes in trees, on window ledges, on signs, even underground. Birds that lay their eggs on the ground usually have speckled eggs that blend in with the color of the BCP DRAFT SCI 64

Second Grade - Science - Lesson 30 - Life Cycles

ground. Woodpeckers that lay their eggs in holes in trees usually have light-colored eggs. Maybe so the parents can see the eggs in the darkness of the nest hole. Ask: Where have you seen birds' nests before? Do you remember what they were made of? Show the children some of the things birds use to build their nests. (Refer to materials list.) Tell them that when it comes to making nests, birds are recyclers.

Tell the children that birds sit on their eggs to keep them warm until they hatch. Then they bring food to their nestlings until the little birds have their adult feathers and can take care of themselves. The birds leave their parents to find mates, build nests and lay eggs of their own. So birds have a life cycle, too--from embryos inside eggs, to nestlings, to adult birds who mate and lay eggs to start the cycle all over again.

Ask the children to imagine that a bird has laid an egg someplace in their neighborhood. It could be anywhere--in a flowerpot, on top of a car, in a shoe. The bird needs help keeping the egg safe from egg eaters. Have the children in their groups write a description of where the egg has been laid and what they can do to make the egg blend in with its surroundings so it won't be seen. (Example: If it is on top of a stop sign, they might want the egg to be red. Tell them they are to design camouflage for the egg. Have the children share their ideas with the class.

Homework Suggestion

See if you can answer this question: Which came first, the chicken or the egg? Remember what you have learned about life cycles.

Possible Guest Speakers

Baltimore Bird Club, Hdqtrs. Cylburn Mansion, 467-0653. These avid birders have slides and experiences to share. Many have been birding all over the world.

Irvine Natural Science Center, Stevenson, MD, 484-2413. Naturalists on staff have programs featuring birds and other animals.

Additional Background Information

In first grade the children learned about the life of Rachel Carson. In the 1950s, when the chemical pesticide DDT was commonly sprayed to kill plant-eating insects, the pesticide collected in the bodies of insect-eating birds. These birds were then eaten by birds of prey (eagles, hawks, falcons). DDT was found in greatest concentration in the bodies of birds of prey. As a result, the egg shells of these birds became weak and the eggs cracked before the embryos were fully developed. In her book Silent Spring, Rachel Carson questioned the use of DDT and described its possible effects on birds, insects and on the balance of nature. Thanks to Carson, use of DDT was eventually banned in the U.S. Since then, birds whose populations had dwindled, including the bald eagle, our national symbol, are now making a comeback.

Second Grade - Science - Lesson 31 - Life Cycles

Background Information for Life Cycles Unit:

Frogs and Pollywogs

Although 300 million years ago there were many kinds of amphibians on earth, today there are only three groups left--the one that includes frogs and toads (jumping ones), the newt and salamander group (tailed ones), and another group of blind, wormlike creatures that one doesn't run into often. All amphibians begin life in the water.

In early spring, male frogs gather in ponds and wet ditches and call to attract females. Male frogs embrace the females and, as the females lay thousands of eggs, release sperm and fertilize the eggs. Each egg is a jelly ball with a black dot inside that is the frog embryo and a clear or whitish part that is the embryo's food supply. Frog eggs stick together in a mass. The slippery texture of the mass makes it harder for fish and turtles to get a mouthful.

Inside the egg, the embryo immediately begins to develop, becoming a comma shape within a few days. Some frog eggs hatch within a week and out wiggle tadpoles (otherwise known as pollywogs) that look nothing like their parents. The tadpoles nibble on the old jelly eggs and small green water plants. They swim and breathe through gills like fish. It is a good thing there are so many tadpoles, because a large number will be eaten by birds, snakes and large water insects. In a short time, the tadpoles grow back legs, then front legs. Their gills grow over and they develop lungs. Finally, the tail shrinks and the baby frog or froglet can hop out of the water and catch tiny insects with its sticky tongue. In two years it will be mature and return to a pond to spawn.


Suggested Books

Back, Christine. Tadpole and Frog. Englewood Cliffs: Silver Burdett, 1984. Includes photographs of various types of tadpoles and excellent photos of frog eggs inside their "jelly balls."

Gibbons, Gail. Frogs. New York: Holiday House, 1993. Includes information on frog hibernation and the difference between frogs and toads in addition to the ever-changing life of a tadpole.

Kellogg, Steven. The Mysterious Tadpole. New York: Dial, 1977. Alphonse the tadpole is changing, but he isn't turning into a frog in this fun and goofy story.

