Oct/Nov 2024

The diagram presents a transverse section of a blood capillary, showing a labelled endothelium wall and the lumen. The diameter indicated is $7\,\mu\text{m}$. What magnification does the drawing have?

The microscope in cell studies

Solutions 1 and 2 each contained a mixture of two different biological molecules. One solution included starch and sucrose, while the other included glucose and protein. A range of reagents was used to test the two solutions for the presence of the biological molecules. The table presents the results that were obtained for the different tests. Which row correctly identifies the two solutions?

Testing for biological molecules

The diagrams illustrate parts of three pairs of amino acids within a protein. These pairs are labelled X, Y and Z. Which row indicates the correct type of interaction that would take place between the two amino acids in each pair?

Proteins

A student performed investigations at $\text{pH }1$-$8$ in order to examine how $\text{pH}$ affects an enzyme-catalysed reaction. The best condition for this enzyme is the acidic conditions in the stomach at $\text{pH }1$-$2$. The concentration of substrate left was recorded after five minutes at each separate $\text{pH}$. Which graph shows the effect of increasing $\text{pH}$ on substrate concentration remaining after five minutes?

Factors that affect enzyme action

Which of the following statements is correct about a non-competitive inhibitor?

Factors that affect enzyme action

Pyrophosphatase enzymes bring about a hydrolysis reaction. $\text{pyrophosphate ions} \xrightarrow{\text{pyrophosphatase}} \text{phosphate ions}$ During experiment 1, a scientist investigated the rate of this reaction using a colorimeter. The absorbance of the solution was recorded at fixed intervals until all the pyrophosphate ions had been changed into phosphate ions. For experiment 2, the scientist carried out the procedure again with a greater concentration of pyrophosphatase. All other variables were kept constant. Which graph shows the effect of increasing the concentration of pyrophosphatase?

Factors that affect enzyme action

Proteases are one type of enzyme that break down proteins. Which of the statements about proteases is correct?

Mode of action of enzymes

The diagram illustrates a section of a cell surface membrane. Which row correctly names the molecules labelled 1 and 2?

Fluid mosaic membranes

The diagram illustrates the average dimensions of an epithelial cell in micrometres ($\mu\text{m}$). Which row gives the epithelial cell’s surface area to volume ratio, and how would this ratio change if the cell width were doubled?

Movement into and out of cells

Which diagram indicates the correct net direction of water movement among the four cells as a result of osmosis? Key: $\psi$ = water potential

Movement into and out of cells

An experiment was done to test how four different treatments affected the permeability of the cell surface membranes and tonoplasts in beetroot cells. The vacuoles of beetroot cells contain a red pigment. This pigment is unable to diffuse through the tonoplasts or the cell surface membranes. $1\,\text{cm}^3$ cubes were removed from beetroot tissue and rinsed in running water for 20 minutes to wash away any pigment that had leaked from cells that were damaged. Two cubes were then put into each of four test-tubes, each containing a different substance, and left to stand for five minutes. Which row gives a correct explanation for the observation recorded for one of the treatments?

Movement into and out of cells

Which statement accounts for why lymphocytes lacking nucleoli die?

Protein synthesis

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

Chromosome behaviour in mitosis

What are the correct functions of mitosis?

Replication and division of nuclei and cells

Which row gives the correct stages of the mitotic cell cycle?

Replication and division of nuclei and cells

Which statements explain how a gene mutation can cause a non-functional protein to be produced?

Proteins

A certain mammal has 64 chromosomes in its muscle cells. How many DNA molecules are present in a cell during early prophase and telophase of mitosis?

Chromosome behaviour in mitosis

The diagram below presents the nucleotide order of a short part of the transcribed strand of a gene: GCG CGC GGC GCG The table gives the amino acids specified by 10 mRNA codons. What is the order of the four amino acids in the polypeptide translated from this short part of a gene?

Proteins

When adenine and cytosine each pair with their complementary bases, how many hydrogen bonds are formed?

Structure of nucleic acids and replication of DNA

Which statement correctly describes how sucrose and amino acids are transported in plant vascular tissue?

Movement into and out of cells

Xylem vessel elements are cells specialised for the movement of water. Which statement correctly pairs an adaptation of a xylem vessel element with its function?

