Start in science. Why do leaves turn different colors in autumn? Leaves change color

"Forest, like a painted tower, purple, gold, crimson"

Leaf color change is one of the first signs of autumn. Lot bright colors in the autumn forest! Birches, ash-trees and lindens turn yellow, euonymus leaves turn pink, patterned rowan leaves turn crimson-red, aspen leaves turn orange and crimson. What is the reason for this color variety?

The leaves of plants, along with green chlorophyll, contain other pigments. To verify this, let's do a simple experiment. First of all, let's prepare the extract of chlorophyll, as we described above. Along with chlorophyll, alcohol also contains yellow pigments. To separate them, pour a small amount of alcohol extract (about two milliliters) into a test tube, add two drops of water and about 4 milliliters of gasoline. Water is introduced in order to facilitate the separation of the two liquids. After closing the test tube with a cork or finger, shake it vigorously. Soon you can see that the lower (alcohol) layer turned golden yellow, and the upper (gasoline) - emerald green. The green color of gasoline is due to the fact that chlorophyll dissolves better in gasoline than in alcohol, so when shaken, it usually completely passes into the gasoline layer.

The golden yellow color of the alcohol layer is due to the presence of xanthophyll, a substance insoluble in gasoline. Its formula is C40H56O2. By chemical nature, xanthophyll is close to carotene present in carrot roots - C40H56, therefore they are combined into one group - carotenoids. But carotene is also found in the leaves of green plants, only it, like chlorophyll, dissolves better in gasoline, so we do not see it: the intense green color of chlorophyll "clogs" the yellow color of carotene, and we do not distinguish it, as xanthophyll previously in alcohol hood. To see carotene, you need to convert the green pigment into a compound that is insoluble in gasoline. This can be achieved with alkali. In the test tube where the separation of xanthophyll occurred, add a piece of alkali (KOH or NaOH). Close the vial with a cork and shake the contents thoroughly. After the separation of the liquids, it can be seen that the pigment distribution pattern has changed: the lower alcohol layers turned green, and the upper, gasoline layers, turned yellow-orange, characteristic of carotene.

These experiments clearly indicate that yellow pigments, carotenoids, are present in the green leaf simultaneously with chlorophyll. With the onset of cold weather, the formation of new chlorophyll molecules does not occur, and the old ones are quickly destroyed. Carotenoids, on the other hand, are resistant to low temperatures, so these pigments become clearly visible in autumn. They give the leaves of many plants a golden yellow and orange tint. What is the importance of carotenoids in plant life? These pigments have been found to protect chlorophyll from being destroyed by light. In addition, by absorbing the energy of the blue rays of the solar spectrum, they transfer it to chlorophyll. This allows green plants more efficient use solar energy for the synthesis of organic matter.

The autumn forest is colored, however, not only in yellow tones. What is the reason for the purple and crimson color of the leaves? Along with chlorophyll and carotenoids, plant leaves contain pigments called anthocyanins. They are highly soluble in water and are not contained in the cytoplasm, but in the cell sap of vacuoles. These pigments are very diverse in color, which depends mainly on the acidity of the cell sap. This is easy to verify by experience.

First of all, prepare an extract of anthocyanins. For this purpose, the leaves of the euonymus or some other plant, painted in autumn in red or purple tones, chop with scissors, place in a flask, add water and heat on a spirit lamp. Soon the solution will turn reddish-blue due to the presence of anthocyanins. Pour the resulting extract of pigments into two test tubes. Add weak hydrochloric or acetic acid to one, and ammonia solution to the other. Under the action of acid, the solution will turn pink, while in the presence of alkali - depending on the amount and concentration of this alkali - green, blue and yellow. Anthocyanins, like carotenoids, are more resistant to low temperatures than chlorophyll. Therefore, they are found in the leaves in the fall. Researchers have found that the formation of anthocyanins is facilitated by the high content of sugars in plant tissues, relatively low temperatures and intense lighting.

The increase in sugar content in autumn leaves occurs due to the hydrolysis of starch. This is essential for transporting valuable nutrients from dying leaves to the interior of plants. After all, starch itself is not transportable in the plant. However, the rate of outflow of sugars formed as a result of its hydrolysis from the leaves at low temperatures small. In addition, when the temperature drops, the respiration of plants is weakened and, consequently, only a small amount of sugars undergoes oxidation. All these factors favor the accumulation of sugars in plant tissues, which are beginning to be used in the synthesis of other substances, in particular anthocyanins.

Other facts also testify to the conversion of excess sugars into anthocyanins. If in a vine by ringing (removing part of the bark in the form of a ring) to impede the outflow of photosynthesis products, then the leaves located above the ring become red in two to three weeks due to the accumulation of anthocyanins. At the same time, so many of them are formed that the green color of chlorophyll becomes invisible.

