There are organisms that do not need oxygen. The first animals required almost no oxygen. And oxygen-free respiration is possible in the cells of the human body

1. All leaves have veins. What structures are they formed from? What is their role in the transport of substances throughout the plant?

The veins are formed by vascular-fibrous bundles that penetrate the entire plant, connecting its parts - shoots, roots, flowers and fruits. They are based on conductive tissues, which carry out the active movement of substances, and mechanical ones. Water and minerals dissolved in it move in the plant from the roots to the above-ground parts through the vessels of the wood, and organic substances move through the sieve tubes of the bast from the leaves to other parts of the plant.

In addition to conductive tissue, the vein contains mechanical tissue: fibers that give the leaf plate strength and elasticity.

2. What is the role of the circulatory system?

Blood carries nutrients and oxygen throughout the body, and removes carbon dioxide and other waste products. Thus, the blood performs the respiratory function. White blood cells perform a protective function: they destroy pathogens that enter the body.

3. What does blood consist of?

Blood consists of a colorless liquid - plasma and blood cells. There are red and white blood cells. Red blood cells give blood its red color because they contain a special substance - the pigment hemoglobin.

4. Offer simple diagrams of closed and open circulatory systems. Point out the heart, blood vessels and body cavity.

Scheme of an open circulatory system

5. Offer an experiment proving the movement of substances throughout the body.

Let us prove that substances move throughout the body using the example of a plant. Let's put a young shoot of a tree in water tinted with red ink. After 2-4 days, take the shoot out of the water, wash off the ink from it and cut off a piece of the lower part. Let us first consider a cross section of the shoot. The cut shows that the wood has turned red.

Then we cut along the rest of the shoot. Red stripes appeared in areas of stained vessels that are part of the wood.

6. Gardeners propagate some plants using cut branches. They plant the branches in the ground and cover them with a jar until they are completely rooted. Explain the meaning of the jar.

Under the can, high constant humidity is formed due to evaporation. Therefore, the plant evaporates less moisture and does not wither.

7. Why do cut flowers fade sooner or later? How can you prevent their rapid decline? Make a diagram of the transport of substances in cut flowers.

Cut flowers are not a full-fledged plant, because they have had the horse system removed, which ensured adequate (as intended by nature) absorption of water and minerals, as well as part of the leaves, which ensured photosynthesis.

The flower withers mainly because there is not enough moisture in the cut plant or flower due to increased evaporation. This begins from the moment of cutting and especially when the flower and leaves have been without water for a long time and have a large evaporation surface (cut lilac, cut hydrangea). Many greenhouse cut flowers find it difficult to tolerate the difference between the temperature and humidity of the place where they were grown and the dryness and warmth of living rooms.

But a flower can fade or grow old, this process is natural and irreversible.

To avoid fading and extend the life of flowers, a bouquet of flowers should be in a special package that serves to protect it from crushing, penetration of sunlight, and the heat of hands. On the street, it is advisable to carry the bouquet with the flowers facing down (moisture will always flow directly to the buds while the flowers are being transferred).

One of the main reasons for flowers wilting in a vase is a decrease in the sugar content in the tissues and dehydration of the plant. This happens most often due to blockage of blood vessels by air bubbles. To avoid this, the end of the stem is immersed in water and an oblique cut is made with a sharp knife or pruning shears. After this, the flower is no longer removed from the water. If such a need arises, the operation is repeated again.

Before placing cut flowers in water, remove all lower leaves from the stems, and also remove thorns from roses. This will reduce the evaporation of moisture and prevent the rapid development of bacteria in the water.

8. What is the role of root hairs? What is root pressure?

Water enters the plant through root hairs. Covered with mucus, in close contact with the soil, they absorb water with minerals dissolved in it.

Root pressure is the force that causes one-way movement of water from roots to shoots.

9. What is the significance of water evaporation from leaves?

Once in the leaves, water evaporates from the surface of the cells and exits into the atmosphere in the form of steam through the stomata. This process ensures a continuous upward flow of water through the plant: having given up water, the cells of the leaf pulp, like a pump, begin to intensively absorb it from the vessels surrounding them, where water enters through the stem from the root.

