Every autumn, the leaves change their color, they turn yellow, red or purple and gradually fall off, becoming dry and brittle. The rustling occurs precisely due to these properties. in the fall? Some believe this is due to frost. As if it was the cold that killed the summer beauty, and now the leaves fall to the ground, gradually covering it with a bright rustling carpet. However, this is not at all true. If you are careful, you will immediately notice that the leaves begin to turn yellow and fall off much more quickly. earlier than the first frosts. Leaf fall is only a seasonal phenomenon, and its causes are hidden in the trees themselves, in their biological mechanism struggle for survival in harsh seasonal conditions.

A small child asks his parents why the leaves turn yellow in the fall? It is very important to answer this question correctly. After all, based on what children are told in their early years, their future worldview is formed. If the leaves do not fall on time, the plants may suffer or die not from freezing, but from lack of moisture. Cold air can be as drying as hot air. The liquid in the soil freezes, and the suction ability of the roots stops, and soon stops altogether. When the flow of moisture to the leaves stops, it still continues through their surface. This is why the leaves turn yellow in the fall. They protect their tree from death. If they remained on the tree, then all the moisture would immediately evaporate from the branches through their surface. Thereby defense mechanism plants are freed from a large excess area. And in order for a tree to shed them, it first needs to turn the leaves into dead ones, which then fall off.

When the leaves turn yellow in the fall, all processes in the plant stop, life itself freezes. This is one of the irreversible phenomena of nature. When the light outside changes, an alarm goes off for the leaves. biological clock, and they begin to change color. This process can be divided into three stages:

• yellowing of some leaves;
• coloring of the illuminated sides of the crowns,
• completion of the process and the first fall.

It's impossible that all trees do this in different time, and the forest becomes bright unevenly. When do the leaves start to turn yellow? In autumn. On the illuminated side of the tree the process occurs faster, and on the shaded side the leaves remain green for a long time.

From a biochemical point of view, this is due to the fact that they stop producing chlorophyll. IN summer time yellow pigment is also present in the leaves, but its amount is insignificant compared to green. Now it is becoming more and more noticeable. And another one interesting feature: red foliage is found only in a well-lit and fairly cool place. Anthocyanins together with carotenoids are responsible for the rich color.

All this explains why the leaves turn yellow in the fall. However, this does not happen with all trees. The leaves of wild rosemary, cranberry, juniper, heather and lingonberry do not turn yellow; under the snow they remain green, because they evaporate very little moisture.

And the way they change color in the fall. Molecules responsible for bright shades yellow and orange are no longer a mystery, but why the leaves turn red still remains a mystery.

Reacting to change in air temperature and a smaller number daylight, leaves stop producing chlorophyll(which gives green color), absorbs blue and partially red light emitted by the Sun.

Since chlorophyll is sensitive to cold, some changes in weather, such as early frosts, will “switch off” its production faster than usual.

Why do leaves turn yellow and fall off?

At this time, orange and yellow pigments, called carotenoids(which can also be found in carrots) and xanthophylls shining 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 Schaberg(Paul Schaberg), plant physiologist with the US Forest Service.

But scientists don't yet have much information about the red color some leaves appear in the fall.

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

Trees produce anthocyanidins when they sense a change in the environment - frosts, ultraviolet radiation, drought and/or fungus.

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

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

Paul Schaberg believes that if anthocyanidins help 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 the next season.

Anthocyanins

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

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

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

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

These pigments are on the tree act as a sunscreen, blocking dangerous radiation and protecting leaves from excess light. They also protect cells from rapid freezing. Their benefits can be compared to those of antioxidants.

High amounts of sunlight, dry weather, freezing weather, low nutrient levels and other stressors increases the sugar concentration in tree sap. This starts the production mechanism large quantity anthocyanins, in a last-ditch effort to build up energy to survive the winter.

Scientists believe that studying anthocyanidins will help to understand the level of illness every tree. This, in turn, will give a clearer picture of the problems in the future. environment.

As a book and cartoon character said Lorax: "The color of the trees will one day be able to tell us what it feels like... this moment tree".

Why do leaves dry out and fall off?

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

Trees that shed their leaves clog leaf attachment points. This does not allow liquids with beneficial substances to reach the leaves, which is why the leaves 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 fluid to "contain" leaves. If they didn't clog the places where leaves start to grow, the trees would simply die.

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

Why don't coniferous trees shed their leaves?

Autumn leaf fall

Autumn leaf fall is an unusually bright and amazing natural phenomenon that amazes with its beauty. Looking at the flying golden leaves that spread in soft carpets, the question certainly arises: how does this process work and why, in fact, do the leaves fall in the fall?

