Plant adaptations. Adaptations of organisms to light, adaptations of plants to light What adaptations contributed to the wide distribution of seed plants
Sunlight is one of the most important environmental indicators for plant life. It is absorbed by chlorophyll and used in the construction of primary organic matter. Almost all houseplants photophilous, i.e. thrive best in full light, but vary in shade tolerance. Taking into account the relation of plants to light, they are usually divided into three main groups: photophilous, shade-tolerant, shade-indifferent.
There are plants that adapt quite easily to sufficient or excess light, but there are also those that develop well only under strictly defined light parameters. As a result of the adaptation of the plant to low light, its appearance changes somewhat. The leaves become dark green and slightly increase in size (linear leaves lengthen and become narrower), the stem begins to stretch, which at the same time loses its strength. Then the growth gradually decreases, because the production of photosynthesis products, going to the building bodies of the plant, sharply decreases. With a lack of light, many plants stop blooming. With an excess of light, chlorophyll is partially destroyed, and the color of the leaves becomes yellow-green. In strong light, plant growth slows down, they turn out to be more squat with short internodes and wide short leaves. The appearance of a bronze-yellow leaf color indicates a significant excess of light, which is harmful to plants. If prompt action is not taken, burns may occur.
The effect of ionizing radiation is manifested in the effect of radiation on a plant organism at different levels of organization of living matter. The direct action consists in the radiation-chemical ionization of molecules together with the absorption of radiation energy, i.e. puts molecules in an excited state. Indirect exposure is accompanied by damage to molecules, membranes, organelles, cells as a result of exposure to water radiolysis products, the number of which sharply increases as a result of irradiation. The effectiveness of radiation damage depends significantly on the oxygen content in the environment. The lower the oxygen concentration, the lower the damage effect. In practice, it is generally accepted that the limit of lethal oxygen doses characterizes the radioresistance of organisms. In an urban environment, plant life is also affected by the location of buildings. From this we can conclude that plants need light, but each plant is photophilous in its own way.
3. Research part
Plant development is closely related to conditions environment. The temperatures characteristic of a given area, the amount of precipitation, the nature of soils, biotic parameters and the state of the atmosphere - all these conditions interact with each other, determine the nature of the landscape and the type of plants.
Each contaminant affects plants in a different way, but all contaminants affect some basic processes. First of all, systems that regulate the intake of pollutants are affected, as well as chemical reactions responsible for the processes of photosynthesis, respiration and energy production. In the course of my work, I realized that the plants that grow near the roads are significantly different from the plants that grow in parks. Dust that settles on plants clogs pores and interferes with respiration processes, and carbon monoxide leads to yellowing, or discoloration of the plant and dwarfing.
I conducted my research on the example of aspen leaves. In order to see how much dust remains on the plant, I needed sticky tape, which I glued to the outside of the leaf. The leaf from the park is slightly polluted, which means that all its processes are functioning normally. [cm. application, photo No. 1,3]. And the leaf, which was in close proximity to the road, is very dirty. It is smaller than its normal size by 2 cm, has a different color (darker than it should be), and therefore has been exposed to atmospheric pollutants and dust. [cm. application, photo No. 2,4].
Another indicator of environmental pollution is the absence of lichens on plants. In the course of my research, I found out that lichens grow on plants only in ecologically clean places, for example: in the forest. [cm. application, photo No. 5]. It is difficult to imagine a forest without lichens. Lichens settle on the trunks, and sometimes on the branches of trees. Lichens grow especially well in our northern coniferous forests. This testifies to the clean air in these areas.
Thus, we can conclude that lichens do not grow at all in the parks of large cities, tree trunks and branches are completely clean, and outside the city, in the forest, there are quite a lot of lichens. The fact is that lichens are very sensitive to air pollution. And in industrial cities it is far from clean. Factories and factories emit many different harmful gases into the atmosphere, it is these gases that destroy lichens.
In order to stabilize the situation with pollution, we first of all need to limit the release of toxic substances. After all, plants, like us, need clean air to function properly.
Conclusion
Based on the research I have done and the sources I have used, I have come to the conclusion that the plant environment has environmental issues that need to be addressed. And the plants themselves take part in this struggle, they actively purify the air. But there are also climatic factors that do not have such a detrimental effect on plant life, but force plants to adapt and grow in conditions suitable for them. climatic conditions. I found out that the environment and plants interact, and without this interaction, plants would die, since plants draw all the components necessary for their life activity from their habitat. Plants can help us deal with our environmental problems. In the course of this work, it became more clear to me why different plants grow in different climatic conditions and how they interact with the environment, as well as how plants adapt to life directly in the urban environment.
Dictionary
Genotype - the genetic structure of an individual organism, the specific set of genes that it carries.
Denaturation is a change in their structure and natural properties characteristic of protein substances when the physical and chemical conditions of the environment change: with an increase in temperature, a change in the acidity of the solution, etc. reverse process called renaturation.
Metabolism is a metabolism, chemical transformations occurring from the moment of receipt nutrients into a living organism until the moment when the end products of these transformations are released into the external environment.
Osmoregulation is a combination of physicochemical and physiological processes, providing the relative constancy of the osmotic pressure (OD) of the liquids of the internal environment.
Protoplasm - the contents of a living cell, including its nucleus and cytoplasm; the material substratum of life, the living substance of which organisms are composed.
Thylakoids are membrane-bound compartments within chloroplasts and cyanobacteria. The light-dependent reactions of photosynthesis take place in the thylakoids.
Stomata - a slit-like opening (stomatal fissure) in the epidermis of above-ground organs of plants and two cells limiting it (closing).
Phytophages are herbivorous animals, which include thousands of species of insects and other invertebrates, as well as large and small vertebrates.
Phytoncides are biologically active substances formed by plants that kill or inhibit the growth and development of bacteria, microscopic fungi, and protozoa.
Photosynthesis - education organic matter green plants and some bacteria using the energy of sunlight. During photosynthesis, carbon dioxide is absorbed from the atmosphere and oxygen is released.
Used information resources when performing educational and research work
1. Akhiyarova G.R., Veselov D.S.: "Hormonal regulation of growth and water metabolism under salinity" // Abstracts of the participants of the 6th Pushchino school - conference of young scientists "Biology - science of the XXI century", 2002.
2. Big encyclopedic dictionary. - 2nd ed., revised. and additional - M .: Great Russian Encyclopedia, 1998. - 1456 p.: ill. Edited by Prokhorov A.M. Ch. editor Gorkin A.P.
3. Vavilov P.P. Crop production, 5th ed. - M .: Agropromizdat, - 1986
4. Vernadsky V.I., Biosphere, vol. 1-2, L., 1926
5. Volodko I.K.: “Trace elements and resistance of plants to adverse conditions”, Minsk, Science and technology, 1983.
6. Danilov-Danilyan V.I.: "Ecology, nature conservation and environmental safety" M.: MNEPU, 1997
7. Drobkov A. A.: "Microelements and natural radioactive elements in the life of plants and animals", M., 1958.
8. Wikipedia: information portal: [Electron. resource] // Habitat [website] Access mode: http://ru. wikipedia.org/wiki/Habitat (10.02.10)
9. Everything about the Earth: information portal: [Electron. resource] // Water shell [site] Access mode: http://www.vseozemle.ru/2008-05-04-18-31-40.html (23.03.10)
10.Sbio. info First bio community: information portal: [Electronic. resource] // Biotic factors of the environment and the types of relationships of organisms caused by them [website] Access mode: http://www.sbio. info/page. php? id=159 (04/02/10)
Appendix
Photo No. 1. Aspen leaf from the park.
