May/June 2018

Which statements concerning resolution and magnification are correct?

The microscope in cell studies

The diagrams display two different arrangements of amino acids in a protein. Which row gives the correct names for the bonds at S or T?

Proteins

The students had to show only the R groups of two cyclic amino acids. Which pair of diagrams is correct for both amino acids?

Proteins

Which words from the table best fill the gaps in the paragraph about enzymes? If the pH of a setting falls below an enzyme’s optimum pH, ……1…… bonds joining neighbouring ……2…… groups that maintain the ……3…… structure are broken.

Factors that affect enzyme action

The influence of substrate concentration on an enzyme-catalysed reaction was recorded under three separate conditions: • with no inhibitor • with a competitive inhibitor • with a non-competitive inhibitor. The graph illustrates the outcomes. Which statement is correct?

Factors that affect enzyme action

Which of the following statements about the cell surface membrane are correct?

Fluid mosaic membranes

Which of these characteristics improve the efficiency of ion uptake by a root hair cell?

Movement into and out of cells

Which features can increase the fluidity of the cell surface membrane at low temperatures?

Fluid mosaic membranes

The diagrams illustrate the form and dimensions of two cell types. The palisade mesophyll cell has a surface area of $2200\,\mu\text{m}^2$. The columnar epithelial cell has a volume of $2250\,\mu\text{m}^3$. Which statement is correct for the palisade cell and epithelial cell in the diagrams?

Movement into and out of cells

A student examined cells in the growing region (meristem) of an onion root and collected the data shown. What percentage of cells have chromosomes that look like two chromatids?

Chromosome behaviour in mitosis

Which of these stages are included in mitosis?

Chromosome behaviour in mitosis

An eyepiece graticule includes a scale marked into 100 divisions. A stage micrometer is marked with 50 divisions, and the separation between each division is $0.040\,\text{mm}$. When a $\times 40$ objective lens is used, the full length of this stage micrometer scale coincides with 15 divisions on the eyepiece graticule. What is the true length of the 100 division scale on the eyepiece graticule?

The microscope in cell studies

In which stage of the cell cycle does DNA replication occur?

Replication and division of nuclei and cells

Which row shows the correct information for guanine?

Structure of nucleic acids and replication of DNA

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

Replication and division of nuclei and cells

Which DNA triplet on the original DNA template codes for the amino acid histidine (His)?

Proteins

In a stained transverse section of a plant stem, the photomicrograph displays the tissues. Students must draw four neighbouring xylem vessel elements. Which drawing, with each one produced on the same scale, is correct?

The microscope in cell studies

What role do the hairs (trichomes) on xerophytic leaves have?

Transport mechanisms

Which characteristics of companion cells are necessary for their function?

Structure of transport tissues

The photomicrograph displays a human blood smear. Which row identifies the labelled cells?

The microscope in cell studies

The diagram illustrates how the electrical activity in the heart muscle changes during a single cardiac cycle. This is known as an electrocardiograph (ECG). Which electrocardiogram shows a heart rate of 75 beats per minute?

The heart

Which effect could result from a lower concentration of carbonic anhydrase?

Factors that affect enzyme action

A prokaryotic cell with a diameter of $1\,\mu\text{m}$ is enlarged by $50\,000$ times in an electron micrograph. What is the cell's diameter in the electron micrograph?

The microscope in cell studies

Which statement gives the correct comparison between blood plasma and tissue fluid in a healthy person?

Movement into and out of cells

The diagram illustrates three features present in tissues of the gas exchange system. Which tubes of the gas exchange system might be shown at position P in the diagram?

Movement into and out of cells

The diagram illustrates an enlarged part of the lungs that contains specialised tissues. Which row correctly matches structures labelled 1 to 6?

The gas exchange system

One short-term consequence of smoking is a reduction in the blood supply to the fingers and toes. Which component of cigarette smoke is responsible for this effect?

