Feb/March 2023

The photomicrograph displays cells taken from a human blood smear. Which calculation correctly determines the actual diameter of the neutrophil visible in the photomicrograph in micrometres ($\mu\text{m}$)?

The microscope in cell studies

The diagram shows a molecule from a cell surface membrane. Which statement about one of the labels is correct?

Fluid mosaic membranes

Which row correctly indicates the levels of protein structure that each type of interaction can hold together?

Proteins

Which molecules include at least three double bonds?

Carbohydrates and lipids

Which diagram shows hydrogen bonding correctly between two water molecules?

Water

Which statement gives an example of an extracellular enzyme?

Mode of action of enzymes

Which row gives the correct description of enzymes that catalyse reactions according to the lock-and-key hypothesis?

Mode of action of enzymes

A scientist studied how quickly hydrogen peroxide decomposed. Four experiments were done using different mixtures: substrate only, substrate + enzyme, substrate + enzyme + competitive inhibitor, substrate + enzyme + non-competitive inhibitor. The results are shown in the graph sketch. Which row gives the correct lines for two of the experimental mixtures?

Mode of action of enzymes

Which one of these substances can diffuse straight through cell surface membranes without the aid of a carrier protein or a channel protein?

Movement into and out of cells

How does the surface area to volume ratio of a cube change if the length of each side is doubled?

Cells as the basic units of living organisms

Which of these events occur in the mitotic cell cycle?

Replication and division of nuclei and cells

A student used a stage micrometer to calibrate an eyepiece graticule. The stage micrometer had divisions of $0.01\,\text{mm}$ each. When the objective lens was set to $\times 10$, 10 eyepiece graticule units lined up with 10 divisions on the stage micrometer. The same microscope was then fitted with a $\times 40$, rather than a $\times 10$, objective lens to measure the diameter of an alveolus. This diameter was measured as 96 eyepiece graticule units. The eyepiece lens was left unchanged. What is the best estimate for the diameter of the alveolus?

The microscope in cell studies

The human body is estimated to contain a total of $2.5 \times 10^{13}$ red blood cells. Each day, about $2.5 \times 10^{11}$ red blood cells are taken out of the circulation and substituted by stem cells in the bone marrow. What percentage of the overall number of red blood cells is replaced per day?

Replication and division of nuclei and cells

DNA polymerase catalyses condensation reactions between molecules during semi-conservative replication of DNA. Which molecules are joined by DNA polymerase?

Replication and division of nuclei and cells

A DNA molecule is formed from two polynucleotide strands. Which statement is correct?

Proteins

The PDx1 protein is present in many different animal species, where it is considered vital for normal metabolism. In sand rats, the gene that codes for the PDx1 protein contains a much smaller proportion of A and T nucleotides than PDx1 genes from other animals. It has been difficult to determine the full DNA sequence of the PDx1 gene in sand rats. Sequencing requires removing nucleotides one at a time from single-stranded DNA. What might explain the difficulty in determining the DNA sequence of the PDx1 gene in sand rats?

Structure of nucleic acids and replication of DNA

Plant tissues were each given a radioactively labelled substance in order to determine which tissues were actively synthesising mRNA. Which radioactively labelled substances would be suitable for this experiment?

Protein synthesis

Which row gives the correct pairing of the structure and function of phloem sieve tube elements?

Structure of transport tissues

Which xylem vessel elements feature assists adhesion during transpiration?

Water

Mass flow refers to the net movement of materials from one location to another in bulk. How many of the vessels named below transport fluids by mass flow? artery; phloem sieve tube; vein; xylem vessel

Movement into and out of cells

Cellulose, lignin and suberin are parts of different plant cell walls. Several descriptions of these cell wall components are given below. Which row accurately links three of the descriptions to the correct cell wall components?

Cells as the basic units of living organisms

The arrows indicate the direction of water movement through a plant root, from water in the soil to the xylem. Which arrows show water movement only in the apoplast pathway?

Movement into and out of cells

Which of the following statements are true for chloroplasts and also for mitochondria?

Cells as the basic units of living organisms

Which row gives the correct identification of sources and sinks of sugars?

Transport mechanisms

The photomicrograph displays a section of tissue containing an artery. Which row correctly identifies the type of artery and whether the blood inside it is oxygenated or deoxygenated?

The microscope in cell studies

Heart surgery may reduce the transmission of impulses through the Purkyne tissue to the right side of the heart. What effect could this reduction have?

The heart

The diagram illustrates a network of blood vessels that delivers blood to muscle tissue in the human body. When the muscle tissue is at rest, which statement correctly compares the blood at X with the blood at Y?

Transport of oxygen and carbon dioxide

Evidence shows that the oxygen dissociation curves for haemoglobin in smaller mammals lie to the right of those for larger mammals. What does this imply about the haemoglobin of smaller mammals?

Proteins

What effect does a higher concentration of carbon dioxide in the blood have?

Transport of oxygen and carbon dioxide

An efficient gas exchange system needs a large surface area and a short diffusion distance. Which row shows correctly how alveoli are adapted to satisfy these requirements?

Movement into and out of cells

What characterises infectious diseases?

