Oct/Nov 2018

A student recorded observations to describe photomicrographs of four cells. cell 1 Grey cytoplasm at the cell edge contains many black lines and spots. A large white region is in the centre of the cell. cell 2 Grey cytoplasm contains many black lines and spots, and these extend across the whole cell. cell 3 Pale blue cytoplasm surrounds one dark blue spot. cell 4 Numerous green structures are enclosed within a rectangular shape with clear boundaries. Which table shows the type of cell and the type of microscope used to take each photograph?

The microscope in cell studies

A triglyceride is made up of glycerol together with three distinct fatty acids: linoleic acid (L), oleic acid (O) and palmitic acid (P). The diagram illustrates one possible way in which the fatty acids L, O and P can be arranged within the molecule. What is the total number of different arrangements of the fatty acids in this triglyceride?

Carbohydrates and lipids

Which statements concerning a peptide bond are correct?

Proteins

Which statements concerning the primary structure of a protein are correct?

Proteins

A mutation took place in the DNA sequence that codes for an enzyme, resulting in a lower rate of a reaction catalysed by this enzyme. Which statements might account for the reduction in the reaction rate?

Mode of action of enzymes

Which row is correct for an enzyme that has a low Michaelis-Menten constant?

Mode of action of enzymes

The diagram illustrates a glycoprotein inserted into the cell surface membrane of a human red blood cell. This glycoprotein forms part of a system of cell surface blood group recognition sites. Which row identifies the function of this glycoprotein and the regions P and Q of the molecule?

Fluid mosaic membranes

The diagram illustrates ions being transported across the cell surface membrane. Within the cell, the concentration of sodium ions ($\text{Na}^+$) is low, while the concentration of potassium ions ($\text{K}^+$) is high. Outside the cell, $\text{K}^+$ is at a low concentration and $\text{Na}^+$ is at a high concentration. The carrier molecule is a pump that swaps $\text{Na}^+$ with $\text{K}^+$. Which ionic movements do the arrows show?

Movement into and out of cells

The indicator cresol red turns from red to yellow when placed in an acid. Several agar blocks containing cresol red were cut into different sizes and then placed in an acid. Every other variable was kept the same. The blocks were measured in $\text{mm}$. Which block turned completely yellow the fastest?

Movement into and out of cells

If red blood cells are placed in pure water, they burst (haemolysis). Which statements account for this haemolysis?

Movement into and out of cells

At each stage of the mitotic cell cycle, how many copies of each DNA molecule are present in a cell?

Replication and division of nuclei and cells

The diagram depicts a slide of a transverse section of a stem. The diagram is drawn at the same size as the actual slide. A student examined this slide with a light microscope at a magnification of $\times 40$. The student then produced a plan drawing of the stem, with a diameter of $20\ \text{cm}$. The student titled the plan ‘Transverse section of a stem $\times 40$’. Which statement explains why this label is incorrect?

The microscope in cell studies

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

Replication and division of nuclei and cells

A mutation takes place in a gene and stops telomerase from being produced. What effect would this mutation have if it occurred in bone marrow stem cells?

Replication and division of nuclei and cells

What products are formed when a DNA molecule replicates?

Replication and division of nuclei and cells

After translation, the alpha polypeptide chain of haemoglobin, $\alpha$-globin, is modified. In this modification, the first amino acid is removed, so 141 amino acid residues remain. How many nucleotides are present in the gene coding for $\alpha$-globin?

Proteins

Which statements accurately describe transport pathways in dicotyledonous plants?

Movement into and out of cells

The photomicrograph illustrates a transverse section of a root. What is the simplest ratio between the diameter of the root (excluding root hairs) and the diameter of the vascular tissue and endodermis?

The microscope in cell studies

Which features of water molecules are important for the upward movement of water through xylem?

Water

Which statement is correct for a phloem sieve tube element that is unloading to a sink?

Movement into and out of cells

Which statement about transpiration is correct?

Movement into and out of cells

The diagram shows a cross-section of the heart and its connected blood vessels. Which statement correctly describes the flow of blood through the heart?

The heart

In which cell structures can cisternae be found?

Cells as the basic units of living organisms

Blood, tissue fluid and lymph do not all have the same composition. Which row gives the composition of lymph?

Movement into and out of cells

Which row indicates how the concentrations of some substances in red blood cells change when carbon dioxide diffuses out of active cells?

Movement into and out of cells

The diagram shows how pressure changes in different structures on the left side of the heart during the cardiac cycle. At the end of which phase is the ventricle filled with blood?

The heart

The photomicrographs display a cross-section through the lining of part of the respiratory system. Which statements are correct?

The gas exchange system

Within the lungs, oxygen and carbon dioxide move across cell surface membranes by diffusion. Which row is correct?

Movement into and out of cells

Which flow diagram accurately shows the effect of tar entering the lungs?

