And the way they change their color in autumn. molecules, responsible for the bright shades of yellow and orange, are no longer a mystery, but why the leaves turn red is still a mystery.

Responding to air temperature change and fewer daylight, the leaves stop producing chlorophyll(which gives green color), absorbing blue and partially red light emitted by the Sun.

Since chlorophyll is sensitive to cold, some weather changes, such as early frosts, will "turn off" its production faster than usual.

Why leaves turn yellow and fall

At this time, orange and yellow pigments called carotenoids(which can also be found in carrots) and xanthophylls shine through leaves that have no green left.

"The yellow color is present in the leaves all summer, but it is not visible until the green disappears," says Paul Shaberg(Paul Schaberg), a plant physiologist with the US Forest Service.

But scientists still have little information about the red color that appears on some leaves in the fall.

It is known that the color red comes from anthocyanides, which, unlike carotenoids, are produced only in autumn. Anthocyanides also give color to strawberries, red apples and plums.

Trees produce anthocyanides when they sense a change in environment - frost, ultraviolet radiation, drought and/or fungus.

But red leaves are also a sign of illness tree. If you notice that the leaves of the tree turned red earlier than usual (at the end of August), most likely the tree is suffering from a fungus, or it has been damaged by a person somewhere.

Why does a tree expend its energy to produce new anthocyanides in a leaf when that leaf is about to fall off?

Paul Schaberg believes that if anthocyanins help the leaves stay on the tree longer, they may help the tree absorb more nutrients before the leaves fall off. The tree can use the absorbed resources to bloom in the next season.

Anthocyanins

The topic of anthocyanins is a little more difficult to study than the rest of the tree components. While all trees contain chlorophyll, carotene, and xanthophylls, not all produce anthocyanins. Even those trees that have anthocyanins produce them only under certain conditions.

Before a tree gets rid of its leaves, it tries to absorb as much more nutrients of them [leaves], at which point anthocyanin comes into play.

Scientists have several answers to the question of why some trees produce this substance and the leaves change their color.

The most widely held theory suggests that anthocyanins protect leaves from overabundance sunlight, while allowing the tree to absorb the beneficial substances stored in the leaves.

On the tree these pigments play a role sunscreen , blocking dangerous radiation and protecting the leaves from an overabundance of light. They also protect cells from rapid freezing. Their benefits can be compared with the benefits of antioxidants.

Too much sunlight, dry weather, freezing weather, low nutrient levels and other stressors increase the concentration of sugar in tree sap. This kicks off the mechanism to produce large amounts of anthocyanins in a last ditch effort to store energy to get through the winter.

Scientists believe that the study of anthocyanides helps to understand the level of the disease every tree. This, in turn, will give a clearer picture of environmental problems in the future.

As the character of the book and cartoon spoke The Lorax: "The color of the trees will one day be able to tell us how it feels on this moment wood".

Why do leaves dry and fall off

With the coming of winter, part the globe receives less sunlight and the air gets colder. When such changes occur, the trees prepare for winter.

Trees that shed their leaves clog leaf attachment points. This prevents liquids from useful substances reach the leaves, causing the leaves to change color and fall off.

Leaf fall symbolizes not only the change of season, this process also helps the tree survive the cold, dry winter air.

In winter, trees do not receive enough liquid to "to contain" leaves. If they did not clog the places where the leaves begin to grow, the trees would simply die.

When spring brings warm air and water, trees start to grow new leaves.

Why don't coniferous trees shed their leaves?

Why do leaves turn yellow and fall off in autumn?

The summer season ends with the last fallen leaves from trees and shrubs. For many people, bare plants cause despondency and longing for summer. But autumn is beautiful! No wonder so many poetic lines are dedicated to this time of year. Why do the leaves of some plants turn red, while others turn yellow? And why are the leaves falling?

Leaf fall is the most striking sign of autumn. These plants adapt to the unfavorable conditions of the season. Seasonal variability of plants begins from the northern latitudes and gradually moves south. Falling leaves are repeated every year and always delight us with their bright colors - from yellow and orange to pink and purple. Leaves fly around even from evergreens in the subtropics and tropics. Only there they do not fall all at once, but gradually throughout the year, and therefore it is not so noticeable.

