Leaf modification. Functions of modified leaves An example of a plant. Pea tendrils features

The leaf is one of the most plastic plant organs. In the process of adaptation to environmental conditions, the entire leaf or part of it may change main function. This leads to qualitative changes in the appearance and internal structure leaf, that is, there are modifications or metamorphoses of the leaf (Fig. 32).

spines

This modification is characteristic of plants living in dry and hot climates, although they often occur in plants of other climatic zones. Spines reduce transpiration and protect plants from being eaten by animals.

Metamorphosis of the entire leaf into a spine is characteristic of cacti. In many astragalus, sainfoin, the rachis of a complex leaf turns into a thorn, in white acacia - stipules.

These are filamentous formations, sensitive to touch and adapted for climbing. In vetch, lentil, pea, the upper part of the rachis and several upper leaves are converted into a tendril. In the leafless rank, all leaflets are reduced, and the rachis is the only antennae (stipules take over the function of photosynthesis.

trapping devices

They are found in plants growing on swampy, peaty, mineral-poor soils. With the help of trapping devices sundew in middle lane, venus flytrap in North America, Nepenthes in tropical Asia use organic food rich in nitrogen and phosphorus, digesting animals. The structure of the trapping devices is different (Nepenthes jars, Venus flytrap traps, sundew leaves), but they are all capable of trapping and digesting insects and other small animals with the help of enzymes secreted by special digestive glands.

Rice. 32. Sheet modifications:

1 - tendril of the leafless rank; 2 - thorn of milkweed shining; 3 - trapping apparatus of Nepenthes.

leaf fall

When the leaves reach the limiting size, aging processes begin in them, leading to the death of the leaf. As the leaves age, the intensity of photosynthesis and respiration decreases, and the content of protein nitrogen and RNA in tissues decreases. The processes of decay, rather than synthesis, begin to predominate. Organic matter drains from old leaf tissues. At the same time, some salts accumulate in the leaves, such as calcium oxalate crystals.

A sure sign of leaf aging is a change in its color. Leaves lose their green color as a result of chloroplast degradation. Yellowing and reddening of the leaves is associated with the accumulation of carotenoids and anthocyanins in them.

In monocots and herbaceous dicots, the leaves gradually die off and collapse, remaining on the stems. At trees and shrubs

Rice. 33. Formation of a separating layer:

1 - wood; 2 - core; 3 - bast; 4 - periderm; 5 - separating layer; 6 - conductive beam; 7 - leaf petiole.

the leaves are falling. Massive leaf fall is called leaf fall. Falling leaves are due to changes occurring in the leaf, namely at the point of attachment of the leaf to the stem. At the base of the petiole, a special separating layer is formed in the transverse direction, consisting of an easily exfoliating parenchyma (Fig. 33). From the side of the stem, the cells closest to the base of the petiole cork and form a protective layer that remains after the leaf falls in the form of a leaf scar. For some time, the leaf is held by veins. But under the influence of the gravity of the leaf and gusts of wind, they are torn, and the leaves fall off.

Leaf fall is an important adaptation of plants to reduce moisture evaporation. It also protects plants from mechanical damage in the winter.

The leaf is one of the most plastic plant organs. In the process of adaptation to environmental conditions, the entire leaf or part of it may change its main function. This leads to qualitative changes in the external appearance and internal structure of the leaf, that is, there are modifications or metamorphoses of the leaf (Fig. 32).

Metamorphosis of the entire leaf into a spine is characteristic of cacti. In many astragalus, sainfoin, the rachis of a complex leaf turns into a thorn, in white acacia - stipules.

They are found in plants growing on swampy, peaty, mineral-poor soils. With the help of trapping devices, the sundew in the middle lane, the Venus flytrap in North America, and the Nepenthes in tropical Asia use organic food rich in nitrogen and phosphorus, digesting animals. The structure of the trapping devices is different (Nepenthes jars, Venus flytrap traps, sundew leaves), but they are all capable of trapping and digesting insects and other small animals with the help of enzymes secreted by special digestive glands.

leaf fall

When the leaves reach the limiting size, aging processes begin in them, leading to the death of the leaf. As the leaves age, the intensity of photosynthesis and respiration decreases, and the content of protein nitrogen and RNA in tissues decreases. The processes of decay, rather than synthesis, begin to predominate. Organic matter drains from old leaf tissue. At the same time, some salts accumulate in the leaves, such as calcium oxalate crystals.

