May/June 2024

The diagram displays a stage micrometer scale as seen through an eyepiece graticule, at a magnification of $\times 200$. At the same magnification, a chloroplast is found to be 4 eyepiece graticule divisions in length. What is the length of the chloroplast?

The microscope in cell studies

In what correct sequence are the cell locations involved in the production of an extracellular enzyme?

Proteins

The graph illustrates the pattern for an enzyme-catalysed reaction. Which labels are right for the x-axis and the y-axis?

Factors that affect enzyme action

Which of the following statements about the Michaelis-Menten constant ($K_m$) are correct?

Mode of action of enzymes

The diagram illustrates how nicotine is carried from the blood plasma into a cell by a cotransporter mechanism. In phloem tissue, a cotransporter mechanism transfers sucrose into the cytoplasm of a companion cell. Which statement accurately describes a similarity between the cotransport of nicotine and the cotransport of sucrose?

Movement into and out of cells

The diagram illustrates a straightforward metabolic pathway. $W \rightarrow X \rightarrow Y \rightarrow Z$ The letters W, X, Y and Z stand for four different substances. At every stage in the diagram, the substrate is changed in a chemical reaction that is catalysed by an enzyme. This reaction forms the next substance in the pathway. Which statements accurately describe the enzymes involved in this metabolic pathway?

Mode of action of enzymes

A student investigated how blood cells respond to two different salt solution concentrations. The student placed each concentration of salt solution onto one of two microscope slides, and then added a small drop of fresh blood to each slide. Both slides were examined with the high-power lens of a microscope, and the student recorded the observations. slide 1: No red blood cells could be seen. slide 2: The red blood cells could be seen but appeared slightly crinkled. Which row gives the correct explanation for the results observed? (key: $\Psi$ = water potential)

Movement into and out of cells

Which statement gives the correct description of facilitated diffusion?

Movement into and out of cells

Which row is correct about stem cells?

Cells as the basic units of living organisms

Eukaryotic organisms enlarge and become bigger because of cell division. The diagram shows several stages of mitosis, with one stage absent, marked X. What happens in stage X?

Chromosome behaviour in mitosis

The graphs display different distance measurements recorded from the beginning of metaphase of mitosis. The graphs are drawn to scale relative to each other. Which row correctly matches each graph to the distance measurement?

Chromosome behaviour in mitosis

What diameter range is usually found in prokaryotic cells?

Cells as the basic units of living organisms

Which row correctly describes the beginning of anaphase of mitosis?

Chromosome behaviour in mitosis

The diagrams illustrate the chemical structures of four bases. Which diagrams represent thymine and cytosine?

Structure of nucleic acids and replication of DNA

The diagram displays the nucleotide sequence of a short region of the transcribed strand of a gene: CGG GCC CCG CGG. The table lists the amino acids that are coded for by 10 mRNA codons. What is the order of the four amino acids in the polypeptide translated from this short section of a gene?

Proteins

What is needed for the process of translation?

Proteins

The electron micrograph displays a longitudinal section through part of a plant stem. What is the name of the structure labelled X?

Structure of transport tissues

What substance causes xylem vessel walls to be impermeable to water?

Structure of transport tissues

The electrical impulse travels through the following tissues during the cardiac cycle. 1 atrioventricular node 2 muscle wall of atria 3 Purkyne tissue 4 sinoatrial node What sequence does the electrical impulse follow during the cardiac cycle?

The heart

The graph illustrates how the volume of the ventricles changes over one cardiac cycle. Which row is correct for the atrioventricular valve at P and for the semilunar valve at R?

The heart

The graph illustrates the effect of varying oxygen concentration on the percentage oxygen saturation of human haemoglobin and cat haemoglobin in normal physiological conditions. The partial pressure of carbon dioxide remained fixed at $5.0\,\text{kPa}$ and the temperature remained fixed at $37^\circ\text{C}$. Which conclusion is supported by the graph?

Proteins

Which statement is correct about the way oxygen combines with haemoglobin?

Proteins

The diagram illustrates a typical animal cell. In which part would nucleic acids be found?

Structure of nucleic acids and replication of DNA

In what ways are alveoli adapted to carry out their function?

Movement into and out of cells

The diagram illustrates oxygen moving by diffusion from the air space within an alveolus into the blood across the gaseous exchange surface. What would increase the rate at which oxygen diffuses from the alveolus into the blood?

