Reproduction · Paper 2 — Free Biology SL Practice Questions

The European white water lily (Nymphaea alba) is a flowering plant that reproduces sexually. Its life cycle involves alternation of generations, with both haploid ($n$) and diploid ($2n$) stages. The gametophyte generation is reduced and dependent on the sporophyte.

A study investigated the reproductive strategies of two freshwater crustacean species, Daphnia pulex and Artemia franciscana. Both species can reproduce asexually (parthenogenesis) or sexually, depending on environmental cues. Population growth rates were measured in controlled laboratory cultures over 30 days: Species — Asexual rate $(\text{day}^{-1})$ — Sexual rate $(\text{day}^{-1})$ Daphnia pulex — $0.32$ — $0.08$ Artemia franciscana — $0.25$ — $0.12$ Genetic diversity was assed using gel electrophoresis of a polymorphic enzyme locus. The number of distinct alleles present in a population of 100 individuals after 30 days was: Species — Asexual reproduction — Sexual reproduction Daphnia pulex — 2 alleles — 8 alleles Artemia franciscana — 3 alleles — 6 alleles

Hieracium pilosella (mouse-ear hawkweed) reproduces both asexually via apomixis (seed production without fertilisation) and sexually. A research team monitored two populations over three growing seasons. Population A (stable field — consistent rainfall and temperature): - Average seed set per plant: $450\,\text{seeds year}^{-1}$ - $95\%$ of seeds produced via apomixis; $5\%$ via sexual reproduction - Seedling survival rate: $72\%$ - $92\%$ of seedlings genetically identical to mother plant (microsatellite analysis) Population B (variable field — unpredictable rainfall, frequent pest outbreaks): - Average seed set per plant: $310\,\text{seeds year}^{-1}$ - $40\%$ of seeds produced via apomixis; $60\%$ via sexual reproduction - Seedling survival rate: $48\%$ - $38\%$ of seedlings genetically identical to mother plant (microsatellite analysis)