B. Life Systems · Growth and Changes in Animals

Comparing Life Cycles (and Coding Them!)

B2.4 B2.3 A2.1 A1.5About 40 minutes

Learning goals

I can compare how different animals change in appearance and behaviour during their life cycles.
I can tell which animals go through metamorphosis and which look like small adults.
I can write clear step-by-step code for a life cycle, use a loop, and fix a bug.

Words to know

appearance
How something looks: its size, shape, colour and body parts.

behaviour
What an animal does: how it moves, eats, hides and cares for its young.

code
Clear instructions, in order, that a computer (or a person pretending to be a robot) can follow.

sequence
The order of the steps. In code, the order matters!

loop
A part of code that repeats. A life cycle is like a loop because it starts again.

bug
A mistake in code.

debug
To find and fix a mistake in code.

Who changes the most?

Think of a monarch, a frog, a robin and a bear. When each one is a baby, does it look like its parent?

A baby bear looks like a small bear. A baby monarch (a caterpillar) looks nothing like a butterfly! Today we compare life cycles and then write code to show one.

A black bear cub walking beside its mother in a green forest. — A bear cub looks like a small copy of its mother. Bears grow up without metamorphosis. AI-generated image

Two big kinds of change

1. Metamorphosis (a big change): The young look and act completely different from the adult. Their body shape changes. Examples: monarch butterfly, ladybug, frog, toad.

2. Growing up (looks like a small adult): The young look like a smaller version of the adult. They mostly get bigger, and maybe grow feathers, antlers or adult teeth. Examples: robin, Canada goose, black bear, moose, snapping turtle, people. (A grasshopper is in between: the nymph looks like a small adult, but it has no wings yet.)

A tadpole and a frog look completely different. A turtle hatchling is shaped like its parent, only smaller.

Animal	How it starts	Big change in shape?	Who cares for the young?
monarch butterfly	egg on milkweed	yes: caterpillar → chrysalis → butterfly	no one; the caterpillar is on its own
wood frog	eggs in a pond	yes: tadpole → frog	no one; tadpoles are on their own
snapping turtle	eggs buried in sand or soil	no; hatchlings look like tiny turtles	no one; the mother lays the eggs and leaves
robin	egg in a nest	no; it grows feathers and gets bigger	both parents feed it
black bear	born live in a den	no; it gets bigger	the mother, for about a year and a half

Comparing 5 Canadian animals' life cycles

Behaviour changes too

As animals grow, they act differently:

A tadpole swims and eats algae. A frog hops and catches insects.
A nestling waits to be fed. An adult robin hunts for worms and builds a nest.
A bear cub follows its mother. An adult bear lives alone and finds its own food.
A turtle hatchling walks straight to the water all by itself!

Code a life cycle

A life cycle happens in a sequence, one step after another, in the right order. Code is also a sequence of clear steps. And a life cycle repeats, just like a loop in code!

Here is code for a frog's life cycle. Read it from top to bottom.

REPEAT forever:

start as an EGG in a pond

hatch into a TADPOLE

grow BACK LEGS

grow FRONT LEGS

become a FROGLET

tail shrinks away

become an ADULT FROG

lay EGGS in a pond

(go back to the top and repeat)

A frog life cycle written as code. The REPEAT makes it a loop.

Worked example

Let's debug the butterfly code

Jayden wrote this code for a monarch, but the butterfly will not work right. Find the bug:

1. start as an EGG 2. become a CHRYSALIS 3. hatch into a CATERPILLAR 4. become a BUTTERFLY 5. lay EGGS on milkweed 6. REPEAT

Read each step and ask: "Does this happen next in real life?"
Step 1, egg: yes, that is the start.
Step 2, chrysalis: no! A caterpillar must hatch from the egg first.
So steps 2 and 3 are in the wrong order. That is the bug.
Debug: swap them. 1 egg, 2 caterpillar, 3 chrysalis, 4 butterfly, 5 lay eggs, 6 repeat.

The bug was the sequence: the chrysalis came before the caterpillar. In code and in life cycles, order matters.

