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ЦТ Biology practice questions

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Question 1Biology as a science: methods of biological research, levels of organization of living matter

Which property is shared by all living systems and is used as a basic criterion for distinguishing living matter from non-living matter?

  1. Constant internal composition maintained by metabolism Correct answer.
  2. Presence of a rigid cell wall
  3. Fixed crystalline structure of molecules
  4. Ability to move from place to place

Explanation

Living systems maintain a relatively stable internal environment through continuous metabolism, exchanging matter and energy with their surroundings. This self-regulation is a universal property of life at every level of organization, whereas the other listed features occur only in some organisms or in non-living objects.

Question 2Biology as a science: methods of biological research, levels of organization of living matter

A researcher studies how a single enzyme molecule changes its shape when it binds a substrate. Which level of organization of living matter does this study directly address?

  1. Biogeocenotic level
  2. Molecular level Correct answer.
  3. Organism level
  4. Population-species level

Explanation

The molecular level deals with the structure and interactions of biological macromolecules such as proteins, nucleic acids and lipids. Studying conformational changes of one enzyme molecule therefore belongs to this level, which is the lowest level of organization of living matter.

Question 3Biology as a science: methods of biological research, levels of organization of living matter

Which method of biological research allows establishing a cause-and-effect relationship between a factor and an observed biological process?

  1. Laboratory experiment with a control group Correct answer.
  2. Comparative analysis of related species
  3. Statistical processing of collected data
  4. Descriptive observation of natural objects

Explanation

A controlled experiment deliberately changes one factor while keeping others constant, so any difference between the experimental and control groups can be attributed to that factor. This is what makes it possible to establish a causal link rather than a mere correlation or description.

Question 4Biology as a science: methods of biological research, levels of organization of living matter

A scientist uses a light microscope to examine a preparation. Which characteristic of the object can be determined with this instrument?

  1. The three-dimensional structure of a protein
  2. The number of mitochondria in a cell
  3. The sequence of nucleotides in a gene
  4. The arrangement of cells in a tissue Correct answer.

Explanation

A light microscope resolves structures at the level of cells and tissues, so the relative arrangement of cells in a preparation can be observed. Molecular details such as nucleotide sequences or protein tertiary structure lie below its resolution limit and require other techniques.

Question 5Biology as a science: methods of biological research, levels of organization of living matter

Which level of organization of living matter is formed by interacting populations of different species together with their abiotic environment?

  1. Biogeocenotic level Correct answer.
  2. Cellular level
  3. Tissue level
  4. Organ level

Explanation

The biogeocenotic level comprises a community of populations of different species together with the abiotic conditions of a defined area, forming a self-regulating ecosystem. It is a supra-organismic level that integrates living and non-living components in a single functional unit.

Question 6Biology as a science: methods of biological research, levels of organization of living matter

In an experiment, two groups of plants are grown under identical conditions except that one group receives a nutrient solution and the other receives pure water. What is the role of the group receiving pure water?

  1. It is a replicate of the experimental group
  2. It is the experimental group
  3. It is the control group Correct answer.
  4. It is an additional variable

Explanation

The group that does not receive the tested factor serves as the control, providing a baseline against which the effect of the nutrient solution is measured. Keeping all other conditions identical ensures that any difference between the groups can be attributed to the added nutrient.

Question 7Biology as a science: methods of biological research, levels of organization of living matter

Which statement correctly describes the relationship between the cellular and organism levels of organization?

  1. Organism level precedes the cellular level in hierarchy
  2. A multicellular organism is an integrated system of cells differentiated by function Correct answer.
  3. Cells exist independently and are never integrated into a whole organism
  4. Organism level exists only in unicellular forms

Explanation

In multicellular organisms, cells differentiate to perform specific functions and become integrated into tissues, organs and organ systems that together form the whole organism. The organism level is therefore higher in the hierarchy and emerges from coordinated cell activity.

Question 8Biology as a science: methods of biological research, levels of organization of living matter

Which technique would be most appropriate for separating cell organelles according to their density?

