2007-09-26 05:50:34 · 11 answers · asked by The Global Geezer 7 in Science & Mathematics ➔ Other - Science
The colour changes are caused by the decomposition of chlorophyll, the substance which makes leaves look green. Other pigments found in leaves include purple anthocyanins and yellow or orange carotenoids, but chlorophyll is such a strong pigment in leaves that it masks all the other colours. It does, however, rely on sunlight and warm temperatures to synthesise, as it's constantly being broken down and remade. The shortening days and cooler nights of autumn trigger changes in the tree; the tissues that support the leaf are gradually severed, causing the nutrient flow to be interrupted - this causes the production of chlorophyll in the leaf to decline and the green colour fades. Carotene is a much more stable compound than chlorophyll, and remains in the leaves even when all the chlorophyll has disappeared, causing the fading leaf to appear yellow or orange. The leaves that appear red or purple, are those containing anthocyanins. And I just LOVE the trees in the Autumn!
2007-09-26 06:15:34 · answer #1 · answered by uknative 6 · 2⤊ 0⤋
In spring and summer leaves are green because of the pigment chlorophyll. As the colder weather comes along, chlorophyll stops being produced and other pigments...xanthophylls and carotenes are prominent. Xanthophylls and and carotenes are yellow and orange, hence the lovely autumn colours.
2007-09-26 14:38:58 · answer #2 · answered by Patricia C 2 · 0⤊ 0⤋
chlorophyll makes the leaves green,
chlorophyll is used as part of photosynthesis to make energy for the tree, however sunlight is needed to produce this energy and as this is scarce in winter, trees tend to store the energy that they have made all summer and they don't photosynthesise as much,
also although leaves help plants to make energy, they cause the plant a lot of water loss through transpiration, so leaves changing colour, dying and dropping off saves the plant this loss
2007-09-26 12:57:56 · answer #3 · answered by lakmii 3 · 2⤊ 0⤋
They "don't"...
The leaves are NATURALLY the colour(s) you see them in the fall. The difference is that the Chloroplasts containing the green chlorophyl die off, and the green bleaches away as the chlorophyl molocules stop being replaced.
2007-09-26 13:55:08 · answer #4 · answered by jcurrieii 7 · 0⤊ 0⤋
The change in daylight causes the cholorophyll to leave the leaf and the leaves then will turn different colors on each tree, eventually falling to the ground.
2007-09-26 12:59:57 · answer #5 · answered by Joan H 6 · 1⤊ 0⤋
I believe it's because the tree is going dormant for winter. It stops producing chlorophyll, which kept the leaves green during the growing season.
2007-09-26 12:55:18 · answer #6 · answered by riderpops 2 · 3⤊ 0⤋
Because the tree draws back in all the chlorophyll in the leaves,,,it makes them green,,,when the is is done the leaf turns colour
2007-09-26 12:54:07 · answer #7 · answered by McCanns are guilty 7 · 2⤊ 1⤋
because the chloroplasts containing chlorophyll are destroyed, and what is remaining are the other plasts containing lycopene or other chemicals revealing underlying colors previously masked by tons of green chlorophyll
2007-09-26 13:18:09 · answer #8 · answered by George D 2 · 1⤊ 0⤋
Because the tree sucks all it's moisture down into the roots for the long winter. Whenever plants/leaves don't get water they turn yellow, shrivel, and die.
2007-09-26 12:54:26 · answer #9 · answered by Tim 6 · 1⤊ 2⤋
they wanna keep in with the autumn fashions
2007-09-26 12:53:28 · answer #10 · answered by ♫ ~ Dizzy Person ~ ♫ 3 · 1⤊ 2⤋