May/June 2020

The photomicrograph reveals the ultrastructure of a section of a cell. Which statement about the kind of cell visible in the photomicrograph is correct?

The microscope in cell studies

The diagram illustrates a protein molecule. Two long polypeptides each form $\alpha$-helices over most of their length and then wind together to make a fibre. At one end, each polypeptide coils into a globular head. Two short polypeptides attach to each globular head. Which description matches the protein structure of this molecule?

Proteins

As the temperature increases, which type of bond will maintain a folded protein in its exact shape for the longest period?

Proteins

Protease enzymes occur in numerous places both inside and outside cells. Four such locations are given. Which of these locations are sites of intracellular hydrolysis?

Mode of action of enzymes

An enzyme has been altered for industrial use. Compared with the unmodified enzyme, it has a lower Michaelis-Menten constant ($K_m$). What is true about the modified enzyme?

Mode of action of enzymes

Reducing some factors will make the cell surface membrane more fluid. Which pair of factors, if decreased, would increase the fluidity of the cell surface membrane?

Fluid mosaic membranes

The diagram illustrates a cell surface membrane. Which of the following statements about the labelled molecules in the membrane are correct?

Fluid mosaic membranes

Potato pieces of equal size were put into test-tubes containing equal volumes of sucrose solution at different concentrations and then left for 30 minutes. Every other variable was kept constant. After 30 minutes, the potato piece in one of the sucrose solution concentrations had remained the same size. What can be concluded from this result?

Movement into and out of cells

Which characteristic of stem cells allows them to replace cells in tissues such as the skin?

Replication and division of nuclei and cells

In prophase, a scientist applies a fluorescent dye to the chromosomes of a diploid animal cell in order to stain the telomeres. This cell contains 32 chromosomes. How many telomeres will the scientist observe?

Chromosome behaviour in mitosis

The diagram illustrates the cell cycle. In which phase do chromosomes condense and become visible?

Chromosome behaviour in mitosis

Which structures occur in typical eukaryotic cells?

Cells as the basic units of living organisms

Which statement is correct about thymine?

Structure of nucleic acids and replication of DNA

A short DNA fragment that was 15 base pairs in length was examined in order to determine the number of nucleotide bases in each polynucleotide strand. Some of the outcomes are shown below. How many nucleotides containing guanine were present in strand 1?

Structure of nucleic acids and replication of DNA

Bacteria were cultivated in a medium in which heavy nitrogen, $^{15}\text{N}$, was the only nitrogen source. After many generations, every bacterial DNA molecule contained heavy nitrogen. The bacteria were then transferred from the heavy nitrogen medium to a medium containing only light nitrogen, $^{14}\text{N}$. Bacteria were taken from each of the following three generations and their DNA was examined. Hybrid DNA includes both heavy and light nitrogen. Which row gives the correct DNA for the first and third generations?

Replication and division of nuclei and cells

A bacterial population is treated with the antibiotic penicillin. The majority of the bacteria die. Nevertheless, some bacteria in the population possess an allele that codes for an enzyme capable of breaking down penicillin. These bacteria are able to survive. Which could account for how these bacterial cells obtained this allele?

Antibiotics

In a dicotyledonous leaf, the palisade mesophyll layer is about twice the thickness of the spongy mesophyll layer. Which plan diagram is the correct one?

The gas exchange system

Several processes help to keep a water potential gradient in plants, enabling water to travel to the highest parts of a plant. Which processes are responsible for keeping this water potential gradient?

Movement into and out of cells

Which statement is correct about how substances absorbed by roots move?

Movement into and out of cells

Which of the four water-molecule arrangements illustrates how water can cohere as it travels upward through a xylem vessel?

Water

Which statement concerning the loading of sucrose into companion cells and then into the phloem sieve tube element is incorrect?

Movement into and out of cells

What accounts for the left and right sides of the heart contracting at the same time?

The heart

A student looked at a slide of human blood using a light microscope and produced a precise drawing of the various cell types. An eyepiece graticule was used so that the relative dimensions of the different cell types were recorded accurately. In the drawing: - red blood cells measured $7\,\text{mm}$ in diameter - lymphocytes measured $6\,\text{mm}$ in diameter - neutrophils measured $14\,\text{mm}$ in diameter. What is the linear magnification of the drawing?