In monocots and herbaceous dicots, the leaves gradually die off and collapse, remaining on the stems. At trees and shrubs

leaves fall. Massive leaf fall is called leaf fall. Falling leaves are due to changes occurring in the leaf, namely at the point of attachment of the leaf to the stem. At the base of the petiole, a special separating layer is formed in the transverse direction, consisting of an easily exfoliating parenchyma (Fig. 33). From the side of the stem, the cells closest to the base of the petiole cork and form a protective layer that remains after the leaf falls in the form of a leaf scar. For some time, the leaf is held by veins. But under the influence of the gravity of the leaf and gusts of wind, they are torn, and the leaves fall off.

Leaf fall is an important adaptation of plants to reduce moisture evaporation. It also protects plants from mechanical damage in the winter.

In the course of evolution, the leaves of plants have changed. To survive and sustain life, the leaves have evolved into spines, tendrils, fleshy plates, and even insect traps.

Leaf functions and variety of forms

Leaves are the vegetative organs of plants, consisting of a petiole and a leaf blade. The leaf as a lateral organ of the shoot carries out:

autotrophic nutrition (photosynthesis);
evaporation of water from the surface (transpiration);
gas exchange.

To be successful, the leaf must have a wide shape to capture a large amount of sunlight, and a thin structure to quickly evaporate and absorb moisture. However, many of these functions are not rational in different regions planets. For example, in an arid climate, it is important to conserve water rather than to evaporate profusely. Therefore, plants with wide thin leaves do not survive in such conditions. On the contrary, in a hot tropical climate, it is important to evaporate as much moisture as possible, which large leaves with numerous veins successfully cope with.

Rice. 1. Tropical plants with giant leaves.

In addition to the restructuring of functions under climatic conditions, the shape of the leaves was transformed depending on the physical impact environment. The carved edges of the maple leaf blade on a powerful petiole allow you to resist strong winds. Small dense leaves tolerate frosts and rains better (cranberries, lingonberries).

Leaves modified into needles help trees remain evergreen even in harsh climates, and herbivores bypass sharp needles.

Rice. 2. Cranberry.

Modifications

The changes affect not only the size and shape of the familiar rounded sheet. The leaves of some plants have changed beyond recognition. The fact that this is a leaf is evidenced by the development from the kidney. The table “Modification of leaves” presents the functions and structure of types of leaf modification.

What have we learned?

From an article on biology (grade 6), we learned about the functions of leaves, evolutionary changes in a leaf in accordance with climatic conditions and weather phenomena, types and features of leaf blade modification.

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spines

Spines are also modifications of plant leaves. They are characteristic of those that grow in arid and desert conditions. Everyone has seen cactus thorns. These are its leaves. In conditions of lack of moisture, when the transpiration process must be minimized, this is an ideal adaptation. With such a small surface of the leaf blade and water, very little will evaporate.

However, the spines of cactus and acacia are a different modification of the leaves. What is the difference? In white acacia, hawthorn, blackthorn, barberry and other similar plants, the spines are modified stipules, and not the plates themselves. Their main function is to protect fragrant flowers and sweet fruits from being eaten by various animals.

needles

The needles of all representatives of the department of gymnosperms are also a modification of the leaves. Everyone remembers the children's riddle about the Christmas tree - "in winter and summer in one color." And all conifers are evergreen in many respects precisely due to the characteristic modifications of the leaves. In cross section, they have a rounded or ribbed shape. Such leaves have a small area, like the spines of cacti. Their stomata, through which gas exchange occurs, are immersed in the integumentary and main part of the leaf. This reduces the rate of water evaporation. IN winter time years, these formations are completely sealed with wax, which reduces transpiration to almost zero. Therefore, at a time when all angiosperms drop their leaves for the winter, conifers and shrubs can boast of lush green decoration.

Leaves of desert plants

It is not easy for plants to survive in arid conditions. What causes the modification of leaves in these plants? They need to have such structural features that will allow them to survive with sudden changes in temperature and lack of moisture. Therefore, their leaves are often covered with a thick layer of hairs, or a waxy coating. They protect plants from excessive moisture loss. There is another device as well. Many types of arid ecosystems store water in thick, fleshy leaves. An example of such a modification is aloe, which is often bred as a houseplant with healing properties.

tendrils

To consider the features of the following organs, let's recall what leaf modifications are found in the legume family. The shoots of most of them are long and thin, and the fruits, when ripe, acquire a mass that does not allow them to stay upright. But it is the most beneficial for the productive implementation of photosynthesis. What leaf modifications are found in peas? Of course, these are mustaches. This is how individual plates from a complex sheet are modified. With their help, the plant clings to the support, and as a result, a weak and thin stem is located in the required position.