Movement into and out of cells

Which tissues can be found in a bronchus?

The gas exchange system

For efficient gaseous exchange to take place in the human lungs, steep concentration gradients must be kept in place. Which row shows correctly how steep concentration gradients can be maintained?

Movement into and out of cells

A scientist studied how an antibiotic affected the treatment of cholera. 320 people who had cholera were split into two groups. One group received the antibiotic, whereas the other group did not receive the antibiotic. Both groups were given fluids that contained sugars and mineral salts (oral rehydration therapy). The scientist noted the number of days each person had diarrhoea. The table below gives the results. Treatment: antibiotic and oral rehydration therapy, mean time person had diarrhoea = 3.2 days; oral rehydration therapy, mean time person had diarrhoea = 5.3 days. Calculate the percentage decrease in the mean time that a person had diarrhoea when the antibiotic was used.

Antibiotics

In what way does the antibiotic penicillin affect the metabolism of a bacterial cell?

Factors that affect enzyme action

Scientists examined multidrug-resistant bacterial infections in children that were caused by one type of bacteria from 2007 to 2015. The proportion of multidrug-resistant infections increased from 0.2% to 1.5%. What percentage increase in multidrug-resistant infections occurred between 2007 and 2015?

Antibiotics

Whooping cough is a very contagious illness of the gas exchange system, caused by the bacterium Bordetella pertussis. Which method gives infants protection against whooping cough and lowers the likelihood of developing this disease later?

Antibodies and vaccination

The electron micrograph displays a kind of blood cell. What conclusion can be drawn from the electron micrograph?

The microscope in cell studies

Why does mitosis play an important role in the immune response?

Replication and division of nuclei and cells

Which structure is present in a typical bacterial cell?

Cells as the basic units of living organisms

What is combined with a B-lymphocyte to create a hybridoma cell in monoclonal antibody production?

Proteins

What is the greatest number of hydrogen bonds that can be formed between one water molecule and other water molecules?

Water

The diagrams illustrate the structures of four amino acids in aqueous solution. Which two structures carry an overall charge?

Proteins

The table lists, for three triglycerides and the fatty acids present in them, how many carbon atoms each molecule has and how many carbon-carbon double bonds it contains. This data is written in the form ‘number of carbon atoms : number of carbon-carbon double bonds’। Which description best fits fatty acid 2 in the $56 : 4$ triglyceride, marked as X in the table?

Carbohydrates and lipids

Collagen molecules are formed from three polypeptide chains that interact with one another. Each individual polypeptide chain contains a repeating amino acid sequence. Glycine appears in almost every third amino acid. Identify the protein structures of collagen that are being described?

Proteins

The masses of the haemoglobin parts are given in the table. There are $1000\,\text{Da}$ in $1\,\text{kDa}$. What is the mass of one haemoglobin molecule in kDa?

Proteins

An electron micrograph shows a prokaryotic cell with a diameter of $1\,\mu\text{m}$ at a magnification of $50\,000$ times. What is the cell diameter in the electron micrograph?

The microscope in cell studies

Which row shows the anticipated effect on $V_{\max}$ and $K_{m}$ when a competitive reversible inhibitor is introduced into an enzyme-catalysed reaction?

Mode of action of enzymes

The graph illustrates how substrate concentration affects the reaction rates of three enzymes, X, Y, and Z. What is the correct sequence of the affinity of these enzymes for their substrates, beginning with the enzyme that has the greatest affinity?

Factors that affect enzyme action

Which row correctly shows the weak and strong bonds present in the tertiary and quaternary structure of a typical protein?

Proteins

Which row gives the correct description of haemoglobin?

Proteins

Which process always occurs without any use of energy from ATP?

Movement into and out of cells

The diagram illustrates molecule X moving into a cell. Which row indicates a characteristic of molecule X and the effect that the concentration of ATP in the cytoplasm has on the rate at which molecule X enters?

Movement into and out of cells

The electron micrograph shows some human blood cells. Which row indicates correctly the net water movement by osmosis and the water potential of the cytoplasm of cell X compared with the solution around the cells?