Lionni, Leo. An Extraordinary Egg. New York: Knopf. Two frogs find a "chicken" egg and care for the strange hatchling until they can return it to its mother (an alligator).

Pfeffer, Wendy. From Tadpole to Frog. New York: HarperCollins (Let's Read and Find Out Science series), 1994. Highly recommended for its accurate and appealing text and illustrations. Valerie Chase from the National Aquarium in Baltimore helped with the facts.

Rockwell, Anne. Ducklings and Pollywogs. New York: Macmillan, 1994. A seasonal cycle at a pond takes in the inhabitants and their life cycles. Illustrations of the bullfrog tadpoles are wonderful.

Rockwell, Anne and Harlow. Olly's Pollywogs. New York: Doubleday, 1970. Olly and his father go on a walk in early spring and find frog eggs in a pond. They take them home, raise them to froghood in an aquarium, then let them go.

Savage, Stephen. Frog. New York: Thomson Learning, 1995.

Second Grade - Science - Lesson 31 - Life Cycles

Snape, Juliet and Charles. Frog Odyssey. New York: Simon & Schuster, 1991. A group of frogs must move when their pond is to be filled in. They pack up their favorite diving post and their tadpoles in a jar and go in search of a new home.

Williams, John. Life Cycle of a Frog. New York: Bookwright Press, 1988. Exceptionally good blow-ups of frog eggs and development of the tadpole.

Winner, Cherie. Salamanders. Minneapolis: Carolrhoda, 1993. Although the text is rather advanced, the photographs of spectacular salamanders are worth the look. Includes several pictures of the red-backed salamander which is commonly seen under dead leaves in the Baltimore area.

Teacher Resource

Lacey, Elizabeth. The Complete Frog. New York: Lothrop, 1989. Everything you want to know about frogs including colorful poison arrow frogs. (Many poison arrow frogs carry their tadpoles on their backs because they won't dry out in the wet environment of the rainforest. The National Aquarium has one of the best collections of poison arrow frogs in the world.) Also has a chapter on frogs in story and legend.


Compare the egg of a frog to a chicken's egg.

Sequence the stages in a frog's life cycle.


Cassette tape recorder and blank tape

Flip book worksheet (attached)*

Photographs of tadpoles in books or cut from magazines


Tell the children that today they are going to learn about the life cycle of a certain amphibian. Tell them you will give them some clues and when they know what the mystery amphibian is, to raise their hands.

Read the following: I like to sing

especially in the spring.

My eggs float on the water

Like polka dot jello.

I have thousands of babies

But not one of them looks like me.

I have a long sticky tongue

to catch my breakfast.

I used to be a pollywog

But now I've changed into a ______.

When you are finished, have the class call out the name of the mystery amphibian. Then reread the clues and fill in the blank. Tell the children that in spring, frogs wake up and come out Second Grade - Science - Lesson 31 - Life Cycles

of the mud at the bottom of ponds and ditches where they have spent the winter. They gather around the pond and sing loudly. Ask: who knows what a frog song sounds like? (br-r-r-ivet, crickety-crick, cro-o-o-ak, bu-u-u-urump, accept all interpretations) List the "songs" on the board. Divide the class into groups and assign frog songs to each group. Tell the children that they are going to make an environmental tape called "Frog Pond in the Springtime." You will conduct the frog chorus and give signals for louder and softer. Record the cacophony for a half-minute or so and then play it back for the children. Let the "Frogs" take a bow after the performance.

Ask: Has anyone ever seen frog eggs or held them? What would it feel like to hold slippery, slimy jello in your hands? That's what frog eggs feel like. Tell the children that when frogs gather in ponds they lay eggs. The females lay thousands of eggs that stick together in jello-y bunches. The males fertilize the eggs with sperm. The polka dots in the jello are tiny frog embryos. Inside each egg is a food supply for the growing embryo.

Show the children pictures of frog eggs (see suggested book list for illustrations). Describe to the children how frog eggs float near the surface of the water, warming in the early spring sunshine. Ask: What did chicken eggs feel like on the outside? It was hard to crack through the shell, wasn't it? Tell the children frog eggs don't need hard shells to protect their wet inside because they won't dry out. They are already floating in water. The mother frog does not sit on the eggs to keep them warm. Ask: Is the inside of a frog egg like the inside of a fertilized chicken egg? (Yes, it has an embryo and a food supply.)

