Water environment

Distribution of organisms by living environment

In the process of the long historical development of living matter and the formation of ever more advanced forms of living beings, organisms, mastering new habitats, were distributed on Earth according to its mineral shells (hydrosphere, lithosphere, atmosphere) and adapted to existence in strictly defined conditions.

The first medium of life was water. It was in it that life arose. As historical development progressed, many organisms began to populate the land-air environment. As a result, land plants and animals appeared, which rapidly evolved, adapting to new living conditions.

In the process of functioning of living matter on land, the surface layers of the lithosphere were gradually transformed into soil, into a kind of, as V.I. Vernadsky put it, a bioinert body of the planet. Both aquatic and terrestrial organisms began to populate the soil, creating a specific complex of its inhabitants.

Thus, on modern Earth, four environments of life are clearly distinguished - aquatic, land-air, soil and living organisms - which differ significantly in their conditions. Let's look at each of them.

General characteristics. The aquatic environment of life, the hydrosphere, occupies up to 71% of the globe's area. In terms of volume, water reserves on Earth are estimated at 1370 million cubic meters. km, which is 1/800 of the volume of the globe. The main amount of water, more than 98%, is concentrated in the seas and oceans, 1.24% is represented by the ice of the polar regions; in fresh waters of rivers, lakes and swamps, the amount of water does not exceed 0.45%.

The aquatic environment is home to about 150,000 species of animals (approximately 7% of the total number on the globe) and 10,000 species of plants (8%). Despite the fact that representatives of the vast majority of groups of plants and animals remained in the aquatic environment (in their “cradle”), the number of their species is significantly less than that of terrestrial ones. This means that evolution on land took place much faster.

The most diverse and rich plant and animal world seas and oceans of the equatorial and tropical regions (especially the Pacific and Atlantic oceans). To the south and north of these belts, the qualitative composition of organisms gradually becomes depleted. In the area of the East Indian archipelago, there are about 40,000 species of animals, and in the Laptev Sea there are only 400. Moreover, the bulk of the organisms of the World Ocean are concentrated in a relatively small area of the sea coasts of the temperate zone and among the mangroves of tropical countries. In vast areas of water far from the coast there are desert areas, practically devoid of life.

Specific gravity rivers, lakes and swamps are insignificant compared to those of the seas and oceans in the biosphere. Nevertheless, they create the supply of fresh water necessary for a huge number of plants and animals, as well as for humans.

The aquatic environment has a strong influence on its inhabitants. In turn, the living matter of the hydrosphere affects the habitat, processes it, involving it in the cycle of substances. It is estimated that the water of the seas and oceans, rivers and lakes decomposes and is restored in the biotic cycle within 2 million years, i.e. all of it has passed through the living matter of the planet more than one thousand times*. Thus, the modern hydrosphere is a product of the vital activity of living matter not only of modern, but also of past geological eras.

A characteristic feature of the aquatic environment is its mobility even in stagnant bodies of water, not to mention flowing, fast-flowing rivers and streams. The seas and oceans experience ebbs and flows, powerful currents, and storms; In lakes, water moves under the influence of wind and temperature. The movement of water ensures supply aquatic organisms oxygen and nutrients, leads to equalization (decrease) of temperature throughout the entire reservoir.

The inhabitants of reservoirs have developed appropriate adaptations to the mobility of the environment. For example, in flowing water bodies there are so-called “fouling” plants firmly attached to underwater objects - green algae (Cladophora) with a trail of shoots, diatoms (Diatomeae), water mosses (Fontinalis), forming a dense cover even on stones in rapid river riffles .

Animals also adapted to the mobility of the aquatic environment. In fish that live in fast-flowing rivers, the body is almost round in cross section (trout, minnow). They usually move against the current. Invertebrates of flowing water bodies usually stay at the bottom, their body is flattened in the dorso-ventral direction, many have various fixation organs on the ventral side, allowing them to attach to underwater objects. In the seas, the strongest influence of moving masses of water is experienced by organisms in the tidal and surf zones. On rocky shores in the surf, barnacles (Balanus, Chthamalus), gastropods (Patella Haliotis), and some species of crustaceans hiding in the crevices of the shore are common.

In the life of aquatic organisms in temperate latitudes, the vertical movement of water in standing reservoirs plays an important role. The water in them is clearly divided into three layers: the upper epilimnion, the temperature of which experiences sharp seasonal fluctuations; temperature jump layer – metalimnion (thermocline), where a sharp temperature difference is observed; bottom deep layer, hypolimnion, where the temperature changes slightly throughout the year.

In summer, the warmest layers of water are located at the surface, and the coldest ones are located at the bottom. This layer-by-layer distribution of temperatures in a reservoir is called direct stratification. In winter, with a decrease in temperature, a reverse stratification is observed: cold surface waters with temperatures below 4 °C are located above relatively warm ones. This phenomenon is called temperature dichotomy. It is especially pronounced in most of our lakes in summer and winter. As a result of temperature dichotomy, a density stratification of water is formed in a reservoir, its vertical circulation is disrupted and a period of temporary stagnation begins.

In spring, surface water, due to heating to 4 °C, becomes denser and sinks deeper, and warmer water rises from the depths to take its place. As a result of such vertical circulation, homothermy occurs in the reservoir, i.e., for some time the temperature of the entire water mass is equalized. With a further increase in temperature, the upper layers of water become less and less dense and no longer sink - summer stagnation sets in.

In autumn, the surface layer cools, becomes denser and sinks deeper, displacing warmer water to the surface. This occurs before the onset of autumn homothermy. When surface waters cool below 4 °C, they again become less dense and again remain on the surface. As a result, water circulation stops and winter stagnation occurs.

Organisms in water bodies of temperate latitudes are well adapted to seasonal vertical movements of water layers, to spring and autumn homothermy and to summer and winter stagnation (Fig. 13).

In lakes at tropical latitudes, the surface water temperature never drops below 4 °C and the temperature gradient in them is clearly expressed down to the deepest layers. Mixing of water, as a rule, occurs here irregularly during the coldest time of the year.

Peculiar conditions for life develop not only in the water column, but also at the bottom of the reservoir, since there is no aeration in the soils and mineral compounds are washed out of them. Therefore, they do not have fertility and serve only as a more or less solid substrate for aquatic organisms, performing mainly a mechanical-dynamic function. In this regard, the greatest ecological significance acquire the size of soil particles, the density of their contact with each other and resistance to washout by currents.

Abiotic factors of the aquatic environment. Water as a living environment has special physical and chemical properties.

The temperature regime of the hydrosphere is fundamentally different from that in other environments. Temperature fluctuations in the World Ocean are relatively small: the lowest is about –2 °C, and the highest is approximately 36 °C. The amplitude of oscillations here, therefore, falls within 38 °C. With depth, the temperature of water in the oceans drops. Even in tropical areas at a depth of 1000 m it does not exceed 4–5°C. At the depths of all oceans there is a layer of cold water (from -1.87 to + 2°C).