  1. Chromatography of proteins
  2. Staining with a vital dye
  3. Centrifugation of a cell homogenate Correct answer.
  4. Electrophoresis in a gel

Explanation

Centrifugation separates particles suspended in a liquid by density and size, so organelles in a homogenate sediment at different speeds and can be isolated in fractions. The other methods separate molecules by charge, size or affinity rather than intact organelles by density.

Question 9Biology as a science: methods of biological research, levels of organization of living matter

A researcher observes that a certain trait appears more often in one population than in another and then formulates a testable proposal to explain it. Which pair of scientific methods does this illustrate?

  1. Modeling and simulation
  2. Classification and description
  3. Observation and hypothesis formation Correct answer.
  4. Experiment and measurement

Explanation

Recording a pattern in natural populations is observation, and proposing an explanation that can be tested is hypothesis formation. Together they form the starting point of the scientific method, which later requires experimental verification of the hypothesis.

Question 10Biology as a science: methods of biological research, levels of organization of living matter

Which feature distinguishes the population-species level from the organism level of organization?

  1. It describes the exchange of matter between an organism and its environment
  2. It involves a gene pool shared by a group of individuals of one species Correct answer.
  3. It concerns the structure of a single individual
  4. It is limited to the interaction of organs within one body

Explanation

At the population-species level the unit is a population, a group of individuals of the same species that share a common gene pool and interbreed. This gene pool and its changes over generations are what distinguish this level from processes occurring within a single organism.

Question 11Biology as a science: methods of biological research, levels of organization of living matter

Why is a hypothesis required to be testable before it can be accepted as a scientific explanation?

  1. Because a hypothesis must be expressed mathematically
  2. Because untestable statements cannot be confirmed or refuted by observation or experiment Correct answer.
  3. Because testability guarantees that the hypothesis is true
  4. Because only hypotheses about molecules are scientific

Explanation

A scientific hypothesis must generate predictions that can be checked against evidence, so that it can be supported or rejected. Without testability there is no way to distinguish a valid explanation from an arbitrary claim, which is why testability is a basic requirement of the scientific method.

Question 12Biology as a science: methods of biological research, levels of organization of living matter

Which of the following is an example of a biological process studied at the tissue level?

  1. Transmission of a nerve impulse along one neuron
  2. Crossing of individuals within a population
  3. Formation of the epithelial lining of the intestine Correct answer.
  4. Circulation of carbon in a forest ecosystem

Explanation

A tissue is a group of cells similar in structure and function, so the formation of an epithelial lining, which involves coordinated cells of one type, is a tissue-level process. The other examples belong to the cellular, population and ecosystem levels respectively.

Question 13Cytology: chemical composition of the cell, cell structure and functions of organelles

Which element is the main structural framework of all organic molecules in the cell?

  1. Iron
  2. Carbon Correct answer.
  3. Phosphorus
  4. Nitrogen

Explanation

Carbon atoms form stable covalent bonds with one another and with other elements, creating chains and rings that serve as the skeleton of carbohydrates, lipids, proteins and nucleic acids. This tetravalent bonding capacity is why carbon is the central element of organic chemistry. Other elements are important but attach to that framework rather than forming it.

Question 14Cytology: chemical composition of the cell, cell structure and functions of organelles

Which group of organic compounds is the primary source of quick energy for the cell?

  1. Proteins
  2. Nucleic acids
  3. Carbohydrates Correct answer.
  4. Lipids

Explanation

Carbohydrates such as glucose are oxidized rapidly in glycolysis and respiration, releasing energy that the cell captures as ATP. Their simple structure allows fast breakdown, which is why they serve as the immediate fuel. Lipids store more energy per gram but are mobilized more slowly.

Question 15Cytology: chemical composition of the cell, cell structure and functions of organelles

What is the monomer unit that repeats to form a polysaccharide such as starch?

  1. Amino acid
  2. Nucleotide
  3. Monosaccharide Correct answer.
  4. Fatty acid

Explanation

Polysaccharides are polymers built by joining monosaccharide units through glycosidic bonds, with the loss of a water molecule in each linkage. Starch, glycogen and cellulose are all assembled from glucose monomers. The other listed molecules belong to entirely different classes of polymers or to lipids.