Tell the children that inside the frog egg the embryo changes just as the chick embryo did. You can see the changes inside because the outsides of frog eggs are clear. At first the embryo looks like a period ( . ), but then it grows and changes to a comma shape. After a day or two you can see it wiggling inside the egg. Some frog eggs hatch in a week and out wiggle animals that don't look like frogs. They are tadpoles (sometimes called pollywogs). Show the children photos or illustrations. Tell them tadpoles swim and breathe through gills like fish do. They nibble on green water plants and try to stay away from birds, turtles, snakes and big water insects who gobble up tadpoles. Many of the tadpoles that hatch get eaten. That is why frogs lay so many eggs.

In a short time, the tadpoles change again. This time they grow hind legs. Then they grow front legs. Their gills grow over and they start using their lungs to breathe air. Finally, after a few weeks, the tadpoles' tails shrink. Now they are baby frogs, called froglets because they are so small. They can hop out of the water, and sit on lily pads or hide in the grass at the edge of the pond. They can open wide frog mouths and catch tiny insects on their sticky tongues, just as grownup frogs do. In winter they will sleep in the mud at the bottom of the pond and wake up in the spring to sing with the other frogs or lay jello-y eggs.

Ask: How many stages in a frog's life cycle can you remember? Write responses on the board. (egg, tadpole, tadpole with back legs, tadpole with front legs, tadpole with shrinking tail, froglet, frog)

Distribute the frog flip book worksheet. The children will cut out the pictures of different stages of the frog's life cycle, put them in order from egg to frog and stack the pictures. In helping the students staple their flip books, be sure the outside edges are reasonably even so the pages will turn smoothly when "flipped."

Second Grade - Science - Lesson 31 - Life Cycles

Optional Activities

Have the children sing the "Frog Song" (music attached). Divide the class into three groups and sing the song as a round. Record the singing on tape after the "Frog Pond in the Springtime" selection and play it back for the children.

An aquarium in the classroom with tadpoles adds greatly to the life cycles unit. Sometimes pet stores have leopard frog or tree frog tadpoles for sale. Distributors of educational supplies such as Edmund Scientifics and Hands-On Science have frog egg hatchery kits available. Once the Grow-A-Frog coupon is sent in, a tadpole is sent by First Class Mail. Unlike the leopard or tree frog tadpoles, this tadpole becomes an African clawed frog (non-native, cannot be released).

Homework Suggestion

What if all the tadpoles from the thousands of eggs that every frog laid survived instead of being gobbled up by birds, turtles, snakes and fish? Write a paragraph about what would happen.

Possible Field Trip

National Aquarium in Baltimore to see the exhibits of poison arrow frogs.

Second Grade - Science - Lesson 32 - Life Cycles

Background Information for Life Cycles Unit:

Darkling Beetles (mealworms) and Metamorphosis

Beetles are the largest group of animals in the world; there are over 300,000 kinds of beetles. Like many insects, they change form three times (four life stages) before they are adult beetles. This process of change is called metamorphosis (met-a-MOR-fo-sis).

First stage is an egg, usually laid on or near a food source. The second is the larva stage of a beetle's life cycle, often called a "grub." Beetle larvae eat and grow through a series of molts, shedding skin and growing bigger with each molt. When a beetle enters the third stage it becomes a pupa. While the larva is an avid eater, the pupa is quiet, resting before changing into the adult form.

Ladybugs follow this same pattern of metamorphosis. The female ladybug usually lays little oval-shaped, yellow eggs on the bottoms of leaves where there is a ready supply of aphids for the hatching larva to eat. The larvae first eat their eggs and then consume aphids (insects that suck the juices from plants) before molting several times, pupating, and then becoming adult ladybugs that eat up to a hundred aphids a day. Gardeners love to find ladybugs in their gardens. Books in the suggested books list marked with an asterisk have stage-by-stage illustrations of ladybug metamorphosis and good read-aloud text.

Female adult darkling beetles (mealworms) lay from 500 to 1,000 small, sticky eggs in flour, corn meal or oatmeal. After two weeks, white larvae hatch and turn yellowish as time goes by. The larvae eat and grow for three months and then go into a pupa stage that lasts two weeks. They emerge as dark brown beetles. Mealworms are often found in kitchens, warehouses and barns where stored cereals have spilled or are not in airtight containers. People usually do not like to find mealworms in their homes.