Scales

To understand why kidney scales are a modification of the leaf, it is necessary to understand the structure of the bulb. Consider it on the example of a common leek. Its bulb, despite the fact that it is located underground, is a modification of the above-ground part of the plant - the shoot. This is easy to prove. The shoot consists of a stem, leaves and buds. The same parts are in the bulb. Its flat stem is called the bottom. A bundle of adventitious roots departs from it. Above are several types of leaves. Young have green color and grow from the kidneys located on the bottom. Juicy and fleshy leaves take on this form in order to store moisture. With its help, the plants in which the bulb is formed, endure drought underground, low temperatures and other adverse events. And dry scales, which are also a modification of the leaves, protect the internal contents of the bulb from mechanical damage.

predatory leaves

Leaf modification can also be very dangerous for other living beings. There is a whole group of insectivorous plants. They are also capable of carrying out the process of photosynthesis, that is, they are autotrophs. But if there are no conditions for its occurrence, then they switch to a heterotrophic mode of nutrition. With the help of modified leaves, they catch insects and digest them. For example, in the tropical plant sarracenia, the leaves are a funnel that borders fragrant nectaries. They also attract insects. Approaching, the victim begins to slide along the edges of the funnel and is trapped. In addition, the leaves also give off special narcotic substances that immobilize insects of any size. On top of the funnel, the sheet is twisted in the form of a hood. This fold prevents rain from getting inside, mixing with digestive enzymes.

Leaf modifications also include the movable tentacles of the sundew, at the ends of which there is a sticky liquid. It attracts insects that land to feast and become trapped.

leaf buds

All leaves are vegetative organs. With their help, the process of asexual reproduction is carried out. For example, if you separate a leaf of an uzambar violet from an adult plant and place it in a container of water, after a while it forms a root. But in a number of plants, the process of reproduction occurs differently. So, at the room Kalanchoe, along the edge of the leaf blade, there are buds, from which young shoots develop independently. They are almost fully formed: they have a small spine and leaves. Falling off, they germinate in the same container as an adult plant. This process is also called self-reproduction.

The value of modifications of plant leaves is great. These adaptations increase vitality and facilitate the process of adaptation. Thanks to the modifications of the leaves, land plants were able to master various climatic zones, differing in the level of moisture, temperature regime and soil properties. In addition to photosynthesis, transpiration, and cellular respiration, leaf modifications allow them to perform other important functions: protection from predators and mechanical damage, regulation of gas exchange and the level of water evaporation, and heterotrophic nutrition.

We all know that thorny cacti grow in the desert. These are wonderful drought-loving plants. All plants have leaves. But where are they with cacti? After all, they only have thorns, you say. And you will do it right, but it turns out that their thorns are leaves! And it is they who allow the plant to survive where others cannot. And there are plants in which the leaves play the role of the stomach! It's hard to believe, but it really happens. We will learn about these and other unusual representatives of leaves in this lesson.

Depending on the conditions, the number of stomata, the thickness of the cuticle, and the number of chloroplasts can change in the leaves.

Ecology- the science of the relationship of living organisms and their community with each other and the environment.

Environmental factors(environmental factors) - conditions or elements of the environment.

The leaves of plants in wet habitats are large, wide, with big amount stomata (monstera, begonia).

The leaves of plants in arid habitats are small, narrow, with few stomata. They have a thick cuticle, dense pubescence, wax coating.

(see Fig. 1) - drought-resistant plants with tough stems and leaves. They are well adapted to dry conditions due to the strong development of mechanical leaf tissues. Without harm, they tolerate the loss of up to 25% of tissue fluid.

Rice. 1. Sclerophyte

(see Fig. 2) - plants that store water in modified succulent leaves or stems. Grow in sunny places. The leaves are light green, gray, which is due to the need to reflect part sun rays(cineraria).

Rice. 2. Succulent

In shade-tolerant plants, the parenchyma consists of 2-3 layers of loosely adjacent cells. Large chloroplasts practically do not shade each other. The leaves are thin, dark green (lilies of the valley).

Sciophytes- shade-loving plants. Need scattered sunlight. Exposure to bright light can cause burns or death.

In plants of open habitats, the leaf parenchyma contains several layers of a sheet of columnar cells adjacent to each other. The leaves are light (water lily).

Heliophytes- photophilous plants. Adapted to life in open, heavily sunlit areas. Does not tolerate prolonged shading. For good growth, they need intensive lighting.

Houseplants

Consider a few indoor plants. Think about the conditions of their growth at home. Draw conclusions, justify.

Make cross sections of aloe, tradescantia, violet leaves. Review and draw. Some epiphytes have a poorly developed root system or do not have it at all. They absorb water and minerals from dust and air with the help of leaves.

These patterns are typical for plants of the same species and even for different leaves of the same plant.

