May/June 2017

Which definition gives the correct meaning of magnification for a drawing of a leaf?

The microscope in cell studies

The following are features of the structures of phospholipids and triglycerides. Which structures make the formation of a lipid bilayer possible in cell surface membranes?

Fluid mosaic membranes

The diagram illustrates the molecular structure of a peptide. Which molecules would be formed by the complete hydrolysis of the peptide?

Proteins

The diagram illustrates a haemoglobin molecule. Which row correctly names the different sections of the molecule?

Proteins

Bacterial cells divide by a process known as binary fission. Which macromolecules need to be synthesised for binary fission?

Replication and division of nuclei and cells

A student performed experiments to study how enzyme concentration affects the rate of hydrolysis (break down) of protein in milk. After the enzyme and milk were combined, the protein was hydrolysed and the mixture went from cloudy to clear. The student used five different enzyme concentrations and measured the time needed to reach the end-point for each one. What would be an appropriate control for this investigation?

Factors that affect enzyme action

What decides the specificity of an enzyme?

Mode of action of enzymes

The graph illustrates how temperature affects the rate at which the enzyme in a biological washing powder breaks down and removes fruit juice stains. Which statements account for the graph’s pattern at temperatures above X?

Factors that affect enzyme action

Which description applies to a carrier protein in cell surface membranes?

Movement into and out of cells

What may occur to a typical bacterium if it is put into an environment with a water potential that is less negative than the water potential inside the cell?

Movement into and out of cells

Through which process do hydrogencarbonate ions move out of red blood cells?

Movement into and out of cells

The electron micrograph displays part of two cells. Which labelled features show that these cells are eukaryotic?

Cells as the basic units of living organisms

In an experiment, fluorescent dyes were used to tag proteins on the outer surface of cell surface membranes. Living human cells were marked with one colour of fluorescent dye and mouse cells with a different colour of fluorescent dye. A human cell and a mouse cell are then fused to make a hybrid cell. Initially, the two fluorescent labels stay separate, but after 40 minutes they are spread at random across the hybrid cell surface membrane. What does this experiment show?

Fluid mosaic membranes

The diagram illustrates the mitotic cell cycle. In which phase does DNA replication occur?

Replication and division of nuclei and cells

The electron micrograph displays a set of human chromosomes. Which label correctly identifies each structure marked W, X and Y?

Chromosome behaviour in mitosis

During mitosis, which statement about chromosome behaviour is correct?

Chromosome behaviour in mitosis

Which is the smallest part of a DNA molecule that can be changed by a mutation and lead to an alteration in the coding of a polypeptide?

Proteins

Which of the following statements about tRNA are correct?

Proteins

The table outlines the roles of four different proteins involved in DNA replication. Which option states the function of these proteins?

Replication and division of nuclei and cells

What type of sugar and what type of bond are present in a DNA molecule?

Structure of nucleic acids and replication of DNA

The diagrams show cross-sections through three plant organs. Which row is the correct one for phloem?

Structure of transport tissues

Sucrose passes from a phloem sieve tube element into a root cell. Which changes in the water potential and in the volume of liquid in the phloem sieve tube element are correct?

Movement into and out of cells

Plant cells are prepared, stained and examined with a student microscope. The illumination came from natural light. What would be seen clearly at $\times 400$ magnification?

The microscope in cell studies

Which of the following statements about water movement in plants are correct?

Movement into and out of cells

The photomicrograph shows a leaf in transverse section. Which features are typical of xerophytes?

The gas exchange system

A maize crop is growing well in a field where the water potential of the soil is $-40\ \text{kPa}$. What is the most likely water potential of the cell sap in the root hair cell?

Movement into and out of cells

Electrical impulses travelling through the cardiac muscle coordinate the contraction of the heart. Which option gives the correct order for part of the sequence of these impulses?

Movement into and out of cells

What features allow the aorta to endure ventricular systole?

The microscope in cell studies

Which row gives the correct information for the pulmonary artery?

