Form and Function — Free Biology SL Practice Questions

A group of students investigated the effect of a drug on protein secretion from pancreatic acinar cells. They measured the concentration of a digestive enzyme in the extracellular medium over $30$ minutes under two conditions: normal cells and cells treated with a drug that disrupts the Golgi apparatus. All cells were maintained at $37°\text{C}$ in an isotonic buffer. Condition — Enzyme concentration at $t = 0\,\text{min}$ — Enzyme concentration at $t = 30\,\text{min}$ Normal cells — $0.0\,\text{mg mL}^{-1}$ — $2.4\,\text{mg mL}^{-1}$ Golgi-disrupted cells — $0.0\,\text{mg mL}^{-1}$ — $0.3\,\text{mg mL}^{-1}$

A researcher studies a eukaryotic cell genetically modified so that its lysosomal membrane is permeable to protons ($\text{H}^+$ ions). The cell is placed in culture medium at $\text{pH}\ 7.2$.

Hepatocytes (liver cells) are highly active in endocytosis and phagocytosis, internalising materials into phagosomes that fuse with lysosomes for digestion. A research team investigates the effect of a novel drug, EndoX, on lysosomal function in hepatocytes. They measure the activity of the lysosomal hydrolase Cathepsin D and the intralysosomal pH under two conditions. Condition — Cathepsin D activity / AU — Intralysosomal pH A — untreated — 85 — 4.8 B — EndoX-treated — 22 — 6.9 - Optimum pH for Cathepsin D (determined in vitro): $4.5$ to $5.0$ - Cytosolic pH of hepatocytes: $7.2$

A research group investigates the potential of stem cells to treat spinal cord injuries. They obtain two types of cells from a patient: multipotent stem cells from the patient's bone marrow, and induced pluripotent stem cells (iPSCs) generated from the patient's skin fibroblasts.

A patient with type 1 diabetes has lost the function of insulin-producing beta cells in the pancreas. Scientists propose to generate new beta cells from stem cells for transplantation.

A research team investigates the potential of induced pluripotent stem cells (iPSCs) to treat a patient with type 1 diabetes mellitus. The patient's own skin fibroblasts are reprogrammed into iPSCs using the Yamanaka factors (Oct4, Sox2, Klf4, c-Myc). These iPSCs are then differentiated into pancreatic beta cells. Data collected after 14 days of differentiation: - Untreated iPSCs: $15\%$ expressed the beta-cell marker PDX1 - Embryonic stem cells (ESCs) under the same protocol: $72\%$ expressed PDX1 - iPSCs pre-treated for 48 hours with a histone deacetylase inhibitor (HDACi): $68\%$ expressed PDX1 - Genome analysis of iPSCs before and after HDACi treatment: no change in DNA sequence; $40\%$ increase in acetylation of histone H3 at the PDX1 gene promoter

A student investigates gas exchange in the leaves of a terrestrial plant, Zebrina pendula. She examines a cross-section under a light microscope and identifies the following layers: upper epidermis, palisade mesophyll, spongy mesophyll, and lower epidermis containing stomata surrounded by guard cells. Large air spaces are visible between the spongy mesophyll cells.

A student compares gas exchange in a flatworm (Planaria) and a woody stem (Tilia europaea). The flatworm lacks specialised respiratory organs. The woody stem is covered by bark containing lenticels.

A group of students investigated the effect of body mass on the tracheal system of insects. They measured the total cross-sectional area of the main tracheal trunks entering the thorax of three species of grasshopper and recorded the data below. They also calculated the rate of oxygen consumption ($\text{VO}_2$) for each species at rest. Species — Body mass / g — Total tracheal cross-sectional area / $\text{mm}^2$ — $\text{VO}_2$ / $\text{mL O}_2\,\text{g}^{-1}\,\text{h}^{-1}$ Schistocerca gregaria — $2.0$ — $0.40$ — $0.18$ Locusta migratoria — $1.5$ — $0.30$ — $0.18$ Chorthippus brunneus — $0.8$ — $0.16$ — $0.18$

A student investigates the effect of temperature on the rate of starch digestion by amylase. She adds amylase to a starch solution at $37\,°\text{C}$ and at $60\,°\text{C}$, then measures the concentration of maltose produced every 2 minutes for 10 minutes. Her results are shown below. Time (min) — Maltose at $37\,°\text{C}$ ($\text{g\,L}^{-1}$) — Maltose at $60\,°\text{C}$ ($\text{g\,L}^{-1}$) 0.0 — 0.0 2 — 1.2 — 0.3 4 — 2.4 — 0.6 6 — 3.6 — 0.9 8 — 4.8 — 1.2 10 — 6.0 — 1.5

A biology student sets up an experiment using dialysis tubing to model the digestion of starch. She fills one bag with a $2\%$ starch solution and a second bag with a $2\%$ starch solution mixed with amylase. Both bags are placed in separate beakers of distilled water at $37\,^\circ\text{C}$. After 30 minutes, she tests the water outside each bag for the presence of starch (using iodine solution) and for reducing sugars (using Benedict's reagent). Results: - Bag 1 (starch only): iodine test — water remains yellow-brown; Benedict's test — water remains blue. - Bag 2 (starch + amylase): iodine test — water remains yellow-brown; Benedict's test — water turns orange-red.