Photo #2. A sheet located next to the roadway.
Photo #3. Dust on sticky tape from a leaf from the park.
Photo #4. Dust on sticky tape from a sheet next to the roadway.
Photo #5. Lichen on a tree trunk in a forest park.
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Creation for everyone vegetable crop The most favorable growth conditions are more available in greenhouses, but even then not always. In the open ground, such conditions can either alternate in periods of growth (months and weeks), or combined in a random optimal coincidence of several environmental conditions and care methods.
And, nevertheless, despite the obvious unfavorability in individual years, the plants still produce annual yields that generally satisfy the owners of gardens.
The ability of crops to produce crops in almost any combination of climatic factors and any lack of care lies in their biological adaptability to growing conditions.
As examples of such adaptations (adaptive abilities), one can point to rapid growth (early maturity), a very deep or widely branched root system closer to the soil surface, a large number of fruit ovaries, a mutually beneficial community of roots with microorganisms, and others.
In addition to these, there are many other mechanisms of adaptation of plants to the prevailing external conditions and opposition to them.
They will be discussed.
overheat protection
Thirty years ago, Moldovan scientists, having studied 200 species of plants (including the majority of vegetables), came to the conclusion that they have peculiar physiological “refrigerators” in the intercellular spaces of the leaves.
Up to 20-40% of moisture in the form of steam generated inside the leaf, and part of the steam absorbed by the leaf from the outside air, condenses (settles) on the cells of internal tissues and protects them from excessive overheating at high outdoor temperatures.
With a sharp increase in air temperature and with a decrease in moisture supply (insufficient or delayed watering), vegetable coolers intensify their activity, due to which carbon dioxide absorbed by the leaf is involved in the process, leaf temperature decreases and water consumption for evaporation (transpiration) decreases.
With a short exposure to heat, the plant will successfully cope with such an unfavorable factor.
Overheating of the sheet can occur when it absorbs excess thermal solar radiation, which is called near infrared in the spectrum of sunlight. Sufficient content of potassium in the leaves helps to regulate such absorption and prevent its excess, which is achieved by timely periodic feeding of this element.
Sleeping buds - frost protection
In case of death of plants from freezing with a strong root system, dormant buds awaken in them, which under normal conditions would not have shown themselves in any way.
Developing new shoots often allow you to get yields that are not worse than without such stress.
Sleeping buds also help plants recover when part of the leaf mass is poisoned (ammonia, etc.). To protect against the toxic effects of ammonia, the plant produces an additional amount of organic acids and complex nitrogen compounds, which help restore vital activity.
With any abrupt changes in the environment (stressful situations), systems and mechanisms are strengthened in plants that allow them to more rationally use the available biological resources.
They allow you to hold out, as they say, until better times.
A little radiation is good
Plants turned out to be adapted even to small doses of radioactive radiation.
Moreover, they absorb them for their own benefit. Radiation enhances a number of biochemical processes, which contributes to the growth and development of plants. And an important role in this is played, by the way, ascorbic acid (vitamin C).
Plants adapt to the rhythms of the environment
The change from daylight to darkness, the alternation during the day of light intensity and its spectral characteristics (due to cloudiness, dustiness of the air, and the height of the sun) forced plants to adapt their physiological activity to these conditions.
They change the activity of photosynthesis, the formation of proteins and carbohydrates, create a certain daily and daily rhythm of internal processes.
Plants are “used” to the fact that with decreasing light the temperature decreases, to the alternation of the air temperature during the day and at night, while maintaining a more stable soil temperature, to different rhythms of absorption and evaporation of water.
With a temporary lack of a number of nutrients in the plant, the mechanism of their redistribution from old leaves to young, growing and tops of the shoots operates.
The same happens with the natural death of the leaves. Thus, there is a saving of food resources with their secondary use.
Plants adapted to produce crops in greenhouses
In greenhouses, where light conditions are often worse than in open ground(due to shading by the coating, lack of separate parts spectrum), photosynthesis as a whole proceeds less intensively than in open ground.
But greenhouse plants have adapted to compensate for it due to a more developed leaf surface and a high content of chlorophyll in the leaves.
Under normal growth conditions, to increase plant mass and form crops, everything happens in concert and is adapted to ensure that the receipt of substances from photosynthesis is greater than their consumption for respiration.
Plants want to live too
All adaptive systems and reactions of plants to certain conditions of existence serve one goal - to maintain a constant internal state (biological self-regulation), without which no living organism can do.
And the proof of the best adaptability of any crop is its yield at an acceptable level in the most unfavorable year.
E. Feofilov, Honored Agronomist of Russia
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The study of methods and methods of adaptation of various plants to environmental influences, which allow them to spread more widely and survive in various environmental conditions. Genetic inheritance of organisms to the possibility of adaptation.
Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.
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Human adaptation to environmental conditions.
Scientific bases of hygienic regulation of environmental factors
Characterization of the processes of human adaptation to environmental conditions.
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Adaptation of organisms to the environment
Types of adaptation of living organisms to the environment.
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The indicator role of plants and animals
Indicator plants are plants that are characterized by a pronounced adaptation to certain environmental conditions.
Adaptation of plants to the environment
The reactions of living organisms to future changes in weather conditions. Examples of using the indicator properties of plants and animals.
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The main factors of the aquatic environment and their influence on organisms
General characteristics of the aquatic environment. Analysis of the adaptation of organisms to various factors - water density, salt, temperature, light and gas regimes.
Features of adaptation of plants and animals to the aquatic environment, ecological groups of hydrobionts.
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Adaptation to low temperatures in animals
The variety of ways in which living organisms adapt to the effects of adverse environmental conditions on earth. Adaptation of animals to low temperatures.
Use of the specific properties of the organism to life in difficult climatic conditions.
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Microorganisms as indicators of environmental pollution
Priority environmental pollutants and their impact on soil biota. Effect of pesticides on microorganisms. Bioindication: concept, methods and features. Determination of soil moisture. Accounting for microorganisms in various media.
Ashby and Hutchinson Wednesday.
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Type of branching of various root systems. Ecological groups of plants in relation to water: (hydato-, hydro-, hygro-, meso-, xero-, sclerophytes and succulents). Regulation of water metabolism in terrestrial animals.
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Adaptability of plants to the environment
The harsher and more difficult the living conditions, the more ingenious and diverse the adaptability of plants to the vicissitudes of the environment. Often the adaptation goes so far that the external environment begins to completely determine the shape of the plant. And then plants belonging to different families, but living in the same harsh conditions, often become so similar in appearance to each other that it can be misleading about the truth of their family ties - hotcooltop.com.
For example, in desert areas for many species, and, above all, for cacti, the shape of the ball turned out to be the most rational. However, not everything that has a spherical shape and is studded with prickly thorns is cacti. Such an expedient design, which makes it possible to survive in the most difficult conditions of deserts and semi-deserts, also arose in other systematic groups of plants that do not belong to the cactus family.