The microscope in cell studies

The graph presents oxygen dissociation curves for adult oxyhaemoglobin at two different carbon dioxide concentrations, 1 and 2. Which conditions could cause curve 1 to alter into the form of curve 2?

Proteins

Which feature of the human gaseous exchange surface and lungs keeps the concentration gradients for carbon dioxide and oxygen at the required level?

Movement into and out of cells

Which option identifies the tissues found in the trachea?

The gas exchange system

The table presents worldwide death totals for certain diseases in 2002. What number of millions of people died in 2002 from the bacterial diseases listed in the table?

Infectious diseases

Which of these lengths have the same value as $1\,\mu\text{m}$?\n\n1 $1000\,\text{mm}$\n2 $0.001\,\text{nm}$\n3 $0.001\,\text{mm}$\n4 $1\,000\,000\,\text{nm}$\n5 $0.01\,\text{mm}$\n6 $1000\,\text{nm}$

The microscope in cell studies

B-lymphocytes and T-lymphocytes are often unable to mount a response to the antigens on pathogens that exist as intracellular parasites. What is the reason for this?

Fluid mosaic membranes

Certain secretory cells make and secrete glycoproteins. What is the correct order of the events as they happen in the secretory cell? 1 exocytosis 2 product collects in secretory vesicle 3 mRNA associates with ribosomes 4 glycoprotein synthesis

Movement into and out of cells

A scientist performed an experiment to separate the organelles in an animal cell according to mass. The scientist combined the cells with a buffer solution that had the same water potential as the cells and then broke open the cells. The mixture was centrifuged several times to produce pellet 1, pellet 2, pellet 3 and pellet 4, with each pellet containing one organelle. What is the function of the organelle obtained in pellet 3?

Cells as the basic units of living organisms

What is the general formula of amylopectin?

Carbohydrates and lipids

Which statement explains how starch’s molecular structure is adapted to its function?

Carbohydrates and lipids

Cows and whales are mammals that make milk to nourish their young. Baby whales grow more rapidly than baby cows. The milk produced by both cows and whales includes saturated fatty acids with different chain lengths. The table gives the percentage of saturated fatty acids with different lengths in cow and whale milk. Which statement correctly describes the ratio of short fatty acids $(4-16$ carbons$)$ to long fatty acids $(18$ or more carbons$)$ in the milk of cows and whales?

Carbohydrates and lipids

Which organelles are surrounded by a single phospholipid bilayer and contain hydrolytic enzymes?

Cells as the basic units of living organisms

Invertase is the enzyme that catalyses the breakdown of sucrose into glucose and fructose. Three different enzyme inhibitors of invertase, X, Y and Z, were studied. The percentage inhibition of invertase was recorded at a range of inhibitor concentrations. The graph shows the findings of the investigation. Which conclusions are valid from these results?

Factors that affect enzyme action

The statements below concern enzymes. Which of these statements are correct according to the induced fit hypothesis?

Mode of action of enzymes

In what way is the Michaelis-Menten constant ($K_m$) used?

Mode of action of enzymes

Proteins in the cell surface membranes of human cells and mouse cells were marked using fluorescent dyes. The human cells were given a red dye, whereas the mouse cells were given a green dye. A human cell and a mouse cell were then fused together to produce a hybrid cell. Initially, the two dyes stayed apart. After 40 minutes, the two dyes were spread evenly throughout the hybrid cell surface membrane. What accounts for this observation?

Fluid mosaic membranes

The diagram illustrates a plant cell. The plant cell is placed in a solution whose water potential is less negative than that of the cell contents. What change will be seen in the cell’s appearance?

Movement into and out of cells

The diagram illustrates the fluid mosaic model of membrane structure. Which molecules within the membrane are the same?

Fluid mosaic membranes

The photomicrograph shows one stage of mitosis. Which statement would be correct for the following stage in mitosis?

Chromosome behaviour in mitosis

The diagram illustrates part of the arrangement of a DNA molecule and the histones attached to it. Which statement about the features labelled P, Q and R during prophase of mitosis is correct?

