What processes provide the cell with energy. Life processes in a cell. Topic: Cellular level
Tasks of parts C1-C4
1. What environmental factors contribute to the regulation of the number of wolves in the ecosystem?
Answer:
1) anthropogenic: reduction of forest area, excessive hunting;
2) biotic: lack of food, competition, spread of diseases.
2. Determine the type and phase of division of the cell shown in the figure. What processes occur in this phase?
Answer:
1) the figure shows metaphase of mitosis;
2) spindle threads are attached to the centromeres of chromosomes;
3) in this phase, bichromatid chromosomes line up in the equatorial plane.
3. Why does plowing the soil improve the living conditions of cultivated plants?
Answer:
1) promotes the destruction of weeds and reduces competition with cultivated plants;
2) promotes the supply of plants with water and minerals;
3) increases the supply of oxygen to the roots.
4. How does a natural ecosystem differ from an agroecosystem?
Answer:
1) great biodiversity and diversity of food connections and food chains;
2) balanced circulation of substances;
3) long periods of existence.
5. Reveal the mechanisms that ensure the constancy of the number and shape of chromosomes in all cells of organisms from generation to generation?
Answer:
1) thanks to meiosis, gametes with a haploid set of chromosomes are formed;
2) during fertilization, the diploid set of chromosomes is restored in the zygote, which ensures the constancy of the chromosome set;
3) the growth of the organism occurs due to mitosis, which ensures the constancy of the number of chromosomes in somatic cells.
6. What is the role of bacteria in the cycle of substances?
Answer:
1) heterotrophic bacteria - decomposers decompose organic substances into minerals, which are absorbed by plants;
2) autotrophic bacteria (photo, chemotrophs) - producers synthesize organic substances from inorganic ones, ensuring the circulation of oxygen, carbon, nitrogen, etc.
7. What features are characteristic of mossy plants?
Answer:
2) mosses reproduce both sexually and asexually with alternating generations: sexual (gametophyte) and asexual (sporophyte);
3) an adult moss plant is the sexual generation (gametophyte) and the capsule with spores is asexual (sporophyte);
4) fertilization occurs in the presence of water.
8. Squirrels, as a rule, live in coniferous forests and feed mainly on spruce seeds. What biotic factors can lead to a decline in the squirrel population?
9. It is known that the Golgi apparatus is especially well developed in the glandular cells of the pancreas. Explain why.
Answer:
1) pancreatic cells synthesize enzymes that accumulate in the cavities of the Golgi apparatus;
2) in the Golgi apparatus, enzymes are packaged in the form of vesicles;
3) from the Golgi apparatus, enzymes are carried into the pancreatic duct.
10. Ribosomes from different cells, the entire set of amino acids and identical molecules of mRNA and tRNA were placed in a test tube, and all conditions for protein synthesis were created. Why will one type of protein be synthesized on different ribosomes in a test tube?
Answer:
1) the primary structure of a protein is determined by the sequence of amino acids;
2) the templates for protein synthesis are identical mRNA molecules, in which the same primary protein structure is encoded.
11. What structural features are characteristic of representatives of the Chordata type?
Answer:
1) internal axial skeleton;
2) the nervous system in the form of a tube on the dorsal side of the body;
3) cracks in the digestive tube.
12. Clover grows in a meadow and is pollinated by bumblebees. What biotic factors can lead to a decline in clover populations?
Answer:
1) decrease in the number of bumblebees;
2)increase in the number of herbivorous animals;
3) propagation of competitor plants (cereals, etc.).
13. The total mass of mitochondria in relation to the mass of cells of various rat organs is: in the pancreas - 7.9%, in the liver - 18.4%, in the heart - 35.8%. Why do the cells of these organs have different mitochondrial content?
Answer:
1) mitochondria are the energy stations of the cell; ATP molecules are synthesized and accumulated in them;
2) intense work of the heart muscle requires a lot of energy, therefore the content of mitochondria in its cells is the highest;
3) in the liver the number of mitochondria is higher compared to the pancreas, since it has a more intense metabolism.
14. Explain why beef that has not passed sanitary control is dangerous to eat undercooked or lightly cooked.
Answer:
1) beef meat may contain bovine tapeworms;
2) an adult worm develops from the finna in the digestive canal, and the person becomes the final host.
15. Name the plant cell organelle shown in the figure, its structures indicated by numbers 1-3, and their functions.
Answer:
1) the organelle depicted is a chloroplast;
2) 1 - grana thylakoids, involved in photosynthesis;
3) 2 - DNA, 3 - ribosomes, participate in the synthesis of the chloroplast's own proteins.
16. Why can’t bacteria be classified as eukaryotes?
Answer:
1) in their cells, the nuclear substance is represented by one circular DNA molecule and is not separated from the cytoplasm;
2) do not have mitochondria, the Golgi complex, or the ER;
3) do not have specialized germ cells, there is no meiosis and fertilization.
17. What changes in biotic factors can lead to an increase in the population of a naked slug that lives in a forest and feeds mainly on plants?
18. The process of photosynthesis occurs intensively in the leaves of plants. Does it occur in ripe and unripe fruits? Explain your answer.
Answer:
1) photosynthesis occurs in unripe fruits (while they are green), since they contain chloroplasts;
2) as they mature, chloroplasts turn into chromoplasts, in which photosynthesis does not occur.
19. What stages of gametogenesis are indicated in the figure by the letters A, B and C? What set of chromosomes do cells have at each of these stages? What specialized cells does this process lead to the development of?
Answer:
1)A - stage (zone) of reproduction (division), diploid cells;
2)B - stage (zone) of growth, diploid cell;
3) B - stage (zone) of maturation, the cells are haploid, sperm develop.
20. How do bacterial cells differ in structure from the cells of organisms in other kingdoms of living nature? List at least three differences.
Answer:
1) there is no formed nucleus, nuclear envelope;
2) a number of organelles are missing: mitochondria, EPS, Golgi complex, etc.;
3) have one ring chromosome.
21. Why are plants (producers) considered the initial link in the cycle of substances and energy conversion in the ecosystem?
Answer:
1) create organic substances from inorganic ones;
2) accumulate solar energy;
3) provide organic substances and energy to organisms in other parts of the ecosystem.
22. What processes ensure the movement of water and minerals throughout the plant?
Answer:
1) from the root to the leaves, water and minerals move through the vessels due to transpiration, as a result of which suction force arises;
2) the upward flow in the plant is facilitated by root pressure, which arises as a result of the constant flow of water into the root due to the difference in the concentration of substances in the cells and the environment.
23. Look at the cells shown in the figure. Determine which letters represent prokaryotic and eukaryotic cells. Provide evidence for your point of view.
Answer:
1) A - prokaryotic cell, B - eukaryotic cell;
2) the cell in Figure A does not have a formed nucleus, its hereditary material is represented by a ring chromosome;
3) the cell in Figure B has a formed nucleus and organelles.
24. What is the complexity of the circulatory system of amphibians compared to fish?
Answer:
1) the heart becomes three-chambered;
2) a second circle of blood circulation appears;
3) the heart contains venous and mixed blood.
25. Why is a mixed forest ecosystem considered more stable than a spruce forest ecosystem?
Answer:
1) there are more species in the mixed forest than in the spruce forest;
2) in a mixed forest the food chains are longer and more branched than in a spruce forest;
3) there are more tiers in a mixed forest than in a spruce forest.
26. A section of a DNA molecule has the following composition: GATGAATAGTGCTTC. List at least three consequences that can result from an accidental replacement of the seventh nucleotide of thymine with cytosine (C).
Answer:
1) a gene mutation will occur - the codon of the third amino acid will change;
2) in a protein, one amino acid may be replaced by another, as a result of which the primary structure of the protein will change;
3) all other protein structures may change, which will lead to the appearance of a new trait in the body.
27. Red algae (purple algae) live at great depths. Despite this, photosynthesis occurs in their cells. Explain why photosynthesis occurs if the water column absorbs rays from the red-orange part of the spectrum.
Answer:
1) photosynthesis requires rays not only from the red, but also from the blue part of the spectrum;
2) the cells of scarlet mushrooms contain a red pigment that absorbs rays from the blue part of the spectrum, their energy is used in the process of photosynthesis.
28. Find errors in the given text. Indicate the numbers of the sentences in which errors were made and correct them.
1. Coelenterates are three-layer multicellular animals. 2.They have a gastric or intestinal cavity. 3. The intestinal cavity includes stinging cells. 4. Coelenterates have a reticular (diffuse) nervous system. 5. All coelenterates are free-swimming organisms.
1)1 - coelenterates - two-layer animals;
2)3 - stinging cells are contained in the ectoderm, and not in the intestinal cavity;
3)5 - among the coelenterates there are attached forms.
29. How does gas exchange occur in the lungs and tissues of mammals? What causes this process?
Answer:
1) gas exchange is based on diffusion, which is caused by the difference in gas concentration (partial pressure) in the air of the alveoli and in the blood;
2) oxygen from the area of high pressure in the alveolar air enters the blood, and carbon dioxide from the area of high pressure in the blood enters the alveoli;
3) in tissues, oxygen from the area of high pressure in the capillaries enters the intercellular substance and then into the cells of the organs. Carbon dioxide from the high pressure area in the intercellular substance enters the blood.
30. What is the participation of functional groups of organisms in the cycle of substances in the biosphere? Consider the role of each of them in the cycle of substances in the biosphere.
Answer:
1) producers synthesize organic substances from inorganic substances (carbon dioxide, water, nitrogen, phosphorus and other minerals), release oxygen (except for chemotrophs);
2) consumers (and other functional groups) of organisms use and transform organic substances, oxidize them during respiration, absorbing oxygen and releasing carbon dioxide and water;
3) decomposers decompose organic substances into inorganic compounds of nitrogen, phosphorus, etc., returning them to the environment.
31. The section of the DNA molecule encoding the sequence of amino acids in a protein has the following composition: G-A-T-G-A-A-T-A-G-TT-C-T-T-C. Explain the consequences of accidentally adding a guanine nucleotide (G) between the seventh and eighth nucleotides.
Answer:
1) a gene mutation will occur - the codes of the third and subsequent amino acids may change;
2) the primary structure of the protein may change;
3) a mutation can lead to the appearance of a new trait in an organism.
32. What plant organs are damaged by cockchafers at different stages of individual development?
Answer:
1) plant roots are damaged by larvae;
2) tree leaves are damaged by adult beetles.
33. Find errors in the given text. Indicate the numbers of the sentences in which errors were made and correct them.
1. Flatworms are three-layered animals. 2. The phylum Flatworms include white planaria, human roundworm and liver fluke. 3. Flatworms have an elongated, flattened body. 4. They have a well-developed nervous system. 5. Flatworms are dioecious animals that lay eggs.
Errors were made in the sentences:
1)2 - the human roundworm is not classified as a Flatworm; it is a Roundworm;
2)4 - in flatworms the nervous system is poorly developed;
3)5 - Flatworms are hermaphrodites.