Mealworms are sold in pet stores as a popular food for pet toads, turtles, fish even birds. When obtaining mealworms from a pet store, be sure to get them in larva, pupa and beetle stages because you won't want to wait weeks for the larva to change (eggs are too tiny to see, but they will be there). They should be stored in a container with holes in the lid for air. Add oatmeal or cornmeal for food and a slice of apple or raw potato for moisture.

Suggested Books

*Bailey, Jill. The Life Cycle of the Ladybug. New York: Bookwright, 1989.

Bennett, Paul. Changing Shape. New York: Thomson Learning, 1994. Closeup photos of ladybugs and other insects as well as frogs.

Buchs, Thomas and K. Zoehfeld. Ladybug at Orchard Avenue. New York: Soundprints, 1996. (Co-published with Smithsonian)

Carle, Eric. The Grouchy Ladybug. New York: HarperCollins, 1976.

De Bourgoing, Pascale. The Ladybug and Other Insects. New York: Scholastic, 1991.

Fischer-Nagel, Andreas. Life of the Ladybug. Minneapolis: Carolrhoda, 1985.

Godkin, Celia. What About Ladybugs? New York: Sierra Club, 1995.

*Johnson, Sylvia. Ladybug. Minneapolis: Lerner, 1984.

Penny, Malcolm. Discovering Beetles. Bookwright Press, 1987.

*Watts, Barrie. Ladybug. Englewood Cliffs: Silver Burdett, 1989.

Second Grade - Science - Lesson 32 - Life Cycles


Review the life cycle of a ladybug.

Observe and describe the larva, pupa and adult stages of the darkling beetle.

Make a population chart of the beetles in the classroom.

Pretend to be a darkling beetle and write a journal of its life.


For each group of four: a container of mealworms (all stages), a pencil, hand lens,

Newspaper for covering the desks, worksheet (see attached)


Ask: Have you ever heard the expression "Snug as a bug in a rug?" Today we are going to look at the life cycle of a creature that is snug as a bug...in our classroom. Show the class the containers and tell them that these are habitats you have created for the creatures with everything they need to live and they are snug inside. Tell them that this creature has a big family; it has 300,000 relatives. Say: We are going to learn a little about one of this creature's relatives-- the ladybug.

Read to the class the book The Life Cycle of the Ladybug, or one of the other * suggested books on ladybugs. Then ask: What kind of an insect is a ladybug? (beetle). There are more kinds of beetles in the world than any other animal. That's why these creatures (the ones in the containers) have so many relatives. Can you guess what is in here? (beetles) These are called darkling beetles. Just like ladybugs, these beetles go through a life cycle and have four different stages in their lives. Ask: Can you remember the four stages of a ladybug's life? (egg, larva, pupa, adult) Write these on the board.

Tell the class that they will be doing scientific work today--observing and recording what they observe. Tell them people who study insects and their life cycles are called entomologists. Write the word on the board. Something for all entomologists to remember: Be gentle. Compared to an insect, you are a giant.

Divide the class into groups of four and have the runners come up and get supplies and darkling beetle worksheet. Tell the children to spread newspaper over the desk, carefully empty the container on the newspaper, then look for insects by gently pushing things around with a pencil. See if they can find larva, pupa and adults. Tell them that there are also tiny eggs in the containers but they are so small, they might not be able to see them, even with a hand lens. After they have recorded their findings, have them return the insects to their habitats.

Make a master chart for the board: Number of darkling beetles in the class

larva pupa adult

Have each group reporter make a report and record the numbers under the appropriate columns. Together, add the numbers to get totals for each life stage and a grand total for how many of these insects are in the class.

Tell the children that now they know the life cycle of the darkling beetle, you want them to pretend they are darkling beetles. Say: Write the story of your life. What was it like being a

hungry larva and a resting pupa? Include pictures. Don't forget to mention your favorite food.

Second Grade - Science - Lesson 33 - Life Cycles

Background Information for Life Cycles Unit:

Caterpillars to Butterflies

Like beetles, butterflies and moths also have four life stages and go through metamorphosis. Female butterflies and moths lay eggs on food plants. The eggs vary in appearance depending on the species. Some are green, barrel-shaped eggs, some look like tiny white pumpkin seeds, etc. When the caterpillars hatch, they begin eating the food plant. This is their most vulnerable period because birds, toads, mice, insects and spiders feed on caterpillars. Some caterpillars (such as the monarch) eat milkweed plants and incorporate a foul-tasting toxin from the plant in their bodies so birds won't eat them. They advertise the fact with bright yellow and black stripes--a warning sign to go elsewhere for a meal. Other caterpillars have spines, horns and scary "eye" marks on their back ends to startle predators long enough to make a getaway. Still other caterpillars blend in with their food plants and feed from the bottom of the leaves where they may not be seen. The caterpillar, or larva, spends all its time eating and eating. Inside the caterpillar there is no growing room. Its old skin splits open and out squeezes a bigger caterpillar. Most caterpillars molt four times before finding a protected spot to spin a cocoon (moth) or form a chrysalis (butterfly) around them.