Worked example

Let's code a turtle hatchling to the pond

A snapping turtle hatchling must walk to the pond without going past the fox. It starts in row 2, on the left, facing right. Write the code.

Look at the grid. The fox is in row 1, second square. The pond is in row 1, fourth square.
Move forward 2. The turtle goes along row 2 to the third square. (It stays away from the fox.)
Turn left. Now it faces up, toward row 1.
Move forward 1. It is in row 1, third square.
Turn right, then move forward 1. It reaches the pond!

Code: move forward 2, turn left, move forward 1, turn right, move forward 1. The turtle reaches the pond safely.

The turtle's path: forward 2, turn left, forward 1, turn right, forward 1.

Funny but true

Computer "bugs" got their name partly from a real bug! In 1947, people working on an early computer found a moth stuck inside it. They taped it into their notebook and wrote that it was the first actual bug found in a computer.

Hands-on activity

Be a robot animal (unplugged coding)

You need: masking tape (or pillows) to make a 4 by 4 grid on the floor, paper arrow cards ("forward", "turn left", "turn right"), and a family member.

Make the grid. Choose one square as the nest (or pond) and one as danger (a fox or a road).
Your family member is a robot fledgling (or turtle). They can only do exactly what the cards say.
Lay out arrow cards in order to get the robot to the nest without crossing danger.
Run the code: read each card aloud while the robot moves.
Did it work? If not, find the bug and debug it. Then switch roles!

Challenge: Make code that uses a loop, like "repeat 3 times: forward 1".

What to look for: clear, exact instructions in the right order, and fixing mistakes calmly. Bugs are normal. Programmers fix them all the time!

Your turn

Name 2 animals that go through metamorphosis.

Name 2 animals whose babies look like small adults.

Who takes care of a snapping turtle hatchling?

Give one behaviour change in a frog's life cycle.

What is a loop in code?

Why is a life cycle like a loop?

What do we call a mistake in code?

More practice: warm-up

Does a baby moose look like a small moose?

Does a caterpillar look like a butterfly?

What does sequence mean?

Who feeds baby robins?

Turtles start life as...

More practice: on your own

Sort into big change or looks like a small adult: ladybug, moose, toad, Canada goose.

Find the bug: egg → froglet → tadpole → frog

Compare the parent care of a bear and a frog.

Write code for a robin's life cycle using a loop.

A robot starts facing right. The code is: forward 1, forward 1, forward 1. How can you write this shorter with a loop?

Challenge

Why do you think animals with no parent care, like frogs and turtles, lay lots of eggs, but a mother bear has only a few cubs (usually 2 or 3) at a time?

A grasshopper's nymph looks like a small adult, but a monarch's caterpillar does not. Which of the two kinds of change does each one fit best?

Write code for this: a goose flies south in the fall and north in the spring, every year. Use a loop.

Check your understanding

Quiz

Which animal goes through metamorphosis?

Which young animal looks most like a small version of its parent?

Who cares for snapping turtle hatchlings?

What is a bug in code?

Why is a life cycle like a loop?

What is wrong with this code: egg → butterfly → caterpillar → chrysalis?

For parents and teachers

Big idea: Comparing life cycles (B2.4): some animals change body shape completely (metamorphosis), while others are born or hatch looking like small adults and mainly grow. Behaviour and parent care also differ a lot.

Coding (A2.1): Grade 2 coding is about clear, precise instructions in the right order (sequence), simple repetition (loops), and finding and fixing mistakes (debugging). No screen is needed: the floor-grid game is real coding practice. If you want a screen activity, free block-coding apps such as ScratchJr work well for this age.

Accuracy notes: Snapping turtles bury their eggs on land, often in sandy or gravelly spots, and provide no care. Grasshoppers are an "in-between" case (gradual change, no pupa).

Common difficulties:

Giving vague robot instructions ("go over there"). Ask, "How many steps? Which way?"
Getting frustrated by bugs. Celebrate finding a bug: that is what programmers do every day.

How to help: Write a bedtime routine as code together, then find a loop in it ("repeat: brush each tooth").