TCE Biology — Level 3
Natural Selection — TCE Biology — Level 3 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.
Key Points
- VISA conditions: Variation exists in the population, traits are Inheritable, a Selection pressure acts, and individuals with advantageous traits leave more offspring.
- Natural selection acts on phenotypes (observable traits) but changes genotype frequencies in the next generation.
- Directional selection: favours one extreme, shifts the mean. Example: antibiotic resistance in bacteria.
- Stabilising selection: favours intermediate phenotypes, reduces variation. Example: human birth weight.
- Disruptive selection: favours both extremes, can drive speciation if reproductive isolation develops.
- Tasmanian devils: facial tumour disease (DFTD) is driving selection for tumour-resistant individuals — a Tasmanian case of ongoing evolution.
Common Mistakes to Avoid
- Saying organisms "want" or "try" to evolve — natural selection has no goal.
- Claiming natural selection creates new alleles — it selects from existing variation; mutations create new alleles.
- Using "fitness" loosely — biological fitness means reproductive success, not strength or size.
- Treating selection as an individual-level process — it operates on populations across generations.
- Forgetting that selection pressure must be consistent for directional change to accumulate.
Exam Strategy
TASC Level 3 natural selection questions give you a case study and ask you to apply VISA and identify the selection mode. Structure: (1) describe variation in the starting population, (2) name the selection pressure, (3) explain which phenotype is favoured, (4) describe allele frequency change, (5) name the mode. Tasmanian examples (DFTD) strengthen local responses.
Sample Flashcards
Q1: Outline the process of evolution by natural selection.
1) Variation: individuals in a population vary in heritable traits. 2) Overproduction and competition: more offspring are produced than can survive. 3) Selection pressure: an environmental factor (predation, disease, climate, food) affects survival. 4) Selective advantage: individuals with a favourable phenotype survive and reproduce more. 5) Inheritance: they pass on the favourable alleles. 6) Over generations the frequency of those alleles increases in the population.
Q2: What is meant by selection pressure, selective advantage and fitness?
A selection pressure is any environmental factor that affects which individuals survive and reproduce. A selective advantage is a phenotype that increases an individual’s chance of surviving and reproducing under that pressure. Fitness, in evolution, means reproductive success — the number of offspring an individual contributes to the next generation — not physical strength.
Q3: Explain how antibiotic resistance evolves in a bacterial population.
A population of bacteria varies; a few cells carry a mutation giving resistance to an antibiotic. When the antibiotic is used (selection pressure), susceptible bacteria die and resistant bacteria survive and reproduce rapidly. The resistance allele increases in frequency until most of the population is resistant. Overuse or incomplete courses of antibiotics increase this selection.
Q4: How has the Australian rabbit population evolved in response to the myxoma virus?
When myxoma virus was released in the 1950s it killed over 99% of infected rabbits. Rabbits with heritable resistance survived and reproduced, so resistance alleles increased in frequency. At the same time, less lethal virus strains spread better (infected rabbits lived longer to be bitten by mosquito vectors), so the virus also evolved. This is natural selection acting on both host and pathogen.
Sample Quiz Questions
Q1: Natural selection causes the mutations that organisms need to survive.
Answer: FALSE
Mutations arise randomly. Natural selection acts on variation that already exists.
Q2: In evolutionary terms, fitness refers to an individual’s reproductive success.
Answer: TRUE
Fitness is the contribution of an individual’s offspring to the next generation.
Q3: Antibiotics cause bacteria to become resistant by changing their DNA.
Answer: FALSE
Resistance alleles arise by random mutation; the antibiotic acts as a selection pressure that favours bacteria already carrying them.
Revision Tip
VISA is a reusable framework — drill a Revizi deck applying it to peppered moths, antibiotic resistance, Darwin's finches, and DFTD for broad exam readiness.
Related Concepts
Last updated: 9 October 2026 · 4 sample flashcards · 4 sample quiz questions