The monarch butterfly hangs motionless upside down in a "J" until its skin splits one last time and hardens into a golden-green chrysalis (the pupa stage). Inside, the larva changes; the old body dissolves and a new body forms. The chewing mouth turns into a mouth with a sucking straw (proboscis - pro-BAHS-kis). Compound eyes and antennae are formed. Then the chrysalis splits open and the butterfly emerges, hangs for a while as it pumps blood into its new wings and then takes to the air.

Moths spin cocoons around themselves and enter the pupa stage. Liquid silk shoots from a special gland in the caterpillar's lip and hardens into a thread when it hits the air. The moth wraps itself in the cocoon and pupates. Some moths, such as the giant Cecropia moth, cannot eat in their adult stage--they have no mouths. Feathery antennae help them locate the scent of other Cecropia's, they mate, lay eggs and then run out of energy and die. Other butterflies and moths hibernate during the winter or migrate like the monarch.

Suggested Books

Carle, Eric. The Very Hungry Caterpillar. New York: Collins, 1979.

Eyewitness Books. Butterflies and Moths. New York: Knopf, 1991.

Heiligman, Deborah. From Caterpillar to Butterfly. New York, HarperCollins, 1996.

Hogan, Paula. The Butterfly. New York: Raintree/Steck Vaughn, 1990.

*Jourdan, Eveline. Butterflies And Moths Around the World. Minneapolis: Lerner, 1981. Text is advanced but photos of butterflies and caterpillars and closeups of eggs are beautiful.

*Lasky, Kathryn. Monarchs. New York: Harcourt, 1993. Includes photos of the parade the people of Pacific Grove, California have each year to welcome the monarch butterflies back after their long migration.

Quiri, Patricia. Metamorphosis. New York: Franklin Watts, 1991. Great photos of each stage of monarch butterfly's metamorphosis.

Second Grade - Science - Lesson 33 - Life Cycles

Ryder, Joanne. Where Butterflies Grow. New York: Dutton, 1989. "Imagine you are someone small inside a tiny egg..." begins this story of a butterfly's metamorphosis.

Selsam, Millicent and Joyce Hunt. A First Look at Caterpillars. New York: Walker, 1987.

Shows the variety of caterpillars and chrysalis shapes.

Watson, Mary. The Butterfly Seeds. New York: Tambourine Books, 1995. A boy must leave his grandfather behind in the old country when the family emigrates to America. He brings with him a gift from his grandfather--butterfly seeds. When he finds no place for butterflies in the city where they settle, the boy creates a windowbox habitat.

Watts, Barrie. Moth. Englewood Cliffs: Silver Burdett, 1990. Features the large luna moth with several photos of emergence from the cocoon and pumping up the new wings.

Teacher Resources

Pyle, Robert and Sarah Hughes. Peterson Field Guide Coloring Books, Butterflies. Boston: Houghton Mifflin, 1983.

The Butterfly Center, Education Dept., Callaway Gardens, P.O. Box 2000, Pine Mountain, GA 31822.

For butterfly kits: Raise a Butterfly Kit, Carolina Biological Supply Co., 1-800-334-5551; Butterfly Garden Classroom Kit, Delta Education, 1-288-442-5444.

Copycat, Butterflies! May/June 1996. Butterfly flip cards to color with their caterpillars on the back. Back issues available, $5 an issue: P.O. Box 081546, Racine, WI 53408.


Learn about the stages in a butterfly's life.

Name and create a new kind of caterpillar.


Worksheet (see attached)

Egg cartons cut in strips (a strip for each child), scissors, glue, pipe cleaners, construction paper, bottle caps, buttons, yarn, crayons, 3 x 5 cards


Remind the children that last time they studied the life stages of beetles. Ask: Do you remember the names of the life stages? (egg, larva, pupa, adult) Write these on the board. Tell the class they will be learning today about another insect and how it changes as it grows.

Read aloud Eric Carle's The Very Hungry Caterpillar.