In fresh inland water bodies of temperate latitudes, the temperature of the surface layers of water ranges from – 0.9 to +25 ° C, in deeper waters it is 4–5 ° C. The exception is thermal springs, where the temperature of the surface layer sometimes reaches 85–93 °C.

Such thermodynamic features of the aquatic environment as high specific heat, high thermal conductivity and expansion upon freezing, create particularly favorable conditions for life. These conditions are also ensured by the high latent heat of fusion of water, as a result of which in winter the temperature under the ice is never below its freezing point (for fresh water about 0 ° C). Since water has the greatest density at 4° C, and when it freezes it expands, in winter ice forms only on top, but the main thickness does not freeze.

Because the temperature regime reservoirs are characterized by great stability; the organisms living in it are characterized by a relative constancy of body temperature and have a narrow range of adaptability to fluctuations in environmental temperature. Even minor deviations in thermal conditions can lead to significant changes in the life of animals and plants. An example is the “biological explosion” of the lotus (Nelumbium caspium) in the northernmost part of its habitat - in the Volga delta. For a long time this exotic plant inhabited only a small bay. Over the last decade, the area of lotus thickets has increased almost 20 times and now occupies over 1,500 hectares of water area. This rapid spread of the lotus is explained by the general drop in the level of the Caspian Sea, which was accompanied by the formation of many small lakes and estuaries at the mouth of the Volga. During the hot summer months, the water here warmed up more than before, which contributed to the growth of lotus thickets.

Water is also characterized by significant density (in this regard, it is 800 times greater than the air medium) and viscosity. These features affect plants in the fact that their mechanical tissue develops very weakly or not at all, so their stems are very elastic and bend easily. Most aquatic plants are characterized by buoyancy and the ability to be suspended in the water column. They rise to the surface and then fall again. In many aquatic animals, the integument is abundantly lubricated with mucus, which reduces friction during movement, and the body takes on a streamlined shape.

Organisms in the aquatic environment are distributed throughout its entire thickness (in oceanic depressions, animals were found at depths of over 10,000 m). Naturally, at different depths they experience different pressures. Deep sea creatures are adapted to high blood pressure(up to 1000 atm), the inhabitants of the surface layers are not susceptible to it. On average, in the water column, for every 10 m of depth, pressure increases by 1 atm. All hydrobionts are adapted to this factor and are accordingly divided into deep-sea and those living at shallow depths.

Water transparency and its light regime have a great influence on aquatic organisms. This especially affects the distribution of photosynthetic plants. In muddy reservoirs they live only in the surface layer, and where there is greater transparency, they penetrate to significant depths. A certain turbidity of water is created by a huge number of particles suspended in it, which limits the penetration of sunlight. Turbidity in water can be caused by particles of mineral substances (clay, silt) and small organisms. The transparency of water also decreases in summer with the rapid growth of aquatic vegetation and the mass reproduction of small organisms suspended in the surface layers. The light regime of reservoirs also depends on the season. In the north, in temperate latitudes, when reservoirs freeze and the ice on top is still covered with snow, the penetration of light into the water column is greatly limited.

The light regime is also determined by the natural decrease in light with depth due to the fact that water absorbs sunlight. In this case, rays with different wavelengths are absorbed differently: red ones are absorbed most quickly, while blue-green ones penetrate to significant depths. The ocean becomes darker with depth. The color of the environment changes, gradually moving from greenish to green, then to blue, blue, blue-violet, giving way to constant darkness. Accordingly, with depth, green algae (Chlorophyta) are replaced by brown (Phaeophyta) and red (Rhodophyta), the pigments of which are adapted to capture sunlight of different wavelengths. The color of animals also naturally changes with depth. In the surface, light layers of water, brightly and variously colored animals usually live, while deep-sea species are devoid of pigments. In the twilight zone of the ocean, animals live that are colored with a reddish tint, which helps them hide from enemies, since the red color in blue-violet rays is perceived as black.

The salinity of water plays an important role in the life of aquatic organisms. As you know, water is an excellent solvent for many mineral compounds. As a result, natural reservoirs have a certain chemical composition. Carbonates, sulfates, and chlorides are of greatest importance. The amount of dissolved salts per 1 liter of water in fresh water bodies does not exceed 0.5 g (usually less); in the seas and oceans it reaches 35 g (Table 6).

Table 6.Distribution of basic salts in various reservoirs (according to R. Dazho, 1975)

Calcium plays an essential role in the life of freshwater animals. Mollusks, crustaceans and other invertebrates use it to build shells and the exoskeleton. But fresh water bodies, depending on a number of circumstances (the presence of certain soluble salts in the soil of the reservoir, in the soil and soil of the banks, in the water of inflowing rivers and streams) vary greatly both in composition and in the concentration of salts dissolved in them. Sea waters are more stable in this regard. Almost all known elements were found in them. However, in terms of importance, table salt takes first place, then magnesium chloride and sulfate and potassium chloride.

Freshwater plants and animals live in a hypotonic environment, that is, an environment in which the concentration of solutes is lower than in body fluids and tissues. Due to the difference in osmotic pressure outside and inside the body, water constantly penetrates into the body, and freshwater hydrobionts are forced to intensively remove it. In this regard, their osmoregulation processes are well expressed. The concentration of salts in the body fluids and tissues of many marine organisms is isotonic with the concentration of dissolved salts in the surrounding water. Therefore, their osmoregulatory functions are not developed to the same extent as in freshwater animals. Difficulties in osmoregulation are one of the reasons that many marine plants and especially animals were unable to populate fresh water bodies and turned out, with the exception of certain representatives, to be typical marine inhabitants (coelenterata - Coelenterata, echinoderms - Echinodermata, pogonophora - Pogonophora, sponges - Spongia, tunicates – Tunicata). At that or Insects practically do not live in the seas and oceans, while freshwater basins are abundantly populated by them. Typically marine and typically freshwater species do not tolerate significant changes in water salinity. All of them are stenohaline organisms. There are relatively few euryhaline animals of freshwater and marine origin. They are usually found, and in significant quantities, in brackish waters. These are freshwater pike perch (Stizostedion lucioperca), bream (Abramis brama), pike (Esox lucius), and the sea mullet family (Mugilidae).

In fresh waters, plants fixed on the bottom of the reservoir are common. Often their photosynthetic surface is located above the water. These are cattails (Typha), reeds (Scirpus), arrowheads (Sagittaria), water lilies (Nymphaea), egg capsules (Nuphar). In others, the photosynthetic organs are submerged in water. These include pondweed (Potamogeton), urut (Myriophyllum), and elodea (Elodea). Some higher freshwater plants are rootless. They either float freely or grow over underwater objects or algae attached to the ground.

If oxygen does not play a role in the air environment significant role, then for water it is the most important environmental factor. Its content in water is inversely proportional to temperature. With decreasing temperature, the solubility of oxygen, like other gases, increases. The accumulation of oxygen dissolved in water occurs as a result of its entry from the atmosphere, as well as due to the photosynthetic activity of green plants. When water is mixed, which is typical for flowing reservoirs and especially for fast-flowing rivers and streams, the oxygen content also increases.