Conversely, cacti do not always take the form of a ball or column dotted with thorns. One of the most famous cactus experts in the world, Kurt Backeberg, in his book The Wonderful World of Cacti, talks about how these plants can look like, placed in certain habitat conditions. Here is what he writes:
“The night in Cuba is full of mysterious rustles and sounds. Large bats, like shadows, silently rush past us in complete darkness, only the space around the old, dying trees glows, in which myriads of fireflies perform their fiery dance.
The impenetrable tropical night with its oppressive stuffiness tightly enveloped the earth. The long journey we made on horseback took away our last strength, and now we, climbing under the mosquito nets, are trying to at least get some rest. The ultimate goal of our expedition is the land of amazingly beautiful green cacti of the Ripsaliaceae group. But now the time has come to saddle the horses. And although we do this simple operation in the early morning, sweat literally floods our eyes.
Soon our small caravan sets off again. After several hours on the road, the greenish gloom of the virgin forest begins to gradually dissipate.
Our eyes open up to the horizon full of sunshine, completely covered with shrubs. Only in some places the tops of stunted trees rise above it, and sometimes you can see single powerful trunks crowned with huge crowns.
However, how strange the tree branches look!
They seem to have a double veil: swaying from the breaths of a warm surface breeze, long thread-stems of one of the species of bromeliads (Tillandsia usneoides) hang from the branches almost to the ground, somewhat similar to long fabulous beards strewn with silver gray hair.
Between them hangs a mass of thin rope plants intertwined into balls: this is the habitat of colonies of leafless epiphytes, cacti related to ripsaliaceae. As if fleeing from the lush terrestrial vegetation, they tend to climb higher into the crowns of trees, closer to the sunlight. What a variety of forms! Here are thin thread-like stems or bulky fleshy outgrowths covered with delicate fluff, there are strongly overgrown shoots resembling ribbed chains in appearance.
The complex interweaving of climbing plants of the most bizarre forms: spiral, jagged, twisted, wavy - seems like a bizarre work of art. During the flowering period, all this green mass is hung with elegant wreaths or decorated with a variety of colors of the smallest specks. Later, the plants put on colorful necklaces of bright white, cherry, golden yellow and dark blue berries.
Cacti, which have adapted to live in the crowns of forest giants and whose stems, like vines, hang down to the ground, are widespread in the tropical forests of Central and South America.
Some of them even live in Madagascar and Ceylon.
Climbing cacti is not a striking example of the ability of plants to adapt to new living conditions? But he is not the only one among many hundreds of others. Common inhabitants of the tropical jungle are climbing and climbing plants, as well as epiphytic plants that settle in the crowns of woody plants.
All of them strive to get out of the eternal twilight of the dense undergrowth of virgin tropical forests as soon as possible. They find their way up to the light without creating powerful trunks and support systems that require huge expenses. building material. They calmly climb up, using the "services" of other plants that act as supports - hotcooltop.com.
In order to successfully cope with this new task, plants have invented various and quite technically advanced organs: clinging roots and leaf petioles with outgrowths on them, thorns on branches, clinging inflorescence axes, etc.
Plants have lasso loops at their disposal; special disks with the help of which one plant is attached to another with its lower part; movable cirriform hooks, first digging into the trunk of the host plant, and then swelling in it; various kinds of squeezing devices and, finally, a very sophisticated gripping apparatus.
We have already given a description of the structure of banana leaves given by G.
Haberlandt. No less colorfully he describes rattan - one of the varieties of climbing palms:
“If you get off the footpath of the Botanical Garden in Bogor (Java Island) and go deeper into the thickets, then after a few steps you can be left without a hat. Dozens of hooks scattered everywhere will cling to our clothes and numerous scratches on the face and hands will call for more caution and attention. Looking around and looking closely at the “grasping” apparatus of plants, in the zone of action of which we found ourselves, we found that the petioles of graceful and very complex rattan leaves have long, up to one or two meters, exceptionally flexible and elastic processes, dotted with numerous hard and, moreover, the same semi-movable spikes, each of which is a hook-hook bent and tilted back.
Any palm leaf is equipped with such a fearsome hook-shaped thorn, which is not so easy to part with what is hooked on it. The elastic limit of the "hook", consisting almost entirely of strong bast fibers, is extremely high.
ADAPTABILITY OF PLANTS TO THE ENVIRONMENT
“You can hang a whole bull on it,” my companion remarked jokingly, drawing attention to my attempts to at least approximately determine the weight that such a “line” is able to withstand. In many palm trees related to rattan, the elongated axes of inflorescences have become such tools for capturing.
The wind easily throws flexible inflorescences from side to side until a support tree trunk is in their way. Numerous hooks-hooks allow them to quickly and securely hook on the bark of a tree.
Firmly fixed with the help of overgrown leaves on several trees standing next to each other (often spikes in the lower part of the leaf petiole or even in the leaf sheath serve as additional means of retention), the completely smooth, snake-like trunk of the rattan, like a loach, climbs up, pushing through numerous branches , sometimes spreading to the crowns of neighboring trees, in order, in the end, to break through with young leaves to the light and rise above the crown of the supporting tree.
There is no further way for him: in vain his shoots will seek support in the air. Aging leaves gradually die off, and the palm gets rid of them. Deprived of "anchors-hooks", palm shoots slide down under the weight of their own weight until the uppermost leaves with their spikes again catch on some support.
At the foot of the trees, one can often see numerous shoots of a palm tree, twisted into loops, completely naked, without leaves, often as thick as an adult's arm. It seems that the shoots, like snakes, are crawling around in search of a new support. In the Bogor Botanical Garden, the longest rattan trunk reaches 67 meters. Rattans 180 meters long, and sometimes even up to 300 meters long, are found in the impenetrable wilds of tropical rainforests!
Reactions to unfavorable environmental factors are destructive for living organisms only under certain conditions, and in most cases they have an adaptive value. Therefore, these responses were called by Selye "general adaptation syndrome". In later works, he used the terms "stress" and "general adaptation syndrome" as synonyms.
Adaptation- this is a genetically determined process of formation of protective systems that provide an increase in stability and the flow of ontogenesis in unfavorable conditions for it.
Adaptation is one of the most important mechanisms that increases the stability of a biological system, including a plant organism, in the changed conditions of existence. The better the organism is adapted to some factor, the more resistant it is to its fluctuations.
The genotypically determined ability of an organism to change metabolism within certain limits, depending on the action of the external environment, is called reaction rate. It is controlled by the genotype and is characteristic of all living organisms. Most of the modifications that occur within the limits of the reaction norm are of adaptive significance. They correspond to changes in the habitat and provide better survival of plants under fluctuating environmental conditions. In this regard, such modifications are of evolutionary importance. The term "reaction rate" was introduced by V.L. Johansen (1909).
The greater the ability of a species or variety to modify in accordance with the environment, the wider its rate of reaction and the higher the ability to adapt. This property distinguishes resistant varieties of agricultural crops. As a rule, slight and short-term changes in environmental factors do not lead to significant violations of the physiological functions of plants. This is due to their ability to maintain the relative dynamic balance of the internal environment and the stability of the basic physiological functions in a changing external environment. At the same time, sharp and prolonged impacts lead to disruption of many functions of the plant, and often to its death.
Adaptation includes all processes and adaptations (anatomical, morphological, physiological, behavioral, etc.) that increase stability and contribute to the survival of the species.