The same is observed not only with a decrease in temperature or banding, but also with a lack of phosphorus. If, for example, tomatoes are grown in a nutrient solution devoid of this element, then the lower part of the leaves, as well as the stems, turn blue. The fact is that in the absence of phosphorus in plants, the process of oxidation of sugars cannot be carried out without combining with the residue phosphoric acid the sugar molecule remains inactive. Therefore, in plant tissues there is an accumulation of excess amounts of sugars, which are used for the synthesis of anthocyanins. An increase in the content of these substances leads to blue stems and leaves of plants experiencing a lack of phosphorus.

The formation of anthocyanins also depends on the intensity of light. If you look closely at the bright color of trees and shrubs in autumn, you will notice that the crimson color is mainly those leaves that are best lit. Move the euonymus bush blazing with fiery colors, and you will see yellow, pale yellow and even green leaves inside. During a rainy and cloudy autumn, the foliage lasts longer on the trees, but it is not as bright due to the lack of sun. Yellow tones predominate, due to the presence of carotenoids, and not anthocyanins. Low temperature also promotes the formation of anthocyanins. If worth warm weather, then the forest changes its color slowly, but as soon as the frost hits, aspens and maples immediately blaze. MM. Prishvin wrote in the miniature “Lamps of Autumn”: “Lamps of autumn lit up in the dark forests, another leaf against a dark background burns so brightly that it even hurts to look at. The linden is already all black, but one bright leaf of it remains, hangs like a lantern on an invisible thread and shines.

flora rainbow

Since we are talking about plant pigments, we should also talk about the reasons for the diversity of flower colors. Why do flowers need their bright, juicy color? Ultimately, in order to attract pollinating insects. Many plants are pollinated only by certain types of insects, so the color of the flowers often depends on which insects the color signals are intended for. The fact is that in relation to color, insects are quite capricious. Let's say bees, bumblebees, wasps prefer pink, purple and blue flowers, and flies usually huddle around yellow ones. Red is the color of many insects, endowed with not very perfect vision, confused with dark gray. Therefore, in our latitudes, pure red flowers are quite rare. The exception is poppy, but its petals also have an admixture of yellow; usually it is this shade that the bees notice. Butterflies distinguish red better than other insects - they, as a rule, pollinate the red flowers of our latitudes, for example, carnations. But among tropical plants, the red color is more common, and this is partly due to the fact that their flowers are pollinated not by insects, but by birds: hummingbirds or sunbirds, whose eyesight is more developed.

It happens that in the same plant, the color of flowers changes with age. This is clearly seen in the early spring lungwort plant: pink color its young flowers change to blue as it ages. The bees no longer visit the old flowers of the lungwort: they, as a rule, are pollinated and do not contain nectar. And in this case, the color change serves as a signal for insects - do not waste time! But in Gilia (USA) - a beautiful plant from the cyanotic family, a relative of phlox, growing in the mountains of Arizona (USA), the flowers initially have a scarlet color, which, as already noted, attracts birds. But when the hummingbirds leave the mountains, the hylia changes the color of the newly appearing flowers: they become pale red or even white.

The color of most flowers is determined by the presence of various pigments. The most common are carotenoids, fat-soluble compounds: carotene, its isomers and derivatives. In solution, they all have a pale yellow, orange or light red color. The names of carotenoids found only in flowers are as beautiful as the color they give: escholxanthin, petaloxanthin, gazaniaxanthin, auroxanthin, chrysanthemaxanthin, rubichrome.

Along with carotenoids, anthocyanins also determine the color of flowers. The shades of these pigments are very diverse - from pink to black-violet. Despite such a variety of colors, all anthocyanins are arranged according to the same type - they are glycosides, that is, sugar compounds with a non-carbohydrate part, the so-called aglycone. An example is the coloring matter contained in cornflower flowers - anthocyanin. Its aglycone - cyanidin - is one of the most common, formed as a result of the cleavage of two glucose molecules from an anthocyanin.

As already mentioned, anthocyanin pigments can change their color depending on the acidity of the medium. Recall two types of geranium common in middle lane: forest geranium and meadow geranium. The forest petals are pink or purple, and the meadow petals are blue. The difference in color is due to the fact that the forest geranium juice is more acidic. If you prepare an aqueous extract from geranium petals, either forest or meadow, and change its acidity, then in an acidic environment the solution will turn pink, and in an alkaline environment - blue. The same operation can be done on the whole plant. If a blooming violet place under a glass cap next to the saucer where it is poured ammonia(it releases ammonia during evaporation), then its petals will turn green; and if instead of ammonia in the saucer there is smoking hydrochloric acid, they will turn red.

We have already said that the same lungwort plant can have flowers of different colors: pink - young and blue - old. The bluing of the petals as they age can be explained by the indicator properties of anthocyanins. The cell sap of the plant, in which the pigment is dissolved, has an acidic reaction, and the cytoplasm is alkaline. Vacuoles with cell sap are separated from the cytoplasm by a membrane that is usually impermeable to anthocyanins. However, with age, defects occur in the membrane, and as a result, the pigment begins to penetrate from the vacuoles into the cytoplasm. And since the reaction here is different, the color of the flowers also changes.