Structure of transport tissues

A student draws an accurate labelled plan diagram of a section of a leaf that contains a vascular bundle. Which statement correctly describes one part of their plan diagram?

The microscope in cell studies

Density gradient centrifugation is used to separate cell structures according to their relative density. Because larger cell structures have a greater density, they sink farther down the centrifuge tube. What is the correct sequence of the cell structures, beginning at the top of the centrifuge tube?

Cells as the basic units of living organisms

Some babies are born with an opening between the right atrium and the left atrium. In these babies, a larger number of red blood cells is found. What is the cause of this rise in red blood cells in these babies?

Transport of oxygen and carbon dioxide

A rise in the carbon dioxide concentration in human blood causes the oxyhaemoglobin dissociation curve to move to the right. What explains this effect?

Proteins

‘Heart block’ is a disease that can lead to a heart rate that is lower than normal. A doctor treating a person with heart block discovered that electrical impulses were initiated normally but were not conducted correctly to the ventricles, so the rate of ventricular contraction was slowed. Which parts may not be functioning correctly in the person with heart block?

Movement into and out of cells

The heart's pumping action generates hydrostatic pressure in the blood. The table gives the hydrostatic pressure in a blood capillary. Arteriole end of capillary: $4.2\ \text{kPa}$ Venule end of capillary: $1.7\ \text{kPa}$ Approximately $90\%$ of the tissue fluid that surrounds a capillary is returned to the blood at the venule end. By what means is this brought about?

Movement into and out of cells

What role do cilia play in the gas exchange system?

The gas exchange system

What tissues make up the walls of a trachea and an alveolus?

The gas exchange system

The photomicrograph shows a section of a bronchus. Which label indicates cartilage?

The microscope in cell studies

Which structures or compounds in a typical cell can be destroyed by penicillin?

Antibiotics

Three statements about cholera and how it is transmitted are given. Which statements explain why cholera outbreaks are likely to happen?

Infectious diseases

What is formed when memory cells divide in a secondary immune response?

Replication and division of nuclei and cells

Which cell structures have nucleic acids?

Structure of nucleic acids and replication of DNA

A vaccine is given to provide immunity against the virus that causes influenza. A different influenza vaccine is required each year because the virus changes by mutation regularly. What is the reason for needing a new influenza vaccine every year?

Proteins

The statements outline events occurring in a secretory cell. 1 The protein is modified in the Golgi body. 2 mRNA exits the nucleus. 3 Ribosomes attach to mRNA during translation. 4 A particular DNA sequence is transcribed. 5 Vesicles merge with the cell surface membrane. 6 Vesicles carry the protein to the Golgi body. Statement 4 is the initial event, and statement 5 is the final event. What is the correct order of the four events in between?

Movement into and out of cells

What number of double-membrane structures found in animal cells are also present in plant cells?

Cells as the basic units of living organisms

A polysaccharide that occurs naturally and is synthesised in a plant consists of a branched chain of $\alpha$-glucose. The unbranched sections of the molecule are joined by $\alpha$-$1,6$ glycosidic bonds, and only a few branches are present, with each branch formed by either an $\alpha$-$1,3$ glycosidic bond or an $\alpha$-$1,4$ glycosidic bond. Which polysaccharide has a structure most like the one described?

Carbohydrates and lipids

The diagram illustrates a triglyceride. An enzyme was used to break down this triglyceride into glycerol and fatty acids. Which scatter plot correctly shows each fatty acid component of the triglyceride?

Carbohydrates and lipids

The diagram illustrates how the alternating arrangement of $\beta$-glucose monomers in a chain enables hydrogen bonds to develop between neighbouring monomers. Hydrogen bonds in cellulose influence tensile strength (the capacity to resist pulling forces without breaking). In what way do the hydrogen bonds shown in the diagram make cellulose a suitable substance for a cell wall?

Carbohydrates and lipids

A light microscope is being used to view two structures on a slide that are $200\,\text{nm}$ apart. What is the true separation between the two structures when the magnification is altered from $\times 40$ to $\times 400$?