Question 16Cytology: chemical composition of the cell, cell structure and functions of organelles

Which bond holds the two strands of a DNA double helix together?

  1. Hydrogen bond Correct answer.
  2. Peptide bond
  3. Ester bond
  4. Glycosidic bond

Explanation

Complementary bases on opposite strands pair through hydrogen bonds: adenine with thymine and guanine with cytosine. These bonds are individually weak, which allows the strands to separate during replication and transcription, yet collectively they stabilize the helix. The sugar-phosphate backbone is held by stronger covalent phosphodiester bonds.

Question 17Cytology: chemical composition of the cell, cell structure and functions of organelles

Which organelle is the site of aerobic ATP synthesis through the electron transport chain?

  1. Golgi apparatus
  2. Mitochondrion Correct answer.
  3. Ribosome
  4. Lysosome

Explanation

The inner mitochondrial membrane carries the electron transport chain and ATP synthase, so oxidative phosphorylation occurs there. The folded cristae increase the membrane area available for these reactions. Other organelles perform synthesis, sorting or digestion rather than bulk ATP production.

Question 18Cytology: chemical composition of the cell, cell structure and functions of organelles

Which structure controls the passage of substances between the nucleus and the cytoplasm?

  1. Nucleolus
  2. Nuclear lamina
  3. Chromatin
  4. Nuclear pore Correct answer.

Explanation

The nuclear envelope is perforated by nuclear pores, which are channels that regulate the transport of proteins, RNA and small molecules in both directions. This selective traffic is essential because transcription and translation occur in separate compartments. The nucleolus and chromatin lie inside the nucleus and do not gate transport.

Question 19Cytology: chemical composition of the cell, cell structure and functions of organelles

Which organelle carries out the synthesis of proteins destined for secretion?

  1. Rough endoplasmic reticulum Correct answer.
  2. Smooth endoplasmic reticulum
  3. Peroxisome
  4. Centriole

Explanation

Ribosomes attached to the rough endoplasmic reticulum synthesize proteins that are threaded into the ER lumen, folded and then routed toward the Golgi and secretion. The bound ribosomes distinguish this compartment from the smooth ER. Peroxisomes and centrioles have unrelated functions.

Question 20Cytology: chemical composition of the cell, cell structure and functions of organelles

Which property of the phospholipid bilayer allows small nonpolar molecules to cross membranes readily?

  1. Its high protein content
  2. Its rigid crystalline lattice
  3. Its hydrophobic interior Correct answer.
  4. Its net positive charge

Explanation

Phospholipids arrange with hydrophilic heads outward and hydrophobic tails inward, producing a nonpolar core. Small uncharged molecules such as oxygen and carbon dioxide dissolve in this oily region and diffuse through. Ions and polar molecules cannot pass this barrier without transport proteins.

Question 21Cytology: chemical composition of the cell, cell structure and functions of organelles

A cell is placed in a hypertonic solution. What happens to an animal cell without a cell wall?

  1. It swells and bursts
  2. It stays unchanged
  3. It forms a rigid wall
  4. It shrinks as water leaves Correct answer.

Explanation

In a hypertonic solution the solute concentration outside exceeds that inside, so water moves out by osmosis. An animal cell lacking a wall cannot resist this loss and shrinks, often crenating. A plant cell would instead show plasmolysis as the membrane pulls away from the wall.

Question 22Cytology: chemical composition of the cell, cell structure and functions of organelles

A toxin blocks the function of the Golgi apparatus. Which process is most directly impaired?

  1. Oxidation of fatty acids
  2. Modification and sorting of secreted proteins Correct answer.
  3. Transcription of DNA into mRNA
  4. Translation of mRNA on ribosomes

Explanation

The Golgi apparatus receives proteins from the endoplasmic reticulum, modifies them by glycosylation and other changes, and sorts them into vesicles for delivery. Blocking it therefore disrupts the secretory pathway downstream of synthesis. Transcription, translation and fatty acid oxidation occur elsewhere.