10. In the spring, the gardener discovered two damaged trees. In one, mice partially damaged the bark; in another, hares gnawed a ring on the trunk. Which tree can die?

A tree whose trunk has been gnawed by hares may die. As a result, the inner layer of bark, called the bast, will be destroyed. Solutions of organic substances move through it. Without their influx, cells below the damage will die.

The cambium lies between the bark and wood. In spring and summer, the cambium divides vigorously, resulting in new phloem cells being deposited toward the bark and new wood cells toward the wood. Therefore, the life of the tree will depend on whether the cambium is damaged.

You probably know that breathing is necessary so that the oxygen necessary for life enters the body with the inhaled air, and when exhaling, the body releases carbon dioxide.

All living things breathe - animals, birds, and plants.

Why do living organisms need oxygen so much that life is impossible without it? And where does carbon dioxide come from in cells, from which the body needs to constantly get rid of?

The fact is that each cell of a living organism represents a small but very active biochemical production. Do you know that no production is possible without energy. All processes that occur in cells and tissues occur with the consumption of large amounts of energy.

Where does it come from?

With the food we eat - carbohydrates, fats and proteins. In cells these substances oxidize. Most often, a chain of transformations of complex substances leads to the formation of a universal source of energy - glucose. As a result of the oxidation of glucose, energy is released. Oxygen is precisely what is needed for oxidation. The energy that is released as a result of these reactions is stored by the cell in the form of special high-energy molecules - they, like batteries or accumulators, release energy as needed. And the end product of nutrient oxidation is water and carbon dioxide, which are removed from the body: from the cells it enters the blood, which carries carbon dioxide to the lungs, and there it is expelled out during exhalation. In one hour, a person releases from 5 to 18 liters of carbon dioxide and up to 50 grams of water through the lungs.

By the way...

High-energy molecules that are the “fuel” for biochemical processes are called ATP - adenosine triphosphoric acid. In humans, the lifespan of one ATP molecule is less than 1 minute. The human body synthesizes about 40 kg of ATP per day, but all of it is almost immediately spent, and practically no ATP reserve is created in the body. For normal life, it is necessary to constantly synthesize new ATP molecules. That is why, without oxygen, a living organism can live for a maximum of a few minutes.

Are there living organisms that do not need oxygen?

Each of us is familiar with the processes of anaerobic respiration! Thus, the fermentation of dough or kvass is an example of an anaerobic process carried out by yeast: they oxidize glucose to ethanol (alcohol); the process of souring milk is the result of the work of lactic acid bacteria, which carry out lactic acid fermentation - convert milk sugar lactose into lactic acid.

Why do you need oxygen breathing if oxygen-free breathing is available?

Then, aerobic oxidation is many times more effective than anaerobic oxidation. Compare: during the anaerobic breakdown of one glucose molecule, only 2 ATP molecules are formed, and as a result of the aerobic breakdown of a glucose molecule, 38 ATP molecules are formed! For complex organisms with high speed and intensity of metabolic processes, anaerobic respiration is simply not enough to maintain life - for example, an electronic toy that requires 3-4 batteries to operate simply will not turn on if only one battery is inserted into it.

Is oxygen-free respiration possible in the cells of the human body?

Certainly! The first stage of the breakdown of the glucose molecule, called glycolysis, takes place without the presence of oxygen. Glycolysis is a process common to almost all living organisms. During glycolysis, pyruvic acid (pyruvate) is formed. It is she who sets off on the path of further transformations leading to the synthesis of ATP during both oxygen and oxygen-free respiration.

Thus, ATP reserves in muscles are very small - they are only enough for 1-2 seconds of muscle work. If a muscle needs short-term but active activity, anaerobic respiration is the first to be mobilized in it - it is activated faster and provides energy for about 90 seconds of active muscle work. If the muscle works actively for more than two minutes, then aerobic respiration kicks in: with it, ATP production occurs slowly, but it provides enough energy to maintain physical activity for a long time (up to several hours).