34. What is a fruit? What is its significance in the life of plants and animals?
Answer:
1) fruit - the generative organ of angiosperms;
2) contains seeds with the help of which plants reproduce and disperse;
3) plant fruits are food for animals.
35. Most bird species fly away from the northern regions for the winter, despite their warm-blooded nature. Indicate at least three factors that cause these animals to fly.
Answer:
1) food items of insectivorous birds become unavailable for obtaining;
2) ice cover on reservoirs and snow cover on the ground deprive herbivorous birds of food;
3) change in daylight hours.
36. Which milk, sterilized or freshly milked, will sour faster under the same conditions? Explain your answer.
Answer:
1) freshly milked milk will sour faster, since it contains bacteria that cause fermentation of the product;
2) when milk is sterilized, the cells and spores of lactic acid bacteria die, and the milk lasts longer.
37. Find errors in the given text. Indicate the numbers of sentences in which errors were made and explain them.
1. The main classes of phylum arthropods are Crustaceans, Arachnids and Insects. 2. The body of crustaceans and arachnids is divided into the head, thorax and abdomen. 3. The body of insects consists of a cephalothorax and abdomen. 4. Arachnids do not have antennae. 5. Insects have two pairs of antennae, and crustaceans have one pair.
Errors were made in the sentences:
1)2 - the body of crustaceans and arachnids consists of a cephalothorax and abdomen;
2)3 - the body of insects consists of a head, chest and abdomen;
3)5 - insects have one pair of antennae, and crustaceans have two pairs.
38. Prove that the rhizome of a plant is a modified shoot.
Answer:
1) the rhizome has nodes in which rudimentary leaves and buds are located;
2) at the top of the rhizome there is an apical bud that determines the growth of the shoot;
3) adventitious roots extend from the rhizome;
4) the internal anatomical structure of the rhizome is similar to the stem.
39. To combat insect pests, people use chemicals. Indicate at least three changes in the life of the oak forest if all herbivorous insects are destroyed by chemical means. Explain why they will happen.
Answer:
1) the number of insect-pollinated plants will sharply decrease, since herbivorous insects are plant pollinators;
2) the number of insectivorous organisms (consumers of the 2nd order) will sharply decrease or they will disappear due to disruption of food chains;
3) some of the chemicals used to kill insects will get into the soil, which will lead to disruption of plant life, death of soil flora and fauna, all violations can lead to the death of the oak forest.
40. Why can treatment with antibiotics lead to intestinal dysfunction? Give at least two reasons.
Answer:
1) antibiotics kill beneficial bacteria living in the human intestines;
2) the breakdown of fiber, water absorption and other processes are disrupted.
41.Which part of the sheet is indicated in the figure by the letter A and what structures does it consist of? What functions do these structures perform?
1) the letter A denotes a vascular-fibrous bundle (vein), the bundle includes vessels, sieve tubes, and mechanical tissue;
2) vessels provide transport of water to the leaves;
3) sieve tubes provide transport of organic substances from leaves to other organs;
4) mechanical tissue cells provide strength and serve as the framework of the leaf.
42. What are the characteristic features of the fungal kingdom?
Answer:
1) the body of fungi consists of threads - hyphae, forming a mycelium;
2) reproduce sexually and asexually (spores, mycelium, budding);
3) grow throughout life;
4) in the cell: the membrane contains a chitin-like substance, a reserve nutrient is glycogen.
43. In a small reservoir formed after a river flood, the following organisms were found: slipper ciliates, daphnia, white planaria, large pond snail, cyclops, hydra. Explain whether this body of water can be considered an ecosystem. Provide at least three pieces of evidence.
Answer:
The named temporary reservoir cannot be called an ecosystem, since it contains:
1) there are no producers;
2) there are no decomposers;
3) there is no closed circulation of substances and food chains are disrupted.
44. Why is a note placed under a tourniquet, which is applied to stop bleeding from large blood vessels, indicating the time it was applied?
Answer:
1) after reading the note, you can determine how much time has passed since the tourniquet was applied;
2) if after 1-2 hours it was not possible to deliver the patient to the doctor, then the tourniquet should be loosened for a while. This will prevent tissue death.
45. Name the structures of the spinal cord, indicated in the figure by numbers 1 and 2, and describe the features of their structure and functions.
Answer:
1)1 - gray matter, formed by the bodies of neurons;
2) 2 - white matter, formed by long processes of neurons;
3) gray matter performs a reflex function, white matter - a conductive function.
46. What role do the salivary glands play in digestion in mammals? List at least three functions.
Answer:
1) the secretion of the salivary glands moistens and disinfects food;
2) saliva participates in the formation of the food bolus;
3) salivary enzymes promote the breakdown of starch.
47. As a result of volcanic activity, an island was formed in the ocean. Describe the sequence of formation of an ecosystem on a newly formed landmass. Please provide at least three items.
Answer:
1) the first to settle are microorganisms and lichens, which ensure the formation of soil;
2) plants settle on the soil, the spores or seeds of which are carried by wind or water;
3) as vegetation develops, animals appear in the ecosystem, primarily arthropods and birds.
48. Experienced gardeners apply fertilizers into the grooves located along the edges of the trunk circles of fruit trees, rather than distributing them evenly. Explain why.
Answer:
1) the root system grows, the suction zone moves behind the root apex;
2) roots with a developed absorption zone - root hairs - are located at the edges of the trunk circles.
49. What modified shoot is shown in the figure? Name the structural elements indicated in the figure by numbers 1, 2, 3, and the functions that they perform.
Answer:
1) onion;
2)1 - a succulent scale-like leaf in which nutrients and water are stored;
3)2 - adventitious roots, ensuring the absorption of water and minerals;
4)3 - bud, ensures shoot growth.
50. What are the structural features and vital functions of mosses? Please provide at least three items.
Answer:
1) most mosses are leafy plants, some of them have rhizoids;
2) mosses have a poorly developed conducting system;
3) mosses reproduce both sexually and asexually, with alternating generations: sexual (gametophyte) and asexual (sporophyte); An adult moss plant is the sexual generation, and the spore capsule is asexual.
51. As a result of a forest fire, part of the spruce forest burned out. Explain how its self-healing will occur. List at least three steps.
Answer:
1) herbaceous, light-loving plants develop first;
2) then birch, aspen, and pine shoots appear, the seeds of which fell with the help of the wind, and a small-leaved or pine forest is formed.
3) under the canopy of light-loving species, shade-tolerant spruce trees develop, which subsequently completely displace other trees.
52. To establish the cause of a hereditary disease, the patient’s cells were examined and a change in the length of one of the chromosomes was discovered. What research method allowed us to establish the cause of this disease? What type of mutation is it associated with?
Answer:
1) the cause of the disease was established using the cytogenetic method;
2) the disease is caused by a chromosomal mutation - the loss or addition of a chromosome fragment.
53. What letter in the figure indicates the blastula in the development cycle of the lancelet. What are the features of blastula formation?
Answer:
1) the blastula is designated by the letter G;
2) the blastula is formed during the fragmentation of the zygote;
3) the size of the blastula does not exceed the size of the zygote.
54. Why are mushrooms classified as a special kingdom of the organic world?
Answer:
1) the body of mushrooms consists of thin branching threads - hyphae, forming mycelium, or mycelium;
2) mycelial cells store carbohydrates in the form of glycogen;
3) mushrooms cannot be classified as plants, since their cells do not have chlorophyll and chloroplasts; the wall contains chitin;
4) mushrooms cannot be classified as animals, since they absorb nutrients over the entire surface of the body, and do not swallow them in the form of food lumps.
55. In some forest biocenoses, to protect chicken birds, mass shooting of daytime birds of prey was carried out. Explain how this event affected the number of chickens.
Answer:
1) at first, the number of chickens increased, as their enemies were destroyed (naturally regulating the number);
2) then the number of chickens decreased due to lack of food;
3) the number of sick and weakened individuals increased due to the spread of diseases and the lack of predators, which also affected the decrease in the number of chickens.
56. The color of the white hare’s fur changes throughout the year: in winter the hare is white, and in summer it is gray. Explain what type of variability is observed in the animal and what determines the manifestation of this trait.
Answer:
1) the hare exhibits modification (phenotypic, non-hereditary) variability;
2) the manifestation of this trait is determined by changes in environmental conditions (temperature, day length).
57. Name the stages of embryonic development of the lancelet, indicated in the figure by letters A and B. Reveal the features of the formation of each of these stages.
A B
Answer:
1) A - gastrula - stage of a two-layer embryo;
2) B - neurula, has the rudiments of a future larva or adult organism;
3) the gastrula is formed by invagination of the wall of the blastula, and in the neurula the neural plate is first formed, which serves as a regulator for the formation of other organ systems.
58. Name the main features of the structure and activity of bacteria. List at least four features.
Answer:
1) bacteria - prenuclear organisms that do not have a formed nucleus and many organelles;
2) according to the method of nutrition, bacteria are heterotrophs and autotrophs;
3) high rate of reproduction by division;
4) anaerobes and aerobes;
5) unfavorable conditions are experienced in a state of dispute.
59. How does the land-air environment differ from the water environment?
Answer:
1) oxygen content;
2) differences in temperature fluctuations (wide amplitude of fluctuations in the ground-air environment);
3) degree of illumination;
4) density.
Answer:
1) seaweed has the property of accumulating the chemical element iodine;
2) iodine is necessary for normal thyroid function.
61. Why is a ciliate slipper cell considered an integral organism? What organelles of the ciliate slipper are indicated in the figure by numbers 1 and 2 and what functions do they perform?
Answer:
1) the ciliate cell performs all the functions of an independent organism: metabolism, reproduction, irritability, adaptation;
2) 1 - small nucleus, participates in the sexual process;
3) 2 - large nucleus, regulates vital processes.
61. What are the structural features and vital functions of mushrooms? Please indicate at least three characteristics.
62. Explain how acid rain harms plants. Give at least three reasons.
Answer:
1) directly damage plant organs and tissues;
2) pollute the soil, reduce fertility;
3)reduce plant productivity.
63. Why are passengers recommended to suck lollipops when taking off or landing an airplane?
Answer:
1) rapid changes in pressure during takeoff or landing of an airplane cause discomfort in the middle ear, where the initial pressure on the eardrum persists longer;
2) swallowing movements improve air access to the auditory (Eustachian) tube, through which the pressure in the middle ear cavity is equalized with the pressure in the environment.
64. How does the circulatory system of arthropods differ from the circulatory system of annelids? Indicate at least three signs that prove these differences.
Answer:
1) arthropods have an open circulatory system, while annelids have a closed circulatory system;
2) arthropods have a heart on the dorsal side;
3) annelids do not have a heart; its function is performed by a ring vessel.
65. What type of animal is the one shown in the picture? What is indicated by numbers 1 and 2? Name other representatives of this type.
Answer:
1) to the type Coelenterates;
2) 1 - ectoderm, 2 - intestinal cavity;
3) coral polyps, jellyfish.