The microscope in cell studies

A glucose solution and a starch solution were mixed together inside a length of dialysis (Visking) tubing, and the tubing was tied shut. The sealed tubing was then put into a boiling tube containing distilled water. Two samples were taken straight away from this water (time 0 minutes) and tested using either iodine solution or Benedict’s solution. The test was then carried out again at 10 minute intervals for 30 minutes. Each time, the iodine solution produced an orange-brown colour. The table gives the outcomes of the Benedict’s test. What conclusion can be drawn from these results?

Movement into and out of cells

Which of the molecules are globular proteins?

Proteins

The starting rate of an enzyme-catalysed reaction was recorded at a range of substrate concentrations. Which graph illustrates the effect of a low concentration of non-competitive inhibitor on the reaction?

Factors that affect enzyme action

Gout is a form of arthritis in which tiny crystals of uric acid develop within and around the joints. It leads to sudden episodes of intense pain and swelling. The diagram illustrates how uric acid is produced from hypoxanthine, with the reaction catalysed by the enzyme xanthine oxidase. Gout may be treated with a drug named allopurinol, which has a shape similar to hypoxanthine. What conclusion can be drawn from this information about the way allopurinol stops uric acid from being formed?

Mode of action of enzymes

Phospholipids are assembled in much the same manner as triglycerides. One sample contained six phospholipid molecules. • The molecular weight of a phosphate ion is $95\,\text{g mol}^{-1}$. • The molecular weight of each separate fatty acid in this sample was determined to be $282\,\text{g mol}^{-1}$. • The molecular weight of glycerol is $92\,\text{g mol}^{-1}$. • The molecular weight of water is $18\,\text{g mol}^{-1}$. What is the molecular weight of the sample in $\text{g mol}^{-1}$?

Carbohydrates and lipids

Which of the following statements about phospholipids in cell surface membranes are correct?

Fluid mosaic membranes

In an experiment, pieces of onion epidermis are placed in three different sucrose concentrations, P, Q and R. The onion pieces are left for an hour and then observed with the low power of a light microscope. Each diagram shows one cell from the epidermis that was placed in each sucrose concentration. What accounts for the appearance of the cells in solution Q?

Movement into and out of cells

The electron micrograph displays rod-shaped bacteria. The bacterium has an actual length of $2.0\,\mu\text{m}$ and a diameter of $0.5\,\mu\text{m}$. Suppose the bacterium is cylinder-shaped. Calculate the surface area to volume ratio of the bacterium?

Cells as the basic units of living organisms

A chicken body cell has $78$ chromosomes in its nucleus. At the beginning of prophase of mitosis, how many DNA molecules are found in a chicken body cell?

Chromosome behaviour in mitosis

The photomicrograph displays cells in mitosis. Which statement explains what will happen next in cell X?

Chromosome behaviour in mitosis

A cell is shown in the micrograph. Which statement explains how it can be identified which type of microscope was used to produce the micrograph?

The microscope in cell studies

Which processes take place in bone marrow cells that are undergoing the mitotic cell cycle?

Replication and division of nuclei and cells

Telomerase is the enzyme that stops telomeres being lost after many mitotic cell cycles. Which cells are required to transcribe the telomerase enzyme?

Replication and division of nuclei and cells

A polypeptide molecule has the amino acid sequence: glycine - leucine - lysine - valine. The table gives DNA triplets for these amino acids. Which tRNA anticodons are required to synthesise this polypeptide?

Proteins

The diagram depicts part of a DNA strand. Which kind of bond is marked X?

Structure of nucleic acids and replication of DNA

Which row gives the correct description of cytosine?

Structure of nucleic acids and replication of DNA

During the making of protein molecules, just one strand of the DNA double helix is utilised. What is the DNA strand called that is used to produce a new protein?

Proteins

The diagram depicts a longitudinal section through a phloem sieve tube together with a companion cell. In which location are the mitochondria found to provide energy for cotransport?

Movement into and out of cells

The diagram shows a phloem sieve tube element and a companion cell, both of which take part in the translocation of sucrose. Which process correctly explains how sucrose is translocated through these cells?

Movement into and out of cells

What types of molecules are transported into companion cells via co-transport?

Movement into and out of cells

The diagram shows a cross-section of the human heart. Which label is correct?

