IB Biology HL Theme A: Unity and diversity questions

Answer: C. The modeled zone spans 1.20–2.00 × 10¹¹ m, so site C at 1.80 × 10¹¹ m is within it. Its sample is liquid, with the hydrophilic probe dissolved and the hydrophobic probe undissolved, matching water’s solvent properties. Many hydrophilic molecules dissolve in water, and most enzymes catalyse reactions in aqueous solution, so these observations support a possible medium for metabolism, but do not establish that life is present.
A: the location and liquid water fit, but dissolution of the known hydrophobic probe does not match the expected solvent pattern.
B: being in the zone does not make ice a liquid aqueous medium for enzyme catalysis.
D: the solvent observations fit, but 2.20 × 10¹¹ m is beyond the survey’s zone.
Remember: the Goldilocks zone makes surface liquid water possible; it does not guarantee water or life.

Answer: B. A clade contains a common ancestor and all its descendants. The branching sequence gives nested clades P+Q and P+Q+R (and the full set); R+S is not a clade because their common ancestor also has P and Q as descendants. Classification can still organize extensive diversity for comparison, while unranked clades avoid implying that fixed taxonomic ranks measure evolutionary divergence.
A: It assumes both traditional classes are clades; class N excludes P and Q even though they descend from the same ancestor as R and S.
C: It treats the limitation of fixed ranks as a reason to discard classification, although classification facilitates comparative study.
D: It assigns rank by group size; the branching pattern does not require nested clades to have class and order ranks.
Remember: clades express common ancestry, whereas taxonomic ranks are fixed categories.

Answer: C. Courtship displays were accepted less often between species than within either species, indicating a behavioural barrier to mating. Although some interspecific matings produced viable offspring, none of the viable hybrids were fertile, so they could not pass alleles to later generations. The results indicate barriers to allele flow but do not show a change in heritable characteristics of a population over time.

A: Confuses viability with fertility; the hybrids were viable but could not reproduce.
B: Reverses the barrier stages: courtship affects mating before fertilization, while sterility occurs in hybrids.
D: Treats a difference between pairings as evidence of heritable change over time; the data do not establish that change.

Remember: Viable offspring can still be sterile and unable to transmit alleles to another generation.