To verify the validity of this point of view, take a bright red petal of some plant, such as a geranium, a rose, and crush it between your fingers. In this case, the contents of the cytoplasm and vacuole will also mix, as a result, the petal at the site of damage will turn blue. However, it would be wrong to associate the color of anthocyanins only with their indicator properties. Research recent years showed that it is also determined by some other factors. The color of anthocyanin pigments can change, for example, depending on which ions they are complexed with. When interacting with potassium ions, the complex acquires a purple color, and with calcium or magnesium ions - blue. If you cut off a flowering bluebell and place it in a solution containing aluminum ions, the petals will turn blue. The same is observed if we combine solutions of anthocyanin and aluminum salts.

Many readers may be familiar with Alexandre Dumas' novel The Black Tulip, which tells in an action-packed form about the breeding of an unusual black tulip variety. Here is how the author of the novel describes it: “The tulip was beautiful, wonderful, magnificent; its stem is eighteen inches high. It stretched slenderly upwards between four green, smooth, even, like an arrow, leaves. Its flower was completely black and shone like amber. For almost five centuries, the failures of gardeners who tried to bring out the black tulip pursued. And so, the Frisian Institute of Floriculture in The Hague made an official statement that in Holland a black tulip was obtained as a result of successive crossing of two varieties - “Queen of the Night” and “Viennese Waltz”. Six Dutch research centers. The resulting flower is ideal in its classic size.

Gardeners also strive to create black roses. Such varieties have been bred that, in dim lighting, really appear black (in fact, they are dark red). Wild black roses grow in the Hawaiian Islands. In honor of Goethe's immortal work Faust, gardeners have created a variety of black pansies called Doctor Faust. Pansies, as you know, were the favorite flowers - the great German poet and botanist.

The black or almost black color of the flowers is due to the presence of anthocyanins in the perianth. In addition to carotenoids and anthocyanins, petals can be colored by other substances, including flavones and flavonols. What pigment gives milky color cherry orchards, turns bird cherry bushes into snow-white snowdrifts? It turns out that there are no white pigments in their petals. The white color gives them. air. If we look at a petal of a bird cherry or any other white flower under a microscope, we can see many transparent and colorless cells separated by vast empty spaces. It is thanks to these air-filled intercellular spaces that the petals strongly reflect light and therefore appear white. And if you crush such a petal between your fingers, then a transparent spot will appear at the place of compression: here the air will be forced out of the intercellular spaces.

And yet in nature there is white paint, for example, it is painted in elegant White color the bark of our beloved birch. This coloring matter is called - betulin, from the Latin name of birch - Betula. Those who believe that birch is the only plant with white bark are mistaken. This is not true. In Australia, the flooded eucalyptus grows. It is so named because it grows in the beds of drying rivers and in the rainy season it turns out to be standing in the water. The trunks of these eucalyptus trees have a pure white color, effectively standing out against the background of the surrounding green thickets.

The three-needle Bunge pine also has white bark. This is rare view, found in nature mainly in the mountains of Central China. The plant is bred throughout the country near palaces and temples. White-trunked pines make an indelible impression. Many more interesting things could be told about the color of plants and plant pigments, which have long attracted the attention of researchers from all over the world. More than 30 years ago, the famous Indian scientist T.R. Seshadri, who studied natural dyes a lot, wrote: “The music of colors is more complex and changeable in nature than the music of sounds. It is even possible that in reality it is even more refined than we think.

Green animals - reality or fantasy!

In the works of the fantastic genre, one can often read about green humanoid creatures. The green color of these organisms, due to chlorophyll, allows them to independently synthesize organic substances from inorganic ones at the expense of light energy. Is this possible in nature? First of all, it should be noted that there are animals on Earth that eat in a similar way. For example, the green euglena, well known to all biologists, is often found in stagnant puddles. Botanists consider euglena an algae, and zoologists still traditionally classify it as an animal. What's the matter?

Euglena moves freely in the water with the help of a flagellum. This mode of locomotion is typical both for a number of protozoa and for some botanical objects, for example, zoospores of certain species of algae. Euglena contains chlorophyll, therefore, with its intensive reproduction, the water in the puddles acquires an emerald green color. The presence of chlorophyll allows it to feed on carbon dioxide like all green plants. However, if the alga is transferred to water containing some organic substances, then it loses its green color and, like animals, begins to feed on ready-made organic substances. Euglena still cannot be called a typical animal, so we will look for other representatives. feeding, like plants, with the help of chlorophyll.

Back in the middle of the 19th century, the German zoologist T. Siebold discovered chlorophyll in the bodies of freshwater hydra and some worms. Later, it was found in organisms of other animals: hydroid polyps, jellyfish, corals, sponges. rotifers, molluscs. It was found that some marine gastropod mollusks that feed on siphon algae do not digest the chloroplasts of these plants, but keep them in the body in a functionally active state for a long time. The chloroplasts of the siphon algae Codium brittle and Codium cobweb, entering the body of mollusks, are not digested, but remain in it.