The circulatory system

The signs of two diseases are given below. Disease 1: coughing up blood; pain on breathing; weight loss. Disease 2: breathlessness; difficulty breathing out; tiredness. Which row shows diseases 1 and 2?

The gas exchange system

Which of the following statements about a non-infectious disease could be correct?

Infectious diseases

The diagram illustrates one method used to investigate the effect of an antibiotic on bacteria. Colonies of bacteria are cultured on a petri dish containing nutrient agar with bacteria. A filter paper disc that has been soaked in antibiotic is put onto the agar. The bacteria are left to grow for 5 days, and the diameter of the zone is measured each day for 5 days. The table presents the results of testing five different types of bacteria. Zones smaller than $13.0\,\text{mm}$ indicate that resistant bacteria are present. Which statement is supported by this data?

Antibiotics

Some animals contain genes that encode small peptides known as cathelicidins. By binding to lipids in bacterial membranes, these peptides kill many different bacteria and therefore weaken or damage those membranes. Scientists have made a synthetic form of cathelicidin that kills bacteria resistant to several antibiotics, including tetracycline. Which pair of statements explains how this synthetic cathelicidin could help to solve the problem of antibiotic resistance?

Fluid mosaic membranes

Hybridomas are used as the starting point for producing large quantities of monoclonal antibodies. Which statement describes the way hybridomas are produced?

Proteins

Which statement correctly describes the properties of antigen-binding sites in antibody molecules?

Proteins

A scientist performed an experiment to separate cell structures in animal cells. The cells were ruptured so that the cell structures were released. This mixture was filtered into a centrifuge tube and then spun in a centrifuge. The heaviest cell structure settled at the base, producing pellet 1, as shown in the diagram. The liquid above pellet 1 was transferred into a clean centrifuge tube and spun again in the centrifuge at a higher speed to separate the next heaviest cell structure. This cell structure settled at the bottom, forming pellet 2. This process was carried out twice more to produce pellet 3 and pellet 4, each of which contained one type of cell structure. Which row indicates the sequence in which the cell structures were collected?

The microscope in cell studies

The statements outline several different ways that monoclonal antibodies can function. Which kinds of monoclonal antibody could be used to treat cancer?

Proteins

Radioactively-labelled nucleotides are added to a cell. In which cell structures would the radioactivity be concentrated first?

Replication and division of nuclei and cells

What is the overall formula for amylose?

Carbohydrates and lipids

The diagram illustrates the links between some important molecules and bonds. What do the circles labelled 1, 2 and 3 represent?

Proteins

In unsaturated lipid molecules, where are the double bonds found?

Carbohydrates and lipids

Phospholipids and triglycerides are significant biological molecules. Which of the following properties are correct for these molecules?

Carbohydrates and lipids

Some cell features are shown below. 1 cell wall 2 cell surface membrane 3 ribosomes Which of these features are present in both plant cells and prokaryotic cells?

Cells as the basic units of living organisms

Which molecules are characterised by C=O bonds?

Carbohydrates and lipids

Which row gives the description of a collagen molecule?

Proteins

A student carried out an investigation into the hydrolysis of the lipid present in high-fat milk, using the enzyme lipase. • $1\,\text{cm}^3$ of enzyme solution was added to $10\,\text{cm}^3$ of high-fat milk. • The temperature was held constant. • The pH of the reaction mixture was measured at time $0$ minutes and then every minute for $20$ minutes. Which statements are supported by the results of the investigation?

Mode of action of enzymes

A student performed an investigation into how temperature affects the rate of an enzyme-catalysed reaction. At each temperature, the substrate concentration was measured after $10$ minutes. All the other variables were kept constant. Which graph shows the effect of increasing temperature on the substrate concentration after $10$ minutes?

Factors that affect enzyme action

The graph illustrates how the rate of an enzyme-catalysed reaction varies with substrate concentration. Determine the Michaelis-Menten constant ($K_m$) for this enzyme under these conditions?

