Cactus reasoning why why why. Research work on the topic “Why does a cactus need spines?” The sharp spines of a cactus are a means of protection or extraction of moisture.

Do you think it's only for self-defense? But no. Their task comes down to more than just this, it is much broader and more interesting. Let's take a look at the spines of cacti together and briefly familiarize ourselves with their functions.

The spines of cacti are extremely diverse. There are sharp ones, like needles, and long and short ones.

Curved and hook-shaped, hard and soft, radiant and intertwined into balls, feathery and hair-like, more like down. It’s impossible to list all the varieties. But, regardless of their external structure, they play a primary role in the life of plants of the cactus family.

First of all, they serve to absorb moisture. After all, in those places where these extraordinary plants grow, there is no rain for long months, and sometimes even years.

As a rule, in deserts there is a sharp change in temperature during the day. At the end of the night there may be only a couple of degrees of heat, and in the middle of the day the air heats up to +40...+50° C. Naturally, under such conditions, intense condensation of water vapor occurs with the formation of abundant dew. It is dew that serves cacti as the main source of moisture.

Cacti are able to absorb water over the entire surface of the stem, but the spines do this especially intensively. They are modified leaves that resemble microscopically thin tubes that actively absorb the slightest moisture. Yes, you won’t get drunk with just one drop. But one adult cactus has thousands of spines! And each one gets its own drop of dew in the morning.

As they say, one step at a time, i.e. Drop by drop, I quenched my thirst.

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The main functions of leaves include photosynthesis and water evaporation. To perform these functions most effectively, the sheet must be plate-shaped, i.e., have a large surface area and be thin. These are the leaves of most plants. However, in some plants, during the process of evolution, the leaves have modified (underwent changes) and become different from ordinary leaves. The reason for this phenomenon is that the leaves began to perform other functions not related to photosynthesis and evaporation.

The leaves of a number of plants in arid habitats have been modified to spines. Such leaves, on the one hand, almost do not evaporate water, and on the other hand, protect plants from being eaten by animals. An example of desert plants with spines are various cacti. Photosynthesis occurs in cells of the thick stem located closer to the surface. The stem also stores water. Thus, the leaves modified into spines lost both of their main functions (photosynthesis and evaporation), but instead began to perform a protective function.

Spiny leaves can be observed not only in desert and semi-desert plants. Barberry, rose bushes, rose hips, etc. have spines. However, not all leaves of these plants are modified into spines, but only some. Moreover, the function of the spines here is the same as that of cacti - protection from being eaten by animals.

The leaves of other plants in arid habitats have adapted to the lack of moisture in a different way. So in aloe and agave the leaves have changed into thick and juicy formations that store water. And to reduce evaporation, such leaves are covered with a waxy coating, hairs, and have fewer stomata. In this case, the leaves have changed so that they have not lost their main functions, but have acquired an additional one - storing water.

There are plants whose leaves are modified to mustache. With these tendrils the plant clings to the support and is held in an upright position. Examples of plants with tendrils are peas, china, vetch and other legumes. In peas, the upper parts of the leaves are turned into tendrils.

In nature, there are insectivorous plants. Their leaves are modified into peculiar fishing devices. When an insect lands on the leaf of a sundew plant, it sticks to it, because the leaf is covered with hairs that secrete a viscous mass. After this, the hairs and the leaf itself curl up. Inside the resulting cavity, the insect is digested due to enzymes secreted by the leaf. From the insect, the sundew assimilates nitrogen-rich organic substances. It is precisely because of the lack of nitrogen and other microelements in their habitat that sundew leaves acquired such a specific function.

Another modification of the leaves is scales. At the same time, the scales are different, because they perform different functions. For example, in the onion bulb, the leaves are transformed into juicy scales, in which a supply of nutrients is deposited. Other scales cover the buds. In this case, they perform a protective function.

* This work is not a scientific work, is not a final qualification work and is the result of processing, structuring and formatting the collected information intended for use as a source of material for independent preparation of educational works.

Cacti are perennial succulents of the cactus family. Mostly inhabitants of deserts and semi-deserts of the American continent.

The leaves of cacti are reduced and replaced by spines in most species; the stems are capacious water reservoirs. All cacti have areoles (metamorphosis of the axillary bud), from which flowers develop and “children” of cacti grow. Their unique appearance, combined with very beautiful flowering, has made these plants very popular among indoor floriculture enthusiasts. For indoor culture, the following species and groups of species are recommended.

