May/June 2025

Which of the following statements about light microscopes are correct?

The microscope in cell studies

Many animals use triglycerides for long-term energy storage. Which statements are correct other functions of triglycerides?

Carbohydrates and lipids

The diagrams illustrate three different bonds. Which of these bonds are present in proteins?

Proteins

What term is used for the quaternary structure of a collagen molecule?

Proteins

The diagram illustrates the structure of the enzyme amylase. Which level of protein structure causes amylase to fold into its globular shape?

Proteins

Which statement accounts for why large volumes of water keep their temperature steady as the air temperature rises?

Water

Which of the following statements about an enzyme’s mode of action are correct?

Mode of action of enzymes

The graph illustrates how raising substrate concentration affects the reaction rate of two enzymes that catalyse reactions using the same substrate. Which statement is the correct one?

Factors that affect enzyme action

The structure of the cell surface membrane is called a ‘fluid mosaic’. Which statement gives the correct meaning of the ‘mosaic’ part of the cell surface membrane?

Fluid mosaic membranes

A student placed a plant tissue in solution S. Over the following 30 minutes, the student examined the cells in the plant tissue with a microscope. During this period, the cytoplasm of the cells contracted and no longer pressed against the cell wall. In many cells, a gap formed between the cytoplasm and the cell wall. Which statements are correct conclusions from these observations?

Movement into and out of cells

A sample of 500 cells undergoing mitosis was observed so that the mitotic stage of each cell could be identified. The table presents the findings. Which row is correct?

Chromosome behaviour in mitosis

Using an electron micrograph of an animal cell with a magnification of $\times 9600$, a student measured the width of a mitochondrion. The measured width on the micrograph was $6\ \text{mm}$. What was the actual width of the mitochondrion?

The microscope in cell studies

The diagram illustrates a chromosome. Which structures are P and Q?

Chromosome behaviour in mitosis

What processes are carried out by stem cells during tissue repair?

Replication and division of nuclei and cells

The enzyme telomerase stops telomeres from being lost after repeated mitotic cell cycles. Which cells produce a high concentration of telomerase by transcription?

Replication and division of nuclei and cells

Which of the following statements are correct?

Cells as the basic units of living organisms

A DNA molecule with two strands was examined, and adenine made up 29% of its nucleotide bases. What percentage of its nucleotide bases is cytosine?

Structure of nucleic acids and replication of DNA

In some cells, non-coding RNA sequences are cut out after transcription. Which row correctly gives the name of these non-coding RNA sequences and the type of cell in which they are removed?

Protein synthesis

Water potentials were determined in a leaf cell, within the leaf’s air spaces, and in the surrounding atmosphere. Which water potential ($\Psi$) values would make it possible for water to move from the leaf into the atmosphere?

Movement into and out of cells

Three liquid samples were collected from different parts of a plant and examined to determine the concentration of four solutes. Which of the samples were collected from phloem sieve tube elements?

Movement into and out of cells

A heating band was placed around the stem of a plant at a height of $1\,\text{m}$ above the ground and left in position for $10$ minutes. In what way will warming a short part of the stem to $60^\f$ change the movement of phloem sap and xylem sap between the roots and leaves?

Movement into and out of cells

The diagram illustrates the layout of an amphibian heart and the way blood flows through it. Which of the following statements about differences between the amphibian heart and a human heart are correct?

The heart

The photomicrograph shows a transverse section of a plant stem. Which statements might describe Q?

The microscope in cell studies

A mutation in one of the genes that codes for haemoglobin alters the affinity of haemoglobin for oxygen. As a result of this mutation, the partial pressure of oxygen needed for haemoglobin to be $50\%$ saturated with oxygen is reduced. Which row indicates the effect of the mutation on the affinity of haemoglobin for oxygen and the change in the position of the oxygen dissociation curve for haemoglobin?

Proteins

Which processes cause the Bohr shift?