Factors that affect enzyme action

This formula indicates how to work out the rate of diffusion across a cell surface membrane. $\dfrac{\text{surface area} \times \text{difference in concentration}}{\text{thickness of membrane}}$ Which row indicates how the quickest rate of diffusion can be obtained?

Movement into and out of cells

The diagram illustrates part of the cell surface membrane of an active animal cell. Region X has a more negative water potential, while region Y has a less negative water potential. Which statements below correctly describe the net movement of molecules across this membrane? 1. Oxygen diffuses from X to Y through molecules M. 2. Carbon dioxide diffuses from X to Y through molecules M. 3. Water travels from Y to X through molecule L.

Movement into and out of cells

Epidermal cells from a plant that has been well watered are put into three solutions with different water potentials. Which row correctly indicates the condition of the plant cells in each solution?

Movement into and out of cells

A nucleus contains a chromosome with a telomere made up of many repeats of the base sequence TTAGGG. The chromosome was taken from four different cells, and the total number of bases in the telomere was measured. Which total number of bases was obtained from the cell that had completed the greatest number of mitotic divisions?

Chromosome behaviour in mitosis

To allow tissues to be repaired successfully during cell replacement, each daughter cell must contain the same chromosome complement as the mother cell. Which stages of mitosis ensure that each daughter cell gets one chromatid from every chromatid pair?

Chromosome behaviour in mitosis

Which of the following statements about light microscopy are correct?

The microscope in cell studies

Which of these statements concerning cytokinesis is always correct? 1. Cell structures are duplicated. 2. Cell structures are distributed between two cells. 3. The nuclear envelope re-forms.

Replication and division of nuclei and cells

Which statement correctly describes how many telomeres are present during prophase in a human body cell?

Chromosome behaviour in mitosis

Which statement accounts for DNA replication being described as semi-conservative?

Replication and division of nuclei and cells

A section of a DNA molecule has the coding sequence AGGCAATGGC. Which of the following statements are correct? 1. There are 3 pyrimidines in this coding sequence. 2. In the double-stranded DNA for this section, there are 26 hydrogen bonds between complementary bases. 3. This double-stranded DNA section contains 20 sugar-phosphate bonds.

Structure of nucleic acids and replication of DNA

XNA is a nucleic acid produced in the laboratory from nucleotides, with one constituent substituted by chemical X. Chemical X does not occur naturally. The coding section of the molecule remains unchanged. Which organic component of a DNA or RNA nucleotide has been substituted by X?

Carbohydrates and lipids

Which of the following statements about tRNA are correct? 1. Temporary hydrogen bonds between bases keep tRNA aligned with mRNA. 2. The base sequence in the tRNA molecules is the same as the base sequence in the mRNA being translated. 3. Both the specificity of the tRNA molecule for glycine and the specificity of the enzyme that loads glycine are needed for correct loading.

Proteins

What function does ATP have in a companion cell as sucrose is loaded into a sieve tube element?

Movement into and out of cells

A potometer was used to determine the transpiration rate of a leafy shoot. Which units could be correct?

Movement into and out of cells

Which set of features is characteristic of a phloem sieve tube element while it is being loaded from a source?

Movement into and out of cells

The diagrams display transverse sections of parts of a plant. Which structures, labelled 1 to 4, are responsible for transporting water and sucrose?

Structure of transport tissues

Which type of cell has the greatest proportion of cell structures surrounded by a single membrane?

Cells as the basic units of living organisms

Which statement accounts for the ventricles contracting after the atria?

The heart

If the left atrioventricular valve in the heart fails to close fully, blood is forced back into the atrium during ventricular systole. What is the immediate effect of this backflow?

The heart

The graph presents two oxygen dissociation curves: one for a tissue at rest and another for that same tissue while exercising. Which factors explain the change in the position of the dissociation curve during exercise relative to the curve for the tissue at rest?

Proteins

Which of these statements about the formation of haemoglobinic acid are correct?

Proteins

Which of these structures include cartilage and cilia?

The gas exchange system

Which statement correctly explains how carcinogens affect lung tissue and lead to tumour formation?