66. How are morphological, physiological and behavioral adaptations to environmental temperature manifested in warm-blooded animals?
Answer:
1) morphological: heat-insulating covers, subcutaneous layer of fat, changes in the surface of the body;
2) physiological: increased intensity of evaporation of sweat and moisture during breathing; narrowing or dilation of blood vessels, changes in metabolic levels;
3) behavioral: construction of nests, burrows, changes in daily and seasonal activity depending on environmental temperature.
67. How is genetic information transferred from the nucleus to the ribosome?
Answer:
1) mRNA synthesis occurs in the nucleus in accordance with the principle of complementarity;
2) mRNA - a copy of a DNA section containing information about the primary structure of the protein, moves from the nucleus to the ribosome.
68. How is the complexity of ferns compared to mosses? Give at least three signs.
Answer:
1) the ferns have roots;
2) ferns, unlike mosses, have developed developed conductive tissue;
3) in the development cycle of ferns, the asexual generation (sporophyte) predominates over the sexual generation (gametophyte), which is represented by the prothallus.
69. Name the germ layer of a vertebrate animal, indicated in the figure by number 3. What type of tissue and what organs are formed from it.
Answer:
1) germ layer - endoderm;
2 epithelial tissue (epithelium of the intestines and respiratory organs);
3) organs: intestines, digestive glands, respiratory organs, some endocrine glands.
70. What role do birds play in the forest biocenosis? Give at least three examples.
Answer:
1) regulate the number of plants (distribute fruits and seeds);
2) regulate the number of insects and small rodents;
3) serve as food for predators;
4) fertilize the soil.
71. What is the protective role of leukocytes in the human body?
Answer:
1) leukocytes are capable of phagocytosis - devouring and digesting proteins, microorganisms, dead cells;
2) leukocytes take part in the production of antibodies that neutralize certain antigens.
72. Find errors in the given text. Indicate the numbers of the sentences in which they are made, correct them.
According to the chromosomal theory of heredity:
1. Genes are located on chromosomes in linear order. 2. Each occupies a specific place - an allele. 3. Genes on one chromosome form a linkage group. 4. The number of linkage groups is determined by the diploid number of chromosomes. 5. Disruption of gene cohesion occurs during the process of chromosome conjugation in the prophase of meiosis.
Errors were made in the sentences:
1)2 - location of the gene - locus;
2)4 - the number of linkage groups is equal to the haploid set of chromosomes;
3)5 - disruption of gene linkage occurs during crossing over.
73. Why do some scientists classify green euglena as a plant, and others as an animal? Provide at least three reasons.
Answer:
1) capable of heterotrophic nutrition, like all animals;
2) capable of active movement in search of food, like all animals;
3) contains chlorophyll in the cell and is capable of autotrophic nutrition, like plants.
74. What processes occur at the stages of energy metabolism?
Answer:
1) at the preparatory stage, complex organic substances are broken down into less complex ones (biopolymers - into monomers), energy is dissipated in the form of heat;
2) in the process of glycolysis, glucose is broken down into pyruvic acid (or lactic acid, or alcohol) and 2 ATP molecules are synthesized;
3) at the oxygen stage, pyruvic acid (pyruvate) is broken down into carbon dioxide and water and 36 ATP molecules are synthesized.
75. In a wound formed on the human body, bleeding stops over time, but suppuration may occur. Explain what properties of blood this is due to.
Answer:
1) bleeding stops due to blood clotting and the formation of a blood clot;
2) suppuration is caused by the accumulation of dead leukocytes that have carried out phagocytosis.
76. Find errors in the given text and correct them. Indicate the numbers of sentences in which errors were made and explain them.
1. Proteins are of great importance in the structure and functioning of organisms. 2. These are biopolymers whose monomers are nitrogenous bases. 3. Proteins are part of the plasma membrane. 4. Many proteins perform enzymatic functions in the cell. 5. Hereditary information about the characteristics of the organism is encrypted in protein molecules. 6. Protein and tRNA molecules are part of ribosomes.
Errors were made in the sentences:
1)2 - monomers of proteins are amino acids;
2)5 - hereditary information about the characteristics of an organism is encrypted in DNA molecules;
3)6- ribosomes contain rRNA molecules, not tRNA.
77. What is myopia? In what part of the eye does the image focus in a nearsighted person? What is the difference between congenital and acquired forms of myopia?
Answer:
1) myopia is a disease of the visual organs in which a person has difficulty distinguishing distant objects;
2) in a myopic person, the image of objects appears in front of the retina;
3) with congenital myopia, the shape of the eyeball changes (lengthens);
4) acquired myopia is associated with a change (increase) in the curvature of the lens.
78. How does the skeleton of the human head differ from the skeleton of the head of great apes? List at least four differences.
Answer:
1) predominance of the cerebral part of the skull over the facial part;
2) reduction of the jaw apparatus;
3) the presence of a chin protuberance on the lower jaw;
4)reduction of brow ridges.
79. Why is the volume of urine excreted by the human body per day not equal to the volume of liquid drunk during the same time?
Answer:
1) part of the water is used by the body or formed in metabolic processes;
2) part of the water evaporates through the respiratory organs and sweat glands.
80. Find errors in the given text, correct them, indicate the numbers of the sentences in which they are made, write down these sentences without errors.
1. Animals are heterotrophic organisms; they feed on ready-made organic substances. 2. There are unicellular and multicellular animals. 3. All multicellular animals have bilateral body symmetry. 4. Most of them have developed various organs of movement. 5. Only arthropods and chordates have a circulatory system. 6. Postembryonic development in all multicellular animals is direct.
Errors were made in the sentences:
1) 3 - not all multicellular animals have bilateral symmetry of the body; for example, in coelenterates it is radial (radial);
2) 5 - the circulatory system is also present in annelids and mollusks;
3) 6 - direct postembryonic development is not inherent in all multicellular animals.
81. What is the importance of blood in human life?
Answer:
1) performs a transport function: delivery of oxygen and nutrients to tissues and cells, removal of carbon dioxide and metabolic products;
2) performs a protective function due to the activity of leukocytes and antibodies;
3) participates in the humoral regulation of the body’s vital functions.
82. Use information about the early stages of embryogenesis (zygote, blastula, gastrula) to confirm the sequence of development of the animal world.
Answer:
1) the zygote stage corresponds to a unicellular organism;
2) the blastula stage, where the cells are not differentiated, is similar to colonial forms;
3) the embryo at the gastrula stage corresponds to the structure of the coelenterate (hydra).
83. The injection of large doses of drugs into a vein is accompanied by their dilution with physiological solution (0.9% NaCl solution). Explain why.
Answer:
1) administration of large doses of drugs without dilution can cause a sharp change in blood composition and irreversible phenomena;
2) the concentration of saline solution (0.9% NaCl solution) corresponds to the concentration of salts in the blood plasma and does not cause the death of blood cells.
84. Find errors in the given text, correct them, indicate the numbers of the sentences in which they were made, write down these sentences without errors.
1. Animals of the arthropod type have an external chitinous cover and jointed limbs. 2. The body of most of them consists of three sections: head, chest and abdomen. 3. All arthropods have one pair of antennae. 4. Their eyes are complex (faceted). 5. The circulatory system of insects is closed.
Errors were made in the sentences:
1)3 - not all arthropods have one pair of antennae (arachnids do not have them, and crustaceans have two pairs);
2)4 - not all arthropods have complex (compounded) eyes: in arachnids they are simple or absent, in insects they can have simple eyes along with complex eyes;
3)5 - the circulatory system of arthropods is not closed.
85. What are the functions of the human digestive system?
Answer:
1)mechanical processing of food;
2) chemical processing of food;
3) movement of food and removal of undigested residues;
4)absorption of nutrients, mineral salts and water into the blood and lymph.
86. How is biological progress characterized in flowering plants? Specify at least three signs.
Answer:
1) a wide variety of populations and species;
2) wide distribution on the globe;
3) adaptability to life in different environmental conditions.
87. Why should food be chewed thoroughly?
Answer:
1) well-chewed food is quickly saturated with saliva in the oral cavity and begins to be digested;
2) well-chewed food is quickly saturated with digestive juices in the stomach and intestines and is therefore easier to digest.
88. Find errors in the given text. Indicate the numbers of the sentences in which they are made, correct them.
1. A population is a collection of freely interbreeding individuals of the same species that inhabit a common territory for a long time. 2. Different populations of the same species are relatively isolated from each other, and their individuals do not interbreed. 3. The gene pool of all populations of one species is the same. 4. The population is the elementary unit of evolution. 5. A group of frogs of the same species living in a deep pool for one summer constitutes a population.
Errors were made in the sentences:
1)2 - populations of one species are partially isolated, but individuals from different populations can interbreed;
2)3 - the gene pools of different populations of the same species are different;
3)5 - a group of frogs is not a population, since a group of individuals of the same species is considered a population if it occupies the same space for a large number of generations.
89. Why is it recommended to drink salted water in the summer when you are thirsty for a long time?
Answer:
1) in summer a person sweats more;
2) mineral salts are removed from the body through sweat;
3) salted water restores the normal water-salt balance between tissues and the internal environment of the body.
90. What proves that a person belongs to the class of mammals?
Answer:
1) similarity in the structure of organ systems;
2) the presence of hair;
3) development of the embryo in the uterus;
4) feeding the offspring with milk, caring for the offspring.
91. What processes maintain the constancy of the chemical composition of human blood plasma?
Answer:
1) processes in buffer systems maintain the reaction of the medium (pH) at a constant level;
2) neurohumoral regulation of the chemical composition of plasma is carried out.
92. Find errors in the given text. Indicate the numbers of the sentences in which they are made and explain them.
1. A population is a collection of freely interbreeding individuals of different species that inhabit a common territory for a long time. 2. The main group characteristics of a population are size, density, age, sex and spatial structure. 3. The totality of all genes in a population is called the gene pool. 4. A population is a structural unit of living nature. 5. Population numbers are always stable.
Errors were made in the sentences:
1)1 - a population is a collection of freely interbreeding individuals of the same species that inhabit the general territory of the population for a long time;
2)4 - the population is a structural unit of the species;
3)5 - population numbers can change in different seasons and years.
93. What structures of the body cover protect the human body from the effects of environmental temperature factors? Explain their role.
Answer:
1) subcutaneous fatty tissue protects the body from cooling;
2) sweat glands produce sweat, which, when evaporated, protects against overheating;
3) hair on the head protects the body from cooling and overheating;
4) changes in the lumen of skin capillaries regulate heat transfer.
94. Give at least three progressive biological characteristics of a person that he acquired in the process of long evolution.
Answer:
1) enlargement of the brain and cerebral part of the skull;
2) upright posture and corresponding changes in the skeleton;
3) liberation and development of the hand, opposition of the thumb.
95. Which division of meiosis is similar to mitosis? Explain how it is expressed and what set of chromosomes in the cell it leads to.