The gas exchange system

Which list is made up only of infectious diseases?

Infectious diseases

Which disease is brought about by a eukaryote?

Infectious diseases

A vaccine is available for most common strains of the influenza virus. The virus responsible for influenza frequently mutates in the gene that codes for its antigenic protein. Which statements account for vaccinated people not being immune to a mutated influenza virus?

Proteins

Which of the following statements give correct descriptions of lymphocytes?

The immune system

Which row gives the correct description of the function of the cell structures?

Cells as the basic units of living organisms

Addison’s disease may arise when antibodies are formed in reaction to an enzyme present in certain organs of the body. Which statements give the correct description of Addison’s disease?

Mode of action of enzymes

The diagram illustrates how different cells and their parts are related. Which row is correct?

Cells as the basic units of living organisms

Which statement correctly compares bacteria cell walls with plant cell walls?

Cells as the basic units of living organisms

During a positive test for a non-reducing sugar, a glycosidic bond is broken and two monosaccharides are produced. Which row correctly identifies the catalyst and the reactants in this reaction?

Testing for biological molecules

Which two statements are correct? A In carbohydrates, carbon and oxygen are present in a $2:1$ ratio. Triglycerides are water-soluble. B Glycolipids occur in all cell surface membranes. Plants store carbohydrates as starch. C Every phospholipid has two saturated hydrocarbon chains. Polysaccharides count as polymers. D The formation of a glycosidic bond releases water. Each phospholipid contains three ester bonds.

Carbohydrates and lipids

What is the overall formula for cellulose?

Carbohydrates and lipids

What is the diameter of a typical prokaryote, for example Streptococcus?

Cells as the basic units of living organisms

Which diagram indicates the point at which a peptide bond would be formed?

Proteins

Which of the following statements about collagen molecules are correct?

Proteins

The protein glutenin is what makes bread dough elastic. The diagram shows a glutenin polypeptide. What description fits the structure of glutenin?

Proteins

Which diagram shows hydrogen bonding between water molecules correctly? The symbol $\delta$ shows the partial charge on an atom in the water molecule.

Water

Aspirin stops an enzyme working by reacting with an amino acid that is an essential component of the enzyme’s 3D structure. A part of the aspirin molecule binds tightly to the amino acid. What term describes this form of inhibition?

Mode of action of enzymes

The table presents the Michaelis-Menten constant, $K_m$, for three enzymes. Enzyme C: $1.5 \times 10^{-2}\ \text{mmol dm}^{-3}$ Enzyme P: $3.0 \times 10^{-4}\ \text{mmol dm}^{-3}$ Enzyme F: $5.0 \times 10^{-6}\ \text{mmol dm}^{-3}$ Which statement correctly interprets the information?

Mode of action of enzymes

The diagram shows a sketch made from an electron micrograph of a typical animal cell. How many phospholipid layers must a molecule of oxygen pass through to move directly from X, outside the cell, to Y, the mitochondrion matrix?

Fluid mosaic membranes

By what route could water molecules pass across the cell surface membrane of animal cells?

Movement into and out of cells

The diagram depicts a xylem vessel in a root together with four neighbouring parenchyma cells. As water ascends the xylem vessel, it is replenished by water from cell D. The water in cell D is then replaced by water from cell C, which causes water to flow from cell A into the xylem. Which cell has the water potential that is least negative?

Movement into and out of cells

Agar cubes may be used to show how altering the surface area to volume ratio affects diffusion. Three different agar cubes, made with a dilute acid, were placed in an indicator solution that moved into the cubes. When the indicator made contact with the acid, its colour changed. The cubes had sizes of $1\ \text{cm}^3$, $2\ \text{cm}^3$ and $3\ \text{cm}^3$, and they were left in the indicator solution for 10 minutes. All the other variables were kept unchanged. The results were shown as diagrams. The results for the $2\ \text{cm}^3$ cube are displayed. Which diagrams show the results for the $1\ \text{cm}^3$ and the $3\ \text{cm}^3$ cubes?

Movement into and out of cells

A specimen of plant tissue is initially examined with a microscope by means of red light of wavelength $650\,\text{nm}$. The same specimen is then viewed again under identical conditions, except that green light of wavelength $510\,\text{nm}$ is used. What change occurs to the magnification and the resolution when green light is used instead of red light?

The microscope in cell studies

The photomicrograph depicts cells at different phases of mitosis. Which of the following statements are correct?

Chromosome behaviour in mitosis

What changes would be needed in a group of mammalian cells dividing by mitosis for a tumour to form?

Replication and division of nuclei and cells

Which row presents some of the events during a mitotic cycle in the correct chronological order?

Replication and division of nuclei and cells

What is the greatest possible number of hydrogen bonds in a DNA segment containing 700 base pairs?