Peireskias have true leaves and grow into large shrubs, often serving as rootstocks for grafting cacti with weak roots onto them.

Prickly pears are characterized by cake-shaped joints of the stem and areoles, on which, in addition to the spines, very sharp small bristles (glochidia) develop, which easily penetrate the skin and clothing. They, however, are often very decorative (for example, in varieties of small-pubescent prickly pear).

Cereuses are distinguished by columnar, faceted stems, which in different species are originally pubescent with long or short hairs, or bare and bluish (Cereus, Cephalocereus, Espostoa, Oreocereus, Lemereocereus, Trichocereus).

The group of "hedgehog-shaped" cacti covers a wide variety of genera, which are characterized by a rounded shape and many spines (hence the name). For indoor breeding we can recommend Echinopsis, Echinocactus, Echinocereus, Rebutia, Ailostera, Lobivia and Pseudolobivia, Parody, Gymnocalycium, Ferocactus, Hamatocactus and many others.

Mammillaria are a group of papillary cacti; differ in a variety of shapes and spines. In mammillaria, the tubercles (papillae) are arranged in a spiral around the stem, and the flowers arise between the areoles on the tubercles.

In contrast to the above species, epiphyllum, rhipsalis, epiphyllopsis, ripsalidopsis and zygocactus are forest cacti. Most of them are epiphytes, so in indoor culture they develop better when grafted (for example, onto peireskia). These are shade-loving plants and do not tolerate direct sunlight. In winter, they require constant moisture. They need to be planted in loose humus soil mixed with sand and coal.

All desert cacti can be cultivated in soil made up of turf and leaf soil with the addition of river sand, small bricks or shards, chalk and charcoal. These are light-loving plants, they need as much sun as possible and grow very well outdoors. In winter, cacti must be kept in a cold (from -6 degrees to -8 degrees) and always dry place. From October to March, cacti should not be watered during cold wintering, then they bloom intensively. The best way to water is to immerse the plant pots in water until there are no more air bubbles, and then dry them well. The bottom of the pot must be covered 3-4 cm with a layer of small shards. Young plants have a higher need for moisture, so in winter they need to be watered once a month and ensure that the soil does not dry out and turn to dust. It is difficult to dry adult cacti, and they easily rot from excess water. Reducing watering in winter does not give the cactus the necessary rest period.

This requires a low temperature, which can be easily achieved by separating the window sill with the cacti on it from the room with glass or plastic film.

Sowing cacti requires special attention. You need to sow the seeds in washed river sand, mixed in half with leaf soil, lightly pressing the seeds. Before emergence, it is advisable to keep the crops at a temperature of 25-30 degrees and spray them only with a spray bottle. At first, the crops should be covered with glass. Small seedlings should be picked several times so that they develop better. In the first year, they should not be overdried, kept in too much sun or in drafts.

It is easier to propagate cacti from cuttings. The cuttings should be cut with a sharp knife, sprinkled with sulfur or coal and left to dry for 3-4 days. The cuttings should be rooted in washed river sand (preferably heated). As soon as roots form and the cuttings begin to grow noticeably, they can be planted in a small container. 3-5 days before transplanting, you should stop watering the cacti so that the earthen ball dries out and the soil easily separates from the roots. After transplantation, the plant should be placed in the shade and not watered for 5 days, so that the roots accidentally wounded during transplantation do not rot. The best time to transplant is spring. To avoid pricking your hands, when replanting cacti, you should hold them with a strip of fairly thick paper folded several times.

Adaptations of cactus to environmental conditions.

Spreading. The homeland of cacti is continental and island America. They are found from Canada to Patagonia and Tierra del Fuego and from the Galapagos Islands to the West Indies. Mexico is richest in species and life forms of cacti. In the United States, cacti are especially abundant in Texas, Arizona and New Mexico, although the natural range of the family covers almost all states, with the exception of Hawaii, where cacti have naturalized after introduction. The thin-branched epiphytic cactus Rhipsalis grows wild in western Africa, Madagascar and Sri Lanka.

