Life Cycles: Frog, Butterfly, and Chicken - Second Grade Science
Every living animal starts life, grows, changes, reproduces, and eventually dies in a repeating pattern known as a life cycle. However, the paths animals take to reach adulthood look completely different across the animal kingdom. While a baby chick hatches from an egg looking like a fluffy miniature chicken, a baby tadpole looks and swims like a fish before morphing into a jumping frog, and a caterpillar transforms through complete metamorphosis inside a chrysalis to become a winged butterfly!
The Wonder of Metamorphosis
Metamorphosis is a biological process where an animal undergoes an astonishing, rapid change in body structure between its juvenile stage and its adult stage.
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| TWO WAYS ANIMALS GROW UP |
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| DIRECT DEVELOPMENT (Chicken) METAMORPHOSIS (Frog/Butterfly) |
| Egg ===> Baby Chick ===> Adult Hen Egg ===> Larva ===> Adult |
| Baby looks like small adult! Baby looks completely different|
| from the adult form! |
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The Frog Life Cycle: An Amphibian Transformation
A frog undergoes metamorphosis, beginning its life completely underwater as an aquatic tadpole before transforming into a land-dwelling adult frog.
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| FROG LIFE CYCLE STAGES |
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| 1. JELLY EGGS ----> Laid in calm pond water in clusters |
| 2. TADPOLE ----> Has swimming tail and gills; eats pond algae |
| 3. TADPOLE WITH LEGS -> Back legs sprout, then front legs appear |
| 4. FROGLET ----> Tail shrinks, lungs develop, climbs ashore |
| 5. ADULT FROG ----> Tail fully absorbed; breathes air; eats bugs |
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( Eggs in Pond )
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v
( Tadpole ) <-- Tail & Gills
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v
( Tadpole with Legs ) <-- Sprouts hind legs
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v
( Froglet ) <-- Tail shrinks, lungs grow
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v
( Adult Frog ) <-- Breathes air, jumps on land!
Stage 1: Jelly Eggs
The mother frog lays thousands of soft, clear jelly-coated eggs in calm pond water. The jelly insulates the embryos and keeps them hydrated.
Stage 2: The Swimming Tadpole
When the egg hatches, a tadpole emerges. A tadpole has no legs, breathes with feathery gills, and swims using a long finned tail, grazing on green pond algae.
Stage 3 and 4: Sprouting Legs and Developing Lungs
As the tadpole grows, hind legs pop out first, followed by front legs. Inside its body, lungs develop to replace gills. As it approaches the froglet stage, its tail is slowly absorbed by its body for nutrition.
Stage 5: The Adult Frog
The fully formed adult frog leaves the pond water. It breathes air with lungs and moist skin, uses powerful hind legs to hop on land, and catches flies with its sticky tongue.
The Butterfly Life Cycle: Complete Metamorphosis
A butterfly experiences complete metamorphosis consisting of four totally distinct stages: egg, larva, pupa, and adult.
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| BUTTERFLY LIFE CYCLE (4 STAGES) |
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| [ 1. EGG ] Laid on host plant leaf |
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| v |
| [ 2. LARVA ] Caterpillar eats leaves ravenously |
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| v |
| [ 3. PUPA ] Chrysalis stage; body rebuilds |
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| v |
| [ 4. ADULT ] Winged butterfly drinks nectar |
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Stage 1: The Egg
The female butterfly glues tiny barrel-shaped eggs onto the underside of specific host plant leaves (for instance, Monarch butterflies lay eggs only on milkweed).
Stage 2: The Larva (Caterpillar)
The hatched caterpillar is an eating machine. It munches leaves non-stop, growing rapidly and shedding its striped skin four to five times.
Stage 3: The Pupa (Chrysalis)
The caterpillar spins a silk pad, hangs upside down in a "J" shape, and sheds its skin one final time to reveal a hard shell called a chrysalis. Inside this quiet capsule, its caterpillar tissues dissolve into a nutrient soup and rebuild into wings, long legs, compound eyes, and antennae!
Stage 4: The Adult Butterfly
The chrysalis splits open, and a glorious butterfly crawls out. It pumps blood-like fluid called hemolymph into its crumpled wings until they expand and dry stiff, ready for flight.
The Chicken Life Cycle: Direct Development
Unlike frogs and butterflies, a bird such as a chicken does not undergo metamorphosis. It exhibits direct development, hatching from an egg as a recognizable miniature bird.
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| CHICKEN LIFE CYCLE STAGES |
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| 1. FERTILIZED EGG ----> Incubated under warm hen feathers for 21 days|
| 2. HATCHING ----> Chick uses egg tooth to pip through shell |
| 3. FLUFFY CHICK ----> Yellow down feathers; pecks grain seeds |
| 4. ADULT ROOSTER/HEN -> Full adult plumage, combs, and lays eggs! |
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The 21-Day Incubation
The mother hen sits on her nest, keeping the hard-shelled eggs at a steady 37.5°C (99.5°F). Inside, the embryo consumes the rich yellow yolk and clear egg white. On day 21, the chick uses a sharp temporary bump on its beak called an egg tooth to crack a ring around the shell and push its way out.
Comparing Life Cycles
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| COMPARING THE THREE LIFE CYCLES |
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| ORGANISM STARTING FORM INTERMEDIATE FORM ADULT FORM |
| Frog Jelly egg Aquatic Tadpole Land Hopper |
| Butterfly Tiny egg Leaf Caterpillar Winged Flyer |
| Chicken Hard-shelled egg Fluffy Chick Adult Hen/Bird |
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Chapter Review Exercises
Question 1: What is metamorphosis, and which of the three animals studied in this chapter does NOT undergo metamorphosis?
Question 2: Describe three structural changes that occur as an aquatic tadpole transforms into an adult frog.
Question 3: What happens to a caterpillar inside the protective shell of a chrysalis during the pupa stage?
Question 4: What is an egg tooth, and how does a baby chick use it to hatch from its egg?
Solutions and Explanations
Solution 1: Metamorphosis is a process of dramatic physical transformation where an animal's body structure changes completely between its juvenile and adult stages. The chicken does not undergo metamorphosis; it develops directly from a hatchling that already resembles an adult bird.
Solution 2: As a tadpole transforms into an adult frog, it grows hind legs and front legs for jumping, its swimming tail is gradually reabsorbed into the body, and its underwater breathing gills are replaced by lungs for breathing air.
Solution 3: Inside the chrysalis during the pupa stage, the caterpillar's body tissues break down into a nutrient liquid and rebuild completely into adult structures, including wings, long legs, antennae, proboscis mouthparts, and compound eyes.
Solution 4: An egg tooth is a small, sharp, temporary calcium spike on the tip of a baby chick's upper beak. The chick uses this tool to peck and crack open the tough eggshell from the inside, after which the egg tooth naturally falls off.