Ask: How did the very hungry caterpillar start his life? (egg) He popped out of the egg as a tiny caterpillar. Tell the children that another name for caterpillar is larva. The caterpillar is the larva stage of a butterfly's life. Then the caterpillar built a cocoon around himself. He wasn't eating anymore, was he? He was quiet. This was his pupa stage. Remember the darkling beetle? What did the beetle do during its pupa stage? (rested, played dead) Then the hungry caterpillar nibbled his way out of his cocoon. Ask: And had he changed? (into a butterfly) Tell the children that all butterflies and moths go through these changes in their lives. Ask: Do caterpillars really Second Grade - Science - Lesson 33 - Life Cycles

eat pizza and ice cream cones? (only very hungry human caterpillars do) After mating with a male butterfly, female butterflies lay eggs on food plants. That way when the very hungry caterpillars pop out of their eggs, they can start eating green leaves right away. They eat and eat. But there isn't any growing room inside a caterpillar's body. So when their skin gets too tight, it splits open and the caterpillar wiggles out wearing a new, bigger skin. This is how the caterpillar grows.

Ask: We know caterpillars eat green leaves, but what animals eat caterpillars? (birds, mice, spiders, toads, other insects) Caterpillars have different ways to protect themselves from caterpillar eaters.

Show the children pictures of the monarch butterfly and caterpillar in one of the * suggested books above. Tell them the monarch caterpillars eat only one kind of leaf--the leaf of the milkweed plant. There is a chemical in the milkweed leaves that makes the caterpillars taste bad to birds and mice. The bright yellow and black stripes on the caterpillar are like an advertisement. They say, "Orange and black make a stinky meal." So the birds and mice leave them alone. Tell the children other caterpillars have horns or spines or big spots that look like scary eyes. Show them pictures of colorful caterpillars from suggested books. Tell the children that when a bird comes to peck one of these caterpillars, it sees the scary eyes and is startled. The caterpillar takes that chance to make a getaway. Other caterpillars are colored green to blend in with green leaves and stay hidden from enemies.

Tell the children you want to read them the names of some butterflies and caterpillars. Ask the children to close their eyes and imagine what these insects might look like. Painted Lady, Giant Swallowtail, Woolybear, Dogface, Hickory Horned Devil, Great Purple Hair Streak, Great Tiger Moth, Fiery Skipper, Checkerspot. Tell the children that you would like them to create their own caterpillars. They can help their caterpillars protect themselves with spines or horns or stripes or create any design for camouflage, for hiding in leaves or flowers. Give each child an egg carton strip and each group a portion of the other supplies. Once each child has created a caterpillar, he or she should invent a caterpillar name for it and write it on a 3 x 5 card.

When the children are finished sharing their caterpillars and caterpillar names, read them this poem.


by David McCord

The little caterpillar creeps

Awhile before in silk it sleeps.

It sleeps awhile before it flies,

And flies awhile before it dies,

And that's the end of three good tries.


The poem and newly created caterpillars can be displayed on the bulletin board as a transition into the next science unit, seasonal changes.

Optional Activity


Match various life stages to adult animals.

Second Grade - Science - Lesson 33 - Life Cycles


Worksheet (see attached)


Read the children this poem:

A Place on Earth

by Gwen Frostic

Each frog and insect, bird and tree

And everything that lives and breathes

Somehow creates its place on earth.

The plants need water to survive

In turn give water to the sky.

A blue jay feeds upon the nuts

Of trees that jays have planted.

The moth that pollinates the flowers

Once ate the leaves before it flew

As each thing ever fosters the thing that fosters it.

And in return must ever give as much as it receives.

That all things shall keep a perfect balance

And earn a place on earth.

Tell the children that they have learned about the life cycles of plants, of birds, of frogs, of beetles and butterflies. Everytime an egg is laid or a seed is planted, the cycle repeats itself, again and again. Ask: Do you have a life cycle? Have the children complete the unit review worksheet.

Additional Background Information

In some parts of Africa, butterflies represent the story of the human life cycle.

First they hatch (are born) as small caterpillars (children). They grow into bigger caterpillars (adults). In old age they become quiet and die (pupa). Then the soul escapes the chrysalis and becomes a butterfly.

On the other hand, in the Middle Ages, butterflies were thought to be witches that flew into people's kitchens and stole butter and milk. That is why it was thought so many were bright yellow and why they called them "butter"flies.

Suggested Homework

Directions: You are in a stage in your life cycle. Draw a picture of yourself.

Additional Background

In some parts of Africa, butterflies represent the story of the human life cycle.