The microscope in cell studies

The statements below show some events in the cardiac cycle, but they are not arranged in the right sequence. Which statement describes the third event to happen in the cardiac cycle?

The heart

The diagram illustrates pressure changes in various regions of the heart throughout one cardiac cycle. At which stage are the semilunar valves open while the atrioventricular valves are shut?

The heart

Which diagram illustrates the events that take place during transport of carbon dioxide by the blood?

Movement into and out of cells

What structures are present in bronchi?

The gas exchange system

Which tissue in the respiratory system is accurately matched to its function?

The gas exchange system

Chronic obstructive pulmonary disease (COPD) includes emphysema. Which changes does emphysema cause to gaseous exchange?

Movement into and out of cells

The diagram illustrates several pathogens that lead to disease in humans and also shows some of the ways they spread. The pathogen types are labelled as follows: 1 bacterium, 2 protoctist, 3 virus. The transmission methods are labelled: X contaminated water, Y coughs and sneezes, Z using a vector. Which row gives the correct number for the pathogen together with the correct letter for its transmission route for cholera and measles?

Infectious diseases

Which factors would cause malaria to be distributed more widely around the world?

Infectious diseases

Teixobactin, an antibiotic, was found in January 2015. It is lethal to some bacteria, including Staphylococcus and Mycobacterium. Most antibiotics act by attaching to proteins. Teixobactin attaches to lipids that are involved in the formation of bacterial cell walls. As a result, bacteria are unlikely to gain resistance to teixobactin rapidly. Which statements account for the fact that bacteria are unlikely to develop resistance to teixobactin quickly?

Carbohydrates and lipids

Which row gives the correct description of the type of immunity acquired by being injected with an antitoxin?

Antibodies and vaccination

A graduated slide is illustrated, with $0.1\,\text{mm}$ intervals observed through an eyepiece graticule. Pollen grains were cultivated in a sugar solution and observed with the eyepiece graticule. Diagram 1 shows the pollen grains at the beginning. Diagram 2 shows the pollen grains after four hours. What is the growth rate of the pollen tubes?

The microscope in cell studies

In an immune response, where can antibodies be found?

Proteins

The table compares two characteristics of a typical eukaryotic cell with those of a typical prokaryotic cell. Which row gives the correct comparison of these cells?

Cells as the basic units of living organisms

The flow chart indicates the outcomes of several tests carried out on a solution containing biochemicals. Benedict’s test: blue; non-reducing sugar test: yellow; iodine test: blue-black; biuret test: purple. Which substances are present in the solution?

Testing for biological molecules

Maltose and sucrose are both disaccharides. Maltose is made from two glucose molecules, whereas sucrose is made from glucose and fructose. Which row gives the molecular formulae for these two disaccharides?

Carbohydrates and lipids

The diagrams illustrate brief segments of several common polysaccharides and modified polysaccharides. The polysaccharides may be described as follows: F is made up of $\beta$-glucose monomers with $1,4$ glycosidic bonds; G is made up of $\alpha$-glucose monomers with $1,4$ glycosidic bonds; H is made up of N-acetylglucosamine monomers with $\beta$-$1,4$ glycosidic bonds. Which row correctly links the numbered diagrams with the descriptions of the polysaccharides?

Carbohydrates and lipids

Which molecules have at least two double bonds?

Carbohydrates and lipids

What does the term resolution of a light microscope mean?

The microscope in cell studies

What is the greatest number of water molecules formed when a triglyceride is synthesised?

Carbohydrates and lipids

What happens when a peptide bond forms between two amino acids?

Proteins

The diagram illustrates the roles of water in living organisms. Which roles depend on hydrogen bonds between water molecules?

Water

The diagram illustrates a metabolic pathway. Reactant $\xrightarrow{\text{enzyme 1}}$ substance X $\xrightarrow{\text{enzyme 2}}$ substance Y $\xrightarrow{\text{enzyme 3}}$ end product. What would happen if a small quantity of a non-competitive inhibitor of enzyme 2 were added?

Factors that affect enzyme action

Two enzymes are introduced into a solution containing a low concentration of a substrate that both can use. Which statement is correct?