Different animals have different needs for oxygen. For example, trout (Salmo trutta) and minnow (Phoxinus phoxinus) are very sensitive to its deficiency and therefore live only in fast-flowing, cold and well-mixed waters. Roach (Rutilus rutilus), ruffe (Acerina cernua), carp (Cyprinus carpio), crucian carp (Carassius carassius) are unpretentious in this regard, and the larvae of chironomid mosquitoes (Chironomidae) and tubifex worms (Tubifex) live at great depths, where there is no oxygen at all or very little. Aquatic insects and mollusks (Pulmonata) can also live in bodies of water with low oxygen levels. However, they systematically rise to the surface, storing fresh air for some time.

Carbon dioxide is approximately 35 times more soluble in water than oxygen. There is almost 700 times more of it in water than in the atmosphere from where it comes. In addition, carbonates and bicarbonates of alkali and alkaline earth metals are a source of carbon dioxide in water. Carbon dioxide contained in water ensures photosynthesis of aquatic plants and takes part in the formation of calcareous skeletal structures of invertebrate animals.

The concentration of hydrogen ions (pH) is of great importance in the life of aquatic organisms. Freshwater pools with a pH of 3.7–4.7 are considered acidic, 6.95–7.3 are considered neutral, and those with a pH greater than 7.8 are alkaline. In fresh water bodies, pH even experiences daily fluctuations. Sea water is more alkaline and its pH changes much less than fresh water. pH decreases with depth.

The concentration of hydrogen ions plays a large role in the distribution of aquatic organisms. At a pH of less than 7.5, grasshopper (Isoetes) and burberry (Sparganium) grow; at 7.7–8.8, i.e., in an alkaline environment, many types of pondweed and elodea develop. In the acidic waters of swamps, sphagnum mosses (Sphagnum) predominate, but elasmobranch mollusks of the genus Unio are absent; other mollusks are rare, but shell rhizomes (Testacea) are abundant. Most freshwater fish can withstand a pH between 5 and 9. If the pH is less than 5, there is a massive death of fish, and above 10, all fish and other animals die.

Ecological groups of hydrobionts. The water column - pelagic (pelagos - sea) is inhabited by pelagic organisms that can actively swim or stay (float) in certain layers. In accordance with this, pelagic organisms are divided into two groups - nekton and plankton. Bottom inhabitants form the third ecological group of organisms - benthos.

Nekton (nekios–· floating)– This is a collection of pelagic actively moving animals that do not have a direct connection with the bottom. These are mainly large animals that can overcome long distances and strong water currents. They are characterized by a streamlined body shape and well-developed organs of movement. Typical nektonic organisms are fish, squid, pinnipeds, and whales. In fresh waters, in addition to fish, nekton includes amphibians and actively moving insects. Many marine fish can move through the water at great speed. Some squids (Oegopsida) swim very quickly, up to 45–50 km/h, sailfish (Istiopharidae) reach speeds of up to 100–10 km/h, and swordfish (Xiphias glabius) reach speeds of up to 130 km/h.

Plankton– soaring, wandering)– This is a set of pelagic organisms that do not have the ability for rapid active movements. Planktonic organisms cannot resist currents. These are mainly small animals - zooplankton and plants - phytoplankton. The plankton periodically includes the larvae of many animals floating in the water column.

Planktonic organisms are located either on the surface of the water, or at depth, or even in the bottom layer. The first form a special group – neuston. Organisms, part of whose body is located in water, and part of which is above its surface, are called pleuston. These are siphonophores (Siphonophora), duckweed (Lemna), etc.

Phytoplankton is of great importance in the life of water bodies, since it is the main producer of organic matter. It includes primarily diatoms (Diatomeae) and green algae (Chlorophyta), plant flagellates (Phytomastigina), peridineae (Peridineae) and coccolithophorids (Coccolitophoridae). In the northern waters of the World Ocean, diatoms predominate, and in tropical and subtropical waters, armored flagellates predominate. In fresh waters, in addition to diatoms, green and blue-green algae (Suanophyta) are common.

Zooplankton and bacteria are found at all depths. Marine zooplankton is dominated by small crustaceans (Copepoda, Amphipoda, Euphausiacea) and protozoa (Foraminifera, Radiolaria, Tintinnoidea). Its larger representatives are pteropods (Pteropoda), jellyfish (Scyphozoa) and floating ctenophora (Ctenophora), salps (Salpae), and some worms (Alciopidae, Tomopteridae). In fresh waters, poorly swimming, relatively large crustaceans (Daphnia, Cyclopoidea, Ostracoda, Simocephalus; Fig. 14), many rotifers (Rotatoria) and protozoa are common.

The greatest species diversity is achieved by plankton in tropical waters.

Groups of planktonic organisms are differentiated by size. Nannoplankton (nannos - dwarf) are the smallest algae and bacteria; microplankton (micros – small) – most algae, protozoa, rotifers; mesoplankton (mesos - middle) - copepods and cladocerans, shrimp and a number of animals and plants, no more than 1 cm in length; macroplankton (macros - large) - jellyfish, mysids, shrimp and other organisms larger than 1 cm; megaloplankton (megalos – huge) – very large, over 1 m, animals. For example, the swimming ctenophore (Cestus veneris) reaches a length of 1.5 m, and the cyanea jellyfish (Suapea) has a bell with a diameter of up to 2 m and tentacles 30 m long.

Planktonic organisms are an important food component of many aquatic animals (including such giants as baleen whales - Mystacoceti), especially considering that they, and especially phytoplankton, are characterized by seasonal outbreaks of mass reproduction (water blooms).

Benthos– depth)– a set of organisms that live at the bottom (on the ground and in the ground) of water bodies. It is divided into phytobenthos and zoobenthos. Mainly represented by attached or slowly moving animals, as well as burrowing animals. Only in shallow water does it consist of organisms that synthesize organic matter (producers), consume (consumers) and destroy (decomposers) it. At great depths, where light does not penetrate, phytobenthos (producers) is absent.

Benthic organisms differ in their lifestyle - mobile, sedentary and immobile; by feeding method - photosynthetic, carnivorous, herbivorous, detritivorous; by size – macro-, meso-microbenthos.

The phytobenthos of the seas mainly includes bacteria and algae (diatoms, green, brown, red). Along the coasts there are also flowering plants: Zostera, Phyllospadix, Rup-pia. The richest phytobenthos is in rocky and stony areas of the bottom. Along the coasts, kelp (Laminaria) and fucus (Fucus) sometimes form a biomass of up to 30 kg per 1 sq. m. On soft soils, where plants cannot firmly attach, phytobenthos develops mainly in places protected from waves.

