May/June 2019

It was explained to a student that the true length of a cell structure is $5\,\mu\text{m}$. The student then had to state an equation that could be used to work out the magnification of an electron micrograph of this cell structure. The student chose some of the letters $q$ to $u$ to represent parts of the equation. $q$ = the length of the cell structure image on the micrograph in centimetres $r$ = the length of the cell structure image on the micrograph in millimetres $s = 1000$ $t = \frac{1}{5}$ $u = 5$ Which equation gives the correct magnification?

The microscope in cell studies

What takes place during condensation of carbohydrates?

Carbohydrates and lipids

Which statement is correct about triglycerides?

Carbohydrates and lipids

What is the smallest number of carbon atoms found in an amino acid?

Proteins

In an investigation, an equal concentration of the enzyme phosphorylase was mixed with different concentrations of glucose phosphate and left at $30^\circ\text{C}$. At intervals of $1$ minute, a single drop of the reaction mixture was taken and placed onto a drop of iodine solution on a white tile. The diagram presents the outcomes of this investigation. What accounts for the pattern seen in the results of this investigation?

Factors that affect enzyme action

How is the Michaelis-Menten constant, $K_m$, for an enzyme defined?

Mode of action of enzymes

The graph illustrates how the rate at which glucose enters a cell varies with the concentration of glucose outside the cell. What causes the plateau at X?

Movement into and out of cells

The diagram depicts the movement of substance Z across a cell surface membrane. Which process is responsible for this movement?

Movement into and out of cells

Visking tubing is frequently used as a model in experiments set up to study osmosis in plants. What might Visking tubing be used to model?

Movement into and out of cells

To make the telomeres visible, a scientist colours the chromosomes in a diploid plant cell with a fluorescent dye. The cell contains $38$ chromosomes. How many telomeres will the scientist see in one of the nuclei during telophase of mitosis?

Chromosome behaviour in mitosis

The photomicrograph shows a cell in mitosis. What is taking place in this cell?

Chromosome behaviour in mitosis

Which characteristics of cilia and root hairs are correct?

Cells as the basic units of living organisms

Which of the listed events are involved in mitosis?

Chromosome behaviour in mitosis

The graph illustrates how the length of the spindle fibres changes during mitosis. Which section of the graph indicates when all the centromeres have separated from the spindle fibres?

Chromosome behaviour in mitosis

A DNA fragment, 19 base pairs in length, was examined to determine how many nucleotide bases were in each of the polynucleotide strands. Some of the findings are shown below. How many nucleotide bases containing C were in strand 1?

The microscope in cell studies

Identify the nucleic acid bases that are purines.

Structure of nucleic acids and replication of DNA

In a genetic engineering experiment, a section of double-stranded DNA with 6000 nucleotides that codes for a particular polypeptide is transcribed and translated. What total number of amino acids are present in this polypeptide?

Proteins

Which statements regarding tRNA are correct?

Proteins

In the photomicrograph, a transverse section of part of a dicotyledonous leaf is shown. Which labels correctly identify 1, 2, 3 and 4?

The microscope in cell studies

Some features found in transport tissues of plants are given. Which of these features occur in phloem sieve tube elements?

Structure of transport tissues

The diagram illustrates how phloem sieve tube elements, xylem vessel elements and companion cells are related. Which row is correct?

Structure of transport tissues

Which statement gives the correct description of a transport pathway in plants?

Movement into and out of cells

Which of the following are functions of microtubules?

Cells as the basic units of living organisms

The photograph presents an external view of the anterior side of a mammalian heart. Which row identifies where the structures labelled P, Q, R and S are located?

The heart

What occurs during ventricular systole?

The heart

Athletes sometimes travel from low altitude to high altitude when preparing for a race. Which of the following statements about the effects of high-altitude training are correct?

Transport of oxygen and carbon dioxide

The graph displays the oxygen haemoglobin dissociation curves at pH 7.6 and at pH 7.2. Which point on the graph indicates the percentage saturation of haemoglobin in blood leaving an active muscle?

Proteins

Which row gives the correct description of the short-term effects of carbon monoxide and nicotine on a smoker’s body?

Proteins

Which statements concerning bronchioles are correct?

The gas exchange system

Which characteristics are significant for the diffusion of oxygen out of an alveolus?

Movement into and out of cells

The diagram illustrates some of the pathogens responsible for disease in humans and several of the ways they are spread. Which pathogen and route of transmission is correct for measles?

Infectious diseases

Which row correctly matches each disease?

The microscope in cell studies

Which of the following statements are correct for myasthenia gravis?

Fluid mosaic membranes

Several cell structures are given below. 1 mitochondria 2 nucleus 3 chloroplasts 4 ribosomes In what order should these cell structures be arranged from the largest to the smallest?