Attempts to free the mollusks from chloroplasts by placing them in the dark for a month and a half were unsuccessful, as well as removing them from eggs. Achloroplast larvae of mollusks died at an early stage of development. Inside an animal cell, chloroplasts are densely packed and occupy a significant volume. Thanks to them, mollusks that do not have a shell turn out to be painted in an intense green color.

Why did siphon algae "fall in love" with mollusks? The fact. that, unlike other green algae, they do not have a cellular structure. Their large, often bizarre body is one giant "cell". The word "cell" I put in quotation marks is not accidental. Although there are no cell walls in the body of siphon algae, one can hardly call them unicellular organisms; rather, it is a conglomerate of not completely separated cells. This is confirmed by the presence of not one, but many cell nuclei. Such a structure was called siphon, and the algae themselves were called siphon. The absence of cell walls, of course, facilitates the process of absorption of algae by animal cells.

Well, what are the chloroplasts of this plant? The body of an alga contains one or more chloroplasts. If there are many of them, they are disc-shaped or spindle-shaped. Single have a mesh structure. Scientists believe that the mesh structure is created as a result of the connection of small chloroplasts with each other.

Many scientists have observed the assimilation of carbon dioxide by chloroplasts in animal cells. In freshly harvested mollusks, green elision, the intensity of photosynthetic carbon dioxide assimilation was 55–67% of the value determined for the intact alga Codium brittle, from which the chloroplasts were “acquired” by the mollusks. It is curious that the content of chlorophyll per 1 gram of fresh tissue mass in algae and animal was similar. Thanks to photosynthesis, mollusks fixed carbon dioxide throughout the 93 days of experience. True, the rate of photosynthesis gradually weakened and by the end of the experiment was 20–40% of the initial one.

In 1971, scientists observed the release of oxygen during the photosynthesis of chloroplasts found in tridacna cells. Tridacna are typical inhabitants of tropical seas. They are especially widespread on the coral reefs of the Indian and Pacific Oceans. The giant among the mollusks looks like a giant tridacna, sometimes reaching a length of 1.4 meters and a total weight of 200 kilograms. Tridacna are interesting for us because of their symbiosis with unicellular algae. Usually they are located at the bottom so that their translucent mantle, protruding between the shell valves, is turned upwards and is strongly illuminated by the sun. In its intercellular space, green algae settle in large numbers. Despite its considerable size, the mollusk feeds only on those substances that are produced by symbiont algae.

In the Mediterranean Sea and off the coast of France in the Atlantic, a convolute worm is found, in which green algae also live under the skin, carrying out the synthesis organic matter from inorganic. Due to the activity of its "lodgers", the worm does not need additional sources write, so his gastrointestinal tract atrophied. At low tide, many convolutes leave their burrows to sunbathe. At this time, the algae under their skin photosynthesize intensely. Some species of these worms are completely dependent on their settlers. So, if the young worm does not “infect” with algae, then it will die of hunger. In turn, the algae that settled in the body of the convolute lose the ability to exist outside of its body. “Infection” occurs with the help of “fresh” algae that have not yet lived in symbiosis with worms at the moment when the larvae of the worm come out of the eggs. These algae are most likely attracted by some substance secreted by the eggs of the worms.

In connection with the consideration of the issue of the functioning of chloroplasts in animal cells, the experiments of the American biochemist M. Nass are of extremely great interest, in which it was shown that the chloroplasts of the siphon algae caulerpa, chara algae nitella, spinach and African violet are captured by connective tissue cells (the so-called fibroblasts) of mice . Usually, in fibroblasts that have swallowed a foreign body (this process scientists call phagocytosis), a vacuole is formed around the absorbed particle. Gradually, the foreign body is digested and absorbed - disappears. When chloroplasts were introduced into the cells, vacuoles did not appear, and fibroblasts did not even try to digest them.

Plastids retained their structure and ability to photosynthesize for three weeks. The cells that turned green due to their presence were dividing normally. At the same time, chloroplasts were spontaneously distributed among daughter cells. Plastids, which were in fibroblasts for about two days, and then again isolated, remained intact. They assimilated carbon dioxide at the same rate as they photosynthesized fresh chloroplasts isolated from plants.

Suppose that in the course of evolution such beings arise or are found on other planets. What should they be? Scientists believe that in such an animal, chlorophyll will be concentrated in the skin, where light freely penetrates, which is necessary both for the synthesis of green pigment and for the formation of organic substances. The "Green Man" must do something the opposite: during the day, like a fairy-tale king, walk in clothes invisible to everyone, and at night, on the contrary, dress to keep warm.

The problem is whether such an organism can get enough food through photosynthesis. Based on the maximum possible intensity of plant photosynthesis in the most favorable conditions of existence, it is possible to calculate how much organic matter the green skin of this person can form. If we assume that 1 square decimeter of a green plant synthesizes 20 milligrams of sugars in 1 hour, then 170 square decimeters of human skin exposed to sunlight can form 3.4 grams during this time. For a 12-hour day, the amount of organic matter will be 40.8 grams. This mass will concentrate about 153 calories of energy. This amount is clearly not enough to meet the energy needs of the human body, which are 2000-4000 calories per day.