A study investigated the effect of acarbose, an amylase inhibitor, on starch digestion in humans. Eight healthy volunteers each consumed a standard meal containing $50\,\text{g}$ of starch. Blood glucose concentration was measured at 30-minute intervals for 180 minutes after the meal. The experiment was repeated one week later with the same volunteers; each volunteer took $100\,\text{mg}$ of acarbose immediately before the meal. Time after meal $(\text{min})$ — Mean blood glucose without acarbose $(\text{mmol}\,\text{L}^{-1})$ — Mean blood glucose with acarbose $(\text{mmol}\,\text{L}^{-1})$ 0 — 4.8 30 — 7.2 — 6.1 60 — 8.5 — 6.8 90 — 7.9 — 6.4 120 — 6.5 — 5.7 150 — 5.6 — 5.2 180 — 5.0 — 4.9

A patient is admitted to the emergency department with a suspected pulmonary embolism. A blood clot has lodged in a branch of the pulmonary artery, obstructing blood flow to a portion of the right lung.

A researcher measures blood pressure and blood velocity in different blood vessels of a mammalian circulatory system. Vessel — Systolic / diastolic pressure (mmHg) — Mean blood velocity ($\text{cm s}^{-1}$) Aorta — 120 / 80 — 40 Arteriole — 60 / 40 — 10 Capillary — 30 / 20 — 0.5 Venule — 20 / 15 Vena cava — 10 / 5 — 25

A medical researcher is investigating a newly discovered mutation in the gene encoding connexin-43, a protein that forms gap junctions in the sinoatrial (SA) node and atrioventricular (AV) node of the human heart. The mutation causes a $40\%$ reduction in the rate of ion flow through these gap junctions. A patient with this mutation has a resting heart rate of $72\,\text{bpm}$ and a stroke volume of $70\,\text{mL}$. Reference values: - Normal PR interval: $0.12$–$0.20\,\text{s}$ - Normal QRS duration: $< 0.12\,\text{s}$ - Normal corrected QT interval: $< 0.44\,\text{s}$ - $\text{CO} = \text{HR} \times \text{SV}$

A point mutation in the $\beta$-globin gene changes the sixth codon from GAG to GTG, substituting glutamic acid (hydrophilic, negatively charged) with valine (hydrophobic, non-polar) in the $\beta$-globin polypeptide. Individuals homozygous for this allele develop sickle cell anaemia; heterozygous individuals carry one normal and one mutant allele.

The enzyme lysozyme is a globular protein that hydrolyses bacterial cell walls. Its structure includes regions of $\alpha$-helix and $\beta$-pleated sheet, stabilised by hydrogen bonds, disulfide bridges, and hydrophobic interactions. A researcher treats lysozyme with a reducing agent that breaks all disulfide bridges (—S—S— bonds) but leaves peptide bonds intact.

Bovine pancreatic trypsin inhibitor (BPTI) is a protein of 58 amino acids. In its native state it has a well-defined tertiary structure stabilised by three disulfide bridges ($-\text{S}-$) between cysteine residues at positions 5–55, 14–38, and 30–51, and it is a potent inhibitor of the enzyme trypsin. A research team treats native BPTI with Compound X, which specifically reduces disulfide bridges to free thiol groups ($-\text{SH}$). After treatment, trypsin-inhibitory activity falls to $5\%$ of the original value. The treated BPTI is then allowed to refold in the presence of oxygen (which can re-oxidise thiol groups to disulfide bridges); after 24 hours, activity recovers to only $12\%$ of the original value. In a separate control experiment, native BPTI is denatured with $8\,\text{M}$ urea — which disrupts hydrogen bonds and hydrophobic interactions but leaves disulfide bridges intact — and then allowed to refold by dialysis to remove the urea. Activity recovers to $98\%$ of the original value.

The intertidal zone of a rocky shore in the Pacific Northwest is home to two species of barnacle: Balanus glandula (acorn barnacle) and Chthamalus dalli (thatched barnacle). Balanus grows faster and outcompetes Chthamalus in the lower intertidal zone but is less tolerant of desiccation during low tide. Chthamalus can survive higher on the shore where air exposure is longer. Researchers measured the fundamental niche of each species in the laboratory by growing them across a gradient of submersion times. - Balanus fundamental niche: $8$–$24$ hours submersion per day - Chthamalus fundamental niche: $2$–$18$ hours submersion per day Researchers then cleared a section of the mid-intertidal zone (average $12$ hours submersion per day) of all barnacles and monitored recolonisation over two years. After two years, only Balanus was present in the cleared zone.

In a freshwater lake in Uganda, two species of cichlid fish (Haplochromis nyererei and Haplochromis pyrrhocephalus) coexist. Both feed on zooplankton but have different mouth morphologies allowing prey capture at different depths. Researchers measured stomach contents of 50 individuals of each species across four depth zones. The table shows the percentage of each species' total feeding time spent in each zone. Depth zone — H. nyererei — H. pyrrhocephalus $0\text{–}2\,\text{m}$ — $10\%$ — $45\%$ $2\text{–}4\,\text{m}$ — $25\%$ — $35\%$ $4\text{–}6\,\text{m}$ — $40\%$ — $15\%$ $6\text{–}8\,\text{m}$ — $25\%$ — $5\%$

A study was conducted in a temperate deciduous forest in Vermont, USA, to investigate the ecological niches of three sympatric warbler species: the Blackburnian Warbler (Setophaga fusca), the Black-throated Green Warbler (Setophaga virens), and the Yellow-rumped Warbler (Setophaga coronata). Researchers recorded foraging height and the percentage of time spent foraging on different tree parts over three breeding seasons. Table 1: Foraging data for three warbler species Species — Mean foraging height $\pm$ SD (m) — Needles/leaves (%) — Branches (%) — Trunks (%) Blackburnian — $14.2 \pm 1.8$ — 78 — 18 — 4 Black-throated Green — $9.7 \pm 2.1$ — 62 — 30 — 8 Yellow-rumped — $5.3 \pm 2.5$ — 45 — 38 — 17