Question 23Cytology: chemical composition of the cell, cell structure and functions of organelles

Why does a plant cell remain firm in a hypotonic solution while an animal cell would burst?

  1. The plant cell lacks aquaporins
  2. The vacuole pumps water outward
  3. The cell wall exerts turgor pressure opposing water entry Correct answer.
  4. The plant cell has no plasma membrane

Explanation

As water enters, the plant cell's vacuole expands and presses the protoplast against the rigid cellulose wall. The wall resists stretching and generates turgor pressure that balances the osmotic influx, so the cell becomes turgid rather than lysing. An animal cell has no such constraint.

Question 24Cytology: chemical composition of the cell, cell structure and functions of organelles

Which feature distinguishes prokaryotic cells from eukaryotic cells?

  1. Presence of a plasma membrane
  2. Absence of a membrane-bound nucleus Correct answer.
  3. Presence of DNA
  4. Presence of ribosomes

Explanation

Prokaryotes keep their circular DNA in a nucleoid region without a nuclear envelope, whereas eukaryotes enclose chromosomes in a true nucleus. This compartmentalization is the defining difference between the two cell types. Ribosomes, plasma membranes and DNA are shared by both.

Question 25Cytology: chemical composition of the cell, cell structure and functions of organelles

Which function is performed by the smooth endoplasmic reticulum in liver cells?

  1. Synthesis of ribosomal RNA
  2. Detoxification of harmful substances Correct answer.
  3. Digestion of worn organelles
  4. Formation of the mitotic spindle

Explanation

Hepatocytes are rich in smooth ER, whose enzymes such as cytochrome P450 oxidize drugs and toxins to make them more soluble for excretion. This compartment also synthesizes lipids and stores calcium. Ribosomal RNA synthesis, autophagy and spindle formation belong to other structures.

Question 26Cytology: chemical composition of the cell, cell structure and functions of organelles

A ribosome is synthesizing a protein that will be exported from the cell. Where does translation begin?

  1. On the inner mitochondrial membrane
  2. In the cytosol on free ribosomes and continues on the rough ER Correct answer.
  3. Inside the lysosome
  4. Inside the Golgi lumen

Explanation

Translation of secretory proteins starts on free ribosomes in the cytosol. A signal peptide then directs the ribosome to the rough ER, where synthesis continues and the growing chain is threaded into the lumen. This co-translational targeting is the standard route for secreted proteins.

Question 27Cytology: chemical composition of the cell, cell structure and functions of organelles

Which component of the cytoskeleton forms the mitotic spindle and tracks for vesicle transport?

  1. Intermediate filaments
  2. Microfilaments
  3. Cellulose fibers
  4. Microtubules Correct answer.

Explanation

Microtubules are hollow tubes of tubulin that assemble into the spindle during mitosis and serve as tracks along which motor proteins move vesicles. Their dynamic instability allows rapid rearrangement. Microfilaments and intermediate filaments have different mechanical roles.

Question 28Cytology: chemical composition of the cell, cell structure and functions of organelles

Which statement best describes the fluid mosaic model of the membrane?

  1. A dynamic lipid bilayer with proteins moving within it Correct answer.
  2. A rigid layer of carbohydrates enclosing the cell
  3. A fixed bilayer with proteins locked in place
  4. A single layer of proteins coated with lipids

Explanation

The model pictures the membrane as a fluid phospholipid bilayer in which proteins are embedded or attached and can move laterally. Cholesterol modulates fluidity, and carbohydrates on the outer surface form the glycocalyx. This dynamic arrangement underlies membrane fusion, transport and signaling.

Question 29Cytology: chemical composition of the cell, cell structure and functions of organelles

Which organelle contains hydrolytic enzymes active at acidic pH and digests material taken in by phagocytosis?

  1. Smooth ER
  2. Peroxisome
  3. Nucleolus
  4. Lysosome Correct answer.

Explanation

Lysosomes maintain an acidic interior by proton pumping and contain acid hydrolases that break down macromolecules, engulfed particles and worn organelles. Their low pH optimizes enzyme activity and protects the cytosol. Peroxisomes use oxidative enzymes instead.