Proteins

A student examined a drop of human blood under a microscope and observed a cell with a very large diameter and a U-shaped nucleus occupying half of the cell’s volume. Which type of cell was the student looking at?

The immune system

How many times does an oxygen molecule have to cross a cell surface membrane to move from the air in the alveolus to the haemoglobin in a red blood cell? (Assume there are no pores between the cells through which the oxygen molecule has to travel.)

Movement into and out of cells

Asthma may occur in both children and adults. The air passages get narrower, which greatly limits the movement of air into the lungs. Salbutamol is a drug that widens the air passages and eases the symptoms of asthma. In what way does salbutamol relieve the symptoms of asthma?

Fluid mosaic membranes

The photomicrograph shows a transverse section of part of the trachea. Which letter identifies a tissue that is able to contract and relax in order to alter the diameter of the airways?

The gas exchange system

Which of the following statements about an infectious disease could be correct?

Infectious diseases

Which statements show why vaccination has not eradicated cholera?

Antibodies and vaccination

Antibiotic resistance poses a serious threat to health worldwide. Which statement identifies a measure that can be taken to lessen the impact of antibiotic resistance?

Antibiotics

Tetanus is an infectious disease caused by a type of bacterium. This bacterium makes a protein that acts as a toxin and leads to illness. Scientists have developed a vaccine for tetanus that contains a harmless version of the toxin known as a toxoid. The toxoid is made by combining the toxin with the chemical formaldehyde. This chemical attaches to the toxin, making it harmless. Which statement about the tetanus vaccine is correct?

Proteins

The diagram comes from an electron micrograph of a cell that secretes enzymes. In what location are the polypeptides for these enzymes synthesised?

Protein synthesis

What impact does a lower number of T-helper cells have on the immune system?

The immune system

Which of the following comparisons between a typical bacterial cell and a typical plant cell are correct?

Cells as the basic units of living organisms

The diagram depicts a virus. Which row correctly names the labelled biological molecules?

Proteins

The iodine test and Benedict’s test were performed on samples of a starch solution. Amylase was added to another sample of the starch solution, which was then incubated for $10$ minutes. After this, the Benedict’s test was done on this sample. What were the outcomes of the tests?

Testing for biological molecules

Which row gives the correct description of $b1$-glucose and $b2$-glucose molecules?

Carbohydrates and lipids

Which of these molecules are monosaccharides?

Carbohydrates and lipids

Which row indicates possible uses of an eyepiece graticule?

The microscope in cell studies

Which characteristic of water makes sweating an effective way for the body to lose heat?

Water

What bonds are present in the levels of structure of a protein molecule?

Proteins

Prokaryotes and eukaryotes both make extracellular enzymes. In the external surroundings of some prokaryotes, extracellular digestive enzymes are present. When phagocytosis occurs in eukaryotic cells, hydrolytic enzymes digest some prokaryotes. Which row indicates the places where extracellular enzymes are made?

Mode of action of enzymes

Amylase breaks down starch molecules. Which substance will keep the same number of molecules throughout this reaction?

Mode of action of enzymes

Which graphs could be used to show how pH affects the rate of enzyme-catalysed reactions?

Factors that affect enzyme action

Following a heart attack, the enzyme lactate dehydrogenase passes into the blood plasma from injured heart muscle. What is needed to measure the activity of lactate dehydrogenase activity in a sample of blood plasma?

Factors that affect enzyme action

Which graph accurately shows $K_m$ and $V_{max}$?

Mode of action of enzymes

As temperature falls, cell membranes become less fluid. Bacteria and yeast are unable to control the temperature of their cells. How do bacteria and yeast keep their cell membranes fluid when the temperature falls?

Fluid mosaic membranes

Samples X, Y and Z are epidermal tissues taken from an onion. Each epidermal tissue sample was placed in one of three different salt solution concentrations for 30 minutes. A student viewed each tissue sample using a light microscope. The student then used a scale to estimate the concentration of each salt solution. The diagram shows the scale. P, Q and R represent the estimated concentration of the three salt solutions. The photomicrographs show the appearance of the tissues in samples X, Y and Z. Which row shows the estimated concentrations of the salt solutions in which samples Y and Z were immersed?