It gets colder in autumn, and water flows into the plants from the roots to the leaves at a slower pace. But it is not main reason leaf fall. Offensive adverse conditions is a signal for the transition of plants to a new cycle of life, which is inherent in genetic code. This indicates to us that the autumn shedding of leaves is not a direct consequence of the onset of adverse conditions. It is together with winter period dormancy is included in the very cycle of plant development. There is also a way to make sure that leaf fall is a physiological process. Why does the leaf separate from the branch? It turns out that with the onset of cold weather at the base of the petiole, where the leaf is attached to the branch with a “leaf pad”, a cork layer forms. The cells of this layer have smooth walls and are easily isolated from each other. It is worth blowing the wind a little harder, and the sheet is separated from the cork layer.

The green color of the leaves in summer is due to large quantity the chlorophyll pigment they contain. This pigment "feeds" the plants, since it is with its help that in the light the plant synthesizes organic substances from carbon dioxide and water, and first of all the main sugar - glucose, and from it - all the rest. nutrients. The composition of chlorophyll includes iron, and when it is destroyed, oxides are formed that have brown-yellow colors. The destruction of chlorophyll is more intense in the light, that is, in sunny weather. That's why on a cloudy rainy autumn leaves retain their green color longer. When sunny days come in autumn, the leaves turn golden-red.

However, along with chlorophyll green leaves contain other pigments - yellow xanthophyll and orange carotene (it determines the color of carrot roots). In summer, these pigments are invisible, as they are masked by a large amount of chlorophyll. In autumn, as the vital activity in the leaf dies out, chlorophyll is gradually destroyed. This is where the yellow and red shades of xanthophyll and carotene appear in the leaf.

In addition to gold, the autumn dresses of trees contain crimson hues. This color is due to a pigment called anthocyanin. Unlike chlorophyll, anthocyanin is not bound inside the cell with plastic formations (grains), but is dissolved in the cell sap. With a decrease in temperature, as well as in bright light, the amount of anthocyanin in the cell sap increases. In addition, stopping or delaying the synthesis of nutrients in the foliage also stimulates the synthesis of anthocyanins.

Fallen leaves can retain their shape and color for a few more days, and then they begin to dry out and acquire a brown color that is not very pleasant for the eye. Some of the leaves remain in place under trees and shrubs, and some are blown away by the wind. For aesthetic reasons, the gardener is often tempted to clear the soil of fallen leaves. Is it necessary? After all, the leaves contain the same chemical compounds that were taken by plants from the soil. True, they acquired a slightly different chemical composition and entered the plant-formed organic matter. Once on the surface of the soil, the leaves become the "prey" of a great variety of different living organisms. Among them, the most important role in the utilization of leaves belongs to earthworms. The products of their vital activity (the feces of worms are called caprolites) contain the entire set of nutrients for plants in almost ready-made. So the leaves, hitting the biological cycle substances, returned to the soil, what they once received in the plant.

And now decide for yourself - to remove foliage from under the trees or not? There are two ways to save useful properties fallen leaves. The first is to leave it in place until spring, followed by digging. At the same time, the leaves will warm upper layer soil. The second path will be somewhat more difficult and last longer. Collect leaves in compost pit and in a year or two return under the trees in a rotted form.

V. A. Rassypnov , professor of ASAU

Sometimes we forget or do not know the banal things that we face every day. These things include autumn leaf fall. In particular, quite respectable people often cannot explain why the leaves turn yellow and fall off in autumn. But we will try to do it without too much scientific red tape. In doing so, you will learn some interesting factors of this phenomenon.

Tree life cycles

To begin with, a tree has several life cycles. This is:

1. Summer;
2. Winter;
3. Autumn;
4. And spring periods.

So, in the summer the plant actively develops. In autumn it prepares for winter, in winter it goes into hibernation, and in spring it awakens, absorbing the largest number nutrients.