Let's take into account that the "green man" does not need to think about food and be too active, since food itself enters his body from the chloroplasts of the skin. It is easy to conclude that the absence physical activity and a sedentary lifestyle will make him look like common plant. In other words, the "green man" will be very difficult to distinguish from prickly pear.

The researchers' calculations show that in order to form a sufficient amount of organic matter, " green Man"In the course of evolution, he must increase the surface of his skin by 20 times. This can happen due to an increase in the number of folds and processes. To do this, he will need to acquire a semblance of leaves. If this happens, then it will become completely inactive and even more like a plant.

Thus, the existence of large photosynthetic animals and humans on Earth and in space is hardly possible. Scientists believe that in any biological system, even remotely resembling the Earth's biosphere, there must necessarily be plant-like organisms that provide food and energy for both themselves and animals. In the second half of the 19th century, it was found that the energy sunlight digested and transformed by the green pigment chlorophyll.

Based on the experiments, we can say that the green color of chlorophyll is determined by the presence of a metal atom in it, regardless of whether it is magnesium, copper or zinc. Modern science has confirmed the correctness of the views of K.A. Timiryazev regarding the exceptional importance of the red rays of the solar spectrum for photosynthesis. It turned out that the coefficient of use of red light during photosynthesis is higher than that of blue rays, which are also absorbed by chlorophyll. Red rays, according to K.A. Timiryazev, play a fundamental role in the process of the universe and the creation of life.

As you know, plants absorb carbon dioxide, which is attached to a five-carbon substance called ribulose diphosphate, where it then further participates in many other reactions. The study of the features of photosynthesis in different plants, will certainly contribute to the expansion of human capabilities in managing their photosynthetic activity, productivity and yield. In general, photosynthesis is one of the fundamental processes of life, on which most of the modern plant fauna on the surface of the earth is based.

Which will clearly show the children why the leaves on the redwoods change color: in the summer they are green, and in the fall they turn yellow.

To do this, you do not need special materials - everything is available both at home and at school. This experiment, which explains why the leaves on the daring trees change color in the fall, is great for preschoolers and students from grades 1-6.

Many people consider it the most beautiful time of the year, because when the leaves turn yellow, nature is painted in such incredible shades, which at the same time keep the memory of a warm summer, but evoke cold from the approach of winter.

But in the fall, children often have a number of traditional questions:

• Why do leaves on trees change color and turn yellow in autumn?
• Is this the work of fairies?
• What about the sun?
• Ah, I know it garden gnome made

This one, which explains why leaves turn yellow or red in autumn, is sure to satisfy even the most curious of children.

Why does a tree need leaves?

In order to understand why leaves change color in autumn, you need to understand why trees are needed at all, and leaves in particular.

Plants are responsible for creating the oxygen we breathe. They produce it by absorbing water from the earth and carbon dioxide from the air. Using sunlight (through photosynthesis), they convert water and carbon dioxide into oxygen and glucose. Oxygen is what allows us to breathe, while glucose is what the plant uses to grow. The term photosynthesis means to combine with light. Chemical substance in a plant that is used for photosynthesis is called chlorophyll. The same chlorophyll that gives plants their green color.

What you need for the experiment:

• glass jars
• coffee filters
• Leaves
• Alcohol
• Notebook and pen for observing

Why do leaves change color in autumn? Experiment for children

In order to find the answer to the question why the leaves on the trees change color and turn yellow in autumn, the children will need to collect some leaves.

After that, together you must sort them by color into prepared containers.

After that, the leaves are poured with alcohol and ground. After crushing and stirring, alcohol will help the color to show even better.

Hint: The time it takes for the color to fully absorb will depend on how many leaves and alcohol have been used.

After 12 hours, the liquid may not yet be completely absorbed, but the effect is already obvious. As the liquid soaks into the filter, the colors from the leaflets diverge.

Explanation of the experiment why the leaves change color

In winter, the days become shorter, which reduces the amount of sunlight for the leaves. Due to the lack of sun, the plants go into a dormant stage and feed on the glucose that they have accumulated over the summer. As soon as it turns on winter mode”, the green color of chlorophyll leaves the leaves. And as bright green tint disappears, we begin to see yellow and orange colors. A small amount of these pigments were in the leaves all the time. For example, maple leaves bright red, as they have an excess of glucose.

If you like the leaves that change color in autumn, you don't have to wait until the lessons start to spend it with the kids.

3rd grade students (Kolnik A. Fursova E)

Autumn roams through the woods.

She's a little sad, sort of.

That will cry in the early morning,

The sky will be covered with clouds

That will sparkle in the sun

More beautiful than the fabulous firebird,

That autumn Ball arrange,

Will cover the earth with leaves

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MBOU "Bykovskaya basic comprehensive school of the Yakovlevsky district of the Belgorod region"

Research work on the topic

Why are the leaves colored in autumn? different colors?»