Fresh water phytobenzos is represented by bacteria, diatoms and green algae. Coastal plants are abundant, located inland from the shore in clearly defined belts. In the first zone, semi-submerged plants grow (reeds, reeds, cattails and sedges). The second zone is occupied by submerged plants with floating leaves (water lilies, duckweeds, water lilies). The third zone is dominated by submerged plants - pondweed, elodea, etc.

All aquatic plants can be divided into two main ecological groups according to their lifestyle: hydrophytes - plants that are submerged in water only with their lower part and usually root in the ground, and hydatophytes - plants that are completely submerged in water, but sometimes float on the surface or have floating leaves.

The marine zoobenthos is dominated by foraminifera, sponges, coelenterates, nemerteans, polychaete worms, sipunculids, bryozoans, brachiopods, mollusks, ascidians, and fish. Benthic forms are most numerous in shallow waters, where their total biomass often reaches tens of kilograms per square meter. m. With depth, the number of benthos drops sharply and at great depths amounts to milligrams per 1 sq. m.

In fresh water bodies there is less zoobenthos than in the seas and oceans, and the species composition is more uniform. These are mainly protozoans, some sponges, ciliated and oligochaete worms, leeches, bryozoans, mollusks and insect larvae.

Ecological plasticity of aquatic organisms. Aquatic organisms have less ecological plasticity than terrestrial ones, since water is a more stable environment and its abiotic factors undergo relatively minor fluctuations. Marine plants and animals are the least plastic. They are very sensitive to changes in water salinity and temperature. Thus, madrepore corals cannot withstand even weak desalination of water and live only in the seas, moreover, on solid ground at a temperature not lower than 20 ° C. These are typical stenobionts. However, there are species with increased ecological plasticity. For example, the rhizome Cyphoderia ampulla is a typical eurybiont. It lives in seas and fresh waters, in warm ponds and cold lakes.

Freshwater animals and plants, as a rule, are much more plastic than marine ones, since freshwater as a living environment is more variable. The most flexible are the brackish-water inhabitants. They are adapted to both high concentrations of dissolved salts and significant desalination. However, there are a relatively small number of species, since environmental factors undergo significant changes in brackish waters.

The breadth of ecological plasticity of aquatic organisms is assessed in relation not only to the entire complex of factors (eury- and stanobionticity), but also to any one of them. Coastal plants and animals, in contrast to the inhabitants of open zones, are mainly eurythermic and euryhaline organisms, since near the shore the temperature conditions and salt regime are quite variable (warming by the sun and relatively intense cooling, desalination by the influx of water from streams and rivers, especially during the rainy season, and etc.). A typical stenothermic species is the lotus. It grows only in well-warmed shallow reservoirs. For the same reasons, the inhabitants of the surface layers turn out to be more eurythermic and euryhaline in comparison with deep-sea forms.

Ecological plasticity serves as an important regulator of the dispersal of organisms. As a rule, aquatic organisms with high ecological plasticity are quite widespread. This applies, for example, to elodea. However, the crustacean brine shrimp (Artemia salina) is diametrically opposed to it in this sense. It lives in small bodies of water with very salty water. This is a typical stenohaline representative with narrow ecological plasticity. But in relation to other factors, it is very plastic and therefore is found everywhere in salt water bodies.

Ecological plasticity depends on the age and developmental phase of the organism. Thus, the marine gastropod Littorina, as an adult, goes without water for a long time every day during low tides, and its larvae lead a purely planktonic lifestyle and cannot tolerate drying out.

Adaptive features of aquatic plants. The ecology of aquatic plants, as noted, is very specific and differs sharply from the ecology of most terrestrial plant organisms. The ability of aquatic plants to absorb moisture and mineral salts directly from the environment is reflected in their morphological and physiological organization. Aquatic plants are primarily characterized by poor development of conductive tissue and root systems. The latter serves mainly for attachment to the underwater substrate and, unlike terrestrial plants, does not perform the function of mineral nutrition and water supply. In this regard, the roots of rooted aquatic plants are devoid of root hairs. They feed on the entire surface of the body. The powerfully developed rhizomes of some of them serve for vegetative propagation and storage of nutrients. These are many pondweeds, water lilies, and egg capsules.

The high density of water makes it possible for plants to inhabit its entire thickness. For this purpose, lower plants that inhabit various layers and lead a floating lifestyle have special appendages that increase their buoyancy and allow them to remain suspended. Mechanical tissue is poorly developed in higher hydrophytes. In their leaves, stems, and roots, as noted, there are air-bearing intercellular cavities. This increases the lightness and buoyancy of organs suspended in water and floating on the surface, and also helps to wash away internal cells with water with gases and salts dissolved in it. Hydatophytes are generally characterized by a large leaf surface with a small total plant volume. This provides them with intense gas exchange when there is a lack of oxygen and other gases dissolved in water. Many pondweeds (Potamogeton lusens, P. perfoliatus) have thin and very long stems and leaves, their covers are easily permeable to oxygen. Other plants have strongly dissected leaves (water buttercup – Ranunculus aquatilis, urut – Myriophyllum spicatum, hornwort – Ceratophyllum dernersum).

A number of aquatic plants have developed heterophyly (various leaves). For example, in Salvinia, submerged leaves serve as mineral nutrition, while floating leaves serve as organic nutrition. In water lilies and egg capsules, the floating and submerged leaves are significantly different from each other. The upper surface of the floating leaves is dense and leathery with a large number of stomata. This promotes better gas exchange with air. There are no stomata on the underside of floating or submerged leaves.

An equally important adaptive feature of plants for living in an aquatic environment is that the leaves immersed in water are usually very thin. Chlorophyll in them is often located in the cells of the epidermis. This leads to an increase in the rate of photosynthesis under low light conditions. Such anatomical and morphological features are most clearly expressed in many pondweeds (Potamogeton), elodea (Helodea canadensis), water mosses (Riccia, Fontinalis), and Vallisneria spiralis.

The protection of aquatic plants from leaching of mineral salts from cells is the secretion of mucus by special cells and the formation of endoderm in the form of a ring of thicker-walled cells.

The relatively low temperature of the aquatic environment causes the death of vegetative parts of plants immersed in water after the formation of winter buds, as well as the replacement of tender thin summer leaves with tougher and shorter winter leaves. At the same time, low water temperature negatively affects the generative organs of aquatic plants, and its high density makes pollen transfer difficult. Therefore, aquatic plants reproduce intensively by vegetative means. The sexual process is suppressed in many of them. Adapting to the characteristics of the aquatic environment, most submerged and floating plants carry flowering stems into the air and reproduce sexually (pollen is carried by wind and surface currents). The resulting fruits, seeds and other rudiments are also distributed by surface currents (hydrochory).

Hydrochorous plants include not only aquatic plants, but also many coastal plants. Their fruits are highly buoyant and can remain in water for a long time without losing their germination. Water transports the fruits and seeds of chastukha (Alisma plantago-aquatica), arrowhead (Sagittaria sagittifolia), sageweed (Butomusumbellatus), pondweed and other plants. The fruits of many sedges (Sagekh) are enclosed in peculiar air sacs and are also carried by water currents. It is believed that even coconut palms have spread throughout the archipelagos tropical islands Pacific Ocean thanks to the buoyancy of its fruits - coconuts. Along the Vakhsh River, along the canals, the gumai weed (Sorgnum halepense) spread in the same way.