Movement into and out of cells

The graph presents the findings from an osmosis test carried out with potato tissue. At what concentration of sodium chloride solution is the water potential the same as that of this potato tissue, and what is true about water movement at that point?

Movement into and out of cells

Which statement concerning a light microscope is correct?

The microscope in cell studies

A pH indicator was used to dye some agar pink. From this pink agar, three agar cubes of different dimensions were cut. The cubes were then put into a beaker and covered with $0.1\,\text{mol dm}^{-3}$ hydrochloric acid. The experiment was kept at a constant temperature of $20^{\circ}\text{C}$. Hydrochloric acid diffused into the agar cubes, so the cubes lost their colour. Which agar cube, the one that became colourless in the shortest time, has the surface area to volume ratio?

Movement into and out of cells

The diagram illustrates the positioning of chromosomes with spindle fibres attached during one stage of mitosis. Which row correctly names the stage of mitosis and states what is occurring?

Chromosome behaviour in mitosis

At what stage of the cell cycle does DNA replication occur?

Replication and division of nuclei and cells

Human body cells in interphase contain 46 chromosomes. What is correct about how many telomeres are present in prophase of a human body cell?

Chromosome behaviour in mitosis

At times, hydrogen bonds are made briefly between the bases on two RNA strands. How many hydrogen bonds are produced when guanine and uracil each pair with their complementary base?

Structure of nucleic acids and replication of DNA

The table lists every possible DNA triplet code for certain amino acids. The amino acid sequence is given below. methionine - isoleucine - cysteine - tryptophan What is the greatest number of different DNA sequences that could code for this amino acid sequence?

Proteins

Which row shows the correct information about transpiration?

Movement into and out of cells

Which characteristics of companion cells and xylem vessel elements enable them to carry out their functions effectively?

Structure of transport tissues

The diagram shows several root cells. Which statement is correct about the pathway indicated by the arrows?

Movement into and out of cells

The graph shows the diameter of a tree trunk at different times. Which statement is the correct one?

Replication and division of nuclei and cells

The electron micrograph displays a cell. What is the cell's actual maximum length?

The microscope in cell studies

Outline diagrams of transverse sections of two plant organs are shown. These are not drawn to scale. Which tissues have proton pumps?

Movement into and out of cells

The diagrams illustrate three kinds of blood cells, and they are all shown to the same scale. Which row displays the cells’ characteristics?

The circulatory system

The graph displays oxygen dissociation curves for three animals. The shape of each curve is affected by respiration rate and the affinity of haemoglobin for oxygen. What conclusion can be drawn from the graph?

Proteins

Which of these statements about a mammalian heart are correct?

The microscope in cell studies

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

Movement into and out of cells

Which row shows the tissues found in the wall of the trachea and in the wall of the bronchus?

The gas exchange system

Which factors help to keep the diffusion gradient for carbon dioxide across the alveolar surface?

Movement into and out of cells

A student recorded notes on two diseases: hand, foot and mouth disease (HFMD) and Lyme disease. HFMD is caused by a viral pathogen and is spread in several ways, including: • drinking water polluted with faeces • breathing in droplets that contain the pathogen. Lyme disease is caused by a bacterial pathogen and is spread through the bite of an infected insect. Which statement gives a correct comparison between the diseases the student has written about and cholera, malaria or tuberculosis (TB)?

Infectious diseases

Which statements account for why antibiotics may fail to treat cholera effectively?

Movement into and out of cells

The statements below outline how a macrophage carries out phagocytosis of a bacterium. 1 Digestive enzymes decompose the bacterium. 2 A lysosome fuses with the vacuole. 3 The macrophage exposes the bacterial antigens on its cell surface membrane. 4 The macrophage takes in the bacterium and places it inside a vacuole. 5 Receptors on the cell surface membrane of the macrophage attach to the bacterium. What is the correct sequence for phagocytosis?