The heart

Which statement provides evidence that mature plant cells contain organelles that perform the same function as lysosomes?

Cells as the basic units of living organisms

The graph shows the way the volume of the left ventricle varies over one cardiac cycle. Which point on the graph indicates the beginning of atrial systole?

The heart

Which statement is accurate?

Cells as the basic units of living organisms

Which row gives the correct description of an artery?

The circulatory system

Which row identifies the features of the gas exchange surface that make diffusion of carbon dioxide and oxygen faster?

Movement into and out of cells

The electron micrograph depicts part of the airways in an insect gaseous exchange system together with the respiring body cells around them. Which statements identify the correct differences between the insect gas exchange system shown in the electron micrograph and the human gas exchange system?

Movement into and out of cells

Which row correctly matches the wall of the trachea with the wall of the bronchus?

The gas exchange system

A bacterial pathogen makes a protein that functions as a toxin. This toxin is harmful to humans. Scientists are developing monoclonal antibodies that can be used to detect whether the toxin is present in the body so that treatment can be started early. Which statements describe steps in the development of these monoclonal antibodies?

Proteins

Which of these statements about penicillin are correct?

Antibiotics

Why does passive immunity persist for only a brief period?

Antibodies and vaccination

Which row gives the correct control or prevention method for each disease?

Infectious diseases

Which cell structures can contain cisternae?

Cells as the basic units of living organisms

Peptidoglycan is coloured purple by the chemical crystal violet. In the presence of crystal violet, which cells would be stained purple?

Cells as the basic units of living organisms

The diagram illustrates several cell structures from one type of cell. Which labelled cell structures are found in typical eukaryotic cells and typical bacterial cells?

Cells as the basic units of living organisms

The diagram depicts a section of a collagen fibril consisting of collagen triple helices. These collagen triple helices are joined to one another by a single type of bond. In the diagram, this bond is marked as X. What is bond X?

Proteins

The table contains some details about the polypeptides that form haemoglobin. Researchers examined the part of the $\beta$-globin polypeptide chain that includes the amino acid cysteine at position $93$. They discovered that: • this region points outwards when no oxygen is bound to the haem group • this region points inwards when oxygen is bound to the haem group • substituting cysteine with another amino acid lowers the Bohr shift. What conclusion can be drawn from the information about cysteine in haemoglobin?

Proteins

What characteristic of glycogen sets it apart from starch?

Carbohydrates and lipids

The diagram depicts a biological molecule. Which molecules would be formed if this biological molecule were hydrolysed?

Carbohydrates and lipids

What sequence of steps is required to determine the actual width of a xylem vessel seen in transverse section with a $\times 10$ objective lens?

The microscope in cell studies

Two different enzymes, P and Q, are examined to determine the optimum pH for each enzyme. The findings indicate that P functions only under acidic conditions. Q has an optimum pH that is slightly alkaline. Which graph shows the correct results for P and Q?

Factors that affect enzyme action

A student studied how substrate concentration affects the rate of an enzyme-catalysed reaction. The student displayed the results on a graph. What is the $K_m$ for this enzyme-catalysed reaction?

Factors that affect enzyme action

Which statements are suitable for describing enzyme molecules and antibody molecules?

Proteins

Which description shows a reversible, non-competitive enzyme inhibitor?

Mode of action of enzymes

Before mitochondria are taken out of cells for microscopy, they are usually placed in a $0.25\ \text{mol dm}^{-3}$ sucrose solution. Why is the sucrose solution used?

Movement into and out of cells

The photomicrograph shows a kind of blood cell. Which statements about these cells are correct?

Transport of oxygen and carbon dioxide

Which row correctly identifies the parts of a phospholipid molecule?

Fluid mosaic membranes

A student put a sucrose solution into dialysis tubing and tied off both ends. As a result, a cylinder was formed with a length of $5.0\ \text{cm}$ and a radius of $2.0\ \text{cm}$. What is the surface area to volume ratio for this cylinder of dialysis tubing?

Movement into and out of cells

Which process is not carried out using mitosis?

Replication and division of nuclei and cells

This photomicrograph shows cells from an onion root tip. Which of the labelled cells are in anaphase, metaphase and prophase?

Chromosome behaviour in mitosis

Which cell structure is present in human cells and in typical plant cells?