As part of the autumn cycle, leaf fall occurs. It is provoked by a reduction in daylight hours, cold and a genetic setting.

If everything is clear with cold and light, then the genetic setting is a signal to drop foliage no matter what. It is laid down at birth. And even if we have eternal summer, the trees will still sleep for a couple of months. It is only possible that some of the leaves will still be preserved.

Why do leaves turn yellow and fall from trees?

The yellowing of everything and everything occurs due to poor nutrition. The roots pump liquid less, and the sun does not allow active photo synthesis.

Thus, the green pigment chlorophyll is produced poorly. It is replaced by other pigments such as carotene. And they are just yellow and crimson.

It is worth noting that yellowness is always present in the leaves. Just in the summer it is interrupted by chlorophyll.

And here's what's interesting, in autumn, in rainy weather, the leaves turn yellow less. And the sun just gives bright colors.

This is due to the fact that chlorophyll, as it were, burns out when there is not enough of it. Therefore, ultraviolet, which greens the foliage in spring, on the contrary colors it in autumn.

Now for the fall of the leaves. According to the genetic setting, a cork layer forms on the branches of trees with reduced nutrition. It sort of separates the leg of the sheet from the surface. As a result, the sheet falls with little pressure or under its own weight.

It is important to note that even fallen leaves contain many nutrients for insects. Therefore, from the point of view of biology, it is wrong to throw away foliage.

Where did the leaf fall come from?

In general, trees began to live in cycles due to global cooling. This phenomenon allows them to survive. The tree clogs the points left after the leaves. And the root begins to pump water at times less.

Thus, there is a huge savings in nutrients. It makes it possible to fall asleep and survive the winter. Without leaf fall, this would have been impossible.

By the way, coniferous plants also have a kind of leaf fall. But it doesn't happen right away. Therefore, it is difficult to see it. But if you look under coniferous plant, then there you can also find a kind of carpet of "thorny leaves".

valentine lame
Synopsis of the GCD "Why do the leaves turn yellow?" in preparatory group

Goals:

1. To teach children to correlate the description of nature in verse with certain time of the year:

Develop auditory attention, speed of thinking.

2. Give children knowledge about why with the onset of autumn yellowing leaves on trees; ideas about the beginning of autumn, about the dependence of the color of brightness leaves from the weather.

3. Develop children's ideas about the signs of autumn, concepts: bush, tree.

4. Exercise in compiling descriptive stories about trees and the ability to determine the name of a tree from the description.

Dictionary activation: chlorophyll, crimson, shrub.

5. To cultivate a desire to study nature, to protect it.

Material: boxes with fruits and leaves trees of the Tula region, familiar to children, a book by Georgy Graubin « Why does the fall fall in autumn?» .

Children, I will read you excerpts from poems, and you listen to them carefully and say what time of the year they are talking about. And why? (reading):

In the morning we go to the yard

Leaves fall like rain,

Rustle underfoot

And fly, fly, fly...

“I bring the harvest. I sow the fields again

I send birds to the south, I undress the trees,

But I do not touch the pines and fir trees

I ... autumn. (children's answers)

Children, how do you determine that autumn has come? (children's answers). That's right, birds fly away to warmer climes, the day is slowly waning, insects disappear, leaves turn yellow and fall, in the fields, orchards and orchards are harvested. - When does autumn come? (children's answers)

According to the calendar, autumn comes on September 1, when the first autumn month begins, schoolchildren go to school. Scientists-astronomers consider the beginning of autumn to be the day of the autumnal equinox, September 23, when the day is equal in longitude to the night. The beginning of autumn in wildlife is considered the appearance yellow leaves on a birch.

Do you know, why leaves turn yellow? Would you like to know this secret? (children's answers) Then listen. (I am reading a story from G. Graubin's book « Why fall leaves in autumn» « Why leaves turn yellow» .