Cells as the basic units of living organisms

Which row shows the cells that can keep dividing continuously and take part in monoclonal antibody production?

Replication and division of nuclei and cells

Which cell structures contain ribosomal RNA (rRNA)?

Protein synthesis

A cell structure in the macrophage destroys bacteria. Some bacteria prevent this cell structure from working. Which cell structure in the macrophage is prevented from working by the bacteria?

Cells as the basic units of living organisms

A solution of amylase was mixed with a starch suspension. After 30 seconds, three samples of the mixture were tested using iodine solution, Benedict’s solution and biuret reagent. Which results would be expected?

Mode of action of enzymes

A student performed Benedict’s test on a range of known concentrations of $\alpha$-glucose. Which graph shows the results accurately?

Testing for biological molecules

The diagram illustrates three hexose sugars. Which row correctly gives examples of carbohydrates that contain these three hexose sugars?

Carbohydrates and lipids

A cell structure has an actual length of $8\,\mu\text{m}$. Which of the following steps are needed to work out the magnification of an electron micrograph of this cell structure? step 1 measure the image length of the cell structure on the micrograph in centimetres step 2 measure the image length of the cell structure on the micrograph in millimetres step 3 divide the image length by $1000$ step 4 multiply the image length by $1000$ step 5 divide the result by $8$ step 6 multiply the result by $8$

The microscope in cell studies

An unchanged volume of the enzyme catalase was mixed with an unchanged volume of hydrogen peroxide solution. The diagram illustrates how the concentration of product altered during the reaction. What accounts for the shape of this graph?

Mode of action of enzymes

A set volume and concentration of substrate and enzyme were combined. Every other variable was held constant. The enzyme-catalysed reaction was allowed to continue until it had finished. Which graph shows the way the rate of reaction changes over time?

Mode of action of enzymes

The fatty acids elaidic acid and oleic acid have identical structural formulae, each containing one double bond in the chain. Even so, the chain shapes are not the same, as the diagram shows. Which row indicates the effect of these fatty acids on the structure and behaviour of a cell surface membrane?

Fluid mosaic membranes

The diagram illustrates a cell surface membrane. Which option gives a correct function of a labelled molecule?

Fluid mosaic membranes

The diagram represents a basic cell signalling pathway where a signal molecule produces a response, for example a secretion. signal molecule → P → Q → response Which row correctly identifies P and Q?

Fluid mosaic membranes

Three chromosome parts and what they do are given. Which part is correctly paired with its function?

Chromosome behaviour in mitosis

The enzyme telomerase stops telomeres from being lost after many mitotic cell cycles. Which cells need to transcribe telomerase enzyme?

Replication and division of nuclei and cells

The diagram illustrates some of the stages that occur in the cell cycle. Which two stages occur during interphase?

Replication and division of nuclei and cells

Which statement gives the correct description of base pairing in a DNA molecule?

Structure of nucleic acids and replication of DNA

Which of the following statements concerning complementary base pairing are correct?

Replication and division of nuclei and cells

What is the usual resolution of a microscope that uses daylight as the light source and has a $\times 10$ eyepiece lens together with a $\times 40$ objective lens?

The microscope in cell studies

The diagram illustrates the possible arrangement of DNA molecules following one replication. Which arrangement is correct?

Replication and division of nuclei and cells

The diagram presents part of the DNA sequence of a gene and a mutated sequence from the same gene. What effects could the mutated sequence have?

Proteins

Which statement is correct about phloem sieve tube elements?

Structure of transport tissues

The diagrams illustrate transverse sections of parts of a plant. Transport tissues are marked 1 to 6. Which combination identifies the tissues whose main role is the transport of water?

Structure of transport tissues

The statements below describe the movement of water across the root to the xylem vessel elements. Which statements describe the apoplast pathway?

Movement into and out of cells

Four plants, A, B, C and D, were cultivated under the same conditions, and their transpiration rates were measured. Which plant is most likely to be a xerophyte?

Movement into and out of cells

Sucrose is transported from a leaf mesophyll cell into a phloem sieve tube element. Which changes in water potential and in the volume of liquid inside the phloem sieve tube element are correct?

Movement into and out of cells

The diagram illustrates a cross-section of a mammalian heart. Which heart chambers are shown by W and X?

The heart

At one stage in a cardiac cycle, the pressure in the right ventricle is less than the pressure in the right atrium and also less than the pressure in the pulmonary artery. Which row is correct?

The heart

The diagram illustrates the route by which carbon dioxide is transported in red blood cells.