Question 30Cytology: chemical composition of the cell, cell structure and functions of organelles

A leaf cell is illuminated and actively photosynthesizing. Which organelle is most directly responsible for fixing carbon dioxide into organic matter?

  1. Mitochondrion
  2. Chloroplast Correct answer.
  3. Ribosome
  4. Golgi apparatus

Explanation

Chloroplasts contain the enzymes of the Calvin cycle in the stroma, where carbon dioxide is fixed into sugars using ATP and NADPH from the light reactions. Thylakoid membranes generate those energy carriers. Mitochondria release energy from organic molecules rather than fixing carbon.

Question 31Cytology: chemical composition of the cell, cell structure and functions of organelles

Which molecule serves as the universal energy currency that couples exergonic and endergonic reactions?

  1. Glucose
  2. ATP Correct answer.
  3. Cholesterol
  4. DNA

Explanation

ATP stores energy in its terminal phosphate bond and releases it when hydrolyzed to ADP and phosphate, driving endergonic reactions. Its rapid regeneration makes it a convenient short-term energy shuttle. Glucose is a fuel reserve rather than the direct currency.

Question 32Cytology: chemical composition of the cell, cell structure and functions of organelles

A cell is treated with a drug that destroys all ribosomes. Which immediate consequence is expected?

  1. ATP synthesis stops
  2. Protein synthesis stops Correct answer.
  3. DNA replication stops
  4. Osmosis stops

Explanation

Ribosomes are the only machinery that translates mRNA into polypeptides, so their destruction halts protein synthesis at once. Existing proteins persist for a time, but no new ones are made. Replication, respiration and osmosis depend on other structures and continue initially.

Question 33Cytology: chemical composition of the cell, cell structure and functions of organelles

Which structural feature of the inner mitochondrial membrane increases the efficiency of oxidative phosphorylation?

  1. Its double lipid coat
  2. Its content of chlorophyll
  3. Its folds called cristae Correct answer.
  4. Its smooth spherical shape

Explanation

The inner membrane is folded into cristae, greatly expanding the surface area that holds respiratory chain complexes and ATP synthase. More membrane area means more capacity for electron transport and proton gradient formation. Chlorophyll and a smooth profile belong to other structures.

Question 34Cytology: chemical composition of the cell, cell structure and functions of organelles

A protein synthesized on the rough ER lacks a functional signal peptide. What is the most likely consequence?

  1. It becomes a membrane lipid
  2. It remains in the cytosol instead of entering the ER Correct answer.
  3. It is glycosylated in the Golgi
  4. It is imported into the nucleus

Explanation

The signal peptide is recognized by a signal recognition particle that targets the ribosome to the ER. Without a functional signal, the ribosome stays free in the cytosol and the polypeptide is released there. Subsequent Golgi processing and nuclear import depend on correct targeting signals.

Question 35Cytology: chemical composition of the cell, cell structure and functions of organelles

A mutation makes the phospholipid tails of membrane lipids shorter and more saturated. How is membrane fluidity most likely affected?

  1. It becomes dependent only on proteins
  2. It decreases because packing becomes tighter Correct answer.
  3. It increases because the bilayer thins
  4. It stays the same because heads are unchanged

Explanation

Shorter, saturated tails pack more tightly and interact more strongly by van der Waals forces, which lowers fluidity. Unsaturated tails with kinks and longer chains normally keep the bilayer more fluid. Cholesterol can buffer such changes but does not reverse the underlying trend.

Question 36Cytology: chemical composition of the cell, cell structure and functions of organelles

A cell is exposed to a drug that blocks ATP synthesis but leaves the plasma membrane intact. Which transport process continues unaffected?

  1. Sodium-potassium pump activity
  2. Simple diffusion of oxygen into the cell Correct answer.
  3. Phagocytosis of bacteria
  4. Active transport of calcium ions

Explanation

Simple diffusion is passive and driven by a concentration gradient, so it needs no ATP and continues when energy production fails. Pumps and endocytosis consume ATP and would slow or stop. This distinction separates passive from active transport.