1.Anatomical and morphological adaptations. In some representatives of xerophytes, the length of the root system reaches several tens of meters, which allows the plant to use groundwater and not experience a lack of moisture in conditions of soil and atmospheric drought. In other xerophytes, the presence of a thick cuticle, pubescence of leaves, and the transformation of leaves into spines reduce water loss, which is very important in conditions of lack of moisture.
Burning hairs and spines protect plants from being eaten by animals.
Trees in the tundra or at high mountain heights look like squat creeping shrubs, in winter they are covered with snow, which protects them from severe frosts.
In mountainous areas with large diurnal temperature fluctuations, plants often have the form of flattened pillows with densely spaced numerous stems. This allows you to keep moisture inside the pillows and a relatively uniform temperature throughout the day.
In marsh and aquatic plants, a special air-bearing parenchyma (aerenchyma) is formed, which is an air reservoir and facilitates the breathing of plant parts immersed in water.
2. Physiological and biochemical adaptations. In succulents, an adaptation for growing in desert and semi-desert conditions is the assimilation of CO 2 during photosynthesis along the CAM pathway. These plants have stomata closed during the day. Thus, the plant keeps the internal water reserves from evaporation. In deserts, water is the main factor limiting plant growth. The stomata open at night, and at this time CO2 enters the photosynthetic tissues. The subsequent involvement of CO2 in the photosynthetic cycle occurs in the daytime already with closed stomata.
Physiological and biochemical adaptations include the ability of stomata to open and close, depending on external conditions. The synthesis in cells of abscisic acid, proline, protective proteins, phytoalexins, phytoncides, an increase in the activity of enzymes that counteract the oxidative breakdown of organic substances, the accumulation of sugars in cells and a number of other changes in metabolism contribute to an increase in plant resistance to adverse environmental conditions.
The same biochemical reaction can be carried out by several molecular forms of the same enzyme (isoenzymes), while each isoform exhibits catalytic activity in a relatively narrow range of some environmental parameter, such as temperature. The presence of a number of isoenzymes allows the plant to carry out the reaction in a much wider range of temperatures, compared with each individual isoenzyme. This enables the plant to successfully perform vital functions in changing temperature conditions.
3. Behavioral adaptations, or avoidance of an adverse factor. An example is ephemera and ephemeroids (poppy, starflower, crocuses, tulips, snowdrops). They go through the entire cycle of their development in the spring for 1.5-2 months, even before the onset of heat and drought. Thus, they kind of leave, or avoid falling under the influence of the stressor. In a similar way, early-ripening varieties of agricultural crops form a crop before the onset of adverse seasonal events: August fogs, rains, frosts. Therefore, the selection of many agricultural crops is aimed at creating early ripe varieties. Perennial plants overwinter as rhizomes and bulbs in the soil under snow, which protects them from freezing.
Adaptation of plants to unfavorable factors is carried out simultaneously at many levels of regulation - from a single cell to a phytocenosis. The higher the level of organization (cell, organism, population), the greater the number of mechanisms simultaneously involved in the adaptation of plants to stress.
Regulation of metabolic and adaptive processes inside the cell is carried out with the help of systems: metabolic (enzymatic); genetic; membrane. These systems are closely related. Thus, the properties of membranes depend on gene activity, and the differential activity of the genes themselves is under the control of membranes. The synthesis of enzymes and their activity are controlled at the genetic level, at the same time, enzymes regulate the nucleic acid metabolism in the cell.
On the organism level to the cellular mechanisms of adaptation, new ones are added, reflecting the interaction of organs. Under unfavorable conditions, plants create and retain such a number of fruit elements that are provided in sufficient quantities with the necessary substances to form full-fledged seeds. For example, in inflorescences of cultivated cereals and in crowns fruit trees under adverse conditions, more than half of the laid ovaries may fall off. Such changes are based on competitive relations between organs for physiologically active and nutrients.
Under stress conditions, the processes of aging and falling of the lower leaves are sharply accelerated. At the same time, the substances necessary for plants move from them to young organs, responding to the survival strategy of the organism. Thanks to the recycling of nutrients from the lower leaves, the younger ones, the upper leaves, remain viable.
There are mechanisms of regeneration of lost organs. For example, the surface of the wound is covered with a secondary integumentary tissue (wound periderm), the wound on the trunk or branch is healed with influxes (calluses). With the loss of the apical shoot, dormant buds awaken in plants and lateral shoots develop intensively. Spring restoration of leaves instead of fallen ones in autumn is also an example of natural organ regeneration. Regeneration as a biological device that provides vegetative reproduction of plants by root segments, rhizomes, thallus, stem and leaf cuttings, isolated cells, individual protoplasts, is of great practical importance for crop production, fruit growing, forestry, ornamental gardening, etc.
The hormonal system is also involved in the processes of protection and adaptation at the plant level. For example, under the influence of unfavorable conditions in a plant, the content of growth inhibitors sharply increases: ethylene and abscissic acid. They reduce metabolism, inhibit growth processes, accelerate aging, fall of organs, and the transition of the plant to a dormant state. Inhibition of functional activity under stress under the influence of growth inhibitors is a characteristic reaction for plants. At the same time, the content of growth stimulants in the tissues decreases: cytokinin, auxin and gibberellins.
On the population level selection is added, which leads to the appearance of more adapted organisms. The possibility of selection is determined by the existence of intrapopulation variability in plant resistance to various environmental factors. An example of intrapopulation variability in resistance can be the unfriendly appearance of seedlings on saline soil and an increase in the variation in germination time with an increase in the action of a stressor.
A species in the modern view consists of a large number of biotypes - smaller ecological units, genetically identical, but showing different resistance to environmental factors. Under different conditions, not all biotypes are equally vital, and as a result of competition, only those of them remain that best meet the given conditions. That is, the resistance of a population (variety) to a particular factor is determined by the resistance of the organisms that make up the population. Resistant varieties have in their composition a set of biotypes that provide good productivity even in adverse conditions.
At the same time, in the process of long-term cultivation, the composition and ratio of biotypes in the population changes in varieties, which affects the productivity and quality of the variety, often not for the better.
So, adaptation includes all processes and adaptations that increase the resistance of plants to adverse environmental conditions (anatomical, morphological, physiological, biochemical, behavioral, population, etc.)
But to choose the most effective way of adaptation, the main thing is the time during which the body must adapt to new conditions.
With the sudden action of an extreme factor, the response cannot be delayed, it must follow immediately in order to exclude irreversible damage to the plant. With long-term impacts of a small force, adaptive rearrangements occur gradually, while the choice of possible strategies increases.
In this regard, there are three main adaptation strategies: evolutionary, ontogenetic And urgent. The task of the strategy is the efficient use of available resources to achieve the main goal - the survival of the organism under stress. The adaptation strategy is aimed at maintaining the structural integrity of vital macromolecules and the functional activity of cellular structures, maintaining vital activity regulation systems, and providing plants with energy.
Evolutionary or phylogenetic adaptations(phylogeny - the development of a biological species in time) - these are adaptations that arise during the evolutionary process on the basis of genetic mutations, selection and are inherited. They are the most reliable for plant survival.