Movement into and out of cells

An indicator solution that was red was combined with agar, and the solid that formed was then divided into small cylindrical blocks. These blocks were put into an acid that changes the indicator to yellow, while every other variable was kept unchanged. The block dimensions are given below. Block 1: height $3\text{ mm}$, diameter $6\text{ mm}$. Block 2: height $6\text{ mm}$, diameter $12\text{ mm}$. Block 3: height $8\text{ mm}$, diameter $16\text{ mm}$. To calculate the surface area of a cylinder, use $2\pi rh + 2\pi r^2$. To calculate the volume of a cylinder, use $\pi r^2 h$. Which row gives the correct surface area (SA) to volume (V) ratio for each block and the time taken for the block to turn yellow?

Movement into and out of cells

Which metabolic processes would be especially active in a cell that has just finished cytokinesis?

Replication and division of nuclei and cells

The diagram illustrates a typical mitotic cell cycle and shows the stage reached in the cell cycle by each of four cells, V, W, X and Y. Which row correctly identifies the cells that fit the two descriptions? DNA replication is complete, but the cell has not yet reached its maximum size. Preparation for microtubule formation is almost complete, but chromosomes have not yet condensed.

Replication and division of nuclei and cells

The diagram depicts a plant cell and some labelled structures. Which of the labelled structures are surrounded by a double membrane?

Cells as the basic units of living organisms

The graph displays the mean length of the spindle fibres during mitosis. Which part of the graph indicates when all the centromeres have become detached from the spindle fibres?

Chromosome behaviour in mitosis

The mRNA codons ACU, ACC, ACA and ACG each code for the same amino acid, threonine. Which anticodons could code for an amino acid that is not threonine?

Proteins

Which bond formation is catalysed by DNA polymerase?

Mode of action of enzymes

In eukaryotes, RNA molecules produced during transcription are altered by removing non-coding sequences. After that, the coding sequences are joined together to make mRNA. What are the coding sequences also known as?

Protein synthesis

Which row correctly states the sinks for sucrose transported by mass flow in plants?

Transport mechanisms

The diagram illustrates a transverse section of transport tissue in a plant. Which row correctly identifies cell 1 and cell 2?

Structure of transport tissues

Which statement gives the correct description of solute movement in the symplast pathway?

Movement into and out of cells

Which statement best explains why water molecules are pulled through xylem vessel elements as a result of transpiration?

Water

The diagram illustrates the internal arrangement of the mammalian heart. Which letter indicates the position of the atrioventricular node?

The heart

The diagram illustrates changes in pressure on the left side of the heart during the cardiac cycle. What occurs in the heart at X?

The heart

Which ribosome size is present in mitochondria and in typical prokaryotic cells?

Cells as the basic units of living organisms

Which blood components are found in tissue fluid?

Movement into and out of cells

In the lungs, dissolved carbon dioxide leaves the capillaries in either of two ways: • by diffusion across the endothelial cells of the capillaries • by leaking through pores in the endothelial cells of the capillaries. What is the minimum number of times that a carbon dioxide molecule, after being carried to the lungs in a red blood cell, has to cross a cell surface membrane in order to reach an air space in an alveolus?

Movement into and out of cells

What keeps the steep concentration gradients necessary for effective gas exchange in the lungs in place?

Movement into and out of cells

In which part of the human gas exchange system is cartilage tissue always found?

The gas exchange system

Scientists measured the density of goblet cells in the lungs and the density of mucus in the lungs for three groups of people: • people who do not smoke and do not have lung disease • people who smoke tobacco but do not have lung disease • people who smoke tobacco and have lung disease. The findings are given in the table. What do these data suggest?

The gas exchange system

What disease is caused by Mycobacterium bovis?

Infectious diseases

An antibiotic prevents cross-links from forming between the molecules that make up bacterial cell walls. Which statements explain why bacteria are killed by the antibiotic?

Antibiotics

Researchers studied how raising the concentration of an antibiotic affected the development of antibiotic resistance in bacteria. Four bacterial groups were cultured, and each group received a different antibiotic concentration. For each group, the number of resistant bacteria and the total bacterial population were recorded at intervals over 24 hours. The graphs present the findings. The antibiotic concentrations shown are $0\,\text{mg dm}^{-3}$, $90\,\text{mg dm}^{-3}$, $215\,\text{mg dm}^{-3}$ and $600\,\text{mg dm}^{-3}$. The bacterial population is measured as $\times 10^6$. Which statements are valid conclusions that can be drawn from these results?

Antibiotics

In a primary immune response, what is the correct order in which the events occur?