Chromosome behaviour in mitosis

The bacterium Escherichia coli splits once every 50 minutes at $36^\circ\text{C}$. E. coli were cultured on a medium that had only heavy nitrogen, $^{15}\text{N}$, until every part of the bacterial DNA contained heavy nitrogen (0 minutes). Some of the bacteria were transferred from the heavy nitrogen medium and then grown in a medium containing only light nitrogen, $^{14}\text{N}$. A sample of bacteria was taken after each of three generations. The DNA was removed and spun in a centrifuge. Hybrid DNA includes both heavy and light nitrogen. The diagram indicates the possible band positions (upper, middle and lower) of the DNA. The real band positions in the first two samples are shown. What fraction of the DNA in the sample collected at 150 minutes will be in the upper position?

Replication and division of nuclei and cells

Some plant tissues were given a radioactively labelled compound in order to find out which tissues were actively making mRNA. Which radioactively labelled compounds would be the best choice for this experiment?

Proteins

The DNA in prokaryotes is not linked to proteins and is arranged in a circular molecule. Which statement explains the way DNA in eukaryotes differs from DNA in prokaryotes?

Structure of nucleic acids and replication of DNA

Electron micrographs can reveal many ribosomes arranged in chains along mRNA molecules. What advantage does this arrangement have, compared with ribosomes being present singly on the mRNA?

Protein synthesis

Which row shows the correct information for adenine?

Structure of nucleic acids and replication of DNA

The graph illustrates the decrease in mass of a potted plant because of transpiration. What might have happened at point X on the graph?

Movement into and out of cells

Which row correctly describes a phloem sieve tube element?

Structure of transport tissues

An aphid, for example a greenfly, feeds on nutrients in the plant by using a narrow tubular mouthpart known as a stylet. It pushes the stylet through the outer surface of a stem or leaf. If a stylet is cut close to the aphid’s head while the stylet remains in the plant, a liquid with a low water potential still keeps flowing out from the plant. Which statement accounts for this?

Movement into and out of cells

Which statement gives the correct description of transport pathways in dicotyledonous plants?

Movement into and out of cells

The graph illustrates how pressure changes over a cardiac cycle. Which row correctly identifies W, X, Y, and Z?

The heart

What does systolic blood pressure mean?

The circulatory system

When humans are kept at high altitudes, their red blood cell count rises. What causes this to happen?

Transport of oxygen and carbon dioxide

Which comparisons between blood, tissue fluid and lymph are correct?

Movement into and out of cells

A newly identified $Pandoravirus$ has a diameter of $1000\,\text{nm}$. The $Mimivirus$ is $400\,\text{nm}$ across. Which of these could be detected with a light microscope that has a maximum resolution of $0.25\,\mu\text{m}$?

The microscope in cell studies

Several different tissues are present in the walls of large blood vessels. Which row correctly names the main tissues found in the three layers of the wall of an artery?

The circulatory system

This photomicrograph displays a cross-section of lung tissue. Which structures can be seen in this photomicrograph?

The gas exchange system

If an athlete smokes immediately before a race, they may be unable to run at full speed because the blood transports less oxygen. Which explanation is correct?

Proteins

Some features needed in an efficient gas exchange system are a large surface area and a short diffusion distance. Which statement correctly explains how alveoli are adapted to satisfy these requirements?

Movement into and out of cells

The diagram illustrates three kinds of cell present in the human gas exchange system. Besides causing cancer, which cell types are directly affected when a person is exposed to tar in cigarette smoke?

The gas exchange system

Several common antibiotics are shown below, and the process blocked by each one is given. 1 rifampicin - blocks RNA polymerase 2 streptomycin - blocks $70\text{S}$ ribosomes 3 neomycin - blocks DNA synthesis 4 ampicillin - blocks peptidoglycan synthesis Which of these antibiotics will influence only the activities of bacterial cells?

Antibiotics

What might lead to malaria reappearing in a country after it had been eradicated?

Infectious diseases

Which illness is caused by a bacterium and may be transmitted through airborne droplets?