Each species of plants in the process of evolution has developed certain needs for the conditions of existence and adaptability to the ecological niche it occupies, a stable adaptation of the organism to the environment. Moisture and shade tolerance, heat resistance, cold resistance and other ecological features of specific plant species were formed as a result of long-term action of the relevant conditions. Thus, heat-loving and short-day plants are characteristic of southern latitudes, less heat-demanding and long-day plants are characteristic of northern latitudes. Numerous evolutionary adaptations of xerophyte plants to drought are well known: economical use of water, deep root system, shedding of leaves and transition to a dormant state, and other adaptations.
In this regard, varieties of agricultural plants show resistance precisely to those environmental factors against which breeding and selection of productive forms is carried out. If the selection takes place in a number of successive generations against the background of the constant influence of some unfavorable factor, then the resistance of the variety to it can be significantly increased. It is natural that the varieties bred by the Research Institute of Agriculture of the South-East (Saratov) are more resistant to drought than the varieties created in the breeding centers of the Moscow region. In the same way, in ecological zones with unfavorable soil and climatic conditions, resistant local plant varieties were formed, and endemic plant species are resistant to the stressor that is expressed in their habitat.
Characterization of the resistance of spring wheat varieties from the collection of the All-Russian Institute of Plant Industry (Semenov et al., 2005)
| Variety | Origin | Sustainability |
| Enita | Moscow region | Medium drought resistant |
| Saratovskaya 29 | Saratov region | drought resistant |
| Comet | Sverdlovsk region. | drought resistant |
| Karazino | Brazil | acid resistant |
| Prelude | Brazil | acid resistant |
| Kolonias | Brazil | acid resistant |
| Thrintani | Brazil | acid resistant |
| PPG-56 | Kazakhstan | salt tolerant |
| Osh | Kyrgyzstan | salt tolerant |
| Surkhak 5688 | Tajikistan | salt tolerant |
| Messel | Norway | Salt tolerant |
In a natural environment, environmental conditions usually change very quickly, and the time during which the stress factor reaches a damaging level is not enough for the formation of evolutionary adaptations. In these cases, plants use not permanent, but stressor-induced defense mechanisms, the formation of which is genetically predetermined (determined).
Ontogenetic (phenotypic) adaptations are not associated with genetic mutations and are not inherited. The formation of such adaptations requires a relatively long time, so they are called long-term adaptations. One of such mechanisms is the ability of a number of plants to form a water-saving CAM-type photosynthesis pathway under conditions of water deficit caused by drought, salinity, low temperatures, and other stressors.
This adaptation is associated with the induction of expression of the phosphoenolpyruvate carboxylase gene, which is inactive under normal conditions, and the genes of other enzymes of the CAM pathway of CO2 uptake, with the biosynthesis of osmolytes (proline), with the activation of antioxidant systems, and with changes in the daily rhythms of stomatal movements. All this leads to very economical water consumption.
In field crops, for example, in corn, aerenchyma is absent under normal growing conditions. But under conditions of flooding and a lack of oxygen in the tissues in the roots, some of the cells of the primary cortex of the root and stem die (apoptosis, or programmed cell death). In their place, cavities are formed, through which oxygen is transported from the aerial part of the plant to the root system. The signal for cell death is the synthesis of ethylene.
Urgent adaptation occurs with rapid and intense changes in living conditions. It is based on the formation and functioning of shock protective systems. To shock protective systems include, for example, the heat shock protein system, which is formed in response to a rapid increase in temperature. These mechanisms provide short-term survival conditions under the action of a damaging factor and thus create the prerequisites for the formation of more reliable long-term specialized adaptation mechanisms. An example of specialized adaptation mechanisms is the new formation of antifreeze proteins at low temperatures or the synthesis of sugars during the overwintering of winter crops. At the same time, if the damaging effect of the factor exceeds the protective and reparative capabilities of the body, then death inevitably occurs. In this case, the organism dies at the stage of urgent or at the stage of specialized adaptation, depending on the intensity and duration of the extreme factor.
Distinguish specific And non-specific (general) plant responses to stressors.
Nonspecific reactions do not depend on the nature of the acting factor. They are the same under the action of high and low temperatures, lack or excess of moisture, high concentrations of salts in the soil or harmful gases in the air. In all cases, the permeability of membranes in plant cells increases, respiration is disturbed, the hydrolytic decomposition of substances increases, the synthesis of ethylene and abscisic acid increases, and cell division and elongation are inhibited.
The table shows a complex of nonspecific changes occurring in plants under the influence of various factors external environment.
Changes in physiological parameters in plants under the influence of stressful conditions (according to G.V., Udovenko, 1995)
| Parameters | The nature of the change in parameters under conditions | |||
| droughts | salinity | high temperature | low temperature | |
| The concentration of ions in tissues | growing | growing | growing | growing |
| Water activity in the cell | Falling down | Falling down | Falling down | Falling down |
| Osmotic potential of the cell | growing | growing | growing | growing |
| Water holding capacity | growing | growing | growing | — |
| Water scarcity | growing | growing | growing | — |
| Protoplasm permeability | growing | growing | growing | — |
| Transpiration rate | Falling down | Falling down | growing | Falling down |
| Transpiration efficiency | Falling down | Falling down | Falling down | Falling down |
| Energy efficiency of breathing | Falling down | Falling down | Falling down | — |
| Breathing intensity | growing | growing | growing | — |
| Photophosphorylation | Decreases | Decreases | — | Decreases |
| Stabilization of nuclear DNA | growing | growing | growing | growing |
| Functional activity of DNA | Decreases | Decreases | Decreases | Decreases |
| Proline concentration | growing | growing | growing | — |
| Content of water-soluble proteins | growing | growing | growing | growing |
| Synthetic reactions | Suppressed | Suppressed | Suppressed | Suppressed |
| Ion uptake by roots | Suppressed | Suppressed | Suppressed | Suppressed |
| Transport of substances | Depressed | Depressed | Depressed | Depressed |
| Pigment concentration | Falling down | Falling down | Falling down | Falling down |
| cell division | slows down | slows down | — | — |
| Cell stretch | Suppressed | Suppressed | — | — |
| Number of fruit elements | Reduced | Reduced | Reduced | Reduced |
| Organ aging | Accelerated | Accelerated | Accelerated | — |
| biological harvest | Downgraded | Downgraded | Downgraded | Downgraded |
Based on the data in the table, it can be seen that the resistance of plants to several factors is accompanied by unidirectional physiological changes. This gives reason to believe that an increase in plant resistance to one factor may be accompanied by an increase in resistance to another. This has been confirmed by experiments.
Experiments at the Institute of Plant Physiology of the Russian Academy of Sciences (Vl. V. Kuznetsov and others) have shown that short-term heat treatment of cotton plants is accompanied by an increase in their resistance to subsequent salinization. And the adaptation of plants to salinity leads to an increase in their resistance to high temperatures. Heat shock increases the ability of plants to adapt to the subsequent drought and, conversely, in the process of drought, the body's resistance to high temperature increases. Short-term exposure to high temperatures increases resistance to heavy metals and UV-B radiation. The preceding drought favors the survival of plants in conditions of salinity or cold.
The process of increasing the body's resistance to a given environmental factor as a result of adaptation to a factor of a different nature is called cross-adaptation.