Adaptive features of aquatic animals. The adaptations of animals to the aquatic environment are even more diverse than those of plants. They have anatomical, morphological, physiological, behavioral and other adaptive characteristics. Even simply listing them is difficult. Therefore, we will name in general terms only the most characteristic of them.

Animals that live in the water column have, first of all, adaptations that increase their buoyancy and allow them to resist the movement of water and currents. Bottom organisms, on the contrary, develop adaptations that prevent them from rising into the water column, that is, they reduce buoyancy and allow them to stay at the bottom even in fast-flowing waters.

In small forms living in the water column, a reduction in skeletal formations is observed. In protozoa (Rhizopoda, Radiolaria), the shells are porous, and the flint spines of the skeleton are hollow inside. The specific density of jellyfish (Scyphozoa) and ctenophora (Ctenophora) decreases due to the presence of water in the tissues. An increase in buoyancy is also achieved by the accumulation of fat droplets in the body (nightlights - Noctiluca, radiolarians - Radiolaria). Larger accumulations of fat are also observed in some crustaceans (Cladocera, Copepoda), fish, and cetaceans. The specific density of the body is also reduced by gas bubbles in the protoplasm of testate amoebae and air chambers in the shells of mollusks. Many fish have swim bladders filled with gas. The siphonophores Physalia and Velella develop powerful air cavities.

Animals passively swimming in the water column are characterized not only by a decrease in weight, but also by an increase in the specific surface area of the body. The fact is that the greater the viscosity of the medium and the higher the specific surface area of the body, the slower it sinks into water. As a result, the animal’s body becomes flattened and all sorts of spines, outgrowths, and appendages form on it. This is characteristic of many radiolarians (Chalengeridae, Aulacantha), flagellates (Leptodiscus, Craspedotella), and foraminifera (Globigerina, Orbulina). Since the viscosity of water decreases with increasing temperature and increases with increasing salinity, adaptations to increased friction are most pronounced at high temperatures and low salinities. For example, the flagellated Ceratium from the Indian Ocean are armed with longer, horn-like appendages than those found in the cold waters of the Eastern Atlantic.

Active swimming in animals is carried out with the help of cilia, flagella, and body bending. This is how protozoa, ciliated worms, and rotifers move.

Among aquatic animals, reactive swimming is common due to the energy of the ejected stream of water. This is typical for protozoa, jellyfish, dragonfly larvae, and some bivalves. The reactive mode of locomotion reaches its highest perfection in cephalopods. Some squids, when throwing out water, develop a speed of 40–50 km/h. Larger animals develop specialized limbs (swimming legs in insects, crustaceans; fins, flippers). The body of such animals is covered with mucus and has a streamlined shape.

Large group animals, mainly freshwater ones, use a surface film of water (surface tension) when moving. For example, spinning beetles (Gyrinidae) and water strider bugs (Gerridae, Veliidae) run freely on it. Small Hydrophilidae beetles move along the lower surface of the film, and pond snails (Limnaea) and mosquito larvae are suspended from it. All of them have a number of features in the structure of their limbs, and their integuments are not wetted by water.

Only in the aquatic environment are motionless animals leading an attached lifestyle found. They are characterized by a peculiar body shape, slight buoyancy (the density of the body is greater than the density of water) and special devices for attachment to the substrate. Some attach themselves to the ground, others crawl along it or lead a burrowing lifestyle, some settle on underwater objects, in particular the bottoms of ships.

Of the animals attached to the ground, the most typical are sponges, many coelenterates, especially hydroids (Hydroidea) and coral polyps (Anthozoa), crinoids (Crinoidea), bivalves (Bivalvia), barnacles (Cirripedia), etc.

Among burrowing animals there are especially many worms, insect larvae, and mollusks. Certain fish (spikefish - Cobitis taenia, flounders - Pleuronectidae, stingrays - Rajidae), and lamprey larvae (Petromyzones) spend significant time in the ground. The abundance of these animals and their species diversity depend on the type of soil (stones, sand, clay, silt). There are usually fewer of them on rocky soils than on muddy soils. Invertebrates, which colonize muddy soils in large numbers, create optimal conditions for the life of a number of larger benthic predators.

Most aquatic animals are poikilothermic, and their body temperature depends on the temperature of the environment. In homeothermic mammals (pinnipeds, cetaceans), a thick layer of subcutaneous fat is formed, which performs a thermal insulation function.

For aquatic animals, environmental pressure matters. In this regard, there are stenobathic animals, which cannot withstand large fluctuations in pressure, and eurybathic animals, which live at both high and low pressure. Holothurians (Elpidia, Myriotrochus) live at depths from 100 to 9000 m, and many species of Storthyngura crayfish, pogonophora, crinoids are located at depths from 3000 to 10,000 m. Such deep-sea animals have specific organizational features: an increase in body size; disappearance or poor development of the calcareous skeleton; often – reduction of the visual organs; strengthening the development of tactile receptors; lack of body pigmentation or, conversely, dark coloring.

Maintaining a certain osmotic pressure and ionic state of solutions in the body of animals is ensured by complex mechanisms of water-salt metabolism. However, most aquatic organisms are poikilosmotic, that is, the osmotic pressure in their body depends on the concentration of dissolved salts in the surrounding water. Only vertebrates, higher crustaceans, insects and their larvae are homoiosmotic - they maintain constant osmotic pressure in the body, regardless of the salinity of the water.

Marine invertebrates generally do not have mechanisms for water-salt metabolism: anatomically they are closed to water, but osmotically they are open. However, it would be incorrect to say that they have absolutely no mechanisms that control water-salt metabolism.

They are simply imperfect, and this is explained by the fact that the salinity of sea water is close to the salinity of the body juices. After all, in freshwater hydrobionts, the salinity and ionic state of mineral substances in the body juices are, as a rule, higher than in the surrounding water. Therefore, their osmoregulatory mechanisms are well expressed. The most common way to maintain constant osmotic pressure is to regularly remove water entering the body using pulsating vacuoles and excretory organs. In other animals, impenetrable covers of chitin or horny formations develop for these purposes. Some people produce mucus on the surface of their body.

The difficulty of regulating osmotic pressure in freshwater organisms explains their species poverty compared to sea inhabitants.

Let us use the example of fish to see how osmoregulation of animals occurs in sea and fresh waters. Freshwater fish remove excess water through the intensive work of the excretory system, and absorb salts through the gill filaments. Marine fish, on the contrary, are forced to replenish their water supplies and therefore drink sea water, and excess salts supplied with it are removed from the body through the gill filaments (Fig. 15).

