How and why leaves change color: A chromatography experiment for fall

In the fall, parents and teachers like to show kids how the leaves change colors. In a matter of weeks or sometimes just days, entire trees will turn from bright green to shades of red, orange, yellow, and brown. But have you ever stopped to wonder why the leaves change color? Or how they do it?

When we were doing our leaves unit study last fall, the kids and I became curious to find answers to the questions of how and why leaves change colors each fall. In this post I’m sharing some video resources we used to educate ourselves as well as an experiment we did that clearly shows that the fall colored pigments are hiding in the green leaves until just the right time.

Note: For more leaf activities, see my Botany Unit Study page. 

The science behind how and why leaves change colors

When my kids asked me why the leaves change colors each fall, I did not initially know the answer. So I turned to the internet to find answers, and I came across a few videos that helped me to understand this phenomenon. I shared these videos with my kids, although the content was a little over their heads. But I stopped the videos where appropriate to provide extra explanation, and by the end we all had a better idea of how and why leaves change their colors.

Here are the three videos we watched:

• Why do leaves change color in the fall? from DNews
• Why do autumn leaves change color? from Scientific American
• Why do leaves change color in the fall? from Super Scienced

From these videos we learned that the green color in leaves is from chlorophyll, which is what leaves use to make their own food. As the days get shorter in autumn, trees sense that winter is approaching. Because their leaves would not survive the cold, dark days of winter, the tree decides to let its leaves go. Therefore, the tree stops producing new chlorophyll.

The chlorophyll already in the leaves breaks down, revealing the other pigments inside the leaves that were previously masked by the green chlorophyll, particularly yellow and orange. Red pigments are then created when sugars in the leaves react with other chemicals to form the red pigments. Location, elevation, temperature, sun exposure, and nutrient content of the soil all have an impact on the color the leaves will turn.

A science activity to show how leaves change colors

After learning how the yellow pigment is always in leaves but only becomes visible once the chlorophyll breaks down, we decided to do a little experiment. Chromatography is a technique that allows one to separate mixtures into individual components. We have done chromatography art projects before to separate the pigments in a marker. But in this case, we decided to use chromatography to separate the green and yellow pigments in some leaves that had not yet begun to turn colors.

Below I share pictures and a brief description of the experiment we did. And you can find a fuller description of the activity from this post at education.com.

We began by collecting green leaves from four different trees in our neighborhood.

We tore the leaves up into small pieces, then placed them into glasses.

We used a butter knife to continue cutting and grinding the leaves. We then covered the leaves with rubbing alcohol.

The leaves required some additional preparation. Please see the directions in this post at education.com for a full explanation.

Once the leaves were ready, we cut thin strips out of coffee filter paper. We placed one end into the rubbing alcohol in the glass. I taped the other end to the outside of the glass to ensure it would not fall in to the glass.

Then we waited for about 90 minutes. We came back and removed the coffee filter strips from the glasses. Through the process of chromatography, the pigments in the leaves had separated into different color bands on our coffee filter strips. Despite the fact that the leaves only looked green to us, there were clear bands of both green and yellow pigments on our coffee filter strips.

Thus, we were able to confirm that the yellow pigments were already inside the leaves even before the color had started turning.

More resources for learning about leaves

More leaf posts from Gift of Curiosity:

• The best way to preserve leaves
• Leaf anatomy
• How leaves “breathe”: A transpiration demonstration
• How leaves get water
• How and why leaves change color in the fall
• Leaf collages art project
• Leaf rubbings activity book
• Fall leaves Sudoku
• Fall leaves lacing cards

For more leaf activities, see my Botany Unit Study page and my Leaves Unit Study Pinterest board.