Chemistry, Biology, preparation for State Exam and Unified State Exam

It is believed that it was brought there in ancient times by birds or humans.
Origin: The ancestors of cacti were, most likely, quite moisture-loving plants with well-developed leaves, possibly vines. As a result of geological processes, the climate in the habitats of ancient cacti became much drier. Plants that failed to adapt to the changed conditions died out, while cacti survived due to partial or complete reduction of leaves.
Adaptations.

The cactus tries to absorb as much moisture as possible and store it for a long time. And then he spends it very slowly. So, the cactus must increase its volume to store more water, but must reduce its surface area to reduce evaporation. From mathematics it is known that the geometric body that has the largest volume with the smallest surface area is a ball. Therefore, cacti are most often found spherical.

The function of the leaves is performed by a green stem of a round, squat or elongated cylindrical shape, ribbed, flat like a leaf or elongated like a vine. They took over the main function of leaves - photosynthesis.

The giant Carnegia cactus lives 150-200 years, sometimes reaching a weight of 7 tons. The widely spread root system is located at the very surface of the soil. This is probably why there are no other cacti within a radius of 15-20 m. Carnegia's resistance to unfavorable environmental conditions is amazing: for example, it can remain without water for more than a year, and the side shoots continue to flower even after the main trunk dies. The trunk of the carnegia is quite dense, and some species of woodpeckers hollow out hollows in it, in which other species of birds can subsequently nest.

Organisms often adapt to the same environment in different ways. Common and different adaptations of shark and dolphin.

Conclusion: adaptations of organisms appear as a result of the action of the driving forces of evolution (the struggle for existence, natural selection, hereditary variability). Thus, natural selection of the entire variety of undirected hereditary changes selects and fixes only those that provide the population or species as a whole with optimal adaptations to given conditions of existence .

Relative nature of fitness.

The adaptation of organisms to the environment is developed in the process of long historical development under the influence of natural causes and is not absolute, but relative, since environmental conditions often change faster than adaptations are formed. Corresponding to a specific habitat, adaptations lose their significance when it changes. The following facts can be evidence of the relative nature of fitness: protective devices against some enemies are ineffective against others (for example, poisonous snakes, dangerous for many animals, are eaten by mongooses, hedgehogs, pigs); the manifestation of instincts in animals may turn out to be inappropriate (moths collect nectar from light flowers, clearly visible at night, but they also fly towards the fire, although they die in the process); an organ that is useful in some conditions becomes useless and even relatively harmful in another environment (the membranes between the toes of mountain geese, which never land on the water); More advanced adaptations to a given habitat are also possible.

Adaptation to the environment is relative in nature, useful only in the conditions in which it was historically formed. When these conditions change, adaptations lose their value or even cause harm to the body.

Where do cacti grow?

Cactaceae, or simply cacti, are perennial flowering plants. It is generally accepted that they emerged evolutionarily about 40 million years ago. At that time, Africa and South America were already separated from each other, and North America had not yet united with South America.

Despite the fact that no fossil remains of cacti from those times have been found, it is believed that they first arose in South America, and came to the northern continent only 5-10 million years ago.

Where do cacti grow in nature?

To this day, cacti grow in the wild mainly on the American continents. It was from there that they were transported by people and carried by birds to Europe.

However, representatives of cacti can be found in nature not only in America. Some species have been growing for quite a long time in tropical Africa, Ceylon and other islands of the Indian Ocean.

Where else do cacti grow: thickets of this plant can be found in Australia, the Arabian Peninsula, the Mediterranean, the Canary Islands, Monaco and Spain. Cacti also grow wild in the territory of the former Soviet Union. In most cases, cacti were artificially brought to these places by humans.

Conditions for growing cacti

Basically, cacti prefer steppes, deserts and semi-deserts. Sometimes they can be found in tropical rainforests. Quite rare, but they still grow on wet coasts.

In Mexico, cacti grow in wormwood, creosote, and high-altitude succulent deserts. In the high deserts, cacti are concentrated mainly on the Mexican Plateau and in the western and eastern parts of the Sierra Madre.

In which deserts do cacti grow: cacti inhabit the deserts of Peru, Chile, Bolivia and Argentina quite widely and densely. There is a rich variety of these plants noted.

In which countries do cacti grow?