Answer:
1) similarities with mitosis are observed in the second division of meiosis;
2) all phases are similar, sister chromosomes (chromatids) diverge to the poles of the cell;
3) the resulting cells have a haploid set of chromosomes.
96.What is the difference between arterial bleeding and venous bleeding?
Answer:
1) with arterial bleeding, the blood is scarlet;
2) it shoots out from the wound with a strong stream, a fountain.
97. A diagram of what process occurring in the human body is shown in the figure? What underlies this process and how does the composition of the blood change as a result? Explain your answer.
capillary
Answer:
1) the figure shows a diagram of gas exchange in the lungs (between the pulmonary vesicle and the blood capillary);
2) gas exchange is based on diffusion - the penetration of gases from a place with high pressure to a place with lower pressure;
3) as a result of gas exchange, the blood is saturated with oxygen and turns from venous (A) to arterial (B).
98. What effect does physical inactivity (low physical activity) have on the human body?
Answer:
physical inactivity leads to:
1) to a decrease in the level of metabolism, an increase in adipose tissue, excess body weight;
2) weakening of skeletal and cardiac muscles, increased load on the heart and decreased endurance of the body;
3) stagnation of venous blood in the lower extremities, vasodilation, circulatory disorders.
(Other wording of the answer is allowed without distorting its meaning.)
99. What characteristics do plants living in arid conditions have?
Answer:
1) the root system of plants penetrates deeply into the soil, reaches groundwater or is located in the surface layer of soil;
2) in some plants, water is stored in leaves, stems and other organs during drought;
3) the leaves are covered with a waxy coating, pubescent or modified into spines or needles.
100. What is the reason for the need for iron ions to enter the human blood? Explain your answer.
Answer:
2) red blood cells provide transport of oxygen and carbon dioxide.
101. Through what vessels and what kind of blood does the chambers of the heart, indicated in the figure by numbers 3 and 5? Which circulatory system is each of these heart structures connected to?
Answer:
1) the chamber marked with number 3 receives venous blood from the superior and inferior vena cava;
2) the chamber indicated by the number 5 receives arterial blood from the pulmonary veins;
3) the heart chamber, indicated by the number 3, is connected to the systemic circulation;
4) the heart chamber, indicated by the number 5, is connected to the pulmonary circulation.
102. What are vitamins, what is their role in the life of the human body?
Answer:
1) vitamins - biologically active organic substances needed in small quantities;
2) they are part of enzymes, participating in metabolism;
3) increase the body’s resistance to adverse environmental influences, stimulate growth, development of the body, restoration of tissues and cells.
103. The body shape of the Kalima butterfly resembles a leaf. How did the butterfly develop such a body shape?
Answer:
1) the appearance of various hereditary changes in individuals;
2) preservation by natural selection of individuals with a changed body shape;
3) reproduction and distribution of individuals with a body shape resembling a leaf.
104. What is the nature of most enzymes and why do they lose their activity when the level of radiation increases?
Answer:
1) most enzymes are proteins;
2) under the influence of radiation, denaturation occurs, the structure of the protein-enzyme changes.
105. Find errors in the given text. Indicate the numbers of the proposals in which they were made, correct them.
1. Plants, like all living organisms, eat, breathe, grow, and reproduce. 2. According to the method of nutrition, plants are classified as autotrophic organisms. 3. When plants respire, they absorb carbon dioxide and release oxygen. 4. All plants reproduce by seeds. 5. Plants, like animals, grow only in the first years of life.
Errors were made in the sentences:
1)3 - when plants respire, they absorb oxygen and release carbon dioxide;
2)4 - only flowering plants and gymnosperms reproduce by seeds, and algae, mosses, and ferns reproduce by spores;
3)5 - plants grow throughout their lives, have unlimited growth.
106. What is the reason for the need for iron ions to enter the human blood? Explain your answer.
Answer:
1) iron ions are part of the hemoglobin of erythrocytes;
2) hemoglobin of erythrocytes ensures the transport of oxygen and carbon dioxide, as it is able to bind with these gases;
3) the supply of oxygen is necessary for the energy metabolism of the cell, and carbon dioxide is its final product that must be removed.
107. Explain why people of different races are classified as the same species. Provide at least three pieces of evidence.
Answer:
1) similarity in structure, life processes, behavior;
2) genetic unity - the same set of chromosomes, their structure;
3) interracial marriages produce offspring capable of reproduction.
108. In ancient India, a person suspected of a crime was offered to swallow a handful of dry rice. If he failed, guilt was considered proven. Give a physiological basis for this process.
Answer:
1) swallowing is a complex reflex act, which is accompanied by salivation and irritation of the root of the tongue;
2) with strong excitement, salivation is sharply inhibited, the mouth becomes dry, and the swallowing reflex does not occur.
109. Find errors in the given text. Indicate the numbers of the sentences in which they are made and explain them.
1. The food chain of biogeocenosis includes producers, consumers and decomposers. 2. The first link in the food chain is consumers. 3. Consumers in the light accumulate energy absorbed in the process of photosynthesis. 4. In the dark phase of photosynthesis, oxygen is released. 5. Decomposers contribute to the release of energy accumulated by consumers and producers.
Errors were made in the sentences:
1)2 - the first link is the producers;
2)3 - consumers are not capable of photosynthesis;
3)4 - oxygen is released in the light phase of photosynthesis.
110. What are the causes of anemia in humans? List at least three possible reasons.
Answer:
1) large blood loss;
2) malnutrition (lack of iron and vitamins, etc.);
3) disruption of the formation of red blood cells in the hematopoietic organs.
111. The wasp fly is similar in color and body shape to the wasp. Name the type of its protective device, explain its significance and the relative nature of the adaptation.
Answer:
1) type of adaptation - mimicry, imitation of the color and body shape of an unprotected animal to a protected one;
2) the resemblance to a wasp warns a possible predator of the danger of being stung;
3) the fly becomes prey for young birds that have not yet developed a reflex to the wasp.
112. Make a food chain using all the objects named below: humus, cross spider, hawk, great tit, housefly. Identify third-order consumers in the constructed chain.
Answer:
1) humus -> housefly -> cross spider -> great tit -> hawk;
2) consumer of the third order - the great tit.
113. Find errors in the given text. Indicate the numbers of sentences in which errors were made, correct them.
1. Annelids are the most highly organized animal cut of other types of worms. 2. Annelids have an open circulatory system. 3. The body of an annelid worm consists of identical segments. 4. Annelids have no body cavity. 5. The nervous system of annelids is represented by the peripharyngeal ring and the dorsal nerve cord.
Errors were made in the sentences:
1)2 - Annelids have a closed circulatory system;
2)4 - Annelids have a body cavity;
3)5 - the nerve chain is located on the ventral side of the body.
114. Name at least three aromorphoses in land plants that allowed them to be the first to develop land. Justify your answer.
Answer:
1) the appearance of integumentary tissue—the epidermis with stomata—promoting protection from evaporation;
2) the emergence of a conducting system that ensures the transport of substances;
3) development of mechanical tissue that performs a supporting function.
115. Explain why there is a large diversity of marsupial mammals in Australia and their absence on other continents.
Answer:
1) Australia separated from other continents during the heyday of marsupials before the appearance of placental animals (geographical isolation);
2) the natural conditions of Australia contributed to the divergence of marsupial characters and active speciation;
3) on other continents, marsupials were replaced by placental mammals.
116. In what cases does a change in the sequence of DNA nucleotides not affect the structure and functions of the corresponding protein?
Answer:
1) if, as a result of a nucleotide replacement, another codon appears, encoding the same amino acid;
2) if the codon formed as a result of a nucleotide replacement encodes a different amino acid, but with similar chemical properties that does not change the structure of the protein;
3) if nucleotide changes occur in intergenic or non-functioning DNA regions.
117. Why is the relationship between pike and perch in the river ecosystem considered competitive?
Answer:
1) are predators, feed on similar food;
2) live in the same body of water, need similar living conditions, mutually oppress each other.
118. Find errors in the given text. Indicate the numbers of sentences in which errors were made, correct them.
1. The main classes of phylum arthropods are Crustaceans, Arachnids and Insects. 2. Insects have four pairs of legs, and arachnids have three pairs. 3. The crayfish has simple eyes, while the cross spider has complex eyes. 4. Arachnids have arachnoid warts on their abdomen. 5. The cross spider and the cockchafer breathe using lung sacs and tracheas.
Errors were made in the sentences:
1)2 - insects have three pairs of legs, and arachnids have four pairs;
2)3 - the crayfish has compound eyes, and the cross spider has simple eyes;
3)5 - the cockchafer does not have lung sacs, but only trachea.
119. What are the structural features and vital functions of cap mushrooms? Name at least four features.
Answer:
1) have a mycelium and a fruiting body;
2) reproduce by spores and mycelium;
3) according to the method of nutrition - heterotrophs;
4) most form mycorrhizae.
120. What aromorphoses allowed ancient amphibians to develop land.
Answer:
1) the appearance of pulmonary breathing;
2) formation of dismembered limbs;
3) the appearance of a three-chambered heart and two circulation circles.
This video lesson is devoted to the topic “Providing cells with energy.” In this lesson we will look at the energy processes in the cell and study how cells are provided with energy. You will also learn what cellular respiration is and what stages it consists of. Discuss each of these steps in detail.
BIOLOGY 9TH GRADE
Topic: Cellular level
Lesson 13. Providing cells with energy
Stepanova Anna Yurievna
candidate of biological sciences, associate professor MGUIE
Moscow
Today we will talk about providing cells with energy. Energy is used for various chemical reactions that occur in the cell. Some organisms use the energy of sunlight for biochemical processes - these are plants, while others use the energy of chemical bonds in substances obtained during nutrition - these are animal organisms. Substances from food are extracted through breakdown or biological oxidation through the process of cellular respiration.
Cellular respiration is a biochemical process in a cell that occurs in the presence of enzymes, as a result of which water and carbon dioxide are released, energy is stored in the form of macroenergetic bonds of ATP molecules. If this process occurs in the presence of oxygen, then it is called “aerobic”. If it occurs without oxygen, then it is called “anaerobic.”
Biological oxidation includes three main stages:
1. Preparatory,
2. Oxygen-free (glycolysis),
3. Complete breakdown of organic substances (in the presence of oxygen).
Preparatory stage. Substances received from food are broken down into monomers. This stage begins in the gastrointestinal tract or in the lysosomes of the cell. Polysaccharides break down into monosaccharides, proteins into amino acids, fats into glycerols and fatty acids. The energy released at this stage is dissipated in the form of heat. It should be noted that for energy processes, cells use carbohydrates, or better yet, monosaccharides. And the brain can only use monosaccharide - glucose - for its work.
Glucose during glycolysis breaks down into two three-carbon molecules of pyruvic acid. Their further fate depends on the presence of oxygen in the cell. If oxygen is present in the cell, then pyruvic acid enters the mitochondria for complete oxidation to carbon dioxide and water (aerobic respiration). If there is no oxygen, then in animal tissues pyruvic acid is converted into lactic acid. This stage takes place in the cytoplasm of the cell. As a result of glycolysis, only two ATP molecules are formed.
