TCE Biology — Level 3
Natural Selection — Flashcards & Quiz
Natural selection is the mechanism by which populations evolve through differential survival and reproduction of individuals with advantageous traits. TCE Biology Level 3 expects you to apply the VISA framework (Variation, Inheritance, Selection pressure, Advantage) to named case studies and distinguish the three modes of selection. Tasmanian devil facial tumour disease is a locally relevant evolutionary case study.
Sample Flashcards
Q1: Explain Darwin's theory of natural selection.
Natural selection is the mechanism of evolution: 1) Variation exists within a population (due to mutations, sexual reproduction). 2) Organisms produce more offspring than can survive (overproduction). 3) There is a struggle for existence (competition for limited resources). 4) Individuals with advantageous traits are more likely to survive and reproduce (survival of the fittest). 5) These traits are inherited by offspring, increasing their frequency in the population over generations.
Q2: Distinguish between directional, stabilising and disruptive selection.
Directional selection: favours one extreme phenotype, shifting the population mean (e.g. antibiotic resistance). Stabilising selection: favours intermediate phenotypes, reducing variation (e.g. human birth weight). Disruptive selection: favours both extreme phenotypes over intermediates, potentially leading to speciation (e.g. beak size in seed-cracking birds).
Q3: What is coevolution and give an example?
Coevolution is the reciprocal evolutionary change between two interacting species, where each exerts selective pressure on the other. It can occur between predator-prey, parasite-host, or mutualistic pairs. Each species evolves in response to changes in the other.
Sample Quiz Questions
Q1: Natural selection acts on the phenotype of an individual, not directly on its genotype.
Answer: TRUE
Natural selection acts on phenotypes (observable traits) because these determine an organism's fitness in its environment. The underlying genotype is what is inherited by offspring.
Q2: Natural selection can introduce new alleles into a population.
Answer: FALSE
Natural selection can only act on existing variation — it selects for or against alleles already present. Only MUTATION introduces new alleles into a population.
Q3: Stabilising selection favours extreme phenotypes over intermediate ones.
Answer: FALSE
Stabilising selection favours INTERMEDIATE phenotypes and selects against extremes, reducing variation. It is DISRUPTIVE selection that favours both extreme phenotypes over intermediates.
Last updated: March 2026 · 3 flashcards · 3 quiz questions