Replication and division of nuclei and cells

Which row correctly identifies both the type of pathogen responsible for cholera and how cholera is transmitted from one person to another?

Infectious diseases

Why is malaria more common among people with HIV/AIDS than among people who do not have HIV/AIDS?

The immune system

In a typical Y-shaped antibody molecule, how many variable regions are present?

Proteins

In which locations can antigens be found?

Fluid mosaic membranes

The table lists different structures that may be present in cells. Which row shows structures that could be present in the root cells of a plant?

Cells as the basic units of living organisms

When an organ is moved from one person to another, the recipient must not reject the foreign organ. At the same time, the recipient’s immune system has to be kept functioning so that death from infections is prevented. What stops the transplanted organ from being rejected?

Fluid mosaic membranes

Which of the following cell structures are found in Plasmodium?

Cells as the basic units of living organisms

A student needed to estimate the concentration of glucose in a solution by carrying out the Benedict’s test. The student was given a $1.0\,\text{mol dm}^{-3}$ glucose solution and instructed to prepare a $0.6\,\text{mol dm}^{-3}$ solution through proportional dilution. Which row gives the correct volumes of the $1.0\,\text{mol dm}^{-3}$ glucose solution and distilled water required to prepare the $0.6\,\text{mol dm}^{-3}$ solution?

Testing for biological molecules

The diagram illustrates a section of a carbohydrate molecule built from glucose. What is the molecule called?

Carbohydrates and lipids

The diagram illustrates how certain biological molecules are related. Which row is correct?

Carbohydrates and lipids

Which diagram represents the reaction used to link two of the monomers that make up cellulose?

Carbohydrates and lipids

Which steps are required to determine the actual width of a xylem vessel seen in transverse section with a $\times 10$ objective lens? 1 Change from mm to $\mu$m by multiplying by $10^3$. 2 Use a stage micrometer on a $\times 4$ objective lens to calibrate the eyepiece graticule. 3 Use an eyepiece graticule to measure the width of the xylem vessel. 4 Multiply the number of eyepiece graticule units by the eyepiece graticule calibration.

The microscope in cell studies

Which property of phospholipids allows a bilayer to form?

Fluid mosaic membranes

Which statement accurately describes collagen?

Proteins

Which of the following statements about the properties of water is correct?

Water

Catechol is a chemical present in several fruits. The enzyme catechol oxidase can oxidise catechol into a quinone. Parahydroxybenzoic acid (PHBA), which has a structure similar to catechol, inhibits catechol oxidase. Phenylthiourea (PTU) also inhibits catechol oxidase by binding to a copper atom in the enzyme. In what way do both of these inhibitors lower enzyme activity?

Mode of action of enzymes

Four students carried out an investigation into how catalase affects hydrogen peroxide. At the start of the experiment, each student switched on a digital timer and stopped it once 25 bubbles had been counted. The reading on the digital timer is shown below. hours 00, minutes 01, seconds 33, hundredths of a second 54. Which of the times recorded by the students is appropriate for this experiment?

Factors that affect enzyme action

What effect does an enzyme have in an enzyme-catalysed reaction?

Mode of action of enzymes

The diagram illustrates a section of the cell surface membrane. Which components function as antigens?

Fluid mosaic membranes

Which processes require ATP as the energy source?

Movement into and out of cells

The diagram depicts a plant cell that is partly plasmolysed. What structure is located at Z?

Movement into and out of cells

Which characteristics of an organism are influenced by a drug that prevents mitosis?

Replication and division of nuclei and cells

The diagram illustrates the roles of four cell structures, W, X, Y and Z. Which row correctly pairs the cell structure with the letter representing a function?

Cells as the basic units of living organisms

Which row shows how a chromosome looks at the start of prophase in mitosis and the number of DNA strands in that chromosome?

Chromosome behaviour in mitosis

The graph illustrates measurements recorded during one mitotic cell cycle. Which stage of mitosis starts at X, and what measurements are represented by curves 1 and 2?