To study the general (nonspecific) mechanisms of resistance, of great interest is the response of plants to factors that cause water deficiency in plants: salinity, drought, low and high temperatures, and some others. At the level of the whole organism, all plants react to water deficiency in the same way. Characterized by inhibition of shoot growth, increased growth of the root system, the synthesis of abscisic acid, and a decrease in stomatal conductance. After some time, the lower leaves rapidly age, and their death is observed. All these reactions are aimed at reducing water consumption by reducing the evaporating surface, as well as by increasing the absorption activity of the root.
Specific reactions are reactions to the action of any one stress factor. So, phytoalexins (substances with antibiotic properties) are synthesized in plants in response to contact with pathogens (pathogens).
The specificity or non-specificity of responses implies, on the one hand, the attitude of the plant to various stressors and, on the other hand, the specificity of plant reactions. various kinds and varieties for the same stressor.
The manifestation of specific and nonspecific responses of plants depends on the strength of stress and the rate of its development. Specific responses occur more often if the stress develops slowly, and the body has time to rebuild and adapt to it. Nonspecific reactions usually occur with a shorter and stronger effect of the stressor. The functioning of non-specific (general) resistance mechanisms allows the plant to avoid large energy expenditures for the formation of specialized (specific) adaptation mechanisms in response to any deviation from the norm in their living conditions.
Plant resistance to stress depends on the phase of ontogeny. The most stable plants and plant organs in a dormant state: in the form of seeds, bulbs; woody perennials - in a state of deep dormancy after leaf fall. The most sensitive plants in young age, since under stress the growth processes are damaged in the first place. The second critical period is the period of gamete formation and fertilization. The effect of stress during this period leads to a decrease in the reproductive function of plants and a decrease in yield.
If stress conditions are repeated and have a low intensity, then they contribute to the hardening of plants. This is the basis for methods for increasing resistance to low temperatures, heat, salinity, and an increased content of harmful gases in the air.
Reliability of a plant organism is determined by its ability to prevent or eliminate failures at different levels of biological organization: molecular, subcellular, cellular, tissue, organ, organismal and population.
To prevent disruptions in the life of plants under the influence of adverse factors, the principles redundancy, heterogeneity of functionally equivalent components, systems for the repair of lost structures.
The redundancy of structures and functionality is one of the main ways to ensure the reliability of systems. Redundancy and redundancy has multiple manifestations. At the subcellular level, the reservation and duplication of genetic material contribute to the increase in the reliability of the plant organism. This is provided, for example, by the double helix of DNA, by increasing the ploidy. The reliability of the functioning of the plant organism under changing conditions is also supported by the presence of various messenger RNA molecules and the formation of heterogeneous polypeptides. These include isoenzymes that catalyze the same reaction, but differ in their physicochemical properties and the stability of the molecular structure under changing environmental conditions.
At the cellular level, an example of redundancy is an excess of cellular organelles. Thus, it has been established that a part of the available chloroplasts is sufficient to provide the plant with photosynthesis products. The remaining chloroplasts, as it were, remain in reserve. The same applies to the total chlorophyll content. The redundancy also manifests itself in a large accumulation of precursors for the biosynthesis of many compounds.
At the organismic level, the principle of redundancy is expressed in the formation and laying at different times of more shoots, flowers, spikelets than is required for the change of generations, in a huge amount of pollen, ovules, seeds.
At the population level, the principle of redundancy is manifested in a large number of individuals that differ in resistance to a particular stress factor.
Repair systems also work at different levels - molecular, cellular, organismal, population and biocenotic. Reparative processes go with the expenditure of energy and plastic substances, therefore, reparation is possible only if a sufficient metabolic rate is maintained. If metabolism stops, then reparation also stops. In extreme conditions of the external environment, the preservation of respiration is especially important, since it is respiration that provides energy for reparation processes.
The reductive ability of cells of adapted organisms is determined by the resistance of their proteins to denaturation, namely, the stability of the bonds that determine the secondary, tertiary, and quaternary structure of the protein. For example, the resistance of mature seeds to high temperatures is usually associated with the fact that, after dehydration, their proteins become resistant to denaturation.
The main source of energy material as a substrate for respiration is photosynthesis, therefore, the energy supply of the cell and related reparation processes depend on the stability and ability of the photosynthetic apparatus to recover from damage. To maintain photosynthesis under extreme conditions in plants, the synthesis of thylakoid membrane components is activated, lipid oxidation is inhibited, and the plastid ultrastructure is restored.
At the organismic level, an example of regeneration is the development of replacement shoots, the awakening of dormant buds when growth points are damaged.
If you find an error, please highlight a piece of text and click Ctrl+Enter.
Task 1. Plant adaptation to seed dispersal
Establish how plants adapted to seed dispersal through insects, birds, mammals, and humans. Fill the table.
Plant adaptations for seed dispersal
|
№ p/n |
plant species |
Insects |
Birds |
Mammal nourishing |
Human |
|
cultural | |||||
|
felt | |||||
|
tripartite | |||||
|
forget-me-not | |||||
|
Burdock ordinary |
What properties do the seeds of the plants listed in the table have that contribute to the spread of seeds by the methods you found? Give specific examples.
The interaction of two populations can theoretically be represented as paired combinations of the symbols "+", "-", "0", where "+" denotes a benefit for the population, "-" - the deterioration of the population, that is, harm, and "0" - the absence significant changes in the interaction. Using the proposed symbolism, define the types of interaction, give examples of relationships and make a table in your notebook.
Biotic relationships
|
relationships |
Symbolic designation |
Definition relationships |
Examples relationships of this type |
1. Using the handout didactic material, make up the food web of the lake ecosystem.
2. Under what conditions will the lake not change for a long time?
3. What actions of people can lead to the rapid destruction of the lake ecosystem?
Individual task for the module "From the ecology of organisms to the ecology of ecosystems" Option 6
Task 1. Adaptation of living organisms to extreme living conditions
Many organisms during their life periodically experience the influence of factors that are very different from the optimum. They have to endure extreme heat, and frosts, and summer droughts, and drying up of water bodies, and lack of food. How do they adapt to such extreme conditions, when normal life is very difficult? Give examples of the main ways of adapting to the transfer of adverse living conditions
Task 2. Biotic relationships.
Determine from the graphs what consequences the relationship between two closely related species of organisms living in the same ecological niche can lead to? What is this relationship called? Explain the answer.
Fig.11. The growth in the number of two types of ciliates-shoes (1 - tailed slipper, 2 - golden slipper):
A - when grown in pure cultures with a large amount of food (bacteria); B - in mixed culture, with the same amount of food
Task 3. Natural ecosystems of the Southern Urals
1. Make up the food web of a river ecosystem.
2. Under what conditions will the river not change for a long time?
3. What actions of people can lead to the rapid destruction of the river ecosystem?
4. Describe the trophic structure of the ecosystem using the ecological pyramids of abundance, biomass, and energy.
Now that we have become familiar with the distinguishing features of the four main groups of plants, namely the bryophytes, ferns, gymnosperms, and angiosperms (flowering plants), it is easier for us to imagine the evolutionary progress made by plants in the process of adapting to life on land.
Problems
Perhaps the most difficult problem that had to be somehow overcome in order to move from an aquatic lifestyle to a terrestrial one was the problem dehydration. Any plant that is not protected in one way or another, for example, not covered with a waxy cuticle, will very soon dry out and undoubtedly die. Even if this difficulty is overcome, other unresolved problems remain. And above all the question of how to successfully carry out sexual reproduction. In the first plants, male gametes participated in reproduction, capable of approaching female gametes only by swimming in water.