The immune system

Which statement about the properties of the antigen-binding sites in different antibody molecules is correct?

Proteins

Which row correctly compares typical prokaryotic cells with typical animal cells?

Cells as the basic units of living organisms

The diagram illustrates one stage in the production of monoclonal antibodies. $X$ + cancer cells → hybridoma cells What does $X$ represent?

Antibodies and vaccination

Which row correctly shows the structures found in typical plant cells and typical animal cells?

Cells as the basic units of living organisms

Which row gives the correct answer for cellulose?

Carbohydrates and lipids

Which of the following statements concerning peptide bond formation are correct?

Proteins

The diagram illustrates naturally occurring D-glucose and a glucose form that may be made in a laboratory, called L-glucose. The enzyme glucose oxidase catalyses the oxidation of D-glucose. The enzyme is unable to catalyse the oxidation of L-glucose. Which statement about L-glucose accounts for this?

Mode of action of enzymes

Tests for biological molecules were performed on three solutions, with each solution containing just one kind of biological molecule. The results were recorded as follows. Solution 1: Benedict’s test - blue to orange Solution 2: Benedict’s test after acid hydrolysis - blue to red Solution 3: biuret test - blue to purple Which solutions would contain either sucrose or amylase?

Testing for biological molecules

An eyepiece graticule may be calibrated with a stage micrometer. What is the valid reason for calibrating an eyepiece graticule?

The microscope in cell studies

The diagram shows various molecules in a solution. Which statement could explain what happens when some of the molecules are combined?

Mode of action of enzymes

The influence of substrate concentration on an enzyme-catalysed reaction was investigated under three separate conditions: • no inhibitor was present • a competitive inhibitor was present • a non-competitive inhibitor was present. The results are shown in the graph. Which row is correct?

Factors that affect enzyme action

Which feature of enzyme activity can be compared using the Michaelis-Menten constant?

Mode of action of enzymes

The number of substrate molecules that one enzyme molecule can turn into product in 1 second is known as the turnover number. It is measured when the conditions are optimum for that particular enzyme-catalysed reaction. Catalase: 2 800 000 Carbonic anhydrase: 600 000 Phosphatase: 971 Protease: 100 By what factor is catalase faster than phosphatase in converting substrate into product?

Mode of action of enzymes

A red indicator solution was combined with agar, and the solid formed was then sliced into small cuboid blocks. The blocks were put into an acid that changes the indicator to yellow, while every other variable was kept the same. The dimensions of the three blocks used are shown. Block 1: $3\,\text{mm} \times 3\,\text{mm} \times 3\,\text{mm}$ Block 2: $8\,\text{mm} \times 8\,\text{mm} \times 8\,\text{mm}$ Block 3: $11\,\text{mm} \times 11\,\text{mm} \times 11\,\text{mm}$ Which row gives the correct surface area (SA) to volume (V) ratio for each block, together with the time needed for the block to turn yellow?

Movement into and out of cells

The statements below outline some of the stages involved in exocytosis of glycoprotein molecules. 1. The Golgi body membrane folds in around glycoprotein molecules. 2. The vesicle attaches to, then fuses with, the cell surface membrane. 3. A vesicle linked to microtubules travels through the cytoplasm. 4. A secretory vesicle is formed. Which sequence of events is correct for exocytosis?

Movement into and out of cells

Four cylinders of equal size, A, B, C and D, were taken from potatoes that had been kept for different periods of time. The cylinders were weighed, placed in $10\%$ salt solution for 45 minutes and then weighed again. The percentage change in mass was then worked out. Which cylinder had a water potential closest to that of the $10\%$ salt solution?

Movement into and out of cells

After one cell cycle, the contents of a daughter cell are compared with those of the parent cell. Which row is correct?

Replication and division of nuclei and cells

A high-power photomicrograph shows a cell at one stage of mitosis. The chromosomes can be seen arranged along the cell equator, but there is no nuclear envelope. Which stage of mitosis is shown in the photomicrograph?

Chromosome behaviour in mitosis

Which statements concerning the cell cycle are correct?

Replication and division of nuclei and cells

The image shows an electron micrograph of a typical eukaryotic cell. What conclusion can be drawn about the eukaryotic cell from the electron micrograph?

The microscope in cell studies

A scientist uses a fluorescent dye to stain the chromosomes in a plant cell in order to view the telomeres. This cell contains 38 chromosomes. How many telomeres would the scientist see in one of the nuclei during telophase of mitosis?