Question 37Cytology: chemical composition of the cell, cell structure and functions of organelles

Two cells have equal volumes but one has a much greater surface area of inner membrane in its mitochondria. What can be inferred about that cell?

  1. It cannot perform glycolysis
  2. It has a higher capacity for oxidative ATP production Correct answer.
  3. It relies only on photosynthesis
  4. It lacks a plasma membrane

Explanation

Respiratory chain complexes and ATP synthase reside on the inner mitochondrial membrane, so greater membrane area supports more electron transport and proton pumping per unit volume. Such cells, for example muscle or cardiac cells, can generate ATP at higher rates. Glycolysis and membrane integrity are unaffected.

Question 38Cytology: chemical composition of the cell, cell structure and functions of organelles

Which chemical element is present in all organic compounds of the cell and forms the backbone of their molecules?

  1. Phosphorus
  2. Nitrogen
  3. Carbon Correct answer.
  4. Iron

Explanation

Organic molecules are defined by chains and rings of carbon atoms covalently bonded to one another, so carbon provides the skeleton to which hydrogen, oxygen and other atoms attach. Nitrogen, phosphorus and iron occur in cells but only in certain classes of compounds, not in every organic molecule.

Question 39Cytology: chemical composition of the cell, cell structure and functions of organelles

A cell is placed in a solution whose solute concentration is lower than that of the cytoplasm, and the plasma membrane is freely permeable to water but not to the solute. What is the immediate result?

  1. Water leaves the cell and the cytoplasm becomes more concentrated
  2. Water enters the cell and the cytoplasm becomes more dilute Correct answer.
  3. No net movement of water occurs because the solutions are isotonic
  4. Solute moves from the cell into the surrounding solution

Explanation

Water diffuses across a selectively permeable membrane from the region of higher water potential, which is the dilute external solution, toward the region of lower water potential inside the cell. The incoming water therefore dilutes the cytoplasm, and in an animal cell this can eventually cause swelling and lysis.

Question 40Cytology: chemical composition of the cell, cell structure and functions of organelles

In a eukaryotic cell, a polypeptide destined for the extracellular space is synthesized and processed along a pathway. Which sequence correctly describes the route of this protein?

  1. Golgi apparatus, rough ER, lysosome, secretory vesicle, plasma membrane
  2. Smooth ER, mitochondrion, Golgi apparatus, secretory vesicle, plasma membrane
  3. Rough ER, transport vesicle, Golgi apparatus, secretory vesicle, plasma membrane Correct answer.
  4. Cytosol, smooth ER, nucleus, transport vesicle, plasma membrane

Explanation

Ribosomes on the rough ER synthesize proteins bearing a signal peptide, which are threaded into the ER lumen and packaged into transport vesicles. These vesicles fuse with the Golgi apparatus for modification and sorting, and the finished products leave in secretory vesicles that fuse with the plasma membrane.

Question 41Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

В каких органоидах клетки протекает световая фаза фотосинтеза?

  1. В тилакоидах гран хлоропласта Correct answer.
  2. В матриксе митохондрии
  3. В строме хлоропласта
  4. В цитоплазме клетки

Explanation

Световая фаза связана с мембранами тилакоидов, где расположены фотосистемы, переносчики электронов и АТФ-синтаза. Именно на этих мембранах идёт фотолиз воды и синтез АТФ и НАДФ·Н. Строма служит местом темновой фазы, а не световой.

Question 42Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

Какой газ выделяется при фотосинтезе и образуется при фотолизе воды?

  1. Водород
  2. Углекислый газ
  3. Азот
  4. Кислород Correct answer.

Explanation

При фотолизе молекулы воды в световой фазе образуются протоны, электроны и молекулярный кислород. Кислород является побочным продуктом и выделяется в атмосферу. Углекислый газ, наоборот, поглощается при фиксации углерода.

Question 43Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

Что служит источником энергии для синтеза органических веществ у хемосинтезирующих бактерий?