It is usually believed that the first plants that mastered the land descended from green algae, in some of the most evolutionarily advanced representatives of which reproductive organs appeared, namely archegonia (female) and antheridia (male); in these organs, gametes were hidden and, consequently, protected. This circumstance and a number of other well-defined devices that help to avoid drying out have allowed some representatives of green algae to take over the land.
One of the most important evolutionary trends in plants is their gradually increasing independence from water.
Listed below are the main difficulties associated with the transition from aquatic to terrestrial existence.
- Dehydration. Air is a drying medium, and water is essential for life for a variety of reasons (Section 3.1.2). Therefore, there is a need for devices for obtaining and storing water.
- Reproduction. The delicate germ cells must be protected, and the motile male gametes (sperms) can only meet the female gametes in water.
- Support. Unlike water, air cannot support plants.
- Nutrition. Plants need light and carbon dioxide (CO 2 ) for photosynthesis, so at least part of the plant needs to be above the ground. However, mineral salts and water are found in the soil or on its surface, and in order to effectively use these substances, part of the plant must be in the ground and grow in the dark.
- Gas exchange. For photosynthesis and respiration, it is necessary that the exchange of carbon dioxide and oxygen occurs not with the surrounding solution, but with the atmosphere.
- environmental factors. Water, especially when there is so much of it, as, say, in a lake or in the ocean, provides a high constancy of environmental conditions. The terrestrial habitat, on the other hand, is much more characterized by the variability of such important factors as temperature, light intensity, ion concentration and pH.
Liverworts and mosses
Mosses are well adapted to the dispersal of spores in terrestrial conditions: it depends on the drying of the box and the dispersal of small, light spores by the wind. However, these plants are still dependent on water for the following reasons.
- They need water to reproduce because the sperm must swim to the archegonium. These plants have developed adaptations that allow them to release sperm only in a humid environment, because only in such an environment do antheridia open. These plants have partially adapted to terrestrial life, since their gametes are formed in protective structures - antheridia and archegonia.
- They do not have special supporting tissues, and therefore the upward growth of the plant is limited.
- Bryophytes do not have roots that can penetrate far into the substrate, and they can only live where there is enough moisture and mineral salts on the surface of the soil or in its upper layers. However, they have rhizoids with which they attach themselves to the ground; this is one of the adaptations to life on a solid substrate.
2.4. Liverworts and mosses are often called amphibians (amphibians) flora. Explain briefly why.
ferns
2.5. Ferns have adapted better to life on land than liverworts and mosses. How is it shown?
2.6. What are the important characteristics of mosses, ferns and liverworts that are poorly adapted to life on land?
Seed plants - conifers and flowering plants
One of the main difficulties that plants face on land is related to the vulnerability of the gametophyte generation. For example, in ferns, the gametophyte is a delicate growth that produces male gametes (sperms) that need water to reach the egg. However, in seed plants, the gametophyte is protected and greatly reduced.
Seed plants have three important advantages: first, they are heterogeneous; secondly, the appearance of non-swimming male gametes and, thirdly, the formation of seeds.
DIVERSITY AND NON-SWIMMING MALE GAMETES.
Rice. 2.34. A generalized scheme of the life cycle of plants, reflecting the alternation of generations. Note the presence of haploid (n) and diploid (2n) stages. The gametophyte is always haploid and always forms gametes by mitotic division. The sporophyte is always diploid and always forms spores as a result of meiotic division.
A very important role in the evolution of plants was played by the emergence of some ferns and their close relatives, which form spores of two types. This phenomenon is called heterogeneity, and the plants are heterosporous. Everything seed plants are heterosporous. They form large spores called megaspores, in sporangia of one type (megasporangia) and small spores, called microspores, in another type of sporangia (microsporangia). Germinating, spores form gametophytes (Fig. 2.34). Megaspores develop into female gametophytes, microspores into male ones. In seed plants, the gametophytes formed by megaspores and microspores are very small in size and are never released from the spores. Thus, the gametophytes are protected from drying out, which is an important evolutionary achievement. However, sperm from the male gametophyte still have to move to the female gametophyte, which is greatly facilitated by the dispersal of microspores. Being very small, they can form in large numbers and be carried by the wind far from the parent sporophyte. By chance, they may be in close proximity to the megaspore, which in seed plants does not separate from the parent sporophyte (Fig. 2.45). This is exactly the way it happens pollination in plants whose pollen grains are microspores. Male gametes are produced in pollen grains.
Rice. 2.45. Schematic representation of the main elements of diversity and pollination.
Seed plants have developed yet another evolutionary advantage. The male gametes no longer need to swim up to the female gametes because the seed plants have evolved pollen tubes. They develop from pollen grains and grow towards female gametes. Through this tube, the male gametes reach the female gamete and fertilize it. Floating sperm are no longer formed, only male nuclei are involved in fertilization.
Consequently, plants have developed a fertilization mechanism that is independent of water. This was one of the reasons why seed plants were so superior to other plants in the development of land. Initially, pollination occurred only with the help of the wind - a rather random process, accompanied by large losses of pollen. However, already in the early stages of evolution, about 300 million years ago in the Carboniferous period, flying insects appeared, and with them the possibility of more efficient pollination. Flowering plants make extensive use of insect pollination, while wind pollination still predominates in conifers.
SEEDS. In early heterosporous plants, megaspores were released from the parent sporophyte like microspores. In seed plants, megaspores do not separate from the parent plant, remaining in megasporangia, or ovules(Fig. 2.45). The ovule contains the female gamete. After fertilization of the female gamete, the ovules are already called seed. Thus, a seed is a fertilized ovule. The presence of an ovule and a seed gives certain advantages to seed plants.
- The female gametophyte is protected by the ovule. It is completely dependent on the parent sporophyte and, unlike the free-living gametophyte, is insensitive to dehydration.
- After fertilization, the seed forms a reserve of nutrients received by the gametophyte from the parent sporophyte plant, from which it is still not separated. This reserve is used by the developing zygote (the next sporophyte generation) after seed germination.
- Seeds are meant to survive unfavourable conditions, and remain dormant until conditions are favorable for germination.
- Seeds can develop various adaptations to facilitate their dispersal.
The seed is a complex structure in which the cells of three generations are assembled - the parent sporophyte, the female gametophyte, and the embryo of the next sporophyte generation. The parent sporophyte provides the seed with everything it needs for life, and only after the seed has fully matured, i.e. accumulates a supply of nutrients for the sporophyte embryo, it separates from the parent sporophyte.
2.7. The chances for the survival and development of wind-borne pollen grains (microspores) are much less than for Dryopteris spores. Why?
2.8. Explain why megaspores are large and microspores are small.
2.7.7. Brief listing of adaptations of seed plants to life on land
The main advantages of seed plants over all others are as follows.
- The gametophyte generation is greatly reduced and completely depends on the sporophyte, well adapted to life on land, inside which the gametophyte is always protected. In other plants, the gametophyte dries out very easily.
- Fertilization occurs independently of water. Male gametes are immobile and dispersed inside pollen grains by wind or insects. The final transfer of male gametes to female gametes occurs with the help of a pollen tube.