Chromosome behaviour in mitosis

In semi-conservative DNA replication, an enzyme unzips the double helix. Which diagram illustrates the way the strands are replicated?

Replication and division of nuclei and cells

A transcription error causes one nucleotide to be removed from the centre of a primary transcript. mRNA is produced from the primary transcript. Which statement describes one possible consequence of this deletion for the protein translated from this mRNA?

Proteins

Which of the following statements about translation are correct?

Proteins

A molecule of mRNA took part in translation. A section of its base sequence is shown below. GAU CUG UAA CGG No introns were present in the part of DNA that was transcribed to produce this mRNA. What is the base sequence of the non-transcribed DNA strand for this section?

Proteins

Which characteristics of water depend on hydrogen bonding between water molecules?

Water

Which substances in xylem tissue are not permeable to water and stop the vessels from collapsing?

Structure of transport tissues

The electron micrograph illustrates a longitudinal section through phloem tissue. Which student’s drawing of a sieve tube element is drawn and labelled correctly?

Structure of transport tissues

Carrier proteins in the cell surface membranes of companion cells take part in moving assimilates into phloem sieve tubes. The diagram shows how two kinds of carrier protein are used in this process. What are the substances labelled X and Y?

Movement into and out of cells

The diagram illustrates how pressure changes over two cardiac cycles. Which arrow shows atrial systole?

The microscope in cell studies

Which characteristics occur in typical eukaryotes as well as in typical bacteria?

Cells as the basic units of living organisms

An abnormal heartbeat may happen because the atria receive electrical stimulation that is ineffective. Which part of the heart could be damaged, leading to this abnormal heartbeat?

The microscope in cell studies

The diagram illustrates the effect that three different carbon dioxide concentrations have on the oxygen dissociation curve for human haemoglobin. X represents partial pressure of carbon dioxide: $3.0\ \text{kPa}$ Y represents partial pressure of carbon dioxide: $5.0\ \text{kPa}$ Z represents partial pressure of carbon dioxide: $7.0\ \text{kPa}$ What effect does an increase in carbon dioxide concentration have on haemoglobin?

Proteins

Which reactions are occurring in the blood within a capillary adjacent to an alveolus? 1. $\text{Hb} + 4\text{O}_2 \rightarrow \text{HbO}_8$ 2. $\text{H}_2\text{O} + \text{CO}_2 \rightarrow \text{H}_2\text{CO}_3$ 3. $\text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^-$ Key: Hb = haemoglobin

Proteins

Which part of the gas exchange system is always supported by cartilage?

The gas exchange system

Carbon dioxide and oxygen diffuse between the air in the alveoli and the blood in the capillaries of the lung. Which partial pressures of these gases would make gaseous exchange possible?

Movement into and out of cells

The diagram shows a transverse section of a trachea. Which labelled tissue stops the trachea from collapsing?

The gas exchange system

Through which layers of cells does an oxygen molecule diffuse as it moves from an alveolus into an alveolar capillary?

Movement into and out of cells

Bacteria can be grouped by comparing differences in cell wall structure. These differences can be revealed with the Gram stain. The diagram below shows part of a Gram-positive bacterium and part of a Gram-negative bacterium, both drawn on the same scale. The antibiotic penicillin destroys bacteria by preventing the formation of cell walls during bacterial cell growth. Which type of bacteria would be killed more readily by penicillin, and why?

Antibiotics

Which statements are connected with TB or its pathogen?

Infectious diseases

The events shown happen during the primary immune response to a particular pathogen. Which row indicates the correct order of these events?

The immune system

Which kind of cell would have the greatest fraction of its volume occupied by membrane-bound cell structures enclosed by a single membrane?

Cells as the basic units of living organisms

Influenza is a contagious disease caused by a virus. A person can catch influenza more than once. Which statements give the reasons why influenza can be caught more than once?

Antibodies and vaccination

Why do the phosphate heads of phospholipids become polar?

Fluid mosaic membranes

Which statements describe features of cellulose that adapt it for its role in plant cells?

Carbohydrates and lipids

Which structure represents $\alpha$-glucose?

Carbohydrates and lipids

What cannot take place as a result of a condensation reaction?

Carbohydrates and lipids

Which statement about the quaternary structure of proteins is correct?

Proteins