Cells as the basic units of living organisms

The diagram outlines the mitotic cell cycle. In which numbered stages of the cell cycle is there a time when every chromosome is made up of sister chromatids held together by a centromere?

Chromosome behaviour in mitosis

The diagram illustrates a section of a nucleic acid molecule. What is the name of bond X?

Structure of nucleic acids and replication of DNA

XNA is a nucleic acid produced in the laboratory. It is constructed from nucleotides in which one part has been substituted with chemical X. Chemical X is organic, but it does not occur naturally. The section of the molecule that carries the code is unchanged. Which part of a DNA or RNA nucleotide has been replaced by the organic chemical X?

The microscope in cell studies

To which strand of DNA does RNA polymerase bind?

Mode of action of enzymes

Which processes take place when messenger RNA is formed?

Proteins

The anticodon for amino acid tryptophan is ACC. Which of the following shows a template DNA sequence that contains the DNA triplet for tryptophan?

Proteins

A student made a plan diagram of some plant tissue. The diagram is shown. There is an error in the way it has been drawn. The maximum width of R is 15 mm on the diagram and its actual width is 250 $\mu$m. The student was asked to add a scale bar to their diagram. Which row is correct?

The microscope in cell studies

Four students have made drawings and added labels to part of a structure shown in an electron micrograph. Which student has labelled their drawing accurately?

The microscope in cell studies

The diagram illustrates some structures involved in transport in the phloem. Which statement is correct?

Movement into and out of cells

The diagram illustrates a transverse section through the root of a dicotyledonous plant. Which statement gives the correct description of how water and solutes move through this root?

Movement into and out of cells

Which of the following statements are true for a typical prokaryotic cell?

Cells as the basic units of living organisms

The graph illustrates how different partial pressures of carbon dioxide ($\text{CO}_2$) alter the oxygen dissociation curve for haemoglobin. What change occurs in the percentage oxygen saturation of haemoglobin at a partial pressure of oxygen of $6\,\text{kPa}$ when the partial pressure of carbon dioxide rises from $1.0\,\text{kPa}$ to $1.5\,\text{kPa}$?

Proteins

What occurs in the heart at the beginning of ventricular diastole?

The heart

The electron micrograph displays a longitudinal section of a blood vessel. Which type of blood vessel is this?

The microscope in cell studies

A student produced a sketch to illustrate how tissue fluid forms. Which label is correct?

Movement into and out of cells

Which structures can be found in the trachea and in all bronchioles?

The gas exchange system

The photomicrograph shows a slice through part of the gas exchange system. Which tissue can be observed?

The microscope in cell studies

What role do the goblet cells play in the gas exchange system?

The gas exchange system

Which organisms can have their cell walls affected by penicillin?

Antibiotics

Worldwide, malaria causes 462 000 deaths each year among children under 5 years old. Insecticide-treated nets may prevent 50% of malaria cases and cut deaths of children under 5 years old by 18%. How many children could be saved if insecticide-treated nets are used?

Infectious diseases

Which row is right?

Testing for biological molecules

The diagram illustrates a typical animal cell. What function does the membrane system labelled X have?

Cells as the basic units of living organisms

Four stages that take place in the primary immune response to a pathogen are given below. P B-lymphocytes divide by mitosis. Q T-helper cells interact with macrophages that have digested pathogens. R Plasma cells secrete antibodies. S T-helper cells activate other lymphocytes. These stages may be ordered to show the sequence in which they happen. Which stage is third in the sequence?

Replication and division of nuclei and cells

What is meant by a lysosome?

Cells as the basic units of living organisms

The diagram illustrates a triglyceride. What are the products formed after hydrolysis of this triglyceride?

Carbohydrates and lipids

Which description gives every component of a human haemoglobin molecule?

Proteins

HIV-1 protease is an enzyme made by the HIV virus. The enzyme consists of two identical chains, each containing $99$ amino acids. In every chain, amino acids $25$, $26$ and $27$ in the sequence make up part of the active site. Which orders of protein structure determine the shape of the active site?

Proteins

Which statements are correct explanations for the way animals lose heat in hot conditions by using the latent heat of vaporisation of water?

Water