Kolnik Arina,

Peremyslev Mikhail

3rd grade students

Supervisor:

Peremyshleva T.I.

elementary teacher

classes

Bykovka 2012-2013 academic year

Autumn roams through the woods.

She's a little sad, sort of.

That will cry in the early morning,

The sky will be covered with clouds

It will sparkle in the sun

More beautiful than the fabulous firebird,

That autumn ball will suit,

Cover the earth with leaves...

Autumn is a very important time for observations. All living things are preparing for change. Autumn has the following periods: the beginning of autumn, gold autumn, deep or late fall and pre-winter. Each period has its own main features. But we are more interested in the second period - golden autumn.

The object of our studyis a school park

Subject of study: autumn leaves of different trees.

Purpose of the study: discover, why do leaves change color in autumn

And they fall off?

Research objectives:

• how long does a leaf live;
• why in autumn the leaves are painted in different colors;
• what are the benefits of dropping leaves for the winter to the plant;
• what is contained in the fallen leaves;
• causes of leaf fall;
• features of leaf fall in some trees and shrubs

Research methods:

Research;

Practical;

Collection and analysis of various sources of information;

Questioning classmates and students elementary school;

Studying the literature on the research topic;

Searching for information on the Internet.

Hypothesis:

- perhaps the leaves contain dyes;

Coloration is influenced by weather conditions;

Leaf fall is a biological phenomenon caused by the vital activity of a plant, or caused by other reasons.

Practical significance:

Using the material in the lessons of the world around;

Creating a slide presentation for wide use;

Registration creative works from leaves.

Stages of work:

1. Preparation for the study.
2. Conducting research.

one). Questioning classmates and elementary school students

2). Excursion to the school park.

3). Excursion to the children's library.

4). Conducting observations.

3. Registration of research work.

4. Preparation and protection of work.

2. Main part .

2.1 How long do leaves live?

Looking through the literature, children's encyclopedia, Internet materials, we realized that the leaf is an important part of the plant. This is a "multi-story factory". The main purpose of the leaves is to capture and convert the energy of sunlight. Thanks to the incessant work, the leaf is nourished, releases water vapor, and breathes. One square meter leaf blade every hour it releases up to four liters of oxygen and takes the same amount of carbon dioxide from the air.

How long does a leaf live? The leaves of our trees live from spring to autumn. If the leaf is green, then it is alive. As soon as they turned yellow, blushed, it means that they grew old and died.

Conclusion:

Plants are our friends! Millions of years ago, it was the leaves of fossil plants that made the atmosphere of our planet habitable.

2.2 Why do leaves turn different colors and fall off in autumn?

Among students primary school we conducted a survey to find out if they know why a tree needs leaves, why leaves change color in autumn and fall off. After analysis, we concluded:

• Why do trees need leaves?

Correctly answered __10_____students, wrong__4______persons, did not think about it at all ___-______

• Why do leaves change their color?

Correctly answered __10_____students, incorrectly ___3___persons, did not think about it at all ___1______

• Why are the leaves falling?

___7____ students answered correctly, ___7___ people answered incorrectly, did not think about it at all ____-_____.

• Which trees are the first to shed their leaves and why?

Correctly answered __5_____students, wrong__2______persons, did not think about it at all ___7______

• Why is it bad for trees to have leaves in winter?

Correctly answered ___4____students, incorrectly ___7____persons, did not think about it at all ___3______

• Which tree is longsheds her leaves and stands in her autumn attire throughout the winter?

___2____ students answered correctly, 10___ people answered incorrectly, did not think about it at all __2______

Analyzing the results of the survey, we found that most students do not know the reason for the change in color. autumn leaves and the reasons for their decline.

2.3 Who painted the trees? What is in fallen leaves?

Emerald greens are replaced by golden orange, orange, fiery red tones. Why is there a replacement color palette trees? Who is guilty?

Studying this problem in the encyclopedic and reference literature, as well as we turned to the materials of the Internet and realized thatPlants look green to us a large number tiny chlorophyll grains located in the cells of leaves and stems. Chlorophyll grains are not eternal, they are destroyed under the influence of light and are reborn only in the light. However, chlorophyll is not the only coloring principle in plant tissues. Leaves have yellow pigments carotenoids, and red-violet anthocyanins.

These pigments begin to quickly appear on the outer part of the leaf and stem only when the air temperature drops, and chlorophyll grains, on the contrary, are destroyed and disappear. And the forests are dressed, as Pushkin said, in "crimson and gold"

Conclusion:

When the air temperature drops on clear sunny days chlorophyll grains are destroyed.As a result, the leaf loses its green color, and yellow pigments, imperceptible until that time, suddenly appear and color the leaf.

2.4 . Causes of leaf fall.What are the benefits of shedding leaves for the winter?