Autumn. Still far from frost, and the trees are already starting to drop foliage. Trees are not immediately freed from leaves. Goes preparation for fall. AT leaves amazing transformations take place.

at first leaves start to turn yellow, although no one adds paint to the juices. Yellow paint is always in the leaves. Only in summer yellow invisible. It is clogged with a stronger color - green. Green color leaves a special substance, chlorophyll, will come. What is the name of the green substance? (children's answers) Chlorophyll in leaves gradually destroyed and restored again under the influence of the sun. In summer, the sun shines for a long time and chlorophyll is restored very quickly and leaf is green all the time. But autumn comes, the nights become longer, the plants receive less light. Chlorophyll is destroyed and does not have time to recover. The green color is fading away foliage and become noticeable yellow: the leaf turns yellow. Why does the leaf turn yellow? (children's answers)

But in autumn leaves become not only yellow, but also red, crimson, purple. It depends on what colorant is in decline sheet.

The autumn forest is rich in its colors. The brightness of autumn leaves depends on what is the weather like.

If the autumn is long, rainy - coloring leaves from excess water and lack of light will be dull, inexpressive.

If cold nights alternate with clear days, then the colors will be juicy, bright.

But at the alder, lilac the leaves will fall green, regardless of the weather. In their leaves except for chlorophyll, no other substances.

Here's the secret you've learned about coloring leaves on trees.

Now let's take a break and play.

Fizkultminutka.

Now, tell me, what is the difference between a tree and a shrub? (children's answers). Correctly, a tree has one thick trunk and many branches, and a bush has several thin trunks.

I invite you to compete "Who will name more trees?" (children answer and get a chip for the correct answer). Now, name the shrubs. (children also get chips). Well done, everyone tried to help their team.

I offer you another game. I have in boxes leaves and fruits different trees. You choose any box for yourself and will have to describe the tree without naming it. The one who correctly describes the tree and who is the first to recognize it will receive one chip. (game in progress).

And now, count the chips and determine for yourself which team was more active today and won.

What did we learn in class today? That's right, we learned: why leaves turn yellow when autumn comes, what determines the brightness of the color leaves, remembered how trees differ from shrubs and described them very well. Were you interested? In the next lesson I will tell you why and how leaves fall.

As soon as the summer passes, restless children's voices begin to ask - " So why do plant leaves turn yellow in autumn?»

All summer the trees proudly stand with bright green crowns, but when autumn comes, the sun no longer warms so much, more and more often the sky frowns with clouds and it drizzles - that's when the plants begin to change color. Their leaves turn red, turn yellow, turn orange - and the autumn forest begins to seem like a special magical place.

In summer, the foliage of trees contains a lot of chlorophyll pigment, it is he who colors the leaves green. This pigment is vital for any tree - with the help of chlorophyll in the light, a plant from carbon dioxide and water synthesizes sugar - glucose. And from that sugar come all the other nutrients. Thus, chlorophyll feeds the plant.

But in green leaves, not only chlorophyll is present, there are other pigments.

• - yellow - vegetable pigment xanthophyll
• - red - this one beautiful colour manifested by pigments anthocyanins
• - orange - pigment carotene, the same pigment is found in large quantities in carrots, which is why carrots have such a bright orange color.

In summer, all these pigments are not noticeable, as they are hidden by a large amount of green chlorophyll. But in autumn, the vital activity in the leaves fades, and chlorophyll gradually begins to break down. This is where all the other “color” pigments begin to appear - in this way in autumn, the leaves of plants turn yellow and fall off.

The sunnier the weather is in autumn, the faster chlorophyll is destroyed in plants. And in cloudy rainy autumn, the leaves on the trees stay green longer. But if, after prolonged rains, sunny weather quickly sets in, or as this time is also called “Indian summer”, then the green color of the leaves changes to golden-red tones in 1-2 days.

red pigment – anthocyanin- unlike chlorophyll, it is not associated with plastic formations, but is dissolved in cell sap. When the temperature drops, there is much more anthocyanin in the cell sap. Therefore, the red color of trees in autumn indicates the attenuation of the vital activity of the leaves - the foliage is preparing to fall off.