HSC Biology — Module 6
Natural Selection — Flashcards & Quiz
Natural selection is the mechanism by which populations evolve over time. In HSC Biology Module 6, you need to understand how variation, competition, and differential reproduction drive adaptation. Key subtopics include directional, stabilising, and disruptive selection, as well as antibiotic resistance as a modern example. Exam questions often require you to distinguish between natural selection and genetic drift, and to explain how selection acts on phenotypes rather than genotypes.
Sample Flashcards
Q1: Outline Darwin's theory of natural selection.
1) Variation exists within populations (genetic differences). 2) More offspring are produced than can survive (overproduction). 3) Individuals compete for limited resources (struggle for existence). 4) Those with favourable traits survive and reproduce more (survival of the fittest). 5) Favourable alleles are passed to the next generation, increasing in frequency over time.
Q2: What is antibiotic resistance and why is it an example of natural selection?
Some bacteria have random mutations that make them resistant to antibiotics. When antibiotics are used, susceptible bacteria die but resistant ones survive and reproduce, passing the resistance allele on. Over time, the population becomes predominantly resistant.
Q3: Distinguish between stabilising, directional and disruptive selection.
Stabilising: favours average phenotypes, reduces variation (e.g. human birth weight). Directional: favours one extreme, shifts mean (e.g. antibiotic resistance). Disruptive: favours both extremes over intermediates, can lead to speciation (e.g. seed size in finches).
Sample Quiz Questions
Q1: Natural selection acts on the phenotype, not directly on the genotype.
Answer: TRUE
Natural selection acts on observable traits (phenotypes). Organisms with phenotypes better suited to the environment survive and reproduce, passing their genotypes on.
Q2: Antibiotics cause bacteria to develop resistance mutations.
Answer: FALSE
Antibiotics do NOT cause mutations. Resistant mutations arise randomly beforehand. Antibiotics SELECT for pre-existing resistant bacteria by killing susceptible ones.
Q3: Stabilising selection favours extreme phenotypes over the average.
Answer: FALSE
Stabilising selection favours the AVERAGE phenotype and reduces variation. DISRUPTIVE selection favours extreme phenotypes.
Related Concepts
Last updated: March 2026 · 3 flashcards · 3 quiz questions