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Why Do Leaves Change Colour in Autumn?

Some autumn colours were in the leaf all summer. Others can develop as the season changes.

Suggested Grades 3–4247 core-passage wordsUpdated 2026-09-18
What you’ll practiseExplain a sequence of changes and distinguish existing pigments from pigments made in autumn.

Device/browser voice. Pronunciation and availability vary.

Three types of pigment: green chlorophyll, yellow-orange carotenoids, and red-purple anthocyanins. The diagram is simplified.ChlorophyllCarotenoidsAnthocyaninsSome pigments are already present; others can form in autumn.
Pigment colours shown schematically. A real leaf can contain a mixture.

Green is not the only colour

A green summer leaf can contain more than one pigment. A pigment is a substance that gives something colour. Chlorophyll, the green pigment, helps a plant capture light energy for making sugars.

Yellow and orange pigments called carotenoids can be present too. During the growing season, the strong green colour often hides them from view.[1]

When the green fades

In many places in Canada, autumn brings shorter days and cooler temperatures. Many deciduous trees begin a seasonal change. Deciduous means that they shed their leaves at a particular time of year.

As chlorophyll breaks down and is not replaced as quickly, its green colour fades. The yellows and oranges become easier to see. The leaf has not been painted from outside; the balance of visible pigments has changed.[1]

Red is a different part of the story

Red and purple colours can come from pigments called anthocyanins. Some leaves produce these during autumn. Light, temperature and sugars in the leaf can affect their production.

This is why “all autumn colours were hidden in summer” is not quite right. Different colours can have different explanations. The species of tree and the weather also help explain why autumn displays vary.[1]

A leaf separates from its branch

The tree also develops a separation layer near the base of the leaf stalk. As the connection weakens, the leaf eventually falls. The tree protects the place where it was attached.

Dropping leaves helps many trees reduce water loss through the winter. Losing leaves does not mean the entire tree has died. Living branches and buds remain, ready for another growing season.[1]

Word Lab

Use the meaning, hear the word, then try it in your own sentence.

pigment

noun

A substance that gives colour.

The leaf contains several pigments.

chlorophyll

noun

A green pigment that helps capture light for photosynthesis.

Chlorophyll makes many summer leaves look green.

carotenoid

noun

A type of plant pigment that can appear yellow or orange.

Carotenoids become easier to see as green fades.

deciduous

adjective

Shedding leaves seasonally.

A maple is a deciduous tree.

gradually

adverb

Little by little, rather than all at once.

The green colour gradually faded.

Check your understanding

Choose an answer, explain your choice, and then check. Hints and retries are welcome.

Cause and effect1. Why do yellow and orange colours become easier to see?
Show answer and explanation

Answer: Chlorophyll fades, revealing other pigments.. As the green pigment breaks down, existing yellow and orange pigments become more visible.

Compare2. How does the passage distinguish many red colours from yellow ones?
Show answer and explanation

Answer: Some red pigments are produced during autumn.. Carotenoids can already be present, whereas anthocyanins may be produced during autumn.

Sequence3. Which sequence matches the passage?
Show answer and explanation

Answer: Chlorophyll fades; other colours become visible; the weakened connection lets the leaf fall.. This sequence follows the changes described. Colour change and separation are connected seasonal processes, not paint arriving from outside.

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Put it in your own words

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Check your own explanation

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Compare with a model response

Yellow and orange carotenoids can already be in the leaf, hidden by chlorophyll. Some red anthocyanins form in autumn, so neither claim explains every colour.

Sources and revision notes

Source check: 2026-09-18. Grade guidance is an editorial suggestion, not a standardised reading score.

  1. US Forest Service — The Joy and Science of Fall Colors
What changed in this edition?

Replaced implausible multiple-choice distractors and clarified the different explanations for yellow/orange and red pigments.

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