Praxis: Why do leaves change colour in the fall?

By Patty Rooks on September 28, 2019.

praxis@praxismh.ca@PraxisMedHat

Fall officially arrived this week. In the northern hemisphere, it arrived on Sept. 23. This is the day of the Autumnal Equinox. This means that the sun is located just above the Earth’s equator and that day and night are roughly equal in length. Some more pronounced ways we can see fall arriving is the changing of the leaves on the trees. It is such a beautiful time of the year with all of the browns, oranges, even reds outside in nature. I hope you take a member to enjoy the beauty of our new season! With that being said, I have had a number of people ask me why do the leaves turn all of these colours? Let’s investigate!

*Remember to ask an adult before doing this experiment.

Materials

– three or four leaves (as green as possible)

– small jar

– plastic wrap

– rubbing alcohol

– scissors

– coffee filters

– bowl or shallow pan

– masking tape

– marker

– rubbing alcohol

– safety goggles

– hot tap water

– wooden spoon

– pencil

Procedure

NOTE: Remember science safety. It is important to remember that when you do science experiments you NEVER eat, drink or smell anything you are working with. This is for your own safety. Always wash your hands when you are finished.

1. Put your safety goggles on.

2. Find two or three green leaves and carefully pick them off of the tree.

3. Take the leaves and using the scissors cut them up into small pieces. Place the chopped up leaf in the jar.

4. Using the masking tape put a label on your jar “poison” do not drink rubbing alcohol. You want to make sure this is labelled clearly.

5. Pour enough rubbing alcohol into the jar so the leaves are completely submerged.

6. Cover the jar with plastic wrap.

7. Set aside for now.

8. Fill the bowl about half full of water.

9. Place your jar in the water for about thirty minutes. You only need the water to go about halfway up the jar you do not want to sink your jar into the water or allow any water in with the rubbing alcohol.

10. Observe every five minutes, giving the jar a little swirl or stir with the spoon. If the water cools off too much replace this as it needs to stay hot. What do you see happening?

11. While you are waiting, cut the coffee filter into long strips.

12. Place the pencil on a flat surface. On the long side of the pencil, place the end of one of the filter paper strips. Roll this filter paper around the pencil.

13. After the leaves have sat for thirty minutes in the rubbing alcohol, remove. Take the plastic wrap off as well.

14. Place the pencil on the top of the jar.

15. Unwind the filter paper so that the tip is just sitting in the rubbing alcohol mixture.

16. Observe closely.

17. What is going on?

What is going on?

In this experiment you extracted the pigments from the green leaves. As the alcohol travelled up the filter paper, you should have seen different colours also stretching out. I hope that you were able to see some green, orange, yellow and even possibly some reds. It all depends on what type of leaf you collected. Try leaves from different trees to see the difference in the colour separation.

Did you know that the green pigments are from chlorophyll, the oranges from carotene, the yellows from xanthophylls and the reds from anthocyanin pigments? You begin to see these colours because as winter approaches, plants begin to photosynthesize much less. The plant realizes that it is wasting its valuable energy making chlorophyll as the cold winter temperatures approach. As photosynthesis slows down, the other pigments in the leaves begin to appear and they turn the beautiful colours we enjoy so much in the fall!

Teachers please do not forget to book your Hands-on Learning Kits, Scientists in the Classroom presentations and Science Fair 101 Program as soon as possible. Spots are filling up fast!

Patty Rooks, Senior Scientific Consultant PRAXIS, “Connecting Science To The Community.” Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook. NOTE our NEW address: #12 826 11 Street S. E., Medicine Hat, Alberta, T1A 1T7 Phone: 403-527-5365, email: praxis@praxismh.ca.

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