Structure of nucleic acids and replication of DNA

Which component is common to the three molecules RNA, DNA, and ATP?

Structure of nucleic acids and replication of DNA

The photomicrographs show the root, stem and leaf of a dicotyledonous plant. Which row gives the correct labels for 1 to 5 on the photomicrographs?

Structure of transport tissues

Which features are shared by phloem sieve tube elements and xylem vessel elements?

Structure of transport tissues

Which statement gives the correct description of an event that occurs during mass flow in phloem sieve tube elements?

Movement into and out of cells

The diagram presents a potato tuber at several stages. Which row indicates a stage when a potato tuber functions as a source and a stage when it functions as a sink?

Movement into and out of cells

What term best describes the function of the atrio-ventricular node in the heart?

The heart

What structures can be found in a Vibrio cholerae cell?

Cells as the basic units of living organisms

The diagram illustrates pressure variations throughout the cardiac cycle. Which arrow shows ventricular systole?

The heart

Which process is able to be carried out by a mature red blood cell?

Transport of oxygen and carbon dioxide

Haemoglobin is able to bind with carbon dioxide, carbon monoxide and oxygen. Which statement about haemoglobin’s binding sites is correct?

Proteins

Which tissues can be found in a bronchus?

The gas exchange system

Tar is present in cigarette smoke. Which of the statements below describe tar's effect on the respiratory system?

The gas exchange system

Symptoms of chronic obstructive pulmonary disease (COPD) include cough, breathlessness and chest infections. Some of the lung changes caused by smoking are shown below. Which changes lead to the cough in COPD?

The gas exchange system

Which of the following statements about infectious diseases are correct?

Infectious diseases

The antibiotic tetracycline attaches to the small subunit of bacterial ribosomes and prevents protein synthesis. Bacteria have developed resistance to tetracycline because of mutations. Which effect could lead to resistance to tetracycline?

Antibiotics

Where can antigens be found?

Fluid mosaic membranes

The graph illustrates the body’s response after being exposed to an antigen for the first and second time. What directly causes the rise in antibody production after the second exposure to antigens?

Antibodies and vaccination

If a plant cell wall is removed by enzyme digestion, the result is an intact membrane-bound structure known as a protoplast. Which statement explains why protoplasts are easily damaged?

Movement into and out of cells

Why has developing an effective vaccine for malaria been so difficult?

Antibodies and vaccination

Which of the following statements are correct for a green plant?

Cells as the basic units of living organisms

Which processes take place in eukaryotes and prokaryotes?

Cells as the basic units of living organisms

A solution sample was examined for reducing sugar, and the outcome was negative. A different sample from the same solution was then examined for non-reducing sugar, and the outcome was positive. Which part of the non-reducing sugar test causes the glycosidic bonds to break?

Testing for biological molecules

Which row correctly names three polysaccharides?

Carbohydrates and lipids

Which row gives the description of a triglyceride?

Carbohydrates and lipids

What statement explains why an electron microscope is needed to observe the cristae of a mitochondrion?

The microscope in cell studies

What is the general formula of glycogen?

Carbohydrates and lipids

Which of the following statements are correct?

Movement into and out of cells

The table gives the diameters of some atoms when they form bonds. The approximate length of the amino acid shown was worked out from the values in the table. What would be the approximate length of a dipeptide formed from this amino acid?

Proteins

Which statement about the usual modes of action of a competitive inhibitor and a non-competitive inhibitor is correct?

Factors that affect enzyme action

Some animals make antimicrobial proteins that defend them against pathogens. These proteins might be used to destroy human pathogens, but when they are used as a medicine they are broken down by protein-digesting enzymes. Substituting one of the amino acids in the protein with one that had been synthesised in the laboratory produced a modified protein that was not broken down. What could explain why this modified protein was not broken down by the protein digesting enzymes?

Mode of action of enzymes

An experiment was done to examine how temperature affects an enzyme-catalysed reaction. At first, the enzyme and its substrate were kept in separate test-tubes and brought up to the necessary temperature. They were then combined and transferred into four tubes A, B, C and D. Each tube was incubated for the stated time and temperature. After that, the mass of product produced was measured. In which tube did the reaction occur at the greatest rate?

Factors that affect enzyme action

In an experiment, the proteins in the cell surface membrane of a living cell were tagged with a fluorescent dye. A small region of the membrane was then viewed with a microscope. A laser was subsequently used to permanently eliminate the fluorescence of the dye molecules in this field of view. Later, fluorescence was observed to reappear in this field of view. What does this experiment demonstrate?

Fluid mosaic membranes

In plants that are adapted to low temperatures, the cell surface membranes alter as the temperature falls, which enables the plants to perform exocytosis. Which alteration takes place in their cell surface membranes?

Fluid mosaic membranes

Which statement best explains endocytosis?