Leaf mosaic- the result of uneven leaf growth. Pouring minimally overlap each other, and therefore they are different in shape and size. It allows the plant to make the most efficient use of the sunlight falling on it.

Heterophilia- diversity, the presence on one plant of leaves that differ significantly from each other in shape. Characteristic for aquatic and semi-aquatic plants: arrowhead, water buttercup, poisonous milestone (see Fig. 3). Their underwater leaves differ sharply in shape from the surface ones.

Rice. 3. Aquatic and semi-aquatic plants

Hetorophilia is also found in mulberries (see Fig. 4), antler(its leaves form a kind of bowl, where, when the branches and leaves of other plants rot, soil is formed in which the roots of this fern are located).

Rice. 4. Mulberry

There are apical, middle and lower formation of leaves. Grassroots formation sheets are located in the ground or underground, protect the recovery buds perennials. Median formation - perform the function of photosynthesis. Apical - protect inflorescences, can be brightly colored, attracting insects (Ivan da Marya).

spines - leaf modification, which prevent animals from eating the plant (barberry) or reduce the evaporation of water (cacti).

During the dry season, some plants (acacia) can shed their leaves, leaving only petioles instead, which reduces water evaporation.

tendrils(see Fig. 5) - a modification of the leaf, which allows it to attach to the support and brings the leaves to the light (peas).

Rice. 5. Pea tendrils

The leaves of insectivorous plants are adapted for insect digestion. Insectivorous plants grow on soils poor in minerals, which they compensate for by feeding on insects (Venus flytrap, sundew (see Fig. 6)).

Rice. 6. Sundew - insectivorous plant

Small insects stick to the sticky hairs of the sundew, the leaf curls up, and the decomposition of the animal begins.

Water storage leaves (aloe) retain moisture that the plant uses during a drought.

The integumentary scales of the kidneys, bulbs, rhizomes perform a protective function.

carnivorous plants

Many plants convert leaves into trapping jugs (see Fig. 7) (sarracenia, darlingtonia, nipenthos).

Rice. 7. Trapping jars of insectivorous plants

The pitcher has a slippery inner surface, rainwater can accumulate inside. Insects that get caught rot in this water.

The leaves of some primitive cacti are not turned into spines (see Fig. 8) (pereskia).

Rice. 8 Pereskia, A Primitive Cactus

During drought, the leaves fall off. Cacti live in the rainforests of South America.

Steppe grasses (feather grass (see Fig. 9)) have narrow leaves with stomata at the top. When dry, the leaf rolls up into a tube, stomata inward.

Rice. 9. Feather

Bibliography

Biology. Bacteria, fungi, plants. Grade 6: textbook. for general education institutions / V.V. Beekeeper. - 14th ed., stereotype. - M.: Bustard, 2011. - 304 p.: ill.
Tikhonova E.T., Romanova N.I. Biology, 6. - M.: Russian word.
Isaeva T.A., Romanova N.I. Biology, 6. - M.: Russian word.

myblog-bio.blogspot.com().
Beaplanet.ru ( .
estnauki.ru ().

Homework

Biology. Bacteria, fungi, plants. Grade 6: textbook. for general education institutions / V.V. Beekeeper. - 14th ed., stereotype. - M.: Bustard, 2011. - 304 p.: ill. - With. 122, tasks and questions 2, 3, 5 ()..
What are the types of leaves? What is their meaning?
What is heterophilia? Give an example.
* Compare the leaves of plants in your yard growing in bright sunshine and indoor plants. What is the difference? What caused such changes?

*View*	*Structural features*	*Meaning*	*plant examples*
	A sheet or part of it converted into a needle. Often grows on a fleshy stem. They can also be formed from shoots, stipules, roots.	Preservation internal moisture, reducing the area of evaporation. Protection from being eaten by animals
	The leaf or part of it extends into a long flagellum, twisting at the end	Maintaining the plant's thin stems vertical position due to tenacity for objects	Peas, beans, lentils
	Strong triangular leaves or fleshy formations. Layering on each other	Closes part of the plant like a lotus, protecting it from drying out and damage	Corn (cob), onion, tree bud
succulent leaf	Dense, fleshy leaves, sometimes curled into forks. Covered in wax	stock nutrients and moisture	Aloe, cabbage, agave
phyllodes	Petioles transformed into a leaf blade capable of photosynthesis. Look like small leaves in two rows	Formed during dry periods to reduce moisture evaporation	australian acacias
	Coated with a viscous or insect-attracting substance. Rolls up or slams shut depending on design	Catching insects in places with a lack of minerals	sundew, portuguese flycatcher, lusitanian dewdrop