Factors that affect enzyme action

The diagram illustrates the fluid mosaic model of membrane structure. Structures 1, 2, 3 and 4 are kinds of molecule. Which kinds of molecules are always the same?

Fluid mosaic membranes

What function does G protein have in cell signalling?

Fluid mosaic membranes

If a small amount of phospholipid is placed in a test-tube of water and the mixture is then shaken vigorously, an emulsion is produced by tiny droplets known as liposomes. Which diagram shows the arrangement of phospholipid molecules in a cross-section of a liposome?

Fluid mosaic membranes

What are the characteristics of facilitated diffusion?

Movement into and out of cells

Which account of chromosome structure is correct?

Chromosome behaviour in mitosis

An electron micrograph reveals a virus of one type at a magnification of $\times 30\,000$. What is the virus's length?

The microscope in cell studies

Which processes make use of mitosis?

Replication and division of nuclei and cells

A drug has been produced to treat some types of cancer. It stops mitosis by attaching to the spindle and stopping sister chromatids from separating and moving to opposite poles of the cell. The photomicrograph displays cells in different phases of mitosis. Which stages of mitosis would still be possible in a cell that is entering prophase and is treated with this drug?

Chromosome behaviour in mitosis

Certain viruses contain single-stranded DNA as their genetic material. To fit inside the protein coat, this DNA molecule must be folded. Which statements about single-stranded DNA are correct?

Structure of nucleic acids and replication of DNA

How many of the following statements are correct about semi-conservative replication of DNA in a eukaryotic cell?

Replication and division of nuclei and cells

A segment of the nucleotide sequence in an mRNA molecule is shown below, with the codons separated by spaces: CAG UAC AGC AAU CUA UAA The translation of these codons is given. Which events would lead to the ending of polypeptide synthesis during translation?

Proteins

External factors can alter the rate of transpiration, and this also changes the water potential gradient of cells in the leaf. Which combination is correct?

Movement into and out of cells

The photomicrograph depicts a transverse section of a leaf. Which xerophytic leaf features can be seen in this section?

Structure of transport tissues

What changes take place as carbohydrates leave a root cell and enter a phloem sieve tube?

Movement into and out of cells

The photomicrograph depicts three white blood cells labelled X, Y and Z. Which row identifies these cells correctly?

The immune system

The graph shows information about blood vessels and blood flow. Which row correctly names the curves?

The circulatory system

Which row correctly identifies a feature of cell structure?

Cells as the basic units of living organisms

Which blood components are found in lymph?

The circulatory system

What accurately describes the importance of the rise in the red blood cell count of humans who move from living at low altitude to high altitude?

Transport of oxygen and carbon dioxide

Which structures in the human gas exchange system contain cartilage for support?

The gas exchange system

Carbon monoxide, nicotine and tar are substances present in tobacco smoke. Which row gives the correct description of how they affect a smoker’s body?

The gas exchange system

Which statements about chronic obstructive pulmonary disease (COPD) are correct?

The microscope in cell studies

Which one of these causative agents of disease is spread by droplet infection?

The microscope in cell studies

The table shows a comparison of total antibiotic use $(X)$ with the percentage of antibiotic-resistant pneumonia cases $(Y)$ across five countries. Which statement is supported by the data?

Antibiotics

Which statement about how bacteria develop resistance to antibiotics is correct?

Antibiotics

A blood cell count can reveal how many white blood cells are present in the blood. In what other part of the body are white blood cells found?

The immune system

Myasthenia gravis is a condition caused by the immune system being unable to tell self from non-self. Antibodies attach to a component of the junctions between a muscle and its nerve. What is the correct description of Myasthenia gravis?

Fluid mosaic membranes

Four students had to pair the function with the appearance of some cell structures in an animal cell. The functions were labelled with a number. 1 organises microtubules to produce the spindle during cell division 2 synthesis of polypeptides 3 packaging of hydrolytic enzymes that will remain in the cell The appearances were labelled with a letter. V membranes that enclose an inner cavity W spherical structures with no membrane bound around them X a double membrane with many pores Y cylindrical structures with no membrane bound around them Z membrane-bound sacs arranged in a flattened stack Which student correctly matched the numbered function with the appearance of the cell structure?

