Biology questions and solutions
Browse original practice and official past-paper questions. Each question has its own link, with its source and worked solution.
385 questions · Page 16 of 17
- Q131 · Original practice · 4 marksFunctioning ecosystems and successionIn controlled cultures without predators, a snail species survives over pH 5–9. In otherwise comparable cultures containing its predator, it occurs only at pH 6–7. The predator can survive throughout pH 5–9.
- Q132 · Original practice · 5 marksFunctioning ecosystems and successionA mound-building invertebrate creates moist refuges used by several other species. It contributes only 0.2% of community biomass. In a replicated removal experiment, the table gives mean species richness after one year. Initial richness was similar. A leaf-feeding species contributes 18% of biomass.
- Q133 · Original practice · 5 marksFunctioning ecosystems and successionTwo similar abandoned grasslands initially retain soil and seed banks. One experiences a major flood every six years; the other does not. Floods remove most woody seedlings but leave soil and many grass roots. After 30 years, the frequently flooded site remains grass-dominated while the other has extensive woodland.
- Q134 · Original practice · 5 marksFunctioning ecosystems and successionTwo landscapes retain the same total area of forest. Landscape P has one large patch; Q has many small patches separated by cleared land. At forest edges, measurements show higher temperature and lower humidity than in the interior. A moisture-sensitive invertebrate is less abundant in Q.
- Q135 · Original practice · 5 marksGenetics and heredityInitially, both strands of one double-stranded DNA molecule carry a stable label. New nucleotides carry no label. Replication is semiconservative: each daughter molecule contains one template strand and one newly synthesised strand. DNA completes two rounds of replication with no loss or exchange of label.
- Q136 · Original practice · 5 marksGenetics and heredityLetters in the diagram represent chromosome segments containing genes. A misaligned exchange between homologous chromosomes produces two chromatids from an original segment order ABCDE. The centromeres remain intact.
- Q137 · Original practice · 5 marksGenetics and heredityA hypothetical species has three homologous chromosome pairs. Consider independent assortment without crossing over. Each pair provides a choice of one maternally or one paternally inherited homologue in a gamete. Assume those choices are independent and homologues can be distinguished.
- Q138 · Original practice · 5 marksGenetics and heredityA primary RNA transcript is written 5′ to 3′ as exon 1 AUGGA, intron UCUCU, exon 2 ACUUUAA. These two exons form the complete coding region, with one start and one terminal stop codon. Ignore the cap and poly-A tail. Use the code excerpt.
- Q139 · Original practice · 5 marksGenetics and heredityCells with the same DNA sequence are tested under four conditions. A specific activating transcription factor is either absent or supplied. The promoter is in open or compact chromatin. The table gives relative mRNA abundance; background values of 1–3 are considered similarly low for this experiment.
- Q140 · Original practice · 6 marksGenetics and heredityThe pedigree shows a known fully penetrant X-linked dominant trait. Allele causes the trait; does not. There are no new mutations. Individual I-2 is unaffected.
- Q141 · Original practice · 7 marksGenetics and heredityOne autosomal coat-colour locus has three alleles with the dominance order . A parent is crossed with a parent. The phenotype is determined by the highest-ranking allele present.
- Q142 · Original practice · 6 marksGenetics and heredityThe gel profiles show alleles at one autosomal locus. A single diploid individual can have at most two allele bands at this locus. The unknown sample U is compared with references R and S. All four size-marker values label alleles, and distinct alleles have distinct sizes. Assume complete amplification, no new mutations and no additional artefact bands.
- Q143 · Original practice · 7 marksGenetics and heredityA vector is 3000 bp. The intended gene insert is 600 bp. One complete digest cuts each circular plasmid once, showing total length. A second complete digest cuts on both sides of the insert. A gene-specific PCR should produce a 200 bp band if the tested region of the intended gene is present. All positive-control reactions work; empty-vector controls give no…
- Q144 · Original practice · 7 marksContinuity of life on EarthA diploid population has 10 AA, 20 Aa and 30 aa adults. All survive to reproduce. In a supplied model, each AA adult contributes 6 gametes, each Aa adult 4, and each aa adult 2 to a pooled sample. Aa gametes contain A or a with equal probability; use expected allele counts. No mutation or migration occurs.
- Q145 · Original practice · 6 marksContinuity of life on EarthComplete genotype counts are shown for two breeding populations. Ten AA adults move from P to Q and join Q’s breeding population. No birth, death, mutation or other movement occurs.
- Q146 · Original practice · 5 marksContinuity of life on EarthEight small and eight large isolated populations begin with f(A) = 0.50 at a neutral locus. After ten generations their frequencies are shown. No mutation or migration occurs, and A and a do not affect survival or reproduction.
- Q147 · Original practice · 6 marksContinuity of life on EarthA heritable body-size trait has three categories. A selection episode produces the survival counts shown. No migration or reproduction occurs during the episode.
- Q148 · Original practice · 5 marksContinuity of life on EarthA river separates two populations of one frog species for thousands of generations. Their allele frequencies diverge. After the river changes course, the frogs meet, interbreed readily under natural conditions and produce viable, fertile offspring.
- Q149 · Original practice · 5 marksContinuity of life on EarthTwo groups descend from one flowering-plant population in the same field. A heritable flowering-time difference develops: group P flowers in March–April and group Q in September–October, even when grown under the same conditions. Pollen cannot persist between these periods. Later experimental crosses also produce sterile hybrids.
- Q150 · Original practice · 5 marksContinuity of life on EarthOne plant species occupies adjoining metal-rich and metal-poor soils without a physical barrier. Plants disperse pollen mainly to nearby plants. Metal-tolerance alleles are common in the metal-rich soil and rare in the metal-poor soil. A narrow boundary zone contains hybrids, many with reduced fertility.
- Q151 · Original practice · 5 marksContinuity of life on EarthIn a hypothetical plant–fly interaction, flowers have short or long tubes and flies have short or long mouthparts. Both traits are heritable. Equal numbers are tested for the same interval. The table gives mean plant seed production and fly egg production for each pairing. Assume these measures reflect relative reproductive success in the experiment.
- Q152 · Original practice · 6 marksContinuity of life on EarthThe matrix shows differences in a conserved DNA region from five hypothetical species. E is a known outgroup. Assume the stated distances reliably reflect relatedness. A and D have similar feeding structures; their common ancestor lacked those structures.
- Q153 · Original practice · 5 marksContinuity of life on EarthTwo lineages differ at six sites in a conserved sequence. Use the supplied model , with independent changes in both lineages and no repeated substitutions. Calibration constrains each lineage’s rate to differences per million years. Treat this as a model range, not a statistical confidence interval.
- Q154 · Original practice · 7 marksContinuity of life on EarthThe two graphs summarise a synthetic fossil dataset. A mass-extinction episode is identified here when the extinction rate exceeds the shown background rate. Each separated above-background peak is one episode. Ages are measured in millions of years before the present.