Unity and Diversity — Free Biology SL Practice Questions

A student places a red blood cell and an Elodea leaf cell into separate beakers of distilled water ($\psi = 0\,\text{kPa}$). The cells are observed under a microscope after 10 minutes. $$\text{Red blood cell: } \psi_s = -800\,\text{kPa}$$ $$\text{Elodea leaf cell: } \psi_s = -800\,\text{kPa},\quad \psi_p = +600\,\text{kPa}$$

A coastal city experiences a sea breeze during the day. The land surface heats to $35\,^{\circ}\text{C}$, while the sea surface remains at $22\,^{\circ}\text{C}$. The specific heat capacity of dry soil is $800\,\text{J\,kg}^{-1}\text{K}^{-1}$ and the specific heat capacity of seawater is $4200\,\text{J\,kg}^{-1}\text{K}^{-1}$.

A medical researcher investigates a polymer hydrogel for controlled drug delivery. The hydrogel consists of cross-linked poly(acrylic acid) (PAA) chains. At physiological pH 7.4, the carboxyl groups (–COOH) dissociate to carboxylate ions (–COO⁻). A positively charged drug molecule, doxorubicin ($\text{DOX}^+$), is loaded into the hydrogel.

A population of a small mammal species lives on an island with two distinct habitats: a dark, forested area and a light, sandy beach. The mammals are preyed upon by birds that hunt by sight. A biologist recorded fur colour frequencies over several generations. Generation 1 — $45\%$ light fur, $55\%$ dark fur — $60\%$ light fur, $40\%$ dark fur Generation 10 — $82\%$ light fur, $18\%$ dark fur — $21\%$ light fur, $79\%$ dark fur - Average offspring per breeding pair, Generation 1: $4.2$ - Average offspring per breeding pair, Generation 10: $3.8$

A farmer notices that a species of weed in his fields has become increasingly resistant to a common herbicide over a period of 8 years. In Year 1, the herbicide at the recommended dose killed $95\%$ of the weed population. By Year 8, the same dose killed only $15\%$ of the weed population. The farmer also observed that individual weed plants exposed to sub-lethal doses of the herbicide sometimes produced offspring that were slightly more resistant, even without direct herbicide exposure to those offspring.

A population of Poecilia reticulata (guppies) lives in a stream in Trinidad. One section of the stream contains the predator fish Crenicichla alta; an adjacent upstream section, separated by a waterfall, is predator-free. The waterfall prevents gene flow between the two populations. Guppies in the predator-present section mature at a smaller size and produce more, smaller offspring than those in the predator-absent section. A researcher recorded the following data over one generation: Section — Average offspring per female — Survival rate to reproductive age Predator-present — 20 — $10\%$ Predator-absent — 8 — $60\%$

A tropical rainforest was fragmented over 30 years due to agricultural expansion. The maps below show the forest distribution before and after this period.

A study examined the impact of agricultural runoff on a lake ecosystem. The graph below shows the concentration of dissolved oxygen $(\text{mg}\,\text{L}^{-1})$ at different depths in the lake before and after a fertilizer spill.

A team of ecologists is studying the impact of deforestation ecosystem service value in a tropical rainforest reserve. The reserve has an area of $500\,\text{km}^2$ and currently supports a population of $1200$ jaguars, a keystone species. The annual economic value of ecosystem services (carbon sequestration, water purification, and pollination) provided by the reserve is estimated at USD $2.5$ million per $\text{km}^2$ at the current jaguar population density. Deforestation reduces the jaguar population by $15\%$ per year. The ecosystem service value per $\text{km}^2$ decreases proportionally to jaguar population density.

A replication fork forms during DNA replication in a bacterium. - Rate of DNA polymerase III: $1000$ nucleotides per second - Length of the bacterial chromosome: $4.6 \times 10^{6}$ base pairs - Energy required to add one nucleotide to a growing strand: $2.0 \times 10^{-19}\,\text{J}$

A segment of double-stranded DNA has the following sequence: $$5'\text{-ATGCCTAG-}3' \quad \text{(coding strand)}$$ $$3'\text{-TACGGATC-}5' \quad \text{(template strand)}$$

A research team investigates regulation of the lac operon in E. coli under different environmental conditions. The relative rate of transcription of the lacZ gene (encoding $\beta$-galactosidase) is measured under three conditions, normalised so that Condition 1 = $0.1$. Condition — Glucose — Lactose — Relative transcription rate 1 — present — absent — $0.1$ 2 — absent — present — $100$ 3 — present — $2.0$

A plant cell chloroplast carries out photosynthesis. Under high light intensity, a single chloroplast produces $5.4 \times 10^{-17}\,\text{mol}$ of glucose per second. The chloroplast contains 200 thylakoid stacks (grana), each with an average of 50 thylakoid discs.

A bacterial culture is grown under optimal conditions. Each ribosome synthesizes a polypeptide of 300 amino acids in $15\,\text{s}$. The average mass of an amino acid is $110\,\text{Da}$, where $1\,\text{Da} = 1.66 \times 10^{-24}\,\text{g}$.

The fluid mosaic model describes the dynamic structure of cell membranes. The below shows a representation of a plasma membrane with various components labelled A to E.

The cladogram below shows proposed evolutionary relationships among five tetrapod groups: amphibians, reptiles, birds, marsupials, and placental mammals. Four shared derived characters (synapomorphies) are mapped onto the tree. Group — Amniotic egg — Endothermy — Mammary glands — Hair/fur Amphibians — — — — Reptiles — ✓ — — — — Birds — ✓ — — Marsupials — ✓ — — — ✓ Placental mammals — ✓ — — — ✓

Researchers studying six insect species (A–F) have identified three shared derived characters: (i) folded wings, (ii) social behaviour, (iii) modified mouthparts for piercing. The presence (+) or absence (–) of each character is shown below. Species — (i) folded wings — (ii) social behaviour — (iii) piercing mouthparts A — – — – B — + — – C — + — – D — + — + E — – — + F — – — + The outgroup (ancestral state) for all three characters is absent (–). Characters evolve only in the direction absent → present (no reversals).

A research team investigates evolutionary relationships among four species of flowering plants (Silene: species P, Q, R, S) and one outgroup species T. A cladogram is constructed from three shared derived characters (synapomorphies). The table below summarises character presence (+) or absence (−). Species — Character 1: Red flowers — Character 2: Fused petals — Character 3: Nectar spur P — + — − Q — + — − R — + — + S — − — − T (outgroup) — − — −