  1. Энергия окисления неорганических веществ Correct answer.
  2. Энергия гидролиза АТФ из готовой пищи
  3. Энергия солнечного света
  4. Энергия окисления готовых органических веществ

Explanation

Хемосинтез основан на использовании энергии, освобождающейся при окислении неорганических соединений, например аммиака или сероводорода. Эта энергия идёт на восстановление углекислого газа до органических веществ. Свет и готовые органические соединения в этом процессе не нужны.

Question 44Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

В каком компартменте клетки происходит кислородный этап клеточного дыхания?

  1. В лизосоме
  2. В цитоплазме
  3. На внутренней мембране митохондрии Correct answer.
  4. В ядре

Explanation

Кислородный этап связан с внутренней мембраной митохондрии, где расположена дыхательная цепь и АТФ-синтаза. Там электроны передаются на кислород, а энергия используется для синтеза АТФ. Цитоплазма служит местом гликолиза, а не этого этапа.

Question 45Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

Какое вещество является непосредственным источником энергии для большинства реакций клеточного обмена?

  1. Глюкоза
  2. НАДФ·Н
  3. Пировиноградная кислота
  4. АТФ Correct answer.

Explanation

АТФ служит универсальным переносчиком энергии: его гидролиз освобождает энергию, которую используют ферментативные реакции. Глюкоза и пировиноградная кислота лишь запасают энергию, которая преобразуется в АТФ при дыхании.

Question 46Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

Какой процесс относят к пластическому обмену?

  1. Гликолиз
  2. Окислительное фосфорилирование
  3. Синтез белка на рибосоме Correct answer.
  4. Фотолиз воды

Explanation

Пластический обмен, или ассимиляция, объединяет реакции синтеза сложных веществ из более простых с затратой энергии. Синтез белка на рибосоме - типичный пример такого процесса. Гликолиз и окислительное фосфорилирование относятся к энергетическому обмену.

Question 47Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

Сколько молекул АТФ суммарно образуется при полном окислении одной молекулы глюкозы до углекислого газа и воды в аэробной клетке?

  1. 4
  2. 36–38 Correct answer.
  3. 18
  4. 2

Explanation

При полном аэробном окислении глюкозы суммарный выход составляет около 36–38 молекул АТФ. Гликолиз даёт 2 АТФ, цикл Кребса и дыхательная цепь добавляют основную часть. Точное число зависит от способа переноса восстановительных эквивалентов.

Question 48Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

Какие продукты образуются при бескислородном расщеплении глюкозы в клетках животных?

  1. Пировиноградная кислота и кислород
  2. Молочная кислота Correct answer.
  3. Углекислый газ и вода
  4. Этиловый спирт и углекислый газ

Explanation

В животных клетках при недостатке кислорода пировиноградная кислота восстанавливается до молочной кислоты. Такая реакция позволяет окислить НАД·Н и продолжить гликолиз. Спиртовое брожение характерно для дрожжей, а не для животных клеток.

Question 49Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

Какое соединение фиксирует углекислый газ в темновой фазе фотосинтеза у растений?

  1. Пируват
  2. Рибоза
  3. Глицерин
  4. Рибулозобисфосфат Correct answer.

Explanation

В цикле Кальвина углекислый газ присоединяется к пятиуглеродному сахару - рибулозобисфосфату. Реакцию катализирует фермент рибулозобисфосфаткарбоксилаза. Образующееся неустойчивое соединение распадается на две молекулы фосфоглицериновой кислоты.

Question 50Metabolism and energy conversion in the cell (photosynthesis, chemosynthesis, energy metabolism, biosynthesis)

Какие вещества переносят электроны от световых реакций к темновым?

  1. Пировиноградная кислота и НАД·Н
  2. АТФ и НАДФ·Н Correct answer.
  3. Углекислый газ и вода
  4. Глюкоза и кислород

Explanation

Световая фаза накапливает АТФ и восстановленный НАДФ·Н, которые затем используются в темновой фазе. АТФ поставляет энергию, а НАДФ·Н - восстановительные эквиваленты для синтеза сахаров. Без этих переносчиков цикл Кальвина не идёт.