Changing conditions in the aquatic environment causes certain behavioral reactions of organisms. Vertical migrations of animals are associated with changes in illumination, temperature, salinity, gas regime and other factors. In the seas and oceans, millions of tons of aquatic organisms take part in such migrations (lowering into the depths, rising to the surface). During horizontal migrations, aquatic animals can travel hundreds and thousands of kilometers. These are the spawning, wintering and feeding migrations of many fish and aquatic mammals.

Biofilters and their ecological role. One of specific features aquatic environment is the presence in it large quantity small particles of organic matter - detritus, formed by dying plants and animals. Huge masses of these particles settle on bacteria and, thanks to the gas released as a result of the bacterial process, are constantly suspended in the water column.

Detritus is a high-quality food for many aquatic organisms, so some of them, the so-called biofilters, have adapted to obtain it using specific microporous structures. These structures, as it were, filter the water, retaining particles suspended in it. This feeding method is called filtration. Another group of animals deposits detritus on the surface of either their own body or on special trapping devices. This method is called sedimentation. Often the same organism feeds by both filtration and sedimentation.

Biofiltration animals (elasmobranch molluscs, sessile echinoderms and polychaete annelids, bryozoans, ascidians, planktonic crustaceans and many others) play a large role in the biological purification of water bodies. For example, a colony of mussels (Mytilus) per 1 sq. m passes through the mantle cavity up to 250 cubic meters. m of water per day, filtering it and precipitating suspended particles. The almost microscopic crustacean Calanus (Calanoida) purifies up to 1.5 liters of water per day. If we take into account the enormous number of these crustaceans, the work they perform in the biological purification of water bodies seems truly enormous.

In fresh waters, active biofilters are pearl barley (Unioninae), toothless mussels (Anodontinae), zebra mussels (Dreissena), daphnia (Daphnia) and other invertebrates. Their importance as a kind of biological “cleaning system” of water bodies is so great that it is almost impossible to overestimate it.

Zoning of the water environment. The aquatic living environment is characterized by clearly defined horizontal and especially vertical zoning. All hydrobionts are strictly confined to living in certain zones that differ in different living conditions.

In the World Ocean, the water column is called pelagic, and the bottom is benthic. Accordingly, ecological groups of organisms living in the water column (pelagic) and on the bottom (benthic) are also distinguished.

The bottom, depending on the depth of its occurrence from the surface of the water, is divided into sublittoral (an area of gradual decline to a depth of 200 m), bathyal ( steep slope), abyssal (ocean bed with an average depth of 3–6 km), ultra-abyssal (the bottom of oceanic depressions located at a depth of 6 to 10 km). The littoral zone is also distinguished - the edge of the coast, which is periodically flooded during high tides (Fig. 16).

The open waters of the World Ocean (pelagial) are also divided into vertical zones corresponding to the benthic zones: epipelagic, bathypelagic, abyssopelagic.

The littoral and sublittoral zones are most richly populated by plants and animals. There is a lot of sunlight, low pressure, and significant temperature fluctuations. The inhabitants of the abyssal and ultra-abyssal depths live at a constant temperature, in the dark, and experience enormous pressure, reaching several hundred atmospheres in the oceanic depressions.

A similar, but less clearly defined zonation is also characteristic of inland fresh water bodies.

Characteristics of the aquatic environment as the main environment of life. Properties of water. Ecological groups of aquatic plants. Adaptive features of aquatic plants. Zoning of the water environment.

Characteristics of the aquatic environment as the main living environment

In the process of historical development, living organisms have mastered four habitats. The first is water. Life originated and developed in water for many millions of years. The second - ground-air - plants and animals arose on land and in the atmosphere and rapidly adapted to new conditions. Gradually transforming upper layer land - lithosphere, they created the third habitat - soil, and themselves became the fourth habitat.

Aquatic habitat is called the hydrosphere.

Water covers 71% of the globe's area and makes up 1/800 of the volume of land or 1370 m3. The bulk of water is concentrated in the seas and oceans - 94-98%, polar ice contains about 1.2% of water and a very small proportion - less than 0.5%, in fresh waters of rivers, lakes and swamps.

About 150,000 species of animals and 10,000 plants live in the aquatic environment, which is respectively only 7 and 8% of the total number of species on Earth. Based on this, it was concluded that evolution on land was much more intense than in water.

Properties of water

The high density of the aquatic environment determines the special composition and nature of changes in life-supporting factors. Some of them are the same as on land - heat, light, others are specific: water pressure (increases with depth by 1 atm for every 10 m), oxygen content, salt composition, acidity. Due to the high density of the environment, the values of heat and light change much faster with an altitude gradient than on land.

Thermal mode. The aquatic environment is characterized by less heat gain, because a significant part of it is reflected, and an equally significant part is spent on evaporation. Consistent with the dynamics of land temperatures, water temperatures exhibit smaller fluctuations in daily and seasonal temperatures. Moreover, reservoirs significantly equalize the temperature in the atmosphere of coastal areas. In the absence of an ice shell, the seas have a warming effect on the adjacent land areas in the cold season, and a cooling and moistening effect in the summer.

The range of water temperatures in the World Ocean is 38° (from -2 to +36°C), in fresh water bodies – 26° (from -0.9 to +25°C). With depth, the water temperature drops sharply. Up to 50 m there are daily temperature fluctuations, up to 400 – seasonal, deeper it becomes constant, dropping to +1-3°C (in the Arctic it is close to 0°C). Since the temperature regime in reservoirs is relatively stable, their inhabitants are characterized by stenothermism. Minor temperature fluctuations in one direction or another are accompanied by significant changes in aquatic ecosystems.

Examples: a “biological explosion” in the Volga delta due to a decrease in the level of the Caspian Sea - the proliferation of lotus thickets (Nelumba kaspium), in southern Primorye - the overgrowth of whitefly in oxbow rivers (Komarovka, Ilistaya, etc.) along the banks of which woody vegetation was cut down and burned.

Due to varying degrees of heating of the upper and lower layers throughout the year, ebbs and flows, currents, and storms, constant mixing of water layers occurs. The role of water mixing for aquatic inhabitants (aquatic organisms) is extremely important, because at the same time, the distribution of oxygen and nutrients within reservoirs is equalized, ensuring metabolic processes between organisms and the environment.

In stagnant reservoirs (lakes) of temperate latitudes, vertical mixing takes place in spring and autumn, and during these seasons the temperature throughout the reservoir becomes uniform, i.e. homothermy occurs. In summer and winter, as a result of a sharp increase in heating or cooling of the upper layers, the mixing of water stops. This phenomenon is called temperature dichotomy, and the period of temporary stagnation is called stagnation (summer or winter). In summer, lighter warm layers remain on the surface, located above heavy cold ones (Fig. 2).

Figure 2. Stratification and mixing of water in the lake (after E. Ponter et al. 1982)

In winter, on the contrary, there is warmer water in the bottom layer, since directly under the ice the temperature of surface waters is less than +4°C and, due to the physicochemical properties of water, they become lighter than water with a temperature above +4°C.