For complete oxidation of glucose, oxygen is required. At the third stage, complete oxidation of pyruvic acid to carbon dioxide and water occurs in the mitochondria. As a result, another 36 ATP molecules are formed.
In total, the three steps produce 38 ATP molecules from one glucose molecule, taking into account the two ATPs produced during glycolysis.
Thus, we examined the energy processes occurring in cells. The stages of biological oxidation were characterized. This concludes our lesson, all the best to you, goodbye!
The difference between breathing and burning. Respiration occurring in a cell is often compared to the combustion process. Both processes occur in the presence of oxygen, releasing energy and oxidation products. But, unlike combustion, respiration is an ordered process of biochemical reactions that occurs in the presence of enzymes. During respiration, carbon dioxide arises as the end product of biological oxidation, and during combustion, the formation of carbon dioxide occurs through the direct combination of hydrogen with carbon. Also, during respiration, a certain number of ATP molecules are formed. That is, breathing and combustion are fundamentally different processes.
Biomedical significance. For medicine, not only the metabolism of glucose is important, but also fructose and galactose. The ability to form ATP in the absence of oxygen is especially important in medicine. This allows you to maintain intense work of skeletal muscle in conditions of insufficient efficiency of aerobic oxidation. Tissues with increased glycolytic activity are able to remain active during periods of oxygen starvation. In the cardiac muscle, the possibilities for glycolysis are limited. She has a hard time suffering from disruption of the blood supply, which can lead to ischemia. There are several known diseases caused by the lack of enzymes that regulate glycolysis:
Hemolytic anemia (in fast-growing cancer cells, glycolysis occurs at a rate exceeding the capabilities of the citric acid cycle), which contributes to increased synthesis of lactic acid in organs and tissues. High levels of lactic acid in the body can be a symptom of cancer.
Fermentation. Microbes are able to obtain energy during fermentation. Fermentation has been known to people since time immemorial, for example, in the making of wine. Lactic acid fermentation was known even earlier. People consumed dairy products without realizing that these processes were associated with the activity of microorganisms. This was first proven by Louis Pasteur. Moreover, different microorganisms secrete different fermentation products. Now we will talk about alcoholic and lactic acid fermentation. As a result, ethyl alcohol and carbon dioxide are formed and energy is released. Brewers and winemakers have used certain types of yeast to stimulate fermentation, which turns sugars into alcohol. Fermentation is carried out mainly by yeast, as well as some bacteria and fungi. In our country, Saccharomycetes yeast is traditionally used. In America - bacteria of the genus Pseudomonas. And in Mexico, “moving rod” bacteria are used. Our yeast typically ferments hexoses (six-carbon monosaccharides) such as glucose or fructose. The process of alcohol formation can be represented as follows: from one glucose molecule two molecules of alcohol, two molecules of carbon dioxide and two molecules of ATP are formed. This method is less profitable than aerobic processes, but allows you to maintain life in the absence of oxygen. Now let's talk about fermented milk fermentation. One molecule of glucose forms two molecules of lactic acid and at the same time two molecules of ATP are released. Lactic acid fermentation is widely used for the production of dairy products: cheese, curdled milk, yoghurts. Lactic acid is also used in the production of soft drinks.
- Types of nutrition of living organisms
- Photosynthesis
- Energy metabolism
1. Life activity of all organisms is possible only if they have energy. According to the method of obtaining energy, all cells and organisms are divided into two groups: autotrophs And heterotrophs.
Heterotrophs(Greek heteros - different, other and trophe - food, nutrition) are not able to synthesize organic compounds from inorganic ones themselves; they need to receive them from the environment. Organic substances serve not only as food for them, but also as a source of energy. Heterotrophs include all animals, fungi, most bacteria, as well as non-chlorophyll terrestrial plants and algae.
According to the method of obtaining food, heterotrophic organisms are divided into Holozoans(animals) capturing solid particles, and osmotrophic(fungi, bacteria) feeding on dissolved substances.
Diverse heterotrophic organisms are capable of collectively decomposing all substances that are synthesized by autotrophs, as well as mineral substances synthesized as a result of human production activities. Heterotrophic organisms, together with autotrophs, constitute a single biological system on Earth, united by trophic relationships.
Autotrophs- organisms that feed (i.e., receive energy) from inorganic compounds, these are some bacteria and all green plants. Autotrophs are divided into chemotrophs and phototrophs.
Chemotrophs- organisms that use energy released during redox reactions. Chemotrophs include nitrifying (nitrogen-fixing) bacteria, sulfur, hydrogen (methane-forming), manganese, iron-forming and carbon monoxide-using bacteria.
Phototrophs- only green plants. The source of energy for them is light.
2. Photosynthesis(Greek phos - gen. fall. photos - light and synthesis - connection) - the formation, with the participation of light energy, of organic substances by the cells of green plants, as well as some bacteria, the process of converting light energy into chemical energy. Occurs with the help of pigments (chlorophyll and some others) in the thylakoids of chloroplasts and chromatophores of cells. Photosynthesis is based on redox reactions in which electrons are transferred from a donor-reducer (water, hydrogen, etc.) to an acceptor (Latin acceptor - receiver) - carbon dioxide, acetate with the formation of reduced compounds - carbohydrates and the release of oxygen, if water is oxidized.
Photosynthetic bacteria that use donors other than water do not produce oxygen.
Light reactions of photosynthesis(caused by light) occur in the grana of chloroplast thylakoids. Visible light quanta (photons) interact with chlorophyll molecules, transferring them to an excited state. An electron in chlorophyll absorbs a light quantum of a certain length and, as if in steps, moves along the chain of electron carriers, losing energy, which serves to phosphorylate ADP into ATP. This is a very efficient process: chloroplasts produce 30 times more ATP than the mitochondria of the same plants. This accumulates the energy necessary for the following - dark reactions of photosynthesis. The following substances act as electron carriers: cytochromes, plastoquinone, ferredoxin, flavoprotein, reductase, etc. Some of the excited electrons are used to reduce NADP + to NADPH. When exposed to sunlight, water breaks down in chloroplasts - photolysis, in this case, electrons are formed that compensate for their losses by chlorophyll; Oxygen is produced as a by-product and released into the atmosphere of our planet. This is the oxygen that we breathe and which is necessary for all aerobic organisms.
The chloroplasts of higher plants, algae and cyanobacteria contain two photosystems of different structures and compositions. When light quanta are absorbed by pigments (the reaction center - a complex of chlorophyll with a protein that absorbs light with a wavelength of 680 nm - P680) of photosystem II, electrons are transferred from water to an intermediate acceptor and through a chain of carriers to the reaction center of photosystem I. And this photosystem is the reaction center will reveal pen chlorophyll molecules in complex with a special protein-KOM, which absorbs light with a wavelength of 700 nm - P700. In the molecules of chlorophyll F1 there are “holes” - unfilled places of electrons transferred to PLDPH. These “holes” are filled with electrons formed during the functioning of the PI. That is, photosystem II supplies electrons to photosystem I, which are spent in it on the reduction of NADP + and NADPH. Along the path of the movement of photosystem II electrons excited by light to the final acceptor - chlorophyll of photosystem I, ADP is phosphorylated into energy-rich ATP. Thus, light energy is stored in ATP molecules and is further used for the synthesis of carbohydrates, proteins, nucleic acids and other vital processes of plants, and through them the vital activity of all organisms that feed on plants.
Dark reactions, or carbon fixation reactions, not associated with light, are carried out in the stroma of chloroplasts. The key place in them is occupied by the fixation of carbon dioxide and the conversion of carbon into carbohydrates. These reactions are cyclic in nature, since some of the intermediate carbohydrates undergo a process of condensation and rearrangements to ribulose diphosphate, the primary acceptor of CO 2, which ensures the continuous operation of the cycle. This process was first described by the American biochemist Melvin Calvin
The transformation of the inorganic compound CO 2 into organic compounds - carbohydrates, in the chemical bonds of which solar energy is stored, occurs with the help of a complex enzyme - ribulose-1,5-diphosphate carboxylase. It ensures the addition of one CO 2 molecule to the five-carbon ribulose-1,5-diphosphate, resulting in the formation of a six-carbon short-lived intermediate compound. This compound, due to hydrolysis, breaks down into two three-carbon molecules of phosphoglyceric acid, which is reduced using ATP and NADPH to three-carbon sugars (triose phosphates). The final product of photosynthesis, glucose, is formed from them.
Some of the triose phosphates, having gone through the processes of condensation and rearrangement, turning first into ribulose monophosphate, and then into ribulose diphosphate, are included again in the continuous cycle of creating glucose molecules. Glucose can be enzymatically polymerized into
starch and cellulose are the supporting polysaccharides of plants.
A feature of the photosynthesis of some plants (sugar cane, corn, amaranth) is the initial conversion of carbon through four-carbon compounds. Such plants received the index C 4 -plants, and photosynthesis in them is carbon metabolism. C4 plants attract the attention of researchers due to their photosynthetic productivity.
Ways to increase the productivity of agricultural plants:
Sufficient mineral nutrition, which can ensure the best course of metabolic processes;
More complete illumination, which can be achieved using certain plant sowing rates, taking into account the light consumption of light-loving and shade-tolerant plants;
Normal amount of carbon dioxide in the air (with an increase in its content, the process of plant respiration, which is associated with photosynthesis, is disrupted);
Soil moisture corresponding to the moisture needs of plants, depending on climatic and agrotechnical conditions.
The importance of photosynthesis in nature.
As a result of photosynthesis on Earth, 150 billion tons of organic matter are formed annually and approximately 200 billion tons of free oxygen are released. Photosynthesis not only provides and maintains the current composition of the Earth's atmosphere, necessary for the life of its inhabitants, but also prevents an increase in the concentration of CO 2 in the atmosphere, preventing overheating of our planet (due to the so-called greenhouse effect). Oxygen released during photosynthesis is necessary for the respiration of organisms and protecting them from harmful short-wave ultraviolet radiation.
Chemosynthesis(Late Greek chemeta - chemistry and Greek synthesis - connection) - an autotrophic process of creating organic matter by bacteria that do not contain chlorophyll. Chemosynthesis is carried out due to the oxidation of inorganic compounds: hydrogen, hydrogen sulfide, ammonia, iron (II) oxide, etc. The assimilation of CO 2 proceeds as during photosynthesis (Calvin cycle), with the exception of methane-forming, homo-acetate bacteria. The energy obtained from oxidation is stored in bacteria in the form of ATP.
Chemosynthetic bacteria play an extremely important role in the biogeochemical cycles of chemical elements in the biosphere. The vital activity of nitrifying bacteria is one of the most important factors in soil fertility. Chemosynthetic bacteria oxidize compounds of iron, manganese, sulfur, etc.
