CourseCourseQ BankQuestion BankDocsDocuments

D4.3.9 (HL)—Phenology

Phenology studies the timing of recurring seasonal biological events such as budburst, migration, breeding, emergence, and disease-vector activity each year.

Syllabus
First assessment 2025
Objective
D4.3.9
Level
HL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks1–2

Common command terms

  • Identify
  • Analyse

Recent exam appearances

November 2025Paper1A ["HL"] · TZ339[ 1 ]D4.3.9 (HL)—Phenology
November 2019Paper2 ["HL"] · TZ01(d)[ 2 ]D4.3.9 (HL)—Phenology
November 2019Paper2 ["HL"] · TZ01(c)[ 1 ]D4.3.9 (HL)—Phenology
Practice this objective

Coverage 2019–2025 · Updated 16 Jul 2026

Phenology Tracks the Timing of Seasonal Events

HL only

Phenology is the timing of recurring biological events such as flowering, migration, breeding or leaf-out.

Temperature, day length and resource cues control schedules. Climate warming can advance or delay events, changing overlap among interacting species.

Record the event, cue, date shift and interacting species before inferring ecological impact.; separate driver, mechanism, response and timescale

Warmer springs advance caterpillar emergence; a bird that migrates on a fixed cue may miss the food peak. This gives a concrete prediction from the stated climate condition.

A date shift alone is not a population decline; consequences depend on synchrony and alternative food. Interpret the result within the stated evidence and scenario limits.

Phenology exam focus

HL only

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through multiple choice, data analysis, commonly using Identify / Analyse.

Command terms

Identify / Analyse

What earns marks

Build the answer around this relationship: Phenology is the study of seasonal timing in biological events.

Representative question

Question 1

[Maximum number: 1]

Which of the following could be a subject of phenological research?

A

Timing of budburst in a tree species each year

B

Changes in allele frequencies in a population over time

C

The relationship between changes in ocean acidification and carbon dioxide concentration

D

The emergence of a new species of migratory bird by divergent evolution

HL Timing and Selection

HL only

HL D4.3 adds timing and evolution. Phenology tracks when seasonal events happen; warming can desynchronize interacting species, shorten insect development, add generations, and change selection pressures so phenotype frequencies shift.

  • timing of flowering, migration, breeding, nesting or insect emergence
  • interacting species shift timing by different amounts
  • warmer temperatures can add generations and attack periods
  • milder winters alter selection and phenotype frequencies

HL Phenology and Climate Selection

HL only

HL climate questions require reasoning from timing to ecological or evolutionary consequence. The answer starts with a seasonal event or life-cycle stage, explains how warming shifts timing or selection pressure, and states the effect on interaction success, number of generations, attack periods, survival, or phenotype frequency.

  • Define phenology and identify the seasonal event being shifted.
  • Explain timing mismatch or faster development using named examples such as plant-reindeer, great tit-caterpillar, or spruce bark beetles.
  • Link climate-altered selection pressure to phenotype frequency change using the tawny owl example.

Concept essentials

  • Phenology is the study of seasonal timing in biological events.
  • Warming can shift when insects, plants, birds, or pathogens are active.
  • Phenological data can identify changes in exposure, reproduction, migration, or resource availability.