Light mode. The intensity of light in water is greatly weakened due to its reflection by the surface and absorption by the water itself. This greatly affects the development of photosynthetic plants. The less transparent the water, the more light is absorbed. Water transparency is limited by mineral suspensions and plankton. It decreases with the rapid development of small organisms in summer, and in temperate and northern latitudes even in winter, after the establishment of ice cover and covering it with snow on top.

In the oceans, where the water is very transparent, 1% of light radiation penetrates to a depth of 140 m, and in small lakes at a depth of 2 m only tenths of a percent penetrates. Rays different parts spectrum are absorbed differently in water; red rays are absorbed first. With depth it becomes darker, and the color of the water first becomes green, then blue, indigo and finally blue-violet, turning into complete darkness. Hydrobionts also change color accordingly, adapting not only to the composition of light, but also to its lack - chromatic adaptation. In light zones, in shallow waters, green algae (Chlorophyta) predominate, the chlorophyll of which absorbs red rays, with depth they are replaced by brown (Phaephyta) and then red (Rhodophyta). At great depths, phytobenthos is absent.

Plants have adapted to the lack of light by developing large chromatophores, which provide a low point of compensation for photosynthesis, as well as by increasing the area of assimilating organs (leaf surface index). For deep-sea algae, strongly dissected leaves are typical, the leaf blades are thin and translucent. Semi-submerged and floating plants are characterized by heterophylly - the leaves above the water are the same as those of land plants, they have a solid blade, the stomatal apparatus is developed, and in the water the leaves are very thin, consisting of narrow thread-like lobes.

Heterophylly: egg capsules, water lilies, arrow leaf, chilim (water chestnut).

The characteristic properties of the aquatic environment, different from land, are high density, mobility, acidity, and the ability to dissolve gases and salts.

Water is characterized by high density ( 1 g/cm3, which is 800 times the density of air) and viscosity.

Plants have very poorly developed or completely absent mechanical tissues - they rely on water itself for support. Most are characterized by buoyancy due to air-carrying intercellular cavities. Characterized by active vegetative reproduction, the development of hydrochory - the removal of flower stalks above the water and the distribution of pollen, seeds and spores by surface currents.

A characteristic feature of the aquatic environment is mobility. It is caused by ebbs and flows, sea currents, storms, and different levels of elevations of river beds.

In flowing reservoirs, plants are firmly attached to stationary underwater objects. The bottom surface is primarily a substrate for them. These are green algae (Cladophora) and diatoms (Diatomeae), and aquatic mosses. Mosses even form a dense cover on fast river riffles.

Natural bodies of water have a certain chemical composition. Carbonates, sulfates, and chlorides predominate. In fresh water bodies, the salt concentration is no more than 0.5 g/l, in the seas - from 12 to 35 g/l (ppm - tenths of a percent). When the salinity is more than 40 ppm, the water body is called hypersaline or oversaline.

In fresh water (hypotonic environment), osmoregulation processes are well expressed. Hydrobionts are forced to constantly remove water penetrating into them; they are homoyosmotic (ciliates “pump” through themselves an amount of water equal to its weight every 2-3 minutes). In salt water (isotonic environment), the concentration of salts in the bodies and tissues of hydrobionts is the same (isotonic) with the concentration of salts dissolved in water - they are poikiloosmotic. Therefore, the inhabitants of salt water bodies do not have developed osmoregulatory functions, and they were unable to populate fresh water bodies.

Aquatic plants are able to absorb water and nutrients from the water - “broth”, with their entire surface, therefore their leaves are strongly dissected and conductive tissues and roots are poorly developed. The roots serve mainly for attachment to the underwater substrate. Most freshwater plants have roots.

In water, oxygen is the most important environmental factor. Its source is the atmosphere and photosynthetic plants. When water is mixed, especially in flowing reservoirs, and as the temperature decreases, the oxygen content increases. There is enough carbon dioxide in water - almost 700 times more than in air. It is used in plant photosynthesis.

In freshwater bodies of water, the acidity of water, or the concentration of hydrogen ions, varies much more than in sea waters - from pH = 3.7-4.7 (acidic) to pH = 7.8 (alkaline). The acidity of water is largely determined by the species composition of aquatic plants. Sphagnum mosses grow in the acidic waters of swamps. The acidity of sea water decreases with depth.

Question 1. Name the main features of the life of organisms in the aquatic environment, in the land-air environment, and in the soil.

The characteristics of the life of organisms in the aquatic environment, the ground-air environment and in the soil are determined by the physical and chemical properties of these living environments. These properties have a significant impact on the action of other factors inanimate nature- stabilize seasonal temperature fluctuations (water and soil), gradually change illumination (water) or completely eliminate it (soil), etc.

Water is a dense medium compared to air, has a buoyant force and is a good solvent. Therefore, many organisms living in water are characterized by poor development of supporting tissues (aquatic plants, protozoa, coelenterates, etc.), special methods of movement (hovering, jet propulsion), breathing characteristics and adaptations to maintaining a constant osmotic pressure in the cells that form their bodies.

The density of air is much lower than the density of water, so terrestrial organisms have highly developed supporting tissues - the internal and external skeleton.

Soil is the top layer of land transformed as a result of the activity of living beings. Between the soil particles there are numerous cavities that can be filled with water or air. Therefore, the soil is inhabited by both aquatic and air-breathing organisms.

Question 2. What adaptations have organisms developed for living in an aquatic environment?

The aquatic environment is denser than the air, which determines adaptations for movement in it.

Active movement in water requires a streamlined body shape and well-developed muscles (fish, cephalopods - squid, mammals - dolphins, seals).

Planktonic organisms (floating in water) have adaptations that increase their buoyancy, such as increasing the relative surface of the body due to numerous projections and setae; decrease in density due to the accumulation of fats and gas bubbles in the body (unicellular algae, protozoa, jellyfish, small crustaceans).

Organisms living in an aquatic environment are also characterized by adaptations to maintain water-salt balance. Freshwater species have adaptations to remove excess water from the body. This is, for example, served by excretory vacuoles in protozoa. In salt water, on the contrary, it is necessary to protect the body from dehydration, which is achieved by increasing the concentration of salts in the body.

Another way to maintain your water-salt balance is to move to places with a favorable salinity level.

And finally, the constancy of the body’s water-salt environment is ensured by water-impermeable integuments (mammals, higher crayfish, aquatic insects and their larvae).

Plants need light energy from the Sun to live, so aquatic plants live only at those depths where light can penetrate (usually no more than 100 m). With increasing depth of habitat in plant cells, the composition of pigments that take part in the process of photosynthesis changes, which makes it possible to capture parts of the solar spectrum penetrating into the depths.

Question 3. How do organisms avoid the negative effects of low temperatures?

At low temperatures, there is a danger of metabolism stopping, so organisms have developed special adaptation mechanisms to stabilize it.