Infectious diseases

Smallpox has been eradicated, whereas malaria and cholera have not been. Which statements give the correct explanation?

The microscope in cell studies

When a person receives a vaccination, immunity to particular pathogens develops. Which of the following effects of vaccination are correct?

The microscope in cell studies

Which structures are present in chloroplasts and mitochondria?

Cells as the basic units of living organisms

What is the immune system’s initial response to a pathogen?

The immune system

By boiling the bones and teeth of dead animals, it is possible to make a kind of glue. This glue is made from the collagen fibres found in bones and teeth. Which statement describes the changes to collagen that happen when the glue is made?

Proteins

What term is used to describe the primary structure of a protein?

Proteins

The diagrams illustrate four monosaccharides with the formula $\text{C}_6\text{H}_{12}\text{O}_6$. Which diagram represents $\alpha$-glucose?

Carbohydrates and lipids

For polysaccharides to be fully digested, every glycosidic bond linking the monomers must be broken. Amylase breaks only $\alpha$-$1,4$ glycosidic bonds. Which row shows the extent to which amylase can completely digest cellulose, amylopectin or amylose molecules?

Carbohydrates and lipids

The diagram presents the outcomes of tests on four solutions that contain biological molecules. Which one shows the solution containing only starch and protein?

Testing for biological molecules

In which cell structure are cisternae located? 1 endoplasmic reticulum 2 Golgi body 3 mitochondrion

Cells as the basic units of living organisms

The graph illustrates energy changes during a chemical reaction. What is the activation energy when an enzyme is present?

Mode of action of enzymes

The graph presents the outcomes of investigations into the effect of amylase on the hydrolysis of starch at three different temperatures. In each investigation, the concentration and volume of the solutions were kept constant. Which conclusion can be drawn?

Factors that affect enzyme action

The graph shows how temperature affects the activity of the protease enzyme papain, both when it is dissolved in solution (free) and when it is trapped in alginate beads. Which statement correctly describes the effect of immobilising papain?

Factors that affect enzyme action

Which row gives the correct description of facilitated diffusion of molecules or ions into a cell?

Movement into and out of cells

The diagram shows an experiment in which solutions P and Q are divided by a partially permeable membrane. Which statement correctly describes the initial movement of molecules ○, □ and ⎯ between solutions P and Q?

Movement into and out of cells

Which functions apply to components of the cell surface membrane?

Fluid mosaic membranes

The diagram illustrates the cell cycle of a mammalian cell. Checkpoints in the mammalian cell cycle stop the cycle from carrying on if errors occur or DNA is damaged. Four checkpoints are given below. 1 Mitosis is prevented when DNA replication is not complete. 2 Anaphase is prevented if chromatids fail to attach correctly to the spindle. 3 DNA replication is prevented when DNA has been damaged. 4 DNA replication ceases if DNA damage has still not been repaired. At which phases of the cell cycle do these checkpoints occur?

Replication and division of nuclei and cells

The photomicrograph displays cells undergoing mitosis. Which statement describes what happens next in cell X?

Chromosome behaviour in mitosis

Which of these statements about nucleotides is correct?

Structure of nucleic acids and replication of DNA

Scientists have developed a nucleic acid (HNA) whose sugar contains the same number of carbon atoms as glucose rather than deoxyribose. Even though HNA can store genetic information, naturally occurring DNA polymerase is unable to replicate HNA. Which statements might account for the fact that naturally occurring DNA polymerase cannot replicate HNA?

Mode of action of enzymes

The diagram shows an eyepiece graticule and part of a stage micrometer scale viewed at $\times 100$ magnification. How is the value, in $\mu\text{m}$, for one eyepiece graticule unit determined?

The microscope in cell studies

Meselson and Stahl studied DNA replication by culturing bacteria in a medium containing heavy nitrogen, $^{15}
\text{N}$, until all the DNA had been labelled. These bacteria, called the parental generation, were then moved to a culture containing only light nitrogen, $^{14}
\text{N}$, and allowed to replicate for two generations. DNA was removed from each bacterial generation and its relative mass was measured. The flow diagram shows the results. Which row accounts for the relative mass of the DNA in the second generation grown in $^{14}
\text{N}$?