Infectious diseases

On an island, a hurricane devastates a large town. Residents leave the town and live in tents, where sanitation is poor. Which disease is most likely to spread within a week after the living conditions change?

Infectious diseases

Which statement gives the correct reason that penicillin has no effect on viruses?

Antibiotics

The electron micrograph displays some cells taken from a root. Which cell structure is not normally present in cells from a root?

Cells as the basic units of living organisms

Which processes are involved in the action of phagocytes?

Movement into and out of cells

Dialysis (Visking) tubing is a man-made partially permeable membrane with pores of around $2.5\,\text{nm}$. Glucose molecules are about $1.5\,\text{nm}$ in diameter, so they are able to move through the membrane pores. What else is able to pass through the pores?

Movement into and out of cells

What do all viruses contain?

Proteins

To determine the glucose concentration in an unknown solution, equal amounts of several glucose solutions with known concentrations were each combined with the same excess volume of Benedict’s solution. Once mixed, the samples were kept in a thermostatically controlled water-bath at $90\,^{\circ}\text{C}$ for three minutes. The unknown solution was then handled in the same way, and the colours of the known and unknown solutions were compared. What is the independent variable in this procedure?

Testing for biological molecules

Which statements are true for amylose and for amylopectin as well?

Carbohydrates and lipids

Which statement gives a correct comparison between saturated triglyceride molecules and unsaturated triglyceride molecules with approximately the same molecular masses?

Carbohydrates and lipids

Table 1.1 shows cell structures that may occur in eukaryotic cells or in prokaryotic cells. A number of these structures are shared by both cell types.

Transport mechanisms

Cysteine is an amino acid that contains sulfur. Fig. 2.1 displays the structure of the molecule produced when two cysteine molecules are joined together. Draw a circle around an R-group in the molecule shown in Fig. 2.1.

Protein synthesis

Fig. 3.1 shows an area of phloem tissue from a transverse section through the stem of a squash plant, Cucurbita pepo.

Transport mechanisms

Tuberculosis (TB), influenza and polio are all examples of infectious diseases.

Antibodies and vaccination

Pneumonia is a serious disease of the lungs that can disrupt gas exchange. A person who has pneumonia may be attached to an ECMO machine. This machine carries out the gas exchange roles of the lungs. A cannula (tube) is inserted into the right atrium and carries blood to the ECMO machine. Inside the ECMO machine, the blood is sent first to an artificial pump and then to an oxygenator, where gas exchange takes place. The blood is then warmed and returned by a second cannula to the vena cava.

The gas exchange system

Collagen is the most abundant structural protein in vertebrates. It gives the skin flexibility and strength. Explain how the structure of a collagen fibre gives the skin strength.

Protein synthesis

Fig. 1.1 is a sketch of a longitudinal section (LS) through a human kidney.

Homeostasis in mammals

The text in Fig. 10.1 is about biodiversity. Fill in the gaps with the most suitable scientific terms.

Biodiversity

Interferon-alpha (IFN-α) may be manufactured as a recombinant human protein to treat certain cancers. The IFNA2 gene codes for IFN-α. One way to make recombinant IFN-α is to use genetically engineered Escherichia coli bacteria carrying recombinant plasmids. Each recombinant plasmid includes the IFNA2 gene; three lac operon regulatory sequences (promoter, operator and lacI); and an antibiotic resistance gene, AMPR. The sequences for the lacI gene and AMPR gene each have their own promoter. Therefore, these genes are always expressed in E. coli bacteria that contain this recombinant plasmid. Fig. 2.1 shows the recombinant plasmid. The promoter regions of the lacI gene and AMPR gene are not shown.

Gene control

Salmon may be genetically modified (GM) so that they make greater amounts of growth hormone, which is a protein. GM salmon altered in this way grow more quickly and reach their maximum body mass at a younger age than non-GM salmon.

Variation

Array comparative genome hybridisation (aCGH) is a method that uses a microarray to examine an entire genome or selected regions of a genome.

Principles of genetic technology

Meiosis is termed a reduction division because the chromosome number in the daughter cells is reduced by half.

Passage of information from parents to offspring

Fig. 6.1 shows a diagram of part of a mitochondrion in section. The four arrows, A, B, C and D, indicate how molecules and ions move.

Respiration

Fig. 7.1 shows a synapse linking a chemoreceptor cell from a human taste bud with a dendrite of a sensory neurone. In an experiment, the microvilli of the chemoreceptor cell were exposed to different concentrations of sodium chloride solution. For each concentration, the membrane potential of the chemoreceptor cell and that of the sensory neurone dendrite were measured. The resting potential of this chemoreceptor cell is $-50\,\text{mV}$ and the resting potential of the dendrite of this sensory neurone is $-70\,\text{mV}$. The results are given in Table 7.1, with sodium chloride concentrations in $\text{g dm}^{-3}$ and membrane potentials in $\text{mV}$.

Control and coordination in mammals

Describe the role of the internal membranes of the chloroplast in photosynthesis.

Photosynthesis as an energy transfer process

Fig. 9.1 shows a relaxed sarcomere in striated muscle.

Control and coordination in mammals