Biology HL

1. 1.

   A hypothetical landscape loses its wetland, retains the same total number of bird species in remaining woodland, and its isolated amphibian population loses several alleles. Explain why unchanged bird species richness does not establish unchanged biodiversity, using three levels of biodiversity.

   [4 marks] · no calculator

   Worked explanation

   1. Separate a single taxon's species count from the diversity of genes, species and ecosystems across a landscape.
   2. Allele loss and habitat-type loss each record a change not captured by the bird count.
   3. An unchanged number can also mask replacement of specialists by widespread species.

   Common mistake: Species richness is not interchangeable with genetic diversity, evenness or diversity of ecosystems.

   Marking points

   • Species richness measures the number of species, not every component of biodiversity.
   • Loss of amphibian alleles reduces genetic diversity.
   • Loss of the wetland reduces ecosystem diversity.
   • Even among birds, unchanged richness can conceal changed species identities or relative abundances.

   Examiner tip: Species richness is not interchangeable with genetic diversity, evenness or diversity of ecosystems.

2. 2.

   Hypothetical surveys find 30 plant species in ten quadrats in year 1 and 22 species in five quadrats in year 2. Explain why a biodiversity decline cannot be quantified confidently from these totals. Propose two improvements and state what repeated comparable surveys could establish.

   [4 marks] · no calculator

   Worked explanation

   1. Sampling half as many quadrats can miss rare species even if the underlying community is unchanged.
   2. Standardize effort and timing and include replication to distinguish a consistent trend from sampling variation.
   3. A trend is evidence of change under the survey design; identifying a driver requires additional comparisons.

   Common mistake: Calculating a percentage fall in raw species totals does not correct for unequal sampling effort.

   Marking points

   • Different sampling effort alone can change the number of species detected.
   • Use equal sampled area/number of quadrats with comparable placement rules.
   • Match season and identification methods and/or use adequate repeated random samples to estimate variability.
   • Repeated comparable surveys can provide evidence of a change in detected species diversity, not prove its cause without further evidence.

   Examiner tip: Calculating a percentage fall in raw species totals does not correct for unequal sampling effort.

3. 3.

   A hypothetical wild plant is threatened by habitat clearance. Its seeds tolerate drying and storage, but its pollinator also depends on that habitat. Compare habitat protection with seed banking and explain why using both may be preferable to relying on either alone.

   [4 marks] · no calculator

   Worked explanation

   1. Use the stated storage tolerance rather than assuming every species can be banked conventionally.
   2. Protecting interactions supports ongoing reproduction and selection in the wild.
   3. A backup collection and a viable habitat address complementary risks, with monitoring and genetic representation still needed.

   Common mistake: Storing seeds is not equivalent to preserving a functioning ecosystem or guaranteeing a successful reintroduction.

   Marking points

   • In situ habitat protection maintains the plant together with its pollinator and ecological interactions.
   • Seed banking preserves stored genetic material as an ex situ safeguard against loss in the wild.
   • A seed bank alone does not preserve the functioning habitat or pollinator and reintroduction still needs suitable conditions.
   • Combining habitat protection with a genetically representative seed collection reduces different risks; neither guarantees success.

   Examiner tip: Storing seeds is not equivalent to preserving a functioning ecosystem or guaranteeing a successful reintroduction.

4. 4.

   Hypothetical surveys use equal sampling effort and detect ten bird species at each of two sites. At site A, one species accounts for 91 of 100 records and each other species for one. At site B, each species accounts for ten records. Compare species richness and evenness, and explain why equal richness does not imply equal community diversity.

   [3 marks] · no calculator

   Worked explanation

   1. Count distinct species separately from the number of records belonging to each species.
   2. The totals are both 100, so the abundance imbalance is not merely a difference in total sampling records.
   3. State the comparison qualitatively without inventing a numerical diversity index not supplied by the task.

   Common mistake: Species richness is the number of species, not the total number of individuals or records.

   Marking points

   • Both sites have species richness of ten.
   • Site B has greater evenness; site A is dominated by one species.
   • Community diversity can reflect both richness and relative abundance, so equal species counts alone do not establish equal diversity.

   Examiner tip: Species richness is the number of species, not the total number of individuals or records.

5. 5.

   A hypothetical endangered plant survives in a threatened habitat. A conservation team proposes storing seeds from a single individual and then allowing the habitat to be destroyed. Evaluate this plan in terms of genetic diversity, ecosystem relationships and complementary conservation measures.

   [4 marks] · no calculator

   Worked explanation

   1. Recognise the benefit of ex situ storage before analysing what it fails to conserve.
   2. A population-level conservation claim needs representative genetic material, not just many seeds from one parent.
   3. In situ and ex situ measures can complement each other; neither seed number nor storage alone guarantees successful reintroduction.

   Common mistake: Many seeds from one individual do not automatically represent the genetic diversity of an entire species.

   Marking points

   • Seed storage may preserve some viable genetic material outside the habitat.
   • Sampling one individual captures only a limited part of the population's genetic variation.
   • A seed bank alone does not preserve pollinators, interactions or the whole habitat.
   • Combine representative collection from suitable individuals/populations with habitat protection/restoration and viability monitoring where feasible.

   Examiner tip: Many seeds from one individual do not automatically represent the genetic diversity of an entire species.

Original, unofficial practice questions from SubjectScout — not official past-paper questions or complete syllabus coverage. Added English teaching explanations are AI-authored; independent teacher review is pending.