B. Life Systems · Growth and Changes in Plants

Plant Life Cycles: From Seed to Seed

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

Learning goals

I can describe the stages in the life cycle of a flowering plant.
I can describe how a plant changes as it grows.
I can compare the life cycles of a bean plant, a maple tree and a pine tree.
I can measure and record a plant's growth.
I can write and debug a short code that models a plant life cycle.

Words to know

life cycle
The stages a living thing goes through as it grows, changes and makes new living things.

germinate
When a seed starts to grow. A root pokes out first, then a shoot.

seedling
A very young plant that has just sprouted from a seed.

sapling
A young tree, taller than a seedling but not yet fully grown.

mature
Fully grown and able to make seeds.

annual
A plant that grows, makes seeds and dies all in one growing season, like a bean plant.

perennial
A plant that lives for many years, like a maple tree or a rhubarb plant.

Remember from Grade 2

In Grade 2 you learned about animal life cycles, like egg → caterpillar → chrysalis → butterfly. Plants have life cycles too! A plant's life cycle starts with a seed and ends with new seeds.

A bean on the windowsill

Luca planted one dry bean in a cup of soil. For three days nothing seemed to happen. On day 5, a curved green hook pushed up out of the soil. By day 14 there was a plant with big leaves. A few weeks later there were small flowers, and then long green pods with new beans inside.

One bean made many beans! That is a life cycle.

A young bean seedling growing in a clear plastic cup of soil on a windowsill, with its roots visible through the cup. — This bean seedling is in an early stage of its life cycle. You can see its first two thick seed leaves, its new true leaves on top, and roots spreading in the soil. AI-generated image

The life cycle of a flowering plant like a bean.

The stages of a bean plant's life cycle

Seed. A dry bean has a baby plant and stored food inside.
Germination. With water, air and warmth, the seed swells and its coat splits. A tiny root pokes out first and grows down. Then a shoot grows up toward the light.
Seedling. The young plant pushes out of the soil. Its first two leaves, the seed leaves, give it food until its true leaves grow.
Adult plant. It grows taller, with more leaves and a bigger root system.
Flowers. The mature plant makes flowers. After pollination...
Fruit with seeds. The flowers become pods (the fruit) with new seeds inside. The seeds fall or are planted, and the cycle begins again.

Seeds and light

Most seeds do not need light to germinate. They sprout in the dark soil using their stored food. But as soon as the seedling comes out of the soil, it needs light to make its own food.

Different plants, different life cycles

All seed plants follow the same big pattern: seed → young plant → mature plant → new seeds. But they do not all take the same time or change in the same ways.

An annual plant, like a bean, sunflower or marigold, goes through its whole life cycle in one growing season (spring to fall). Then it dies, and only its seeds live through the winter.
A perennial plant, like a maple tree, a strawberry plant or rhubarb, lives for many years. It can make flowers and seeds again and again.

Stage	Bean plant	Sugar maple tree	Eastern white pine tree
seed	bean	"key" with a wing	small seed with a wing, inside a cone
young plant	seedling (days)	seedling, then sapling (years)	seedling, then sapling (years)
mature plant	in a few weeks	after many years	after many years
makes new seeds in	pods (fruit) from flowers	keys (fruit) from flowers	cones (no flowers)
how long it lives	one growing season	often more than 100 years	often more than 100 years

Comparing three life cycles. All start as seeds and end by making new seeds.

How plants change as they grow

As a plant grows, it changes in many ways:

It gets taller and its stem gets thicker.
It grows more leaves and more roots.
A tree's stem becomes woody and is covered in bark.
It starts to make flowers (or cones), then fruits and seeds.
Trees grow a new ring of wood inside the trunk every year. Counting the rings on a stump tells you about how old the tree was!

Worked example

Let's order a sunflower's life cycle

These sunflower stages are mixed up: big yellow flower head, seedling with two seed leaves, striped seed, flower head full of seeds, tall plant with a big bud. Put them in order.

Every sunflower starts as a striped seed.
It germinates and becomes a seedling with two seed leaves.
It grows into a tall plant with a big bud.
The bud opens into a big yellow flower head.
After pollination the head becomes full of seeds. Birds eat some; others fall and grow next spring.

seed → seedling → tall plant with a bud → flower head → head full of seeds

Day	Height above the soil
5	2 cm
7	5 cm
10	9 cm
14	15 cm

Luca's bean plant measurements.

Luca's measurements as a line graph. The line keeps going up, showing the plant grew taller every time Luca measured. From day 7 to day 14 it grew 10 cm (15 − 5).

Worked example

Let's read growth data

Look at Luca's table. How much did his bean plant grow from day 7 to day 14?