Chromosome behaviour in mitosis

The diagram illustrates the structural outlines of two nucleotide bases found in DNA. These two bases are joined by two hydrogen bonds, which are drawn as dashed lines. Which row correctly names these two nucleotide bases?

Structure of nucleic acids and replication of DNA

DNA polymerase catalyses condensation reactions between molecules during semi-conservative replication of DNA. Which two molecules does DNA polymerase join?

Replication and division of nuclei and cells

What happens in each of DNA replication, transcription and translation?

Proteins

A section of DNA taken from a person who has a genetic disease is: TAGTAACCACAAAGG. The matching DNA sequence from a person who does not have this genetic disease is: TAGTAAAACCACAAAGG. Some possible mRNA codons for certain amino acids are listed in the table. Which amino acid is absent in a person with this genetic disease?

Proteins

The photomicrograph shows a cross-section of a plant organ. Which statement could describe this organ?

The microscope in cell studies

Which diagram accurately shows part of a sieve tube element?

Structure of transport tissues

Which process involved in water transport through xylem vessels relies on hydrogen bonding between water molecules?

Water

Which statements regarding water movement in plants are correct?

Movement into and out of cells

Which cell structures generate ATP? 1 the chloroplasts 2 the mitochondria 3 the nucleus

Cells as the basic units of living organisms

Which blood vessel has walls that are the thickest?

The circulatory system

Which statement concerning the function of the heart, blood vessels and blood in the mammalian circulatory system is correct?

The circulatory system

What causes the maximum uptake of oxygen while blood moves through the capillaries of the lungs?

Movement into and out of cells

At high altitudes, the oxygen content of the air can be one third of the level at sea level. As a person climbs a mountain, the body slowly adapts to the altitude. What increases during this adjustment period?

Transport of oxygen and carbon dioxide

What causes a concentration gradient to be maintained between the blood and the air inside the alveolus?

Movement into and out of cells

The diagram indicates three features present in the tissues of the gas exchange system. Which structures of the gas exchange system could be represented at position X and at position Y in the diagram? 1 bronchiole 2 trachea 3 bronchus

The gas exchange system

Blood tests on people who smoke cigarettes regularly indicate that about $5\%$ of their haemoglobin is carrying carbon monoxide. People who use e-cigarettes inhale a vapour that contains no carbon monoxide. A person who usually smokes cigarettes stops and changes to e-cigarettes, then has a blood test performed after one month. Which chemical in the blood would be present at a lower concentration in this blood test?

Proteins

Emphysema is one form of chronic obstructive pulmonary disease, COPD. In people who have emphysema, the concentration of a plasma protein that blocks the enzyme elastase is very low. Elastase breaks down the elastic fibres in the bronchioles and alveoli. Which of the following are consequences of the reduced inhibitor level in people with emphysema?

Factors that affect enzyme action

Certain antibiotics act by attaching to ribosomes. Which statement accounts for the fact that these antibiotics kill bacterial cells but do not kill most human cells?

Antibiotics

In what location are antigens found?

Fluid mosaic membranes

As mucus is released from a goblet cell, the following events occur. 1 attachment of carbohydrate to protein 2 merging of the vesicle with the cell surface membrane 3 release of a glycoprotein 4 detachment of a vesicle from the Golgi body In what order do these events occur?

Movement into and out of cells

The diagram makes it possible to identify different kinds of immunity. Which row correctly names the types of immunity labelled 1, 2 and 3?

The immune system

Which row might be correct for a virus?

Cells as the basic units of living organisms

Which size interval would encompass most prokaryotic cells?

Cells as the basic units of living organisms

Three biological molecule solutions are examined for sugars. The table gives the colours of the solutions after the test. Which solutions had glucose present before the test?

Testing for biological molecules

A solution that contains equal masses of amylose and amylopectin is fully hydrolysed. Which molecules will be present after hydrolysis?

Carbohydrates and lipids

Which molecules include the following bonds?

Carbohydrates and lipids