If we outline the geography of cactus growth by country, the list will be approximately as follows: Mexico, Brazil, Bolivia, Chile, Argentina, USA (Texas, Arizona, New Mexico), Canada, China, India, Australia, Spain, Monaco, Madagascar, Sri- Lanka, Western Africa.

As ornamental plants, people have learned to grow cacti in open ground almost everywhere, with the possible exception of the Arctic. As indoor plants, cacti have long populated the entire planet.

24.09.2014

South America and part of North America are considered to be the homeland of cacti. Evolutionarily, cacti as representatives of the world of flora appeared approximately 40 million years ago. They belong to the succulent plant family. The thorns appeared not as a decorative element, but with meaning. They have evolved over many centuries to become a true survival organ.

The main thick stem of the cactus contains a strategic reserve of nutrient moisture. Another feature of the cactus is its incredibly long roots, which go underground and occupy an impressive radius of the surface in its growing area. Therefore, they can collect life-giving moisture over a fairly large area. Do not think that cacti do not tend to have leaves, like all plants known to us. It’s just that the function of its leaves is performed by these very spines - a modified version of the leaves. The spines are based on a material similar to organic matter - chitin.

Cacti abandoned the leaves of the usual shape for us for a completely objective reason. As a rule, cacti grow in dry places, and wide leaves would be completely irrational and evaporate precious water in large quantities. The functions of the leaves were partially taken over by the thick, fleshy trunk. On its surface there are very thin stomata, which, if necessary, open their pores and absorb carbon dioxide necessary for photosynthesis.

Another unique feature of the spines is that they attract small droplets of water to themselves using electrostatics. Therefore, rain is not always needed for a cactus to drink. In the climate where cacti exist, the temperature fluctuates quite widely. Dew steadily forms in the air, which is a constant source of moisture for cacti.

In addition to the role of getting water, the spines also perform a defensive function. Few of the animal and plant worlds have adapted to survive so successfully in desert dunes, and many animals would happily feast on such a succulent plant. And this is where the thorns come into play, which no animal can handle. Thanks to their spines, cacti are able to be reproductive. The spines secrete nectar, which attracts insects, which act as pollinators.

It is curious that the length of the spines depends on climatic conditions. The milder the climate, the rarer the thorns. But they are quite long, because... They are assigned only a protective function. The drier the climate, the correspondingly more spines there are on the trunk of the cactus. The spines contain large quantities of mineral salts and calcium carbonate. So, in order for the thorns to grow, there must be a sufficient amount of calcium in the soil. That is why you need to add old plaster or marble chips to the soil for growing cacti.

Most cacti have a fairly thick main stem, which stores a strategic supply of water.The cactus has another structural feature - very long roots. But the most amazing thing about cacti is their spines, which cover the stem of the plant and are a kind of modification of leaves, the presence of which is characteristic of all plants. The cacti have abandoned their leaves, since they will simply evaporate the moisture that is so necessary in the growing conditions of the cactus. But how does a cactus survive without leaves? Their function is partially taken over by the stem, which is equipped with stomata that are closed and absorb the necessary carbon dioxide. Without carbon dioxide, the vital process of photosynthesis for plants is impossible.

In addition to protecting against excess moisture evaporation, the spines, on the contrary, help the cactus obtain much-needed water. The initial function of extracting moisture is provided by the roots of the cactus, which are very long, but located in the upper layers of the soil. Due to its very long roots, the cactus covers a large area of ​​soil and can absorb as much moisture as possible. But, it only rains in arid areas extremely rarely, and sometimes they do not wet the soil to the required depth. In such a situation, a cactus without thorns would simply die. The thing is that the spines have a unique ability to attract tiny droplets of water electrostatically. You don't have to wait for rain. Temperature fluctuations in the places where cacti grow are quite high, so abundant dew forms in the air, which is the main source of life-giving moisture.

The cactus was worried about its safety by acquiring thorns. Since the cactus stores a large supply of water, which is especially scarce in deserts, many animals are not averse to feasting on such a juicy fruit. It is here that large thorns come to protect this plant, which no animal can handle.
Also, the spines help the cactus in the pollination process. They secrete a special nectar that attracts pollinating insects. This ensures the process of reproduction of cacti.

If the cactus grows in a fairly mild climate zone, where there is enough moisture, then the spines on it are quite rare and very long. In this case, they are assigned only a protective function. The more a cactus needs moisture, the more spines there will be on its trunk.