Replication and division of nuclei and cells

Which of the following statements is correct?

Cells as the basic units of living organisms

The diagrams display transverse sections of parts of a plant. In the transverse sections, which tissues transport most amino acids?

The microscope in cell studies

The statements below describe the way water travels across the root to the xylem vessel elements in plants. Which statements are correct for both the apoplast pathway and the symplast pathway?

Movement into and out of cells

The diagram illustrates the tissues involved in sucrose transport in a plant. In which region is the sucrose concentration greatest?

Movement into and out of cells

Which characteristics enable root hair cells to absorb water efficiently?

Movement into and out of cells

Three structures that take part in controlling heart activity are given below. 1 atrioventricular node 2 Purkyne tissue 3 sinoatrial node What is the correct sequence in which they are involved?

The heart

As blood moves from an artery into a vein, the pressure in the vessels varies. The four graphs show data for the blood vessels in the order given. Which graph correctly represents these changes?

The circulatory system

In the blood, in what form is most carbon dioxide carried?

Movement into and out of cells

When a doctor or nurse draws a blood sample from a person, a needle is used to enter a vein rather than an artery. Which reasons account for veins being used?

The microscope in cell studies

A bacterium can be made to synthesise a eukaryotic protein. To do this, a eukaryotic gene is inserted into the bacterial DNA so that it can be translated. What explains the fact that a bacterial cell can make a eukaryotic protein but is unable to make a eukaryotic glycoprotein?

Proteins

The diagram shows an unfinished summary of haemoglobin’s role in transporting carbon dioxide. Which labelled set is correct?

Proteins

Which statement describing a part of the gas exchange system is correct?

Movement into and out of cells

When a person has an asthma attack, the tubes in the gas exchange system become narrower and more mucus is formed. Which changes take place during an asthma attack?

The gas exchange system

Which effects arise from paralysis of cilia caused by smoking?

The gas exchange system

What is the smallest number of cell membranes that a molecule of carbon dioxide and a molecule of oxygen cross during gas exchange between alveoli and the plasma in the capillaries?

Movement into and out of cells

Which statement about measles is correct?

Infectious diseases

Certain antibiotics are added to animal feed to help lower disease. Why should these antibiotics not be used to treat human diseases?

Antibiotics

In what sequence do the following processes take place so that a population of bacteria becomes resistant to a new antibiotic?

Antibiotics

Which form of new vaccine production would matter most in the effort to eradicate measles in developing countries?

Antibodies and vaccination

The photomicrograph shows human blood, and three kinds of white cell are labelled. Which row correctly names these white cells?

The immune system

In both typical eukaryotic cells and typical prokaryotic cells, which structures are present? 1 $70\text{S}$ ribosomes 2 $80\text{S}$ ribosomes 3 circular DNA

Cells as the basic units of living organisms

A monoclonal antibody that was specific to a virus was made. An enzyme was then used to treat this antibody so that the bonds linking the variable region and the constant region were broken. The separate variable and constant regions were afterwards added to cells infected by the virus. Which statements are correct?

Proteins

Steps 1-4 are carried out to test for a non-reducing sugar. 1 Place $5\,\text{cm}^3$ of solution in a test-tube. 2 Add several drops of acid. 3 Neutralise using alkali. 4 Add $6\,\text{cm}^3$ of Benedict’s solution. At what point is the solution boiled?

Testing for biological molecules

Which diagram represents the monomer that forms cellulose?

Carbohydrates and lipids

The diagram illustrates some of the links between cellulose, collagen and haemoglobin. Which row is correct?

Proteins

The diagram represents a protein molecule. Two long polypeptides each adopt $\alpha$-helices over most of their length, and these wind around one another to make a fibre. At one end, each polypeptide folds into a globular head. Two short polypeptides attach to each head. What describes the protein structure of this molecule?

Proteins

Which of the following statements concerning both amylose and amylopectin are correct?

Carbohydrates and lipids