Movement into and out of cells

The table sets out a comparison of certain biochemical molecules in P, Q, R and S. Which row correctly names P, Q, R and S?

Carbohydrates and lipids

Two individuals, G and H, each received an injection to help protect them from a particular pathogen. One person was given antibodies by injection. The other person was given a vaccine by injection. The graph shows the concentrations of the antibody against this pathogen in the blood of G and H over the 20 days after their injections. Which row correctly states the type of immunity shown by G and H?

Proteins

Which cell structures contain enzymes and have a double membrane surrounding them?

Cells as the basic units of living organisms

What is the relative size order of cell structures?

Cells as the basic units of living organisms

One portion of a sucrose solution is tested for reducing sugars and stays blue, but when a separate portion of the same solution is tested for non-reducing sugars the solution turns red. What accounts for these observations?

Testing for biological molecules

Which molecules possess at least two double bonds?

Carbohydrates and lipids

Amylose, amylopectin and glycogen are each polysaccharides. Enzyme X hydrolyses $\alpha$-1,4-glycosidic bonds at the ends of a polysaccharide molecule, releasing one maltose molecule at a time. Which row indicates how completely each of these molecules will be hydrolysed by enzyme X? (Assume that each polysaccharide contains the same number of monomers before hydrolysis starts.)

Carbohydrates and lipids

The diagram illustrates an eyepiece graticule being calibrated with the help of a stage micrometer. Each division on the stage micrometer scale is $0.1\,\text{mm}.$ Which row gives a correct calculation for calibrating each eyepiece graticule unit and includes the correct units?

The microscope in cell studies

The diagrams illustrate how some glucose polymers can be grouped. Which row correctly names P, Q and R?

Carbohydrates and lipids

Which molecules yield products that contain a carboxyl group after hydrolysis?

Proteins

Which bonds take part in keeping the secondary and tertiary levels of protein structure stable?

Proteins

The diagrams illustrate the structures of four amino acids in solution: glycine, lysine, alanine and aspartate. Which of these amino acids carry no overall charge?

Proteins

Which property of water means that the temperatures of the oceans and the cytoplasm inside cells change by relatively small amounts?

Water

Histidine and proline are two amino acids often present in enzymes. Histidine has a polar R-group, whereas proline has a non-polar R-group. Where would most histidines and prolines be located?

Proteins

The action of an enzyme can be influenced by a competitive inhibitor. Which row gives the correct effect of a competitive inhibitor on the value of $K_m$ and the reason for this?

Factors that affect enzyme action

The diagram illustrates part of a eukaryotic cell surface membrane. Which components function as antigens in cell surface membranes?

Fluid mosaic membranes

Three biological molecules found in cell surface membranes are described below. • X is a molecule made up of carbon, hydrogen and oxygen, with a non-polar part and one section that projects from the membrane and is able to form hydrogen bonds. • Y is a molecule with a hydrophilic end that forms hydrogen bonds with the water outside the membrane, and a hydrophilic part that lies within the cell membrane. • Z is a molecule that can arrange itself in the membrane because it has a hydrophilic region at one end and two hydrophobic extensions located within the membrane. Which row correctly identifies a carrier protein and a glycolipid?

Fluid mosaic membranes

Antimycin is a chemical substance that blocks mitochondria from functioning. Which transport mechanisms across the cell surface membrane could be directly affected by antimycin?

Movement into and out of cells

The diagram was produced from an electron micrograph of an animal cell. Which diagram would show the same cell as seen with a simple light microscope, when daylight is the only source of light?

The microscope in cell studies

A learner filled a beaker until it was half full with solution X. A sealed Visking tubing bag that contained solution Y was then put into the beaker. After 30 minutes, the liquid in the beaker was orange and the liquid inside the Visking tubing was blue-black. What substances were present in solutions X and Y at the beginning to produce these results?