A leaf is not only an organ in which nutrients and mineral salts are created, but water also evaporates through the leaves. Throwing off a multi-colored outfit, deciduous trees that need a lot of moisture are saved from the winter drought. A large birch, for example, evaporates 7 tons of water during the warm months, and in winter you cannot draw so much from the soil. The second reason. In the pulp of the leaf under a microscope, you can find dead cells clogged with salt crystals. And if in May beech leaves contain 5% of mineral salts, then by October they become 11%. The leaves are overloaded with unnecessary substances and the tree sheds its leaves, thereby freeing itself from excess minerals. The leaves are prepared for falling off in advance: a layer of special cells with thick walls is formed between their petiole and twig - the so-called cork. Cork does not let water and juices through. Leaves cannot eat, weaken. Now a light breeze, a few drops of dew, andeven its own weight, so that the sheet separates from native branch on which he held on so tightly. We are seeing leaf fall.

Conclusion:

Leaf fall is a preparation for winter, not only cold, but most importantly, dry season.If our deciduous trees remained for the winter in their green dress, they would inevitably die as a result of a lack of moisture, since the evaporation of water by their leaves would not stop, and the flow of water into the plant could almost completely stop.

2.5 Features of leaf fall in some trees and shrubs. Why coniferous plants able to overwinter in a green dress?

The significance of leaf fall in the life of our deciduous trees is especially noticeable when compared with conifers. Conifers - spruce and especially pine - are drought-resistant plants. Their needles evaporate many times less water than the foliage of our hardwoods. Because of this, they are able to overwinter in a green form. This ability to save moisture is achieved by our conifers by the special structure of their needles. The needles have a number of drought-resistant adaptations: a thick skin that surrounds the needles on all sides, and a bluish wax coating, which also reduces evaporation; great importance also has an arrangement of stomata in special depressions. On the contrary, the leaves of our deciduous trees lack any special drought-resistant adaptations. They have a wide surface and thin skin. Speaking here about the importance of leaf fall in the life of our trees, one cannot help but pay attention to the fact that by shedding foliage, they thereby protect themselves from mechanical damage under the weight of snow. Often in winter one can observe how, even in a leafless state, large branches of trees break under the pressure of snow; wide leaf surface, on thewhich would have settled a lot of snow, would have made this phenomenon catastrophic.

Watching over deciduous trees and bushes of our school park, we made a table. What trees, And in what order do they take off their clothes? How long does leaf fall last?

When the leaves on the trees begin to change color, people immediately look forward to the approach of autumn. Have you ever wondered why leaves change color from green to yellow, orange and even red? Everything has a scientific explanation.

What makes leaves green?

Chlorophyll is the pigment that colors leaves green. During the spring and summer, the leaves receive enough daytime sunlight to nourish them and allow them to produce chlorophyll on a regular basis. Plants transform sunny color into the energy that helps them grow. This is the process of photosynthesis, which explains why the leaves appear very lush and green during the warm seasons.

What happens in autumn?

Daylight hours are getting shorter and plants are getting less sunlight. The production of chlorophyll slows down, which leads to a decrease in the green pigment in the leaves. Other components contained in the leaves, carotenoids and anthocyanins, are also responsible for the color change.

What determines the color of autumn leaves?

Carotenoids, which are also found in bananas and carrots, are responsible for yellow, orange and brown colors. Of course, carrot trees do not exist, but the component itself can be contained in certain trees, prevailing over anthocyanins. If any of the tree species contains more anthocyanins, then the leaves turn red. Temperature and soil conditions also play a role in leaf color change.

Eventually, the leaves become dehydrated due to lack of sunlight and photosynthesis, so they begin to fall, decorating the streets and heralding winter!

According to materials:

Deinekina Ekaterina

Research on the topic "Why are the leaves green in summer and yellow and red in autumn"

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Why are the leaves green in summer and colorful in autumn?

“Forest, like a painted tower,

Lilac, gold, crimson…”

I. Bunin

1. Why are the leaves of plants green in summer?

Of the 25 people interviewed, the answer to this question was:

“I don’t know” - 8 people;

“enough light, heat and water” - 16 people.

2. Why do the leaves change color with the onset of autumn?

“I don’t know” - 12 people;

"from old age" -7 people;

"from the cold" - 6 people.

As you can see the answers are different. So I decided to put forward my hypothesis:the leaves of plants are of different colors, because they contain substances that give the leaves shades of green, yellow and red.

Target research to find out:

* What substances give the leaves different colors?

* Why do the leaves on the trees turn shades of yellow and red in autumn?

To achieve this goal, I set the following tasks :

1. Understand what a tree leaf is made of
2. Why are leaves green in summer?
3. What substances give leaves their yellow and red color?

In order to deal with these issues, in my work I used the following methods :

1. studied the literature on the topic
2. look up information online
3. conducted a scientific experiment

1. I built my work on the following plan :

1. Collected and studied information about the external and internal structure sheet.
2. Conducted a scientific experiment that proves the presence of coloring pigments.

What is a leaf made of?

The leaf is one of the main organs of plants. It has a flat shape. A leaf may consist of a leaf blade, a petiole, stipules, and a base with which it is attached to the stem.