Movement into and out of cells

Two distinct cell types, P and Q, were disrupted with ultrasound and their material examined. In each type of cell, small circular DNA was present. For P, all of the circular DNA had the same base sequence, whereas for Q there were two forms, each with a different base sequence. What may be concluded about the identity of cell types P and Q?

Cells as the basic units of living organisms

The diagram depicts a transverse section of an artery. Which statement describes the tissues found in layer X?

The circulatory system

The large arteries near the heart contain a thick elastic layer in their walls. Which of the following statements about this layer are correct?

The circulatory system

What tissues are found in the walls of a trachea and an alveolus?

The gas exchange system

The surface tension of the liquid layer that lines the alveoli pulls the walls towards the inside, so the alveoli may collapse. Which statements could explain how this is prevented?

Carbohydrates and lipids

The diagram illustrates some of the effects caused by nicotine and carbon monoxide in cigarette smoke. Which row is the correct one?

Proteins

Which row accurately names the causative organism for each disease?

Infectious diseases

The guidance below was provided to someone who was going to a country where an infectious disease outbreak had occurred. • ensure food is thoroughly cooked and eaten while hot • remove the skin from fruit and vegetables before eating them • drink only water that has been boiled and allowed to cool • wash hands frequently using soap and water that has been boiled and cooled Which infectious disease would this guidance help to prevent?

The microscope in cell studies

What is one social factor that can influence the spread of malaria?

Infectious diseases

Which of the following count as specific immune responses?

The immune system

Newborn babies possess natural passive immunity. Which statement is correct about this type of immunity?

Proteins

Which of the features shown in the diagram may also be found in viruses?

Infectious diseases

The diagrams illustrate three distinct antibody structures. IgG IgA IgM Which row is the correct one?

Proteins

When a milk sample is heated with Benedict’s solution, a yellow colour is seen. Which statement about the milk sample is correct?

Testing for biological molecules

Which statement about polysaccharides may be used to describe amylose and cellulose? 1 has $1,4$ glycosidic bonds 2 has $1,6$ glycosidic bonds 3 is a polymer made from glucose

Carbohydrates and lipids

Which diagram illustrates how a peptide bond is formed?

Proteins

In enzyme-catalysed reactions, the arrangement of the amino acids in the active site is significant. When enzymes are made, amino acids are assembled in the correct arrangement to create the active site. Which levels of protein structure must be involved in the formation of the active site?

Proteins

Which characteristics influence the tensile strength of collagen? 1 the helical arrangement of collagen chains 2 the small R group of the amino acids in collagen 3 the insoluble character of collagen 4 the links between collagen molecules

Proteins

Which pair of lenses in a light microscope produces the highest magnification?

The microscope in cell studies

The diagram illustrates some links between carbohydrate features. Which row correctly pairs the carbohydrate with some of its characteristics?

Carbohydrates and lipids

Which line gives the description of a triglyceride?

Carbohydrates and lipids

The diagram represents three triglycerides, X, Y and Z. Which statement is correct for these triglycerides?

Carbohydrates and lipids

Which characteristics of collagen give it high tensile strength?

Proteins

Which levels of protein structure would always be altered if an enzyme acts by the induced fit hypothesis?

Mode of action of enzymes

The enzyme β-galactosidase is able to catalyse the hydrolysis of four substrates, A, B, C and D, which have similar structures. Each substrate has a different $K_m$ value. Which substrate does β-galactosidase have the lowest affinity for?

Mode of action of enzymes

Which statement about competitive inhibitors of enzymes is correct?

Factors that affect enzyme action

The diagram shows the fluid mosaic model of membrane structure. Which two of the numbered components help to make the membrane fluid?

Fluid mosaic membranes

These cell surface membranes in some cells are made mostly of phospholipids and cholesterol, with only a few proteins. Which transport mechanisms across these membranes will be reduced?

Movement into and out of cells

A glycoprotein found in the cell surface membrane of human cells is known as ICAM-1. ICAM-1 functions as a cell adhesion molecule, and the common cold virus also uses it to bind to human cells. Which statements about ICAM-1 are true?

Fluid mosaic membranes

This photomicrograph displays some mesophyll tissue taken from a dicotyledonous leaf. What is the magnification of the photomicrograph?

The microscope in cell studies

A student first measured the mass of a potato cylinder and then placed it into a test-tube filled with salt solution. After one hour, the potato cylinder was taken out of the salt solution. It was dried with blotting paper and weighed again. The student noted that the potato had a lower mass. Which row gives the correct explanation of the results the student obtained?

Movement into and out of cells

In a typical human chromosome, certain components occur in greater numbers than others. Which list orders the parts from the greatest number to the smallest number?

Chromosome behaviour in mitosis

The enzyme telomerase stops telomeres from being lost after many mitotic cell cycles. Which cells are required to transcribe telomerase enzyme?