Chemosynthesis was discovered by Russian microbiologist Sergei Nikolaevich Vinogradsky (1856-1953) in 1887.
3. Energy metabolism
Three stages of energy metabolism are carried out with the participation of special enzymes in various parts of cells and organisms.
The first stage is preparatory- occurs (in animals in the digestive organs) under the action of enzymes that break down molecules of di- and polysaccharides, fats, proteins, nucleic acids into smaller molecules: glucose, glycerol and fatty acids, amino acids, nucleotides. This releases a small amount of energy, which is dissipated as heat.
The second stage is oxygen-free, or incomplete oxidation. It is also called anaerobic respiration (fermentation), or glycolysis. Glycolysis enzymes are localized in the liquid part of the cytoplasm - the hyaloplasm. Glucose undergoes breakdown, each molene in which is stepwise cleaved and oxidized with the participation of enzymes to two three-carbon molecules of pyruvic acid CH 3 - CO - COOH, where COOH is a carboxyl group characteristic of organic acids.
Nine enzymes are sequentially involved in this glucose conversion. During the process of glycolysis, glucose molecules are oxidized, i.e., hydrogen atoms are lost. The hydrogen acceptor (and electron) in these reactions are nicotinamide nindinucleotide (NAD+) molecules, which are similar in structure to NADP+ and differ only in the absence of a phosphoric acid residue in the ribose molecule. When pyruvic acid is reduced due to reduced NAD, the final product of glycolysis appears - lactic acid. Phosphoric acid and ATP are involved in the breakdown of glucose.
In summary, this process looks like this:
C 6 H 12 O 6 + 2 H 3 P0 4 + 2 ADP = 2 C 3 H 6 0 3 + 2 ATP + 2 H 2 0.
In yeast fungi, a glucose molecule without the participation of oxygen is converted into ethyl alcohol and carbon dioxide (alcoholic fermentation):
C 6 H 12 O 6 +2H 3 P0 4 +2ADP - 2C 2 H b 0H+2C0 2 +2ATP+2H 2 O.
In some microorganisms, the breakdown of glucose without oxygen can result in the formation of acetic acid, acetone, etc. In all cases, the breakdown of one glucose molecule is accompanied by the formation of two ATP molecules, in the high-energy bonds of which 40% of the energy is stored, the rest is dissipated as heat.
The third stage of energy metabolism(oxygen splitting stage , or stage of aerobic respiration) occurs in mitochondria. This stage is associated with the mitochondrial matrix and inner membrane; it involves enzymes representing an enzymatic ring “conveyor” called Krebs cycle, named after the scientist who discovered it. This complex and long way of working of many enzymes is also called tricarboxylic acid cycle.
Once in the mitochondria, pyruvic acid (PVA) is oxidized and converted into an energy-rich substance - acetyl coenzyme A, or acetyl-CoA for short. In the Krebs cycle, acetyl-CoA molecules come from different energy sources. In the process of PVK oxidation, electron acceptors NAD + are reduced to NADH and another type of acceptor is reduced - FAD to FADH 2 (FAD is a flavin adenine dinucleotide). The energy stored in these molecules is used for the synthesis of ATP - a universal biological energy accumulator. During the aerobic respiration stage, electrons from NADH and FADH 2 move along a multi-step chain of their transfer to the final electron acceptor - molecular oxygen. Several electron carriers are involved in the transfer: coenzyme Q, cytochromes and, most importantly, oxygen. When electrons move from stage to stage of the respiratory conveyor, energy is released, which is spent on the synthesis of ATP. Inside the mitochondria, H + cations combine with O 2 ~ anions to form water. In the Krebs cycle, CO 2 is formed, and in the electron transfer chain - water. In this case, one glucose molecule, completely oxidized with the access of oxygen to C0 2 and H 2 0, contributes to the formation of 38 ATP molecules. From the above it follows that the main role in providing the cell with energy is played by the oxygen breakdown of organic substances, or aerobic respiration. When there is a deficiency of oxygen or its complete absence, oxygen-free, anaerobic breakdown of organic substances occurs; The energy of such a process is only enough to create two ATP molecules. Thanks to this, living beings can survive without oxygen for a short time.
The living cell has an inherently unstable and almost implausible organization; The cell is able to maintain a very specific and beautifully complex order of its fragile structure only thanks to the continuous consumption of energy.
As soon as the supply of energy stops, the complex structure of the cell disintegrates and it goes into a disordered and unorganized state. In addition to providing the chemical processes necessary to maintain the integrity of the cell, in various types of cells, due to the conversion of energy, the implementation of a variety of mechanical, electrical, chemical and osmotic processes associated with the life of the body is ensured.
Having learned in relatively recent times to extract the energy contained in various non-living sources to perform various work, man began to comprehend how skillfully and with what high efficiency the cell transforms energy. The transformation of energy in a living cell is subject to the same laws of thermodynamics that operate in inanimate nature. According to the first law of thermodynamics, the total energy of a closed system with any physical change always remains constant. According to the second law, energy can exist in two forms: the form of "free" or useful energy and the form of useless dissipated energy. The same law states that with any physical change there is a tendency to dissipate energy, that is, to reduce the amount of free energy and to increase entropy. Meanwhile, a living cell needs a constant supply of free energy.
The engineer obtains the energy he needs mainly from the energy of chemical bonds contained in the fuel. By burning fuel, it converts chemical energy into thermal energy; it can then use the thermal energy to rotate, for example, a steam turbine and thus obtain electrical energy. Cells also receive free energy by releasing the energy of chemical bonds contained in the “fuel”. Energy is stored in these connections by those cells that synthesize the nutrients that serve as such fuel. However, cells use this energy in a very specific way. Because the temperature at which a living cell functions is approximately constant, the cell cannot use thermal energy to do work. In order for work to occur due to thermal energy, heat must move from a more heated body to a less heated one. It is absolutely clear that the cell cannot burn its fuel at the combustion temperature of coal (900°); Nor can it withstand exposure to superheated steam or high voltage current. The cell has to extract and use energy under conditions of a fairly constant and, moreover, low temperature, a dilute iodine environment and very slight fluctuations in the concentration of hydrogen ions. In order to acquire the ability to obtain energy, the cell, over the course of centuries of evolution of the organic world, has improved its remarkable molecular mechanisms, which operate unusually effectively in these mild conditions.
The cellular mechanisms for extracting energy are divided into two classes, and based on the differences in these mechanisms, all cells can be divided into two main types. Cells of the first type are called heterotrophic; These include all the cells of the human body and the cells of all higher animals. These cells require a constant supply of ready-made fuel of a very complex chemical composition. Such fuels are carbohydrates, proteins and fats, i.e., individual components of other cells and tissues. Heterotrophic cells obtain energy by burning or oxidizing these complex substances (produced by other cells) in a process called respiration, which involves molecular oxygen (O2) of the atmosphere. Heterotrophic cells use this energy to perform their biological functions, releasing carbon dioxide into the atmosphere as an end product.
Cells belonging to the second type are called autotrophic. The most typical autotrophic cells are the cells of green plants. In the process of photosynthesis, they bind the energy of sunlight, using it for their needs. In addition, they use solar energy to extract carbon from atmospheric carbon dioxide and use it to build the simplest organic molecule - the glucose molecule. From glucose, the cells of green plants and other organisms create more complex molecules that make up their composition. To provide the energy necessary for this, cells burn part of the raw materials at their disposal during respiration. From this description of the cyclic transformations of energy in the cell, it becomes clear that all living organisms ultimately receive energy from sunlight, with plant cells receiving it directly from the sun, and animals indirectly.
The study of the main questions posed in this article rests on the need for a detailed description of the primary energy extraction mechanism used by the cell. Most of the steps in the complex cycles of respiration and photosynthesis have already been studied. It has been established in which organ of the cell this or that process occurs. Respiration is carried out by mitochondria, which are present in large numbers in almost all cells; photosynthesis is ensured by chloroplasts - cytoplasmic structures contained in the cells of green plants. The molecular mechanisms that reside within these cellular structures, composing their structure and enabling their functions, represent the next important step in the study of the cell.
The same well-studied molecules - adenosine triphosphate (ATP) molecules - transfer free energy obtained from nutrients or sunlight from the centers of respiration or photosynthesis to all parts of the cell, ensuring the implementation of all processes that require energy consumption. ATP was first isolated from muscle tissue by Loman about 30 years ago. The ATP molecule contains three interconnected phosphate groups. In a test tube, the end group can be separated from the ATP molecule by a hydrolysis reaction that produces adenosine diphosphate (ADP) and inorganic phosphate. During this reaction, the free energy of the ATP molecule is converted into thermal energy, and entropy increases in accordance with the second law of thermodynamics. In the cell, however, the terminal phosphate group is not simply separated during hydrolysis, but is transferred to a special molecule that serves as an acceptor. A significant part of the free energy of the ATP molecule is retained due to phosphorylation of the acceptor molecule, which now, due to increased energy, acquires the ability to participate in processes that require energy consumption, for example, in the processes of biosynthesis or muscle contraction. After the removal of one phosphate group in this coupled reaction, ATP is converted to ADP. In cellular thermodynamics, ATP can be thought of as the energy-rich, or "charged" form of the energy carrier (adenosine phosphate), and ADP as the energy-poor, or "discharged" form.
Secondary “charging” of the carrier is, of course, carried out by one or the other of the two mechanisms involved in energy extraction. During the process of respiration of animal cells, the energy contained in nutrients is released as a result of oxidation and is used to build ATP from ADP and phosphate. During photosynthesis in plant cells, the energy of sunlight is converted into chemical energy and is spent on “charging” adenosine phosphate, i.e., on the formation of ATP.
Experiments using the radioactive isotope of phosphorus (P 32) showed that inorganic phosphate is incorporated into and out of the terminal phosphate group of ATP at a high rate. In the kidney cell, the turnover of the terminal phosphate group occurs so quickly that its half-life takes less than 1 minute; this corresponds to an extremely intense energy exchange in the cells of this organ. It should be added that the activity of ATP in a living cell is by no means black magic. Chemists know many similar reactions by which chemical energy is transferred in nonliving systems. The relatively complex structure of ATP apparently arose only in the cell to ensure the most effective regulation of chemical reactions associated with energy transfer.
The role of ATP in photosynthesis has only recently been clarified. This discovery made it possible to largely explain how photosynthetic cells, in the process of carbohydrate synthesis, bind solar energy - the primary source of energy for all living beings.
The energy from sunlight is transmitted in the form of photons, or quanta; Light of different colors, or different wavelengths, is characterized by different energies. When light falls on certain metal surfaces and is absorbed by these surfaces, photons, as a result of collisions with the electrons of the metal, transfer their energy to them. This photoelectric effect can be measured due to the electric current generated. In the cells of green plants, sunlight with certain wavelengths is absorbed by the green pigment - chlorophyll. The absorbed energy transfers electrons in the complex chlorophyll molecule from the basic energy level to a higher level. Such “excited” electrons tend to return to their main stable energy level, releasing the energy they absorbed. In a pure preparation of chlorophyll isolated from a cell, the absorbed energy is re-emitted in the form of visible light, similar to what happens in the case of other phosphorescent or fluorescent organic and inorganic compounds.