Biologists have discovered multicellular creatures in the Mediterranean Sea that do not use oxygen for their vital functions. Until now, it was believed that oxygen-free metabolism is characteristic only of unicellular organisms and viruses. The researchers' article, in which they describe unusual creatures, appeared in the journal BMC Biology. The Nature News portal writes briefly about the work.

Creatures measuring less than one millimeter live at depths of more than 3 thousand meters. They belong to the group Loricifera, microscopic marine invertebrates. Outwardly, they look like bags, from the opening of which “tentacles” emerge.

Previously, researchers had already found multicellular organisms in places deprived of oxygen, but experts were not sure whether they lived there permanently. The authors of the new work believe that the loricifera they discovered always live in an extremely oxygen-depleted environment.

“Ordinary” multicellular organisms obtain energy using special organelles called mitochondria, which require oxygen to function. Loricephera, found in the Mediterranean Sea, obtain energy using other organelles - hydrogenosomes. Hydrogenosomes do not require oxygen to function, and they are also present in microorganisms living in the absence of O2.

Details

Based on materials: Lenta.ru

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Oxygen is necessarily included in living matter. It is unlikely that it can be replaced in living systems by any other element.

But in addition to chemically bound oxygen, the vast majority of organisms also need free molecular oxygen for respiration.

The fact that oxygen is used in respiration, and not other gases, is explained by its properties: oxygen easily enters into chemical compounds with many substances, and these reactions are accompanied by the release of thermal energy. Sometimes, for example, luminous animals and bacteria also release light energy. There is no other substance that, when reacting with body substances, would ensure the release of such large amounts of energy.

Atmospheric oxygen is especially necessary for higher animals. Birds and land mammals cannot live without it even for a few minutes. Aquatic mammals, adapted to long stays under water (from 15 minutes to 1 hour 45 minutes), actually use it no less, since they create a supply of air in the lungs.

Thus, on planets whose atmosphere is devoid of or contains little oxygen, there can hardly be creatures similar to the animals of the Earth. However, let’s not prejudge the question and let’s see whether life can exist at all without atmospheric oxygen or with a small amount of it.

According to a number of scientists, oxygen in the Earth's atmosphere appeared as a result of the life of green plants. Apparently, when life on our planet was just beginning, there was no oxygen in its atmosphere. The first organisms from which plants subsequently emerged did not require free oxygen; they were anaerobic. Primary green plants, obviously, also did not yet have the function of respiration. This process arose only at the next stage of evolution.

Among modern organisms there are also many anaerobic ones. These are some bacteria and yeasts. They do not breathe oxygen, but receive energy from the oxidation of various substances. This is “oxygen-free respiration,” or fermentation. There are types of microbes for which oxygen is poisonous and causes death; There are also those who can live without oxygen, but when it is available, they use it for respiration, which goes along with fermentation.

In green plants and lower animals, the relationship to oxygen is also extremely diverse. All green plants respire, but fluctuations in the amount of oxygen in the environment do not have a noticeable effect on the rate of respiration. Only when its content in the atmosphere decreases to 2-1% (10-20 times less than normal) does the respiration rate of most plant species decrease. At the same time, anaerobic metabolism begins, due to which the plant can live for some time even in the complete absence of oxygen.

The oxygen requirement of aquatic plants is even less, since water usually contains significantly less oxygen than the atmosphere. The water in some reservoirs contains 2000 times less oxygen than in the air.

Finally, some new studies show that in the internal tissues of a plant the composition of the gaseous environment is often devoid of even a remote resemblance to the usual composition of air. Respiration here is close to anaerobic. Among animals, many protozoa and multicellular invertebrates also live and reproduce with an insignificant amount of oxygen and even in its complete absence Dozens of species and ciliates, amoebas and flagellates, living in almost oxygen-deprived silts, in sewage, in stagnant lake water, are constantly in essentially anaerobic conditions. Most of them can live in the presence of oxygen, but from an oxygen-rich environment, they crowd out other organisms.