Replication and division of nuclei and cells

The diagram illustrates a cell in mitosis. Which description correctly identifies the cell?

Chromosome behaviour in mitosis

A gene directs the synthesis of a protein, p53, which attaches to damaged DNA during interphase and stops it from being copied. A carcinogen in cigarette smoke alters this gene. Which statement explains why this mutation may cause cancer?

Replication and division of nuclei and cells

What function does DNA polymerase carry out?

Replication and division of nuclei and cells

Which row gives the correct properties of the nitrogenous base thymine?

Structure of nucleic acids and replication of DNA

Meselson and Stahl studied DNA in bacteria. They first grew the bacteria in a medium containing only heavy nitrogen, $^{15}\text{N}$, until every DNA molecule in the bacterial cells was heavy. The bacteria were then transferred from the heavy nitrogen medium to a medium containing only light nitrogen, $^{14}\text{N}$. A sample of bacteria from the second generation was taken and the DNA was analysed. Hybrid DNA includes both heavy and light DNA. Which row gives the percentage of heavy DNA strands and the percentage of hybrid DNA molecules in the second generation produced in the medium containing light nitrogen?

Replication and division of nuclei and cells

The table lists the DNA triplet codes for several amino acids. The base sequence on the DNA strand that codes for a polypeptide is shown. $\text{CCA TTC ACG GCG TTA GCA}$ During DNA replication, two mutations take place in this sequence. Which mutated DNA would produce no change in the polypeptide synthesised?

Proteins

A group of students were asked to examine the photomicrograph of a cross-section of an unfamiliar material and record observations. The students described X as: 1 circular 2 a hollow tube 3 a spherical structure. Which descriptions are correct?

The microscope in cell studies

The diagram illustrates a typical animal cell as it appears under an electron microscope. Which of the numbered structures are required for proteins to be released at the cell surface membrane?

Protein synthesis

Watering crop plants with water that contains low concentrations of salt raises the salt concentration in the soil. Why does this increase in salt concentration eventually kill the crop?

Movement into and out of cells

The photomicrograph displays a transverse section of a portion of a plant root. Which tissue prevents the movement of water along the apoplastic pathway?

Movement into and out of cells

The table presents some details about three blood vessels, P, Q and R, taken from a mammal. Which row correctly identifies blood vessels P, Q and R?

The circulatory system

Which row correctly identifies the places where a type of molecule or cell is found?

Carbohydrates and lipids

The graph illustrates how the percentage saturation of haemoglobin with oxygen varies at different partial pressures of oxygen. In which range of partial pressures of oxygen does the percentage saturation of haemoglobin change most per kPa?

Proteins

How many layers of cell surface membrane lie between an oxygen molecule in the air space of an alveolus and the closest haemoglobin molecule?

Movement into and out of cells

Which biochemical is produced, and what happens to the oxygen dissociation curve of adult haemoglobin when carbon dioxide binds to haemoglobin?

Proteins

The diagram has been used to identify four infectious diseases. Which row correctly names the infectious diseases?

The microscope in cell studies

In what way does penicillin affect bacteria?

Mode of action of enzymes

Growth factors are chemicals that trigger a cell to divide. Growth factors are carried through the body in the blood, and they bind to cells whose surfaces contain complementary growth factor receptors. In some cells, there are too many growth factor receptors on the surface, so the cells keep dividing and a tumour forms. Trastuzumab is used to treat some cancers. Trastuzumab acts by attaching to a particular growth factor receptor on a tumour cell. This prevents the cell from dividing and causes the cell to die. What is meant by trastuzumab?

Fluid mosaic membranes

Because lysosomes differ in shape and size, they are difficult to recognise. Which statement describes a lysosome?

Cells as the basic units of living organisms

Which phrase describes artificial active immunity?

Antibodies and vaccination

Which of the following statements about ATP are correct?

The microscope in cell studies

A unicellular organism is found within a fish’s body. It is rod-like in shape, measures $700\,\mu\text{m}$ in length, is surrounded by a cell wall and contains cytoplasm with thousands of copies of small, circular DNA. Which statement about this unicellular organism is correct?

Cells as the basic units of living organisms

A solution of amylase was added to a suspension of starch. The mixture was stirred and maintained at $40^\circ\text{C}$ for 45 minutes. Samples were then tested using different reagents. What set of results would be expected?

Mode of action of enzymes

The diagram illustrates three hexose sugars, labelled 1, 2 and 3. Which row correctly gives examples of carbohydrates in which these three hexose sugars are found?

Carbohydrates and lipids

What may happen during a condensation reaction?

Carbohydrates and lipids