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The Real Reason Leaves Change Color In the Fall

The Real Reason Leaves Change Color In the Fall

You’ve probably heard that leaves of deciduous
trees change color in autumn because they lose their green chlorophyll molecules, allowing
the underlying yellow-orange pigments to shine through. However, this doesn’t explain why
the leaves change color in the first place. Deciduous trees drop their leaves each year
to avoid the high cost of winterizing them, but this seasonal shedding would be too wasteful
to be worth doing if it meant/far too wasteful if the trees lost all of the valuable nutrients
they laboriously extracted from the soil to build their leaves earlier in the year. So each fall, deciduous trees recycle their
leaves before dropping them. That means taking apart cells and photosynthetic apparatus from
the inside out in order to recoup their nitrogen and phosphorus and store it in twigs and branches
until next spring. This is actually really tricky, because as
the disassembly starts, the chlorophyll molecules that absorb sunlight for photosynthesis are
still absorbing the sun’s energy. But with no photosynthesis happening, they end up passing
the unused energy along to oxygen molecules, which become dangerously reactive when energized.
These molecules wreak havoc, damaging the parts of the leaf that are in the process
of recovering and transporting nutrients back to the rest of the tree. To keep this destruction to a minimum, leaves
break down their chlorophyll into less dangerous molecules that are typically transparent,
though sometimes yellow. Either way, with the bright green molecules gone, yellow and
orange pigments that were there all along (helping with photosynthesis), are no longer
overshadowed, and ta-da! Yellow and orange leaves. Some trees take an extra autumnal precaution
against chlorophyll-induced-destruction: as the leaf dismantling starts, they build new,
special pigments to shade chlorophyll from sunlight until it can be broken down. These
new pigments tend to be red or purple in color, so trees that use them have red leaves in
the fall – sometimes insanely bright red. In the end, these exquisite gold and russet
displays help deciduous trees recover as much as 50% of the nitrogen and phosphorus from
their old leaves to help grow fresh new green ones in the spring. They are perhaps the world’s
prettiest recycling plants.

100 comments on “The Real Reason Leaves Change Color In the Fall

  1. Interesting! Would be great to see a similar video on the leaves of other plants (both as they grow and as they dry upp, e.g. if you forget to water a plant for a long time)

  2. I know that nobody will see this comment but I have freedom of speech yo man! Schools are so dumb they give you textbooks that explain everything wrongly, like velocity adds together and light has no gravity or gravity comes from mass… One of them included that autumn has no sunlight so chlorophyll breaks down. I watched this video so I told my teacher that autumn has sunlight and she responded to me like: Not enough for plants to do photosynthesis and textbooks are always correct. I am a bit tired of the whole wrong textbooks thing and then Americans got the common core thing where its maths is all wrong. What a world


  4. "…the world's prettiest recycling plants."

  5. I love the video but can someone explain to me how does the change from chlorophyll into chlorophyll catabolite reduces the destruction by reactive oxygen? Does Photosynthesis still takes place ? I don't understand this part!

  6. So, if one of those trees was put on the equator would they still loose the leaves? On the Equator there are no seasons, just perpetual summer.

  7. That 50% recycling of resources in the leaves in fall is merely the direct recovery percentage. Once the leaves fall to the ground, break down into detritus, and are metabolized by the bacteria and fungal colonies at the base of the tree and along its roots, a tree recovers even more of its spent resources, indirectly!

  8. Ahh yes. If those leaves get that red, I think it would be nice to figure out how to make it ourselves. Maybe it will be better in food than Red 40

    Wherever you can,
    (Not just in Tropical Rainforests)
    Rainforests can grow all around the world.
    They can be a Major Mitigator for many of the problems around the world.
    Encourage rain,
    Filter water,
    Retain topsoil,
    Remove pollution from the air and soil,
    Remove CO2 from the atmosphere,
    Create wood for materials,
    Cool the environment,
    Enrich topsoil,
    Help create freshwater aquifers and reservoirs,
    And Many
    Produce food for humans.

  10. 45% are people talking about the puns.
    45% are people saying that's a pun.
    9% are people who doesn't know what a pun is, and it just rhymes.
    1% are people who is saying some of em are not a pun

  11. I literally asked this to my older sister.
    I asked, why do leaves change color and fall off during fall and winter?

  12. The REAL reason that leaves change color in the fall: the trees are going on a diet so when the leaves fall off they have enough space to grow new leaves. They don’t wanna become obese

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