become more noticeable at this time of year

Chlorophyll, carotenoids and flavonoids are present in leaves all year round, but the

Poet John Keats may have written an ode to the rich colours of autumn, but one chemistry teacher has explained exactly why the leaves change hue.

Already summer's leaves have already begun their transition to vibrant oranges, reds and magentas and this is down to a range of chemical compounds - including those that make carrots orange and tomatoes red.

Bournemouth-based teacher Andy Brunning who is the author of the blog, Compound Interest explained that the compounds – chlorophyll, carotenoids, flavonoids - are present in leaves all year round, but become more noticeable at this time of year.

Season of mists and mellow fruitfulness: Chemistry teacher Andy Brunning explained that the compounds – chlorophyll, carotenoids, flavonoids (shown above) - are present in leaves all year round, but become more noticeable at this time of year, explaining why leaves change colour to bright yellows and rich reds

Chlorophyll is the chemical compound responsible for the green colouration of most leaves.

The chemical is held within chloroplasts in the cells of leaves and is an essential ingredient in photosynthesis, in which plants use energy from the sun to convert carbon dioxide and water into sugars.

Plants need warm temperatures and sunlight to produce chlorophyll so as autumn begins and the nights draw in, chlorophyll production slows and the existing amounts of chemical compounds in the leaves decomposes.

Notable carotenoids include beta-carotene, which makes carrots orange, lutein, which contributes to the yellow colour of egg yolks, and lycopene, which is also responsible for the red colour of tomatoes. Anthocyanins aren’t present in leaves all year round but create the bright red and magenta hues

THE COLOURFUL COMPOUNDS Green: Chlorophyll gives plants their green colour. It dominates for most fo the year but less is produced when there is less light during the daytime. Yellow: Carotenoids and flavonoids are always present in leaves but come to the fore in autumn, turning leaves yellow. One example of a carotenoid is lutein which makes egg yolks yellow. Orange: Carotenoids contribute orange colours. Beta-carotene is one of the most common carotenoids in plants and is responsible for the orange colour of carrots. Red: Anthocyanin synthesis is kick-started by the onset of autumn, producing the red and magenta hues in leaves. Advertisement

As a result, other compounds present in the leaves are more noticeable.

Carotenoids and flavonoids are examples of these compounds.

The colours of the compounds are created because of the chemical bonds they contain. These can be single bonds, which consist of one shared pair of electrons between adjacent atoms, or double bonds, which consist of two shared pairs of electrons between adjacent atoms.

The colour-causing molecules in autumn leaves contain systems of alternating double and single bonds, which is known as conjugation.

A large amount of conjugation in a molecule can lead to them being able to absorb wavelengths of light in the visible spectrum, which leads to the appearance of colour.

The colours of the compounds that alter the hues of leaves (stock image) are created because of the chemical bonds they contain. These can be single bonds, which consist of one shared pair of electrons between adjacent atoms, or double bonds, which consist of two shared pairs of electrons between adjacent atoms

Both families of compounds contribute yellows, whilst carotenoids also contribute oranges and reds.

These compounds do degrade along with chlorophyll as autumn progresses, but at much slower rate so their colours become visible.

Notable carotenoids include beta-carotene, which makes carrots orange; lutein, which contributes to the yellow colour of egg yolks; and lycopene, which is also responsible for the red colour of tomatoes.

Anthocyanins, are another member of the flavonoid class of compounds, but they aren’t present in leaves all year round.

As the days get darker, their synthesis begins because of increased concentration of sugars in the leaves, combined with light.

No one is exactly sure why they do this, but some scientists think they may perform some kind of light-protective role, allowing the tree to protect its leaves and stop them from falling for the maximum amount of time.

Anthocyanins provide the vivid red, purple and magenta shades seen in autumn leaves.