- Fertilized ovules (seeds) remain for some time on the parent sporophyte, from which they receive protection and food before they are dispelled.
- In many seed plants, secondary growth is observed with the deposition of large amounts of wood that has a supporting function. Such plants grow into trees and shrubs that can effectively compete for light and other resources.
Some of the most important evolutionary trends are summarized in fig. 2.33. Seed plants also have other features that are inherent in plants not only of this group, but also play the role of adaptations to life on land.
Rice. 2.33. Systematics of plants and some main trends in plant evolution.
- True roots provide the extraction of moisture from the soil.
- Plants are protected from drying out by an epidermis with a watertight cuticle (or plug formed after secondary growth).
- The epidermis of the terrestrial parts of the plant, especially the leaves, is penetrated by many tiny slits called stomata through which gas exchange occurs between the plant and the atmosphere.
- Plants also have specialized adaptations to life in hot arid conditions (Ch. 19 and 20).
Adaptation is the development of any trait that contributes to the survival of the species and its reproduction. In the course of their life, plants adapt to: atmospheric pollution, soil salinity, various biotic and climatic factors, etc. All plants and animals are constantly adapting to their environment. To understand how this happens, it is necessary to consider not only the animal or plant as a whole, but also the genetic basis of adaptation.
In each species, the program for the development of traits is embedded in the genetic material. The material and the program encoded in it are passed on from one generation to the next, remaining relatively unchanged, so that representatives of one species or another look and behave almost the same. However, in a population of organisms of any kind, there are always small changes in the genetic material and, therefore, variations in the characteristics of individual individuals. It is from these diverse genetic variations that the process of adaptation selects those traits that favor the development of those traits that most increase the chances of survival and thereby the preservation of genetic material. Adaptation, therefore, can be seen as the process by which genetic material improves its chances of being retained in subsequent generations in a changing environment.
All living organisms are adapted to their habitats: swamp plants - to swamps, desert plants - to deserts, etc. Adaptation (from the Latin word adaptatio - adjustment, adaptation) - the process, as well as the result of adapting the structure and functions of organisms and their organs to conditions habitat. The general adaptability of living organisms to the conditions of existence consists of many individual adaptations of very different scales. Dryland plants have various adaptations to obtain the necessary moisture. This is either a powerful system of roots, sometimes penetrating to a depth of tens of meters, or the development of hairs, a decrease in the number of stomata on the leaves, a reduction in the area of \u200b\u200bthe leaves, which can dramatically reduce the evaporation of moisture, or, finally, the ability to store moisture in the succulent parts, as, for example, in cacti and euphorbia.
The harsher and more difficult the living conditions, the more ingenious and diverse the adaptability of plants to the vicissitudes of the environment. Often the adaptation goes so far that the external environment begins to completely determine the shape of the plant. And then plants belonging to different families, but living in the same harsh conditions, often become so similar in appearance to each other that this can be misleading as to the truth of their family ties.
For example, in desert areas for many species, and, above all, for cacti, the shape of the ball turned out to be the most rational. However, not everything that has a spherical shape and is studded with prickly thorns is cacti. Such an expedient design, which makes it possible to survive in the most difficult conditions of deserts and semi-deserts, also arose in other systematic groups of plants that do not belong to the cactus family. Conversely, cacti do not always take the form of a ball or column dotted with thorns.
Common inhabitants of the tropical jungle are climbing and climbing plants, as well as epiphytic plants that settle in the crowns of woody plants. All of them strive to get out of the eternal twilight of the dense undergrowth of virgin tropical forests as soon as possible. They find their way up to the light, without creating powerful trunks and support systems that require huge building material costs. They calmly climb up, using the "services" of other plants that act as supports. In order to successfully cope with this new task, plants have invented various and quite technically advanced organs: clinging roots and leaf petioles with outgrowths on them, thorns on branches, clinging inflorescence axes, etc. Plants have lasso loops at their disposal; special disks with the help of which one plant is attached to another with its lower part; movable cirriform hooks, first digging into the trunk of the host plant, and then swelling in it; various kinds of squeezing devices and, finally, a very sophisticated gripping apparatus.
Plant resistance to low temperatures is divided into cold resistance and frost resistance. Cold resistance is understood as the ability of plants to tolerate positive temperatures slightly above zero. Cold resistance is characteristic of plants of the temperate zone (barley, oats, flax, vetch, etc.). Tropical and subtropical plants are damaged and die at temperatures from 0º to 10º C (coffee, cotton, cucumber, etc.). For the majority of agricultural plants, low positive temperatures are not harmful. This is due to the fact that during cooling, the enzymatic apparatus of plants is not upset, resistance to fungal diseases does not decrease, and no noticeable damage to plants occurs at all.
The degree of cold resistance of different plants is not the same. Many plants of southern latitudes are damaged by cold. At a temperature of 3 ° C, cucumber, cotton, beans, corn, and eggplant are damaged. Varieties vary in cold tolerance. To characterize the cold resistance of plants, the concept of the temperature minimum at which plant growth stops is used. For a large group of agricultural plants, its value is 4 °C. However, many plants have a higher temperature minimum and therefore are less resistant to cold.
Resistance to low temperatures is a genetically determined trait. The cold resistance of plants is determined by the ability of plants to maintain the normal structure of the cytoplasm, to change the metabolism during the period of cooling and the subsequent increase in temperature at a sufficiently high level.
Frost resistance - the ability of plants to tolerate temperatures below 0 ° C, low negative temperatures. Frost-resistant plants are able to prevent or reduce the effect of low negative temperatures. Frosts in winter with temperatures below -20 ° C are common for a significant part of the territory of Russia. Annual, biennial and perennial plants are exposed to frost. Plants endure winter conditions in different periods of ontogeny. In annual crops, seeds (spring plants), sprouting plants (winter crops) overwinter, in biennial and perennial crops - tubers, root crops, bulbs, rhizomes, adult plants. The ability of winter, perennial herbaceous and woody fruit crops to overwinter is due to their rather high frost resistance. The tissues of these plants may freeze, but the plants do not die.
Biotic factors are a set of influences exerted by organisms on each other. Biotic factors affecting plants are divided into zoogenic and phytogenic.
Zoogenic biotic factors are the influence of animals on plants. First of all, they include the eating of plants by animals. The animal can eat the whole plant or its individual parts. As a result of animals eating branches and shoots of plants, the crown of trees changes. Most of the seeds are fed to birds and rodents. Plants that are damaged by phytophagous animals are forced to fight for their existence and, in order to protect themselves, grow thorns, diligently grow the remaining leaves, etc. An environmentally significant factor is the mechanical impact exerted by animals on plants: this is damage to the entire plant when eaten by animals, as well as trampling. But there is also a very positive side to the influence of animals on plants: one of them is pollination.
Phytogenic biotic factors include the influence of plants located at a short distance on each other. There are many forms of relationships between plants: interlacing and fusion of roots, interweaving of crowns, lashing of branches, the use of one plant by another for attachment, etc. In turn, any plant community affects the totality of abiotic (chemical, physical, climatic, geological) properties of its habitat. We all know how strongly the difference between abiotic conditions is expressed, for example, in a forest and in a field or steppe. Thus, it is worth noting that biotic factors play an important role in plant life.