Cells as the basic units of living organisms

A monoclonal antibody, which is specific to a virus, was treated with an enzyme so that the bonds joining the variable and constant regions were broken. The separated variable and constant regions were then placed into cells infected by the virus. Which statements are correct?

Proteins

The characteristics of certain cells and cell structures that produce ATP are shown below. 1 has an outer boundary membrane and a folded inner membrane 2 has a peptidoglycan cell wall outside an outer boundary membrane 3 has a double boundary membrane and layers of inner membranes Which row correctly identifies these components?

Cells as the basic units of living organisms

Mitochondria are believed to have arisen from prokaryotic cells that were taken into an ancestral cell. Which feature did these prokaryotes lose as they evolved into mitochondria?

Cells as the basic units of living organisms

A student performed Benedict’s test on a sample and obtained a negative result. What should the student do to confirm that there are no sugars in the sample?

Testing for biological molecules

The diagrams illustrate three hexoses. In which carbohydrates are these three hexoses found?

Carbohydrates and lipids

The diagram illustrates part of the chemical structure of a naturally occurring polysaccharide. Which types of glycosidic bonds are present?

Carbohydrates and lipids

A student was shown a photomicrograph of a cell and informed of the image magnification. The student had to calculate the cell's actual size. Which row in the table describes how this is done?

The microscope in cell studies

The flow chart illustrates part of the process of collagen formation. Three polypeptide chains joined together by X bonds make a triple helix. Intermolecular bonds hold the triple helix together to produce Y, and these then produce Z. Which row correctly gives X, Y and Z?

Proteins

Which of these molecules contain at least two double bonds? 1 a saturated fatty acid 2 collagen protein 3 haemoglobin molecule

Proteins

Two experiments, X and Y, were performed with an enzyme obtained from humans. In experiment X, the temperature was kept constant at $37^{\circ}\text{C}$. For experiment Y, the temperature rose from $37^{\circ}\text{C}$ to $80^{\circ}\text{C}$. Every other variable was unchanged. Which graph represents the results?

Factors that affect enzyme action

Which factor influences the rate of an enzyme-catalysed reaction when a non-competitive inhibitor is present? 1 the concentration of enzyme 2 the concentration of inhibitor 3 the concentration of substrate

Factors that affect enzyme action

Which description explains the fluid-mosaic model of membrane structure?

Fluid mosaic membranes

Blocks of agar are coloured with a pH indicator and then used to explore the diffusion of an acid solution. Which block would undergo a complete colour change most quickly?

Movement into and out of cells

The diagram illustrates the water potential of three neighbouring plant cells, P, Q and R. Which indicates the net movement of water between cells P, Q and R?

Movement into and out of cells

Which row gives the correct description of the chromosome structures present during mitosis?

Chromosome behaviour in mitosis

The diagram indicates how long each stage of the cell cycle takes relative to the others. Which row gives the stages of the cell cycle in the correct order?

Replication and division of nuclei and cells

Scientists have produced a nucleic acid, HNA, whose sugar has the same number of carbon atoms as glucose rather than deoxyribose. Even though HNA can store genetic information, naturally occurring DNA polymerase cannot copy HNA. Which statements could account for naturally occurring DNA polymerase being unable to copy HNA?

Mode of action of enzymes

The electron micrograph displays part of a eukaryotic cell. Which cell structure is a site where protein synthesis occurs?

Protein synthesis

Which statements concerning the nucleotide that contains uracil are correct?

Proteins

DNA replication takes place in a number of stages. Which of the following statements about DNA replication are correct?

Replication and division of nuclei and cells

The order of bases in mRNA that codes for the first eight amino acids in the $\beta$-polypeptide of adult haemoglobin is: GUG-CAC-CUG-ACU-CCU-GAG-GAG-AAG. For haemoglobin C, which causes haemolytic anaemia, the order is: GUG-CAC-CUG-ACU-CCU-AAG-GAG-AAG. The coding for seven of the amino acids is given. Which alteration takes place in the amino acid sequence of adult haemoglobin to produce haemoglobin C?

Proteins

Some antibiotics destroy prokaryotes by attaching to RNA polymerase. What impact will this have on protein synthesis?

Proteins

The diagrams illustrate transverse sections of parts of plants. Which labelled region has cells that are dead?