Movement into and out of cells

An indicator is colourless in acid and pink in alkali. In one experiment, a petri dish of agar was set up with an acidic solution of this indicator. From the centre, a disc of agar measuring $1\text{ cm}$ in diameter was taken out to form a well. A white card with circular marker lines spaced $1\text{ cm}$ apart was positioned below the petri dish. $1\text{ cm}^3$ of alkali solution was added to the well in the agar and a stop-watch was started. A pink circular disc formed and diffused through the agar. It reached the first marker line after a short time, but needed longer to reach the second marker line and a very long time to reach the third marker line. What accounts for these observations?

Movement into and out of cells

A prokaryotic cell with a diameter of $0.25\,\mu\text{m}$ is enlarged $50\,000$ times in an electron micrograph. What will its diameter be on the electron micrograph?

The microscope in cell studies

At each stage of the mitotic cell cycle, how many copies of each DNA molecule are present in a cell?

Replication and division of nuclei and cells

Centromere, chromatids and telomeres are components of a chromosome in a eukaryotic cell. Which row gives the correct description of these structures?

Chromosome behaviour in mitosis

Which bases in nucleic acids are classed as purines?

Structure of nucleic acids and replication of DNA

A double-stranded DNA segment contains $120$ nucleotides and codes for part of a polypeptide. What is the maximum length of this polypeptide section?

Proteins

Four students were asked to propose a set of four labels to add to a diagrammatic plan of a transverse section of a dicotyledonous leaf. Which student proposed a correct set of labels?

Structure of transport tissues

Photomicrograph X displays a transverse section of a typical stem. Photomicrograph Y displays a longitudinal section of one kind of cell shown in photomicrograph X. Which letter shows the cells from photomicrograph Y?

Structure of transport tissues

Which process causes water to move upwards through xylem vessels in a plant root after the shoot has been removed?

Movement into and out of cells

What changes happen to the water potential and the volume of liquid in a phloem sieve tube element as carbohydrate enters a sink?

Movement into and out of cells

The graph displays how the diameter of a tree trunk changes over time. Which statement accounts for these changes?

Movement into and out of cells

What is present in all blood vessels, lymph and tissue fluid?

Water

During experimental measurements, which methods may be affected by parallax errors?

The microscope in cell studies

Which reactions occur in blood as it flows through active tissues?

Transport of oxygen and carbon dioxide

The graph illustrates the percentage saturation of haemoglobin with oxygen over a range of partial pressures of oxygen, with two different partial pressures of carbon dioxide shown. One curve is drawn for the partial pressure of carbon dioxide in the lungs, and the other curve is drawn for the partial pressure of carbon dioxide in the liver. Which points on the curves represent the percentage saturation of haemoglobin in the lungs and in the liver?

Transport of oxygen and carbon dioxide

A person relocates from sea level to live at a high altitude. After spending three months at high altitude, which change would be present in this person while at rest?

Transport of oxygen and carbon dioxide

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

Movement into and out of cells

Chronic obstructive pulmonary disease (COPD) includes bronchitis and emphysema. Which row identifies the effects of bronchitis?

The gas exchange system

Which factors influence the spread of malaria?

Infectious diseases

Which diseases are not treatable using antibiotics?

Antibiotics

In one West African country, a measles vaccination programme was started while a measles epidemic was occurring. Subsequently, it was discovered that vaccinated children were more likely to survive through childhood than unvaccinated children, even when there were no measles epidemics. The vaccine had provided the children with some defence against other pathogenic infections. Which statement could explain this additional protection?

Antibodies and vaccination

Which graph illustrates how antibody concentration changes after a second exposure to the same infection?

Proteins

In which locations are antigens found?

Fluid mosaic membranes

The diagram shows a sketch based on an electron micrograph of a typical animal cell. What is the function of the membrane system labelled X?

Cells as the basic units of living organisms

Whooping cough is a very infectious disease of the gas exchange system, caused by the bacterium $\text{Bordetella pertussis}$. Which method protects infants from whooping cough and lowers the likelihood of developing this disease later in life?

Antibodies and vaccination

The diagram shows a sketch made from an electron micrograph of a typical animal cell. In which part would nucleic acid be located?

Cells as the basic units of living organisms

The diagram illustrates some similarities among chloroplasts, mitochondria and typical prokaryotes. Which row is correct?

Cells as the basic units of living organisms

A student performed tests on equal volumes of four different solutions to find out whether protein, starch and reducing sugar were present in each one. The results are displayed in the table. Which conclusion can be drawn from these results?

Testing for biological molecules

Which words correctly finish the description of amylose? The ....1.... amylose is a ....2.... that is formed from ....3.... of ....4.... glucose.

Carbohydrates and lipids

Which of the following statements about glycosidic bonds are correct?

Carbohydrates and lipids