Biology interleaved practice

1. (Subtopic 1.1.3 — living/non-living/once-living)

• Growing fern = living — shows growth, metabolism, responsiveness.
• Dried wood = once-living — was part of a living tree (had cells, grew) but no longer performs life functions.
• Rock = non-living — never carried out life processes; no cells/metabolism. Why this subtopic: the trap is that wood looks "dead like a rock," but its cellular/biological origin makes it once-living, requiring the three-way distinction rather than a simple living/non-living split.

2. (Subtopic 1.1.17 — SI units & prefixes) Convert all to metres:

• $2.5 \text{ mm} = 2.5\times10^{-3} \text{ m}$
• $400 \ \mu\text{m} = 4.0\times10^{-4} \text{ m}$
• $0.0015 \text{ m} = 1.5\times10^{-3} \text{ m}$
• $3\times10^{5} \text{ nm} = 3\times10^{5}\times10^{-9} = 3.0\times10^{-4} \text{ m}$ Order smallest→largest: $4.0\times10^{-4} = 400\,\mu\text{m}$, then $3.0\times10^{-4}$ nm value...

Careful re-sort: $3.0\times10^{-4}$ and $4.0\times10^{-4}$: $3.0\times10^{-4} < 4.0\times10^{-4}$. Final order: $3\times10^{5}\text{ nm}\ (3.0\times10^{-4}) < 400\,\mu\text{m}\ (4.0\times10^{-4}) < 0.0015\text{ m}\ (1.5\times10^{-3}) < 2.5\text{ mm}\ (2.5\times10^{-3})$. Why: requires converting every prefix to a common base — students must choose conversion over eyeballing.

3. (Subtopic 1.1.4 — metabolism: anabolism vs catabolism)

• Glucose breakdown = catabolic — large molecule broken to smaller ones, releasing energy (exergonic).
• Anabolic example: building proteins from amino acids, or synthesising glycogen — requires energy input. Why: direction of the reaction (break vs build) determines the category; students must map energy release↔catabolism, energy consumption↔anabolism.

4. (Subtopics 1.2.1 & 1.2.2 — atomic structure, atomic/mass number) (a) Atomic number = protons = 11 (sodium). (b) Mass number = protons + neutrons = $11+12 =$ 23. (c) Charge = protons − electrons = $11 - 11 =$ 0 (neutral). (d) If it lost one electron it becomes a $+1$ ion — changes charge/reactivity (not the element identity, since protons unchanged). Why: distinguishes atomic number (protons only) from mass number (protons+neutrons); the charge sub-part guards against confusing ionisation with isotopy.

5. (Subtopics 1.1.15 & 1.1.16 — variables & controls)

• Independent variable: fertiliser concentration (what's changed).
• Dependent variable: plant height (what's measured).
• Controlled variables (any two): water amount, light exposure, plant species, soil type, temperature.
• No-fertiliser group = the control; it provides a baseline to show that any height difference is due to fertiliser and not other factors. Why: must correctly assign cause (IV) vs effect (DV) and recognise a control group's role — a different skill from #6/#7.

6. (Subtopics 1.1.10 & 1.1.11 — levels of organization + emergent properties) Order: atom → molecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem → biosphere. Emergent property: a property that appears at a level of organization that none of the individual parts possess alone — e.g., a cell is alive though its individual molecules are not; life "emerges" from their organization. Why: ordering tests the hierarchy; the definition tests understanding that wholes ≠ sum of parts.

7. (Subtopic 1.1.14 — hypothesis/theory/law)

• Hypothesis: a testable, tentative proposed explanation for a specific observation.
• Theory: a broad, well-substantiated explanation supported by large amounts of evidence (e.g., cell theory / theory of evolution).
• Law: a description of a consistently observed pattern in nature, often expressed concisely, but does not explain why. Why: common misconception is that a theory is "just a guess" — the ranking clarifies evidential weight.

8. (Subtopics 1.2.4, 1.2.5, 1.1.5 — bond types + homeostasis) (a) Within water: polar covalent bond (O–H); electrons shared unequally, O more electronegative. (b) Between water molecules: hydrogen bond (weaker). (c) Hydrogen bonds give water a high specific heat, so it resists temperature change — helping organisms maintain a stable internal body temperature (homeostasis). Why: integrates chemistry (bond hierarchy) with a life characteristic — students must not confuse intramolecular covalent with intermolecular hydrogen bonds.

9. (Subtopics 1.1.8 & 1.1.5 — responsiveness vs homeostasis) (a) Responsiveness (irritability) — the body detects the cold stimulus and reacts (shivering is a response). (b) It is also homeostasis because shivering generates heat to keep core temperature constant — the response serves to maintain a stable internal environment. So responsiveness is the mechanism; homeostasis is the goal. Why: deliberately ambiguous to force distinguishing a response from the regulatory purpose it serves.

10. (Subtopics 1.2.3 & 1.2.6 — isotopes + CHNOPS) (a) Isotopes of each other. (b) Same protons (6), different neutrons (C-12 has 6, C-14 has 8) → different mass number. (c) Element = Carbon (C in CHNOPS). Biological use: radioactive isotopes used in radiometric dating (C-14), or as tracers to track metabolic pathways. Why: isotopes share atomic number but differ in mass — links back to #4's number concepts, testing whether students pick "isotope" vs "ion."

[
  {
    "claim": "Q4: mass number of atom with 11 protons and 12 neutrons is 23 and it is neutral",
    "code": "protons=11\nneutrons=12\nelectrons=11\nmass_number=protons+neutrons\ncharge=protons-electrons\nresult = (mass_number==23) and (charge==0)"
  },
  {
    "claim": "Q2: correct smallest-to-largest ordering of the four lengths in metres",
    "code": "vals={'3e5 nm':3e5*1e-9,'400 um':400e-6,'0.0015 m':0.0015,'2.5 mm':2.5e-3}\norder=[k for k,_ in sorted(vals.items(), key=lambda x:x[1])]\nresult = order==['3e5 nm','400 um','0.0015 m','2.5 mm']"
  },
  {
    "claim": "Q10: C-12 and C-14 have equal protons but differ by 2 neutrons",
    "code": "c12_p, c12_n = 6, 6\nc14_p, c14_n = 6, 8\nresult = (c12_p==c14_p) and (c14_n-c12_n==2)"
  }
]