Many types of trees are freed from leaves to survive in unfavorable conditions. weather conditions. In the tropics and subtropics, foliage falls off at the beginning of the dry season, in regions with temperate climate trees lose their leaves in the fall as cold weather approaches. Trees that shed leaves certain time years are known as deciduous trees. Trees whose leaves do not fall are called evergreen trees.

Most species of deciduous trees have wide leaves, which crumble in cold or dry weather. Evergreen trees, unlike deciduous trees, grow in humid, warm climates or have needles that are weather-resistant.

: Evergreen trees retain their leaves throughout the year because their foliage is covered with wax, which protects against cold, and their cells contain antifreeze agents. chemical substances, which prevent the tree from freezing when low temperatures ah environment. Deciduous trees, on the other hand, are very susceptible to cold.

Evergreen trees retain foliage throughout the year

Reasons for leaf fall:

• duration daylight hours;
• leaf damage;
• arid climate;
• cold climate;
• tree pollination.

Length of daylight

Destruction of chlorophyll in the leaf during shortening of daylight hours

In autumn, the length of daylight hours gradually decreases. As exposure to daylight decreases, the leaves' production of chlorophyll, the green pigment the plant uses to absorb sunlight and then converts it into nutrients; and the process of photosynthesis (which is carried out with the participation of chlorophyll) slows down until it stops. As a result, the production of sucrose, which plants use as food, stops and, consequently, the supply of nutrients to the tree is limited. To reduce the need for nutrients and resist cold or drought, trees shed their leaves.

: It is noticed that forest trees They shed leaves faster than urban ones. This is due to the fact that there is more lighting in the city, including artificial lighting (lanterns, light from windows, cars, etc.).

Leaf damage

By late summer, the leaves have been damaged by insects, disease or general wear and tear and are ready to be renewed. As fall arrives, trees face low ambient temperatures, cold winds and other conditions that also damage leaves. For these reasons, the leaves fall off. In addition, in addition to nutrients, leaves collect harmful substances(metabolites, excess mineral salts). Therefore, by getting rid of leaves, the plant is cleansed.

Arid climate

Deciduous trees shed their leaves during drought to avoid drying out.

In hot weather, leaves evaporate a lot of moisture. The roots of the tree, while supplying the leaves, lose a large amount of water. Coniferous foliage, so-called. evergreen trees, are not subject to shedding, since their needles, occupying small area surfaces require less moisture compared to deciduous trees. Thus, deciduous trees shed their leaves during dry periods to reduce the need for moisture and avoid drying out.

Cold climate

In autumn, trees, sensing the reduction in daylight and lower air temperatures, begin to prepare for the cold. To conserve sufficient water and energy resources for winter period, plants accumulate nutrients and get rid of leaves. This process occurs cyclically and does not harm the plant. This is how autumn leaves begin to fall.

Nutrient Accumulation

Trees collect valuable nutrients (nutrients) from leaves and store them in the roots for further application. Chlorophyll (the pigment that colors leaves green color) is the first to decompose into batteries. By the way, in connection with this, the leaves change color in the fall from green to orange, crimson, and gold.

Separating leaves from a tree

A separating layer of cells separates the leaf from the branch, resulting in the process of leaf fall

Leaves are cut from the tree by a detachment layer, which forms where the leaf stem meets the branch and is a collection of cells. As the autumn days shorten, this layer clogs the vessels on the leaf stem, which move water into the leaf and nutrients into the tree. Once the stem is clogged, the layer becomes dry and scaly and, through decomposition, separates the leaf from the tree. In the spring, in place of fallen leaves, new stems appear and leaves grow.

Trees, having gotten rid of their leaves, enter a state of suspended animation, which is compared to deep sleep. At this time, the plant uses nutrient reserves deposited in the summer.

Benefits of fallen leaves

Fallen leaves continue to benefit trees

Fallen leaves do not lose their ecological significance. As they decompose, their beneficial substances flow into the soil and feed future generations of plant and animal life. This gives the tree the nutrients it needs to grow new leaves. In addition, the layer of discarded leaves covering the soil warms the tree and protects it from freezing during the cold season.

It is likely that fallen leaves represent main factor the survival of not only trees, but forests in general.

Tree pollination

Tree shedding of leaves also increases pollination efficiency flowering plants. When branches lack leaves, wind pollen spreads to large areas and, accordingly, covers more trees.

The answer to the question why leaves fall in autumn is obvious: leaf fall helps trees conserve energy and water, i.e. performs energy saving function and supports water balance in the plant body. Shedding leaves is a way for trees to adapt to weather conditions.

In addition, the loss of leaves on trees does not depend solely on climate change, it is natural process, incorporated by nature into the biological cycle ( houseplants also shed leaves), which helps them renew themselves.