Movement into and out of cells

A cell is undergoing mitosis. At this point, each chromosome in the cell is made up of two chromatids. The chromosomes have not arranged themselves along the equator. Which stage of mitosis is being described?

Chromosome behaviour in mitosis

The diagrams illustrate two phases of the cell cycle in different organisms. The quantity of specific structures in each diagram is counted. Which row gives the correct overall total for the various structures?

Chromosome behaviour in mitosis

Which of the following statements about tRNA are correct?

Protein synthesis

Why is the genetic code referred to as universal?

Proteins

What correctly states how many and what kind of bonds link cytosine and guanine in a DNA molecule?

Structure of nucleic acids and replication of DNA

Three proteins with quaternary structure are given below. • Type IX collagen is made up of three different polymers. • The principal form of haemoglobin has two alpha globins and two beta globins. • HIV protease is composed of two identical polymers. Which row gives the correct number of genes required to code for each protein?

Proteins

The photomicrograph shows a slice of vascular tissue taken from the stem of a plant. Which statement about this photomicrograph is correct?

Structure of transport tissues

The diagram illustrates a bond between two molecules moving in a xylem vessel. Which row correctly identifies bond R and states the function of the bond between these molecules in allowing them to be transported in a xylem vessel?

Water

By what routes can water and solutes pass through a leaf?

Movement into and out of cells

Norovirus has a diameter of $30\,\text{nm}.$ Mimivirus has a diameter of $400\,\text{nm}.$ Which viruses are able to be observed using a light microscope whose maximum resolution is $0.25\,\mu\text{m}$?

The microscope in cell studies

Atrial septal defect (ASD) is a heart defect that is present in some newborn babies. ASD is a gap between the right and left atria. What possible effects may babies born with ASD have compared with babies born without ASD?

The heart

Which of the following statements is correct?

Cells as the basic units of living organisms

Which statement describes the function of the atrioventricular node in the heart?

The heart

A sample of adult haemoglobin was examined to find its oxygen saturation. All the other variables were kept constant. At a partial pressure of $0\,\text{kPa}$, the saturation was $0\%$. The saturation rose to $97\%$ at a partial pressure of $14\,\text{kPa}$. Which row gives possible percentage saturation values for haemoglobin at intermediate partial pressures?

Proteins

The photomicrograph depicts a cross-section through part of the human gas exchange system. Which row gives the label and function of smooth muscle?

The microscope in cell studies

What characteristic of the human gas exchange system helps keep a steep diffusion gradient?

Movement into and out of cells

The diagram illustrates the structure of an antibody. Which statements about the antibody are correct?

Proteins

Which statement could describe how resistance to penicillin develops in bacteria?

Mode of action of enzymes

A number of events that occur in phagocytosis are shown. In which sequence do these events happen during phagocytosis?

Movement into and out of cells

What roles do plasma cells play during an immune response?

The microscope in cell studies

Which cell structures house ribosomal RNA?

Protein synthesis

Which disease is brought about by a eukaryotic pathogen?

Infectious diseases

Immature red blood cells possess all the usual organelles and cell structures found in animal cells. Mature red blood cells are specialised cells that have lost their organelles and cell structures. Which statement gives the correct comparison between red blood cells and typical plant cells?

Cells as the basic units of living organisms

A culture of human cells had the cell surface membranes stripped away, so the cell contents were released. Bacteria then contaminated this material. The material was afterwards centrifuged, which separated the different cell structures by size and mass. Which cell structure would be separated out together with the bacteria?

Cells as the basic units of living organisms

The diagram shows the structure of a virus. Which row gives the correct descriptions of the structures labelled 1 and 2?

Infectious diseases

Which statement concerning a macromolecule is correct?

Proteins

What occurs to molecules of sucrose when they are heated in acid?

Carbohydrates and lipids