Structure of transport tissues

The diagram illustrates how tissues are arranged in part of a transverse section of a plant organ. Which row correctly names tissues 1, 2 and 3?

Structure of transport tissues

The circumference of a tree stem was measured continuously over 48 hours. The results are displayed on the chart recording. What accounts for the changes in circumference recorded across the 48 hours?

Movement into and out of cells

Which statement correctly describes movement in phloem?

The microscope in cell studies

Which statements concerning blood vessels are correct?

The circulatory system

The photomicrograph displays three white blood cells labelled X, Y and Z. Which row identifies these cells correctly?

The immune system

Certain stains can be used to identify cell structures in living cells. A weak solution of one stain makes the entire cell turn blue. The blue colour quickly fades from most cell structures. The cell structures that release energy remain blue. Which type of cell structure is likely to remain blue?

Cells as the basic units of living organisms

The enzyme carbonic anhydrase catalyses the reaction: $\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{HCO}_3^- + \text{H}^+$ Which statements describe the function of the enzyme carbonic anhydrase?

Mode of action of enzymes

The graph displays the oxygen dissociation curves for adult haemoglobin at two partial pressures of carbon dioxide W and X. Which two statements are correct?

Proteins

A person has two blood tests taken one month apart. The number of each cell type in a fixed sample size is counted. What might this indicate about the person from the results after one month?

Replication and division of nuclei and cells

A student was asked to explain how four microscope slides differed when they showed sections cut from different regions of the gas exchange system. Which option gives the correct identification of the parts of the gas exchange system?

The microscope in cell studies

Cigarette smoke includes carbon monoxide, nicotine and tar. Which row gives the correct description of how these substances affect the body?

Transport of oxygen and carbon dioxide

Chronic obstructive pulmonary disease (COPD) comprises chronic bronchitis and emphysema. Which sequence is correct as emphysema develops? 1 Macrophages move into the alveolar air spaces. 2 Tar paralyses cilia. 3 Macrophages secrete elastase. 4 Bacteria build up in the alveoli.

The microscope in cell studies

If a person smokes cigarettes, what immediate effect will this have on the red blood cells?

Proteins

Which statement about tuberculosis (TB) is correct?

Infectious diseases

A list of some common antibiotics is shown below. The effect of each antibiotic is given. 1 rifampicin - prevents RNA polymerase from functioning 2 streptomycin - prevents $70$S ribosomes from functioning 3 neomycin - stops DNA synthesis 4 ampicillin - blocks peptidoglycan synthesis Which of these antibiotics would affect only the activities of bacterial cells?

Antibiotics

Which way of acquiring immunity is known as natural active immunity?

The microscope in cell studies

A carbon dioxide molecule is positioned at the centre of a mitochondrion. If no other cell structures are in its path, how many phospholipid layers must the carbon dioxide molecule cross in order to leave the cell?

Fluid mosaic membranes

Which statements give the correct reasons why smallpox has been eradicated, whereas malaria and cholera have not? 1 Cholera vaccines give immunity for only a short time. 2 Plasmodium antigens alter during the life cycle. 3 Smallpox antigens stay unchanged. 4 Vaccines are effective only against viruses.

Proteins

Which row identifies the type of ribosome present in each of the different structures?

Cells as the basic units of living organisms

A positive Benedict’s test produces this colour because copper oxide is formed. The mass of copper oxide is directly proportional to the amount of reducing sugar present. Fruit juice samples were tested with the Benedict’s test to check for reducing sugars and non-reducing sugars. The table gives the mass of copper oxide obtained after boiling with Benedict’s solution and after acid hydrolysis followed by boiling with Benedict’s solution. Which sample had the greatest amount of non-reducing sugar?

Testing for biological molecules

Which polysaccharides have $1,4$ and $1,6$ glycosidic bonds? 1. the polysaccharide amylopectin 2. the polysaccharide amylose 3. the polysaccharide cellulose 4. the polysaccharide glycogen

Carbohydrates and lipids

The diagram shows a small section of a polypeptide. If the section shown were fully hydrolysed, what products would be formed?

Proteins

The enzyme trypsin hydrolyses proteins to amino acids, but it does not work when the pH is very low because its 3D shape would alter. What causes this change in 3D shape?

Factors that affect enzyme action