The leaves are often called plant lungs. With the help of leaves, plants breathe, evaporate moisture and carry out photosynthesis. At the beginning of autumn, the processes of photosynthesis and moisture evaporation slow down in the leaves. During the first autumn frosts, under the influence of low temperatures, the green pigment chlorophyll, responsible for photosynthesis, is destroyed.

At the same time, other pigments become noticeable, coloring the leaves yellow, brown and red. The leaves age and become ballast for plants, which have already accumulated minerals and metabolic products. Therefore, shedding leaves has a healing significance for the plant - it is preparation for winter.

As a result, the evaporation of moisture by the plant in autumn and especially in winter, when the roots absorb water less well, is significantly reduced. Fallen leaves protect plants from freezing and serve as natural mulch.

Source:

Trees need leaves to provide nutrition. They also produce oxygen, which feeds the living. A large amount of chlorophyll gives the leaves green color. This pigment is used sun rays transforms carbon dioxide and water into useful substances. With such processes, the tree does not stand still, but grows.

Preparing for the cold

When the time comes to prepare for the cold season, the plants suspend their vital activity. This process occurs with the onset of autumn. Leaves consume less water. The chlorophyll pigment is destroyed faster under the rays of the sun. When autumn is sunny and dry, they acquire yellow. When autumn is rainy, the leaves remain green for a long time.

Different colour

From all that has been said, one more riddle will arise: Why are some leaves red? Everything is quite simple. There are also other pigments present in the leaves, but they are not visible when they are green. When chlorophyll is broken down, other colors appear.

Falling leaves mean the arrival of cold weather.

Line UMK V.V. Pasechnik. Biology (5-9)

Biology

The world

Why do the leaves on trees turn yellow and fall off in the fall?

With the arrival of autumn appearance trees are changing. The dense green crowns are replaced by bright crimson-red “caps” of leaves, which then completely fall off. Why green leaves change their color, and why do trees get rid of their leaves every year? We understand the details of the life of trees with scientific point vision.

Leaves the color of summer

A special substance is responsible for the emerald foliage of any plant chlorophyll- a pigment that gives leaves a green color. It not only provides fresh herbal color, but also nourishes plants by participating in the formation of glucose and other nutrients.

This pigment is produced through the process of photosynthesis. Leaves absorb carbon and release oxygen. This happens in comfortable conditions- in the presence of heat and sun. In addition to oxygen, photosynthesis also produces the chlorophyll we know.

With the onset of the cold season, sunny days become shorter: the weather is no longer pleasant with warmth, and there is less light. Chlorophyll ceases to be actively produced and is replaced by other pigments.

Every Hunter Wants to Know

The autumn colors of the foliage are due to special pigment substances. Carotene is responsible for Orange color. This pigment can be found not only on autumn crowns trees, but also in ordinary carrots. Yellow leaves appear due to xanthophyll, and red ones due to anthocyanin.

The conditions for the production of pigments are different. If chlorophyll needs a lot of heat and sun, then xanthophyll and carotene need enough heat and a little light. But to get a lot of purple leaves, you need cold weather and bright sun. Frost and plenty of light are the conditions for the appearance of large amounts of anthocyanin in the foliage.

Proposed notebook - part educational complex to the textbook by A. A. Pleshakov, N. I. Sonin “Biology. Introduction to biology. 5th grade." Special signs mark tasks aimed at developing meta-subject skills (planning activities, identifying various features, comparing, classifying, establishing cause-and-effect relationships, converting information, etc.) and personal qualities students. The material in the notebook is arranged in the same sequence as in the textbook.

Yellow leaves swirl over the city

In autumn, trees make us happy at first bright colors, but with the approach of winter they begin to get rid of leaves. Why and why does this happen?

With the arrival of the cold season, the soil begins to freeze. Trees stop receiving required quantity moisture and nutrients. Life processes begin to stop, plants go into hibernation. In order not to waste energy on nutrition, plants are forced to get rid of excess load - and shed their leaves.

At the base of the petiole (the narrow part of the leaf, the place of attachment leaf blade to the stem) a special separating cork layer is formed, blocking the “delivery” of nutrients from the tree. It becomes increasingly difficult for weakened leaves to stay on the branches and gradually they begin to fall off. As with the appearance of a multi-colored crown, so with the fall of leaves, all processes do not occur instantly. That is why at first we see a measured change in the colors of the foliage, and then the trees slowly get rid of their bright attire.

Leaf fall - required condition the existence of trees, helping them renew their foliage annually. With the arrival of spring, the trees again begin to receive required amount water from the thawed soil and revive their lush crown.

But also among coniferous trees there are exceptions, for example, larch. It grows in harsh conditions and cannot evaporate moisture in winter. Therefore, like deciduous trees, they also shed their needles as winter approaches.