Thus, chlorophyll, being in a test tube, by itself is not capable of storing or using light energy; this energy quickly dissipates, as if a short circuit had occurred. However, in the cell, chlorophyll is sterically bound to other specific molecules; therefore, when, under the influence of the absorption of light, it comes into an excited state, "hot", or rich in energy, the electrons do not return to their normal (unexcited) energy state; instead, electrons are torn from the chlorophyll molecule and carried by electron carrier molecules, which transfer them to each other in a closed chain of reactions. Making this path outside the chlorophyll molecule, the excited electrons gradually give up their energy and return to their original places in the chlorophyll molecule, which is then ready to absorb the second photon. Meanwhile, the energy given up by the electrons is used to form ATP from ADP and phosphate - in other words, to “charge” the adenosine phosphate system of the photosynthetic cell.
The electron carriers that mediate this photosynthetic phosphorylation process have not yet been fully identified. One of these carriers appears to contain riboflavin (vitamin B2) and vitamin K. Others are tentatively classified as cytochromes (proteins containing iron atoms surrounded by porphyrin groups, which in location and structure resemble the porphyrin of chlorophyll itself). At least two of these electron carriers are capable of binding part of the energy they carry to restore ATP from ADP.
This is the basic scheme for converting light energy into the energy of ATP phosphate bonds, developed by D. Arnon and other scientists.
However, in the process of photosynthesis, in addition to the binding of solar energy, carbohydrate synthesis also occurs. It is now believed that some of the "hot" electrons of the excited chlorophyll molecule, together with hydrogen ions originating from water, cause the reduction (i.e., the acquisition of additional electrons or hydrogen atoms) of one of the electron carriers - triphosphopyridine nucleotide (TPN, in reduced form TPN-N).
In a series of dark reactions, so named because they can occur in the absence of light, TPH-H causes the reduction of carbon dioxide to carbohydrate. Most of the energy required for these reactions is supplied by ATP. The nature of these dark reactions was studied mainly by M. Calvin and his colleagues. One of the byproducts of the initial photoreduction of TPN is hydroxyl ion (OH -). Although we do not yet have complete data, it is assumed that this ion donates its electron to one of the cytochromes in a chain of photosynthetic reactions, the final product of which is molecular oxygen. Electrons move along the chain of carriers, making their energetic contribution to the formation of ATP, and, ultimately, having spent all their excess energy, they enter the chlorophyll molecule.
As one would expect based on the strictly regular and sequential nature of the photosynthesis process, chlorophyll molecules are not randomly located in chloroplasts and, of course, are not simply suspended in the liquid filling the chloroplasts. On the contrary, chlorophyll molecules form ordered structures in chloroplasts - grana, between which there is an interlacing of fibers or membranes separating them. Inside each grana, flat chlorophyll molecules lie in stacks; each molecule can be considered analogous to a separate plate (electrode) of an element, grana - to elements, and the totality of grana (i.e. the entire chloroplast) - to an electric battery.
Chloroplasts also contain all those specialized electron carrier molecules that, together with chlorophyll, are involved in extracting energy from “hot” electrons and using this energy to synthesize carbohydrates. Chloroplasts extracted from the cell can carry out the entire complex process of photosynthesis.
The efficiency of these miniature solar-powered factories is amazing. In the laboratory, subject to certain special conditions, it can be shown that during the process of photosynthesis, up to 75% of the light falling on a chlorophyll molecule is converted into chemical energy; However, this figure cannot be considered completely accurate, and there is still debate about this. In the field, due to unequal illumination of the leaves by the sun, as well as for a number of other reasons, the efficiency of solar energy use is much lower - on the order of several percent.
Thus, the glucose molecule, which is the end product of photosynthesis, must contain a fairly significant amount of solar energy contained in its molecular configuration. During the process of respiration, heterotrophic cells extract this energy by gradually breaking down the glucose molecule in order to “conserve” the energy it contains in the newly formed phosphate bonds of ATP.
There are different types of heterotrophic cells. Some cells (for example, some marine microorganisms) can live without oxygen; others (for example, brain cells) absolutely require oxygen; others (for example, muscle cells) are more versatile and are able to function both in the presence of oxygen in the environment and in its absence. In addition, although most cells prefer to use glucose as their main fuel, some of them can exist solely on amino acids or fatty acids (the main raw material for the synthesis of which is the same glucose). Nevertheless, the breakdown of a glucose molecule in liver cells can be considered an example of an energy production process typical of most heterotrophs known to us.
The total amount of energy contained in a glucose molecule is very easy to determine. By burning a certain amount (sample) of glucose in the laboratory, it can be shown that the oxidation of a glucose molecule produces 6 molecules of water and 6 molecules of carbon dioxide, and the reaction is accompanied by the release of energy in the form of heat (approximately 690,000 calories per 1 gram molecule, i.e. . for 180 grams of glucose). Energy in the form of heat is of course useless to a cell, which operates at a virtually constant temperature. The gradual oxidation of glucose during respiration occurs, however, in such a way that most of the free energy of the glucose molecule is stored in a form convenient for the cell.
As a result, the cell receives more than 50% of all energy released during oxidation in the form of phosphate bond energy. Such a high efficiency compares favorably with that which is usually achieved in technology, where it is rarely possible to convert more than one-third of the thermal energy obtained from fuel combustion into mechanical or electrical energy.
The process of glucose oxidation in the cell is divided into two main phases. During the first, or preparatory, phase, called glycolysis, the six-carbon molecule of glucose is broken down into two three-carbon molecules of lactic acid. This seemingly simple process consists of not one, but at least 11 steps, with each step catalyzed by its own special enzyme. The complexity of this operation may seem to contradict Newton's aphorism “Natura entm simplex esi” (“nature is simple”); However, it should be remembered that the purpose of this reaction is not to simply split the glucose molecule in half, but to release the energy contained in it from this molecule. Each of the intermediates contains phosphate groups, and the reaction ends up using two ADP molecules and two phosphate groups. Ultimately, as a result of the breakdown of glucose, not only two molecules of lactic acid are formed, but, in addition, two new ATP molecules are formed.
What does this lead to in energy terms? Thermodynamic equations show that when one gram of glucose is broken down to form lactic acid, 56,000 calories are released. Since the formation of each gram-molecule of ATP binds 10,000 calories, the efficiency of the energy capture process at this stage is about 36% - a very impressive figure, based on what we usually have to deal with in technology. However, these 20,000 calories converted into phosphate bond energy represent only a tiny fraction (about 3%) of the total energy contained in a gram molecule of glucose (690,000 calories). Meanwhile, many cells, for example, anaerobic cells or muscle cells, which are in a state of activity (and at this time incapable of respiration), exist due to this insignificant use of energy.
After breaking down glucose into lactic acid, aerobic cells continue to extract most of the remaining energy through the process of respiration, during which three-carbon lactic acid molecules are broken down into one-carbon carbon dioxide molecules. Lactic acid, or rather its oxidized form, pyruvic acid, undergoes an even more complex series of reactions, each of these reactions again being catalyzed by a special enzyme system. First, the three-carbon compound breaks down to form the activated form of acetic acid (acetyl coenzyme A) and carbon dioxide. The "two-carbon moiety" (acetyl coenzyme A) then combines with a four-carbon compound, oxaloacetic acid, to produce citric acid, which contains six carbon atoms. Citric acid, through a series of reactions, is converted back into oxaloacetic acid, and the three carbon atoms of pyruvic acid fed into this cycle of reactions ultimately produce carbon dioxide molecules. This “mill”, which “grinds” (oxidizes) not only glucose, but also fat and amino acid molecules, previously broken down into acetic acid, is known as the Krebs cycle or citric acid cycle.
The cycle was first described by G. Krebs in 1937. This discovery represents one of the cornerstones of modern biochemistry, and its author was awarded the Nobel Prize in 1953.
The Krebs cycle traces the oxidation of lactic acid to carbon dioxide; However, this cycle alone cannot explain how the large amounts of energy contained in the lactic acid molecule can be extracted in a form suitable for use in a living cell. This energy extraction process that accompanies the Krebs cycle has been intensively studied in recent years. The overall picture is more or less clear, but many details remain to be explored. Apparently, during the Krebs cycle, electrons, with the participation of enzymes, are torn from intermediate products and transferred along a number of carrier molecules, collectively called the respiratory chain. This chain of enzyme molecules represents the final common path of all electrons removed from nutrient molecules in the process of biological oxidation. In the last link of this chain, electrons eventually combine with oxygen to form water. Thus, the breakdown of nutrients through respiration is the reverse process of photosynthesis, in which the removal of electrons from water produces oxygen. Moreover, the electron carriers in the respiratory chain are chemically very similar to the corresponding carriers involved in the process of photosynthesis. Among them there are, for example, riboflavin and cytochrome structures, similar to those of the chloroplast. This confirms Newton's aphorism about the simplicity of nature.
As in photosynthesis, the energy of electrons passing along this chain to oxygen is captured and used to synthesize ATP from ADP and phosphate. As a matter of fact, this phosphorylation occurring in the respiratory chain (oxidative phosphorylation) has been better studied than the phosphorylation occurring during photosynthesis, which was discovered relatively recently. It is firmly established, for example, that there are three centers in the respiratory chain in which the “charging” of adenosine phosphate occurs, i.e., the formation of ATP. Thus, for every pair of electrons removed from lactic acid during the Krebs cycle, an average of three ATP molecules are formed.
Based on the total ATP yield, it is now possible to calculate the thermodynamic efficiency with which a cell extracts the energy made available to it by glucose oxidation. The preliminary breakdown of glucose into two molecules of lactic acid produces two molecules of ATP. Each lactic acid molecule ultimately transfers six pairs of electrons to the respiratory chain. Since each pair of electrons passing through the chain causes the conversion of three ADP molecules into ATP, 36 ATP molecules are produced during the process of respiration itself. When each gram molecule of ATP is formed, about 10,000 calories are bound, as we have already indicated, and, therefore, 38 gram molecules of ATP bind approximately 380,000 of the 690,000 calories contained in the original gram molecule of glucose. The efficiency of the coupled processes of glycolysis and respiration can thus be considered to be at least 55%.
The extreme complexity of the respiration process is another indication that the enzymatic mechanisms involved could not function if the constituent parts were simply mixed together in solution. Just as the molecular mechanisms associated with photosynthesis have a certain structural organization and are contained in the chloroplast, the respiratory organs of the cell - mitochondria - represent the same structurally ordered system.
A cell, depending on its type and the nature of its function, can contain from 50 to 5000 mitochondria (a liver cell contains, for example, about 1000 mitochondria). They are large enough (3-4 microns in length) to be seen with a regular microscope. However, the ultrastructure of mitochondria is visible only under an electron microscope.