Plants are least adapted to sudden temperature fluctuations. When the temperature drops sharply below 0 °C, the water in the tissues can turn into ice, which can damage them. But plants are able to withstand small negative temperatures by binding free water molecules into complexes that are incapable of forming ice crystals (for example, by accumulating up to 20-30% sugars or fatty oils in cells).

With a gradual decrease in temperature during seasonal climate changes, a period of dormancy begins in the life of many plants, accompanied by either partial or complete death of terrestrial vegetative organs (herbaceous forms), or a temporary cessation or slowdown of the main physiological processes - photosynthesis and transport of substances.

In animals, the most reliable protection against low environmental temperatures is warm-bloodedness, but not all have it. The following ways of adaptation of animals to low temperatures can be distinguished: chemical, physical and behavioral thermoregulation.

Chemical thermoregulation is associated with an increase in heat production with decreasing temperature through the intensification of redox processes. This path requires the expenditure of a large amount of energy, so animals in harsh climatic conditions need more food. This type of thermoregulation is carried out reflexively.

Many cold-blooded animals are able to maintain optimal body temperature through muscle function. For example, in cool weather, bumblebees warm up their bodies by shivering to 32-33 °C, which gives them the opportunity to take off and feed.

Physical thermoregulation is associated with the presence of special body coverings in animals - feathers or hair, which, due to their structure, form an air gap between the body and the environment, since it is known that air is an excellent heat insulator. In addition, many animals living in harsh climatic conditions accumulate subcutaneous fat, which also has thermal insulating properties.

Behavioral thermoregulation is associated with moving in space in order to avoid temperatures unfavorable for life, creating shelters, crowding into groups, changing activity at different times of the day or year.

Question 4. What are the main features of organisms that use the bodies of other organisms as a habitat?

The living conditions inside another organism are characterized by greater constancy compared to the conditions external environment, therefore, organisms that find a place in the body of plants or animals often completely lose the organs and systems necessary for free-living species (sensory organs, organs of locomotion, digestion, etc.), but at the same time they develop adaptations for staying in the host’s body (hooks, suckers, etc.) and effective reproduction.

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Question 1. Name the main features of the life of organisms in the aquatic environment, in the land-air environment, and in the soil.

The characteristics of the life of organisms in the aquatic environment, the ground-air environment and in the soil are determined by the physical and chemical properties of these living environments. These properties have a significant impact on the action of other factors of inanimate nature - they stabilize seasonal temperature fluctuations (water and soil), gradually change illumination (water) or completely eliminate it (soil), etc.

The density of air is much lower than the density of water, so terrestrial organisms have highly developed supporting tissues - the internal and external skeleton.

Question 2. What adaptations have organisms developed for living in an aquatic environment?

The aquatic environment is denser than the air, which determines adaptations to movement in it.

Active movement in water requires a streamlined body shape and well-developed muscles (fish, cephalopods - squid, mammals - dolphins, seals).

Another way to maintain your water-salt balance is to move to places with favorable salinity levels.

And finally, the constancy of the body’s water-salt environment is ensured by water-impermeable integuments (mammals, higher crayfish, aquatic insects and their larvae).

Question 3. How do organisms avoid the negative effects of low temperatures?

At low temperatures, there is a danger of metabolism stopping, so organisms have developed special adaptation mechanisms to stabilize it.

Question 1. Name the main features of the life of organisms in the aquatic environment, in the ground-air environment, and in the soil.

The characteristics of the life of organisms in the aquatic environment, the ground-air environment and in the soil are determined by the physical and chemical properties of these living environments. These properties have a significant impact on the action of other factors of inanimate nature - they stabilize seasonal temperature fluctuations (water and soil), gradually change illumination (water) or completely eliminate it (soil), etc.

Water is a dense medium compared to air, has a buoyant force and is a good solvent. Therefore, many organisms living in water are characterized by poor development of supporting tissues (aquatic plants, protozoa, coelenterates, etc.), special methods of movement (hovering, jet propulsion), and features of respiration and adaptation. We aim to maintain a constant osmotic pressure in the cells that form their bodies.

The density of air is much lower than the density of water, so terrestrial organisms have highly developed supporting tissues - the internal and external skeleton.

Soil is the top layer of land, transformed as a result of the vital activity of living beings. Between the soil particles there are numerous cavities that can be filled with water or air. Therefore, the soil is inhabited by both aquatic and air-breathing organisms.

Question 2. What adaptations have organisms developed for living in an aquatic environment?

The aquatic environment is denser than the air, which determines adaptations to movement in it.

For active movement in water, a streamlined body shape and well-developed muscles are required (fish, cephalopods - squid, mammals - dolphins, seals).

Planktonic organisms (floating in water) have adaptations that increase their buoyancy, such as increasing the relative surface of the body due to numerous projections and bristles; decrease in density due to the accumulation of fats and gas bubbles in the body (single-cell algae, protozoa, jellyfish, small crustaceans).

Another way to maintain your water-salt balance is to move to places with a favorable level of salinity.

And finally, the constancy of the body’s water-salt environment is ensured by water-impermeable integuments (mammals, higher crayfish, aquatic insects and their larvae).

Plants need the light energy of the Sun to live, so aquatic plants live only at those depths where light can penetrate (usually no more than 100 m). With increasing depth of habitat in plant cells, the composition of pigments that take part in the process of photosynthesis changes, which makes it possible to capture parts of the solar spectrum penetrating into the depths.

Question 3. How do organisms avoid the negative effects of low temperatures?

At low temperatures, there is a danger of metabolism stopping, which is why organisms have developed special adaptation mechanisms to stabilize it.

Plants are least adapted to sudden temperature fluctuations. When the temperature drops sharply below 0°C, the water in the tissues can turn into ice, which can damage them. But plants are able to withstand small negative temperatures by binding free water molecules into complexes that are incapable of forming ice crystals (for example, by accumulating up to 20-30% sugars or fatty oils in cells).

With a gradual decrease in temperature in the process of seasonal climatic changes, a period of dormancy begins in the life of many plants, accompanied by either partial or complete death of terrestrial vegetative organs (herbaceous forms), or a temporary cessation or slowdown of the main physiological processes - photosynthesis and transport of substances.

Chemical thermoregulation is associated with an increase in heat production with a decrease in temperature through the intensification of redox processes. This path requires the expenditure of a large amount of energy, so animals in harsh climatic conditions need more food. This type of thermoregulation is carried out reflexively.

Many cold-blooded animals are able to maintain optimal body temperature through muscle work. For example, in cool weather, bumblebees warm up their bodies by shivering to 32-33 °C, which gives them the opportunity to take off and feed. Material from the site

Question 4. What are the main features of organisms that use the bodies of other organisms as a habitat?

The living conditions inside another organism are characterized by greater constancy compared to the conditions of the external environment, therefore organisms that find a place in the body of plants or animals often completely lose the organs and systems necessary for free-living species (sense organs, organs - movements, digestion, etc.), but at the same time they develop adaptations for retention in the host’s body (hooks, suction cups, etc.) and effective reproduction.

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