With negligible or even complete absence of oxygen in the environment, some roundworms, species of crustaceans (for example, copepods) and elasmobranch mollusks can live. Even among insects there are aquatic forms that live with little or no oxygen in the water. These are, for example, the larvae of one species of beetle (Donacia), chironomus mosquito (Chironomus thummi) and others. The development of chironomus larvae can reach fledging in water containing 0.3 mg of oxygen per liter, i.e. 1000 times less than in ordinary air

All higher vertebrates need oxygen for breathing, but even in them, individual body cells can temporarily switch to anaerobic metabolism, and the cells of some tissues generally require a small amount of oxygen. Essentially, only the cells of the central nervous system of vertebrates are very sensitive to a lack of oxygen.

The need for oxygen in humans and higher animals also fluctuates depending on adaptation to a particular environment.

Sheep, accustomed to mountain conditions, feel normal at an altitude of 4000 m, where oxygen is 35-40% less than at sea level.

About 6000 m above sea level lies the highest limit of life for most animals. Only a few species of mouse-like rodents and birds of prey are found at such high altitudes. But it is unlikely that only the rarefied atmosphere and lack of oxygen hinder their life even more. The development of life here is, of course, hampered by low temperatures and eternal ice, lack of soil and plant food, strong winds, etc.

For a person adapted to life on the plain, a decrease in pressure and the amount of oxygen causes severe disorders - mountain sickness. However, after special training, a person can rise and stay for some time at an altitude of 7000-8000 m. At the heights of Tibet and in the Andes (at an altitude of 5300 m) there are permanent human settlements, showing that a person can adapt to half the oxygen content in the atmosphere compared with that available at sea level.

In these people, all body tissues absorb oxygen much more energetically, their hemoglobin content and oxygen capacity of the blood are increased.

In experiments with animals, it was found that during acclimatization in mountain conditions, an energetic “struggle” occurs in the body for the delivery of oxygen to the tissues. Cells begin to use oxygen more fully due to increased activity of oxidative enzymes. In addition, tissues become more tolerant of a lack of oxygen and can even switch to an anaerobic type of respiration.

In the laboratory, studies were carried out on insects, it turned out that in species of insects living at sea level, where the pressure is about 760 mm Hg, the heart stops working at a pressure of 25-20 mm Hg. They can still live if the oxygen is 30 times higher less than in the atmosphere But the species living in the mountains at an altitude of 1000 m are much more stable. Their heart pulsation was still observed at a pressure of 15 mm of mercury. In insects that live at even higher altitudes (3200 m), the heart stopped only at a pressure of 5 mm of mercury. , i.e. at such rarefaction of the atmosphere, which exists approximately at an altitude of 100-200 km from the Earth.

So, the possibilities for living with a lack of oxygen for terrestrial organisms are quite large. But at the same time, most of them have a sharp decrease in activity. Without getting ahead of ourselves and without going into a discussion of the issue of life outside the Earth, we will nevertheless point out that, for example, on Mars the need of organisms for oxygen, with the same vital energy, may be less than on Earth. The fact is that due to the smaller size and lower density of Mars, the gravity from it is almost 3 times less than on Earth, and the functioning of organs will require significantly less energy obtained through respiration. In addition, at low environmental temperatures, tissues and cells are saturated with oxygen with less oxygen in the environment.

Finally, it is known that the cells of organisms are capable of accumulating and using elements found in nature in extremely small quantities, in a dispersed state. Therefore, it would not be surprising if, with a small amount of oxygen in the environment, organisms develop various adaptations to capture oxygen.

This means that if on the planets accessible to our study there is so little oxygen that it cannot be detected from Earth using spectral analysis, this is not yet a reason to deny the possibility of life on them. Of course, a small amount of oxygen sets limits for the existence of animals like our vertebrates, with their high energy level of metabolism and higher nervous activity. But organisms of a different structure can exist.

The judgment about what life can be like with a small amount of oxygen does not need to be simplified. If it were possible to establish that in previous eras there was more oxygen of biogenic origin in the atmosphere of Mars than now, then it would be necessary to assume that life on Mars became poorer, but at the same time a few highly specialized forms could arise.

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