Why do leaves change their colour in autumn ?

Answer 1

Leaves don't actually change colour.


The ,yellow,orange,and red colours are always present in the leaves, but are normally masked by the large amounts of green chlorophyll.


In the fall, the leaves on most trees, lose their chlorophyll, this allows the yellow,orange and red, colours in the leaves to be come visible.

Answer 2

The leaves contain chlorophyll, a green pigment that overpowers the carotenoids, yellows and oranges, that are already present in the leaf--you just can't se them until the fall, the tree stops using photosynthesis so it loses the green pigment chlorophyll and the remaining colors underneath begin to show through.

In fall favorable weather conditions may dictate the color, which could be red or yellow in some cases. Warm sunny days followed by cool nights and temperatures below 45 degrees F. prevent the sugar from moving out of the leaves. The red pigment anthocyanin forms from sugar trapped in the leaves. Thus red leaves as well as the yellow ones described above. Some leaves just turn brown which just means the leaf died.

Answer 3

We all enjoy the colors of autumn leaves. Did you ever wonder how and why a fall leaf changes color? Why a maple leaf turns bright red? Where do the yellows and oranges come from? To answer those questions, we first have to understand what leaves are and what they do.
Leaves are nature's food factories. Plants take water from the ground through their roots. They take a gas called carbon dioxide from the air. Plants use sunlight to turn water and carbon dioxide into glucose. Glucose is a kind of sugar. Plants use glucose as food for energy and as a building block for growing. The way plants turn water and carbon dioxide into sugar is called photosynthesis. That means "putting together with light." A chemical called chlorophyll helps make photosynthesis happen. Chlorophyll is what gives plants their green color.

As summer ends and autumn comes, the days get shorter and shorter. This is how the trees "know" to begin getting ready for winter.

During winter, there is not enough light or water for photosynthesis. The trees will rest, and live off the food they stored during the summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can't see them in the summer, because they are covered up by the green chlorophyll.

The bright reds and purples we see in leaves are made mostly in the fall. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves.

It is the combination of all these things that make the beautiful colors we enjoy in the fall.

Answer 4

Plants need to be able to survive the winter months, so they take the nutrients from the leaves and transfer it to the roots and other parts of the plant. This is so it has reserves it needs to produce new leaves in the spring.

What you are seeing is the plant moving its energy, the nitrogen (a component of chlorophyll) and other elements out of the leaves, which is why the leaves turn colors. when a plant has a nitrogen deficiency, the lower leaves begin to turn yellow first, the same concept applies to plants going into 'dormancy'.

Answer 5

With the slowly cooling nights and sunny cool to warm days of fall the tree cuts off all photosynthesis and the green of chlorophyll begins to fade revealing the other colors in the leaves which were always there but were masked by the color of the chlorophyll.

Answer 6

because some substances acumillate at the petiole region of leaf leading to stoppage of food, water and minerals.so, leaf donot perform photosynthesis(as photosynthesis requirs both light and water) and chlorophyll lost makes the change in color and falling of leaf along with petiole and a new leaf may or maynot come.

Answer 7

like humans plants too have biological clock in them n with the change of enviorment certain philological changes occur in them one of them is losing chlorophyll(which is responsible 4 there green colour)thus these turn yellow

Answer 8

Because the nutrition cuts off to them so the tree can shed them and go dormant for the winter.

Answer 9

it is the tree that sucks the chlorophile out of the leaves in order top survive the winter.

Answer 10

In simple terms...

The tree kills them to sustain life.