Find the height on day 14: 15 cm.
Find the height on day 7: 5 cm.
Subtract: 15 − 5 = 10.

It grew 10 cm from day 7 to day 14.

Coding a life cycle

A code is a list of steps that a computer follows in order. We can write a code to model (show) a plant's life cycle. A loop repeats steps so we do not have to write them again and again.

start with: seed

add water and warmth

show: seed germinates

show: seedling

repeat 3 times:

grow 5 cm taller

add 2 leaves

show: adult plant

show: flowers

show: pods with seeds

go back to start

A code that models the life cycle of a bean plant. The loop grows the plant 3 times.

Worked example

Let's debug the code

Mia's code has a bug (a mistake):

start with: seed → show: flowers → show: seedling → show: adult plant → show: pods with seeds

Find and fix the bug.

Read each step and ask: "Does this happen next in real life?"
After a seed, does a plant make flowers? No! It must first germinate and become a seedling.
The step show: flowers is in the wrong place. It must come after show: adult plant.

Fixed code: seed → seedling → adult plant → flowers → pods with seeds. Testing each step against real life is how coders find bugs.

Just for fun

What has rings but no fingers?

A tree trunk! Each ring is one year of growth.

Hands-on activity

Bean diary

You need: 3 dry beans (kidney, lima or pinto beans from the grocery store), a clear plastic cup, paper towel, water, a ruler and a notebook.

Soak the beans in water overnight.
Line the inside of the cup with a folded paper towel. Stuff crumpled paper towel in the middle so the lining presses against the cup.
Slide the beans between the cup and the paper towel, about halfway down, so you can see them.
Pour a little water in the bottom so the paper towel stays damp (not flooded).
Every day, draw what you see and write the date. When the shoot is above the cup, measure its height in cm.
After 2 weeks, move the strongest seedling into a pot of soil to keep watching its life cycle.
Make a life cycle poster from your diary to share with your family.

Coder's corner: write a short code with a loop that matches what your bean did, for example "repeat 4 times: grow 2 cm".

Grown-up note: Use beans meant for cooking, not treated garden seeds. Raw kidney beans are not safe to eat, so make sure the soaked beans do not get eaten. Wash hands after handling.

Your turn

Put these stages in order: adult plant, seed, flowers, seedling, fruit with seeds.

What three things does a seed need to germinate?

When a seed germinates, which grows first: the root or the shoot?

What is an annual plant? Give an example.

What is a perennial plant? Give an example.

Where does a pine tree make its seeds?

Give two ways a tree changes as it grows.

More practice: warm-up

What is a seedling?

What is a young tree called?

What does "germinate" mean?

What comes right after flowers in a bean's life cycle?

Does a maple tree live for one year or many years?

More practice: on your own

A bean plant was 4 cm tall on Monday and 11 cm tall a week later. How much did it grow?

Why can a seed germinate in the dark soil but a seedling needs light?

How is a pine tree's life cycle different from a maple tree's?

A tree stump has 47 rings. About how old was the tree?

Find the bug: seed → seedling → pods with seeds → flowers → adult plant

Challenge

In Ontario, why do annual plants like beans leave seeds behind in the fall instead of staying alive all winter?

Sunflower A grew from 30 cm to 75 cm in 3 weeks. Sunflower B grew from 40 cm to 80 cm in the same 3 weeks. Which grew more? By how much?

Write a short code with a loop that models a maple tree that grows for 5 years and then makes keys.

Check your understanding

Quiz

What is the correct order of a flowering plant's life cycle?

When a bean germinates, what comes out first?

Which plant is an annual?

A young tree is called a...

A bean plant was 6 cm tall and later 14 cm tall. How much did it grow?

What does a loop do in a code?

How does a pine tree's life cycle differ from a bean plant's?

For parents and teachers

Big idea (B2.3): All seed plants follow a cycle of seed → young plant → mature plant → new seeds, but the timing and the changes differ (annuals vs perennials, flowering plants vs conifers). Measuring and recording growth and making a life cycle poster practise communication (A1.5). The code blocks model a concept and practise debugging (A2.1).

Common difficulties:

Thinking seeds need light to sprout. Most do not; they need water, air (oxygen) and warmth. The seedling needs light once it emerges.
Reading a ruler from 1 instead of 0. Show your child to line up the 0 mark with the soil.
Thinking the life cycle ends when the plant dies. Stress that the seeds carry it on.

How to help: The bean diary is the heart of this lesson. Remind your child to check it daily and to measure in centimetres. Use cooking beans rather than treated garden seed, and keep soaked kidney beans away from snacking: raw kidney beans are toxic until fully cooked. Count rings on a cut stump or firewood log together.