In electron micrographs one can see that the mitochondrion has two membranes, with the inner membrane forming folds that extend into the body of the mitochondrion. A recent study of mitochondria isolated from liver cells showed that the enzyme molecules involved in the Krebs cycle are located in the matrix, or soluble part of the internal contents of the mitochondria, while the enzymes of the respiratory chain, in the form of molecular “assemblies,” are located in the membranes. Membranes consist of alternating layers of protein and lipid (fat) molecules; The membranes in the grana of chloroplasts have the same structure.
Thus, there is a clear similarity in the structure of these two main “power stations”, on which the entire vital activity of the cell depends, because one of them “stores” solar energy in the phosphate bonds of ATP, and the other converts the energy contained in nutrients into ATP energy .
Advances in modern chemistry and physics have recently made it possible to clarify the spatial structure of some large molecules, for example, molecules of a number of proteins and DNA, i.e. molecules containing genetic information.
The next important step in studying the cell is to find out the location of large enzyme molecules (which are themselves proteins) in the mitochondrial membranes, where they are located along with lipids - an arrangement that ensures the proper orientation of each catalyst molecule and the possibility of its interaction with the subsequent link of the entire working mechanism. The “wiring diagram” of the mitochondria is already clear!
Modern information regarding the power plants of the cell shows that it leaves far behind not only classical energy, but also the newest, much more brilliant achievements of technology.
Electronics has achieved amazing success in the layout and reduction of the size of the components of computing devices. However, all these successes cannot be compared with the absolutely incredible miniaturization of the most complex energy conversion mechanisms developed in the process of organic evolution and present in every living cell.
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Abundant growth of fat trees,
which root on the barren sand
approved, clearly states that
fat sheets fat fat from the air
absorb...
M. V. Lomonosov
How is energy stored in a cell? What is metabolism? What is the essence of the processes of glycolysis, fermentation and cellular respiration? What processes take place during the light and dark phases of photosynthesis? How are the processes of energy and plastic metabolism related? What is chemosynthesis?
Lesson-lecture
The ability to convert one type of energy into another (radiation energy into the energy of chemical bonds, chemical energy into mechanical energy, etc.) is one of the fundamental properties of living things. Here we will take a closer look at how these processes are realized in living organisms.
ATP IS THE MAIN CARRIER OF ENERGY IN THE CELL. To carry out any manifestations of cell activity, energy is required. Autotrophic organisms receive their initial energy from the Sun during photosynthesis reactions, while heterotrophic organisms use organic compounds supplied with food as an energy source. Energy is stored by cells in the chemical bonds of molecules ATP (adenosine triphosphate), which are a nucleotide consisting of three phosphate groups, a sugar residue (ribose) and a nitrogenous base residue (adenine) (Fig. 52).
Rice. 52. ATP molecule
The bond between phosphate residues is called macroergic, since when it breaks, a large amount of energy is released. Typically, the cell extracts energy from ATP by removing only the terminal phosphate group. In this case, ADP (adenosine diphosphate) and phosphoric acid are formed and 40 kJ/mol are released:
ATP molecules play the role of the cell's universal energy bargaining chip. They are delivered to the site of an energy-intensive process, be it the enzymatic synthesis of organic compounds, the work of proteins - molecular motors or membrane transport proteins, etc. The reverse synthesis of ATP molecules is carried out by attaching a phosphate group to ADP with the absorption of energy. The cell stores energy in the form of ATP during reactions energy metabolism. It is closely related to plastic exchange, during which the cell produces the organic compounds necessary for its functioning.
METABOLISM AND ENERGY IN THE CELL (METABOLISM). Metabolism is the totality of all reactions of plastic and energy metabolism, interconnected. The cells constantly synthesize carbohydrates, fats, proteins, and nucleic acids. The synthesis of compounds always occurs with the expenditure of energy, i.e. with the indispensable participation of ATP. Energy sources for the formation of ATP are enzymatic reactions of oxidation of proteins, fats and carbohydrates entering the cell. During this process, energy is released and stored in ATP. Glucose oxidation plays a special role in cellular energy metabolism. Glucose molecules undergo a series of successive transformations.
The first stage, called glycolysis, takes place in the cytoplasm of cells and does not require oxygen. As a result of successive reactions involving enzymes, glucose breaks down into two molecules of pyruvic acid. In this case, two ATP molecules are consumed, and the energy released during oxidation is sufficient to form four ATP molecules. As a result, the energy output of glycolysis is small and amounts to two ATP molecules:
C 6 H1 2 0 6 → 2C 3 H 4 0 3 + 4H + + 2ATP
Under anaerobic conditions (in the absence of oxygen), further transformations can be associated with various types fermentation.
Everybody knows lactic acid fermentation(milk souring), which occurs due to the activity of lactic acid fungi and bacteria. The mechanism is similar to glycolysis, only the final product here is lactic acid. This type of glucose oxidation occurs in cells when there is a lack of oxygen, such as in intensely working muscles. Alcohol fermentation is close in chemistry to lactic acid fermentation. The difference is that the products of alcoholic fermentation are ethyl alcohol and carbon dioxide.
The next stage, during which pyruvic acid is oxidized to carbon dioxide and water, is called cellular respiration. Reactions associated with respiration take place in the mitochondria of plant and animal cells, and only in the presence of oxygen. This is a series of chemical transformations before the formation of the final product - carbon dioxide. At various stages of this process, intermediate products of oxidation of the starting substance are formed with the elimination of hydrogen atoms. In this case, energy is released, which is “conserved” in the chemical bonds of ATP, and water molecules are formed. It becomes clear that it is precisely in order to bind the separated hydrogen atoms that oxygen is required. This series of chemical transformations is quite complex and occurs with the participation of the internal membranes of mitochondria, enzymes, and carrier proteins.
Cellular respiration is very efficient. 30 ATP molecules are synthesized, two more molecules are formed during glycolysis, and six ATP molecules are formed as a result of transformations of glycolysis products on mitochondrial membranes. In total, as a result of the oxidation of one glucose molecule, 38 ATP molecules are formed:
C 6 H 12 O 6 + 6H 2 0 → 6CO 2 + 6H 2 O + 38ATP
The final stages of oxidation of not only sugars, but also proteins and lipids occur in mitochondria. These substances are used by cells, mainly when the supply of carbohydrates comes to an end. First, fat is consumed, the oxidation of which releases significantly more energy than from an equal volume of carbohydrates and proteins. Therefore, fat in animals represents the main “strategic reserve” of energy resources. In plants, starch plays the role of an energy reserve. When stored, it takes up significantly more space than the energy equivalent amount of fat. This is not a hindrance for plants, since they are immobile and do not carry supplies on themselves, like animals. You can extract energy from carbohydrates much faster than from fats. Proteins perform many important functions in the body, and therefore are involved in energy metabolism only when the resources of sugars and fats are depleted, for example, during prolonged fasting.
PHOTOSYNTHESIS. Photosynthesis is a process during which the energy of solar rays is converted into the energy of chemical bonds of organic compounds. In plant cells, processes associated with photosynthesis occur in chloroplasts. Inside this organelle there are membrane systems in which pigments are embedded that capture the radiant energy of the Sun. The main pigment of photosynthesis is chlorophyll, which absorbs predominantly blue and violet, as well as red rays of the spectrum. Green light is reflected, so chlorophyll itself and the parts of plants that contain it appear green.
There are two phases in photosynthesis - light And dark(Fig. 53). The actual capture and conversion of radiant energy occurs during the light phase. When absorbing light quanta, chlorophyll goes into an excited state and becomes an electron donor. Its electrons are transferred from one protein complex to another along the electron transport chain. The proteins of this chain, like pigments, are concentrated on the inner membrane of chloroplasts. When an electron moves along a chain of carriers, it loses energy, which is used for the synthesis of ATP. Some of the electrons excited by light are used to reduce NDP (nicotinamide adenine dinucleotiphosphate), or NADPH.
Rice. 53. Reaction products of the light and dark phases of photosynthesis
Under the influence of sunlight, water molecules are also broken down in chloroplasts - photolysis; in this case, electrons appear that compensate for their losses by chlorophyll; This produces oxygen as a by-product:
Thus, the functional meaning of the light phase is the synthesis of ATP and NADPH by converting light energy into chemical energy.
Light is not needed for the dark phase of photosynthesis to occur. The essence of the processes taking place here is that the ATP and NADPH molecules produced in the light phase are used in a series of chemical reactions that “fix” CO2 in the form of carbohydrates. All dark phase reactions take place inside chloroplasts, and the carbon dioxide ADP and NADP released during “fixation” are again used in light phase reactions for the synthesis of ATP and NADPH.
The overall equation for photosynthesis is as follows:
RELATIONSHIP AND UNITY OF PLASTIC AND ENERGY EXCHANGE PROCESSES. The processes of ATP synthesis occur in the cytoplasm (glycolysis), in mitochondria (cellular respiration) and in chloroplasts (photosynthesis). All reactions occurring during these processes are reactions of energy exchange. The energy stored in the form of ATP is consumed in plastic exchange reactions for the production of proteins, fats, carbohydrates and nucleic acids necessary for the life of the cell. Note that the dark phase of photosynthesis is a chain of reactions, plastic exchange, and the light phase is energy exchange.
The interrelation and unity of the processes of energy and plastic exchange is well illustrated by the following equation:
When reading this equation from left to right, we get the process of oxidation of glucose to carbon dioxide and water during glycolysis and cellular respiration, associated with the synthesis of ATP (energy metabolism). If you read it from right to left, you get a description of the reactions of the dark phase of photosynthesis, when glucose is synthesized from water and carbon dioxide with the participation of ATP (plastic exchange).
CHEMOSYNTHESIS. In addition to photoautotrophs, some bacteria (hydrogen bacteria, nitrifying bacteria, sulfur bacteria, etc.) are also capable of synthesizing organic substances from inorganic ones. They carry out this synthesis due to the energy released during the oxidation of inorganic substances. They are called chemoautotrophs. These chemosynthetic bacteria play an important role in the biosphere. For example, nitrifying bacteria convert ammonium salts that are not available for absorption by plants into nitric acid salts, which are well absorbed by them.
Cellular metabolism consists of reactions of energy and plastic metabolism. During energy metabolism, organic compounds with high-energy chemical bonds - ATP - are formed. The energy required for this comes from the oxidation of organic compounds during anaerobic (glycolysis, fermentation) and aerobic (cellular respiration) reactions; from sunlight, the energy of which is absorbed in the light phase (photosynthesis); from the oxidation of inorganic compounds (chemosynthesis). ATP energy is spent on the synthesis of organic compounds necessary for the cell during plastic exchange reactions, which include reactions of the dark phase of photosynthesis.
- What are the differences between plastic and energy metabolism?
- How is the energy of sunlight converted into the light phase of photosynthesis? What processes take place during the dark phase of photosynthesis?
- Why is photosynthesis called the process of reflecting planetary-cosmic interaction?
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