The internal structure of the leaf can be seen under a microscope. Outside, the leaf is covered with skin. Under the skin are the pulp of the leaf, which consists of two types of tissues: columnar tissue and spongy tissue. Plants appear green to us from a large number of tiny chlorophyll grains located mainly in the cells of the columnar tissue of the leaves. They are better lit, they form the most organic substances in the light. Through loose spongy tissue, gas exchange occurs and water evaporates. Chlorophyll grain does not remain unchanged in the plant. It is short lived. Capturing solar energy, chlorophyll is destroyed under the influence of light and re-created in the plant, and its formation can also occur only under the condition of good lighting.

In order to prove the presence of chlorophyll in the leaves, we conducted an experiment.

Experience 1.

We placed green leaf in a test tube with strong alcohol. Before our eyes, the leaf begins to turn pale, while alcohol, on the contrary, quickly turns green. This process of leaf discoloration is caused by the fact that chlorophyll dissolves in alcohol and especially quickly when heated or even gently boiled alcohol in a water bath.

Conclusion: the leaf became pale, and the alcohol solution turned into green color. Consequently, chlorophyll grains give the leaf a green color, but under the influence of adverse conditions, the chlorophyll grains are destroyed, and other substances give the leaf shades of yellow and red.

To make sure that the composition of the sheet includes substances yellow color let's continue the experiment.

Together with chlorophyll, yellow pigments also pass into alcohol; to separate them, we poured some gasoline into the hood. After shaking this mixture, after a while you can notice that gasoline floats to the top, while the layer of alcohol remains at the bottom. In this case, the alcohol will have an emerald color; gasoline will take on a golden yellow color from the yellow pigments of the leaf remaining in it - xanthophyll and carotene. The separation of chlorophyll from yellow pigments is based on its greater solubility in gasoline than in alcohol.

So, I was convinced that chlorophyll is not the only coloring substance in plant tissues. From the encyclopedia, I learned that along with it, special pigments are constantly present, known as xanthophyll and carotene. The first of them has a pure yellow color, the second - an orange tint. Carotene is responsible for the characteristic color of the carrot root, where it is found in very high quantities.Yellow pigments are always present in the green of the plant, but in summer they are completely invisible, as they are masked by the intense green color of chlorophyll.

The autumn coloring of the leaves is especially attractive with its crimson tones. However, these tones are not found in all trees. Crowns of maples and aspens are removed in crimson; an elegant, pinkish color is taken by the foliage of the euonymus; garlands turn dark purple wild grapes. Along with this, lindens, oaks and birches are devoid of red hues, they cast only various yellow and golden tones. What causes the red color of autumn leaves?It is caused by a special coloring matter, anthocyanin, which is extremely widespread in plants.Unlike chlorophyll, anthocyanin is not associated with plastic formations inside the cell. It is dissolved in cell sap and rarely occurs as small crystals. To verify this, we conducted a second experiment.

Experience 2.

Anthocyanins are very easy to extract from any red or blue parts of the plant. To do this, we boiled a certain amount of beets and saw that the water was stained from anthocyanin in a lilac or dirty red color.

Conclusion : The leaves contain a coloring matter - anthocyanin.

I also learned that a group of scientists from the University of North Carolina at Charlotte found new patterns in the appearance of red and yellow leaves in autumn.

The research was led by Emily Habink, who researched different types of trees in different areas.

It turned out that red leaves usually appear on trees that grow on poor soil, and yellow - on trees that grow on rich soil. It has also been found that red leaves allow for more efficient use of the nutrients contained in them in conditions of their deficiency.

So, as a result of the study of red maple and amber tree, she found that in elevated areas, where the soil is poorer, these trees have much redder leaves than those of the same species in fertile floodplain areas. Therefore, the data obtained support the theory that the production of substances that color the leaves in red, helps the leaves to last as long as possible and allows the tree to stock up more efficiently. nutrients for the winter.

As a result of my research, I found out:

1. The leaves contain dyes: chlorophyll, carotene, xanthophyll, anthocyanin.

2. Yellow pigments are always present in the greenery of a plant, but in summer they are completely invisible, as they are masked by the intense color of chlorophyll.

3. Under adverse conditions, chlorophyll is destroyed, and the leaves become red or yellow. These substances capture everything in autumn more space in a leaf, because for their formation it is necessary that it becomes cooler, and that the life of the plant freezes. Also, according to scientists, the yellow or red color of the leaves depends on the composition of the soil on which they grow,red leaves usually appear on trees that grow on poor soil, and yellow leaves on trees that grow on rich soil.

4. Thus. as a result of my research, I found out that none of my classmates could give an exact answer to the questions I posed. Having studied the material on this topic, I was convinced that my hypothesis was confirmed, and now I can tell my friends what the color of the leaves depends on.

Literature:

1. David Burney "The Great Illustrated Encyclopedia of Wildlife"

1. Zapartovich B.B., Krivoruchko E.N., Solovyova L.I.

With love for nature. Didactic material science for elementary school. "Pedagogy", 1978.

2. Ponamareva I.I., Kornilova O.A., Kuchmenko V.S.

Biology. Plants. bacteria. Mushrooms. "Venta-graph", 1999.