Finally! It’s time to share our TOP 110 IB Biology Extended Essay research questions, collected by IB extended essay writers for HL and SL students.

These questions are carefully categorized to align with IB EE requirements — all are focused, researchable, and grounded in biological theory, suitable for experimental or secondary data analysis.

🟩 25 Simple but Interesting Biology Extended Essay Topics

(manageable lab-based or researchable questions)

1. To what extent does light intensity affect the rate of photosynthesis in Elodea?
2. How does temperature affect enzyme activity of catalase on hydrogen peroxide?
3. To what extent does salt concentration affect the germination of radish seeds?
4. How does pH affect the growth of Escherichia coli in a controlled environment?
5. How does the surface area to volume ratio affect the rate of osmosis in potato cubes?
6. To what extent does caffeine concentration affect the heart rate of Daphnia?
7. How does different wavelength (color) of light affect the rate of photosynthesis in algae?
8. How does detergent concentration affect cell membrane permeability in beetroot cells?
9. To what extent does water temperature affect dissolved oxygen levels in aquatic ecosystems?
10. How does the concentration of glucose affect the respiration rate of yeast?
11. To what extent does music affect the growth rate of bean plants?
12. How does the type of sugar influence fermentation rate in yeast?
13. To what extent does temperature affect the transpiration rate in bean plants?
14. How does the presence of nitrates affect algal bloom formation in freshwater samples?
15. How does soil pH affect the growth rate of Arabidopsis thaliana?
16. To what extent does mold growth differ on organic vs. non-organic bread?
17. How does humidity affect the transpiration rate in tomato plants?
18. How does the concentration of ethanol affect microbial growth inhibition?
19. How does the age of leaves affect the rate of photosynthesis?
20. To what extent does wind speed affect the rate of transpiration in plants?
21. How does time of day affect the sugar concentration in maple sap?
22. How does the depth of a pond affect biodiversity of aquatic macroinvertebrates?
23. To what extent does exercise intensity affect human breathing rate?
24. How does exposure to acidic conditions affect the germination of cress seeds?
25. How does leaf color (variegated vs. green) affect chlorophyll content and photosynthesis?

🟦 25 Unique and Not Overused Biology EE Questions

(fresh and original ideas, rarely used in school labs)

26. How does blue light exposure affect circadian rhythm gene expression in fruit flies?
27. To what extent does magnetic field exposure affect the growth of Lactobacillus acidophilus?
28. How does different compost type affect soil microbial diversity over 4 weeks?
29. To what extent do antioxidant levels vary in fruits ripened in natural vs. artificial conditions?
30. How does urban noise pollution affect the stress hormone levels in pigeons (via feather cortisol)?
31. To what extent does varying UV light exposure affect mutation rates in E. coli?
32. How does simulated acid rain affect the leaf microstructure of spinach plants?
33. To what extent do different sugar types affect biofilm formation in dental bacteria?
34. How does chewing gum affect the bacterial count of the human oral cavity?
35. How does the presence of caffeine affect reaction time in humans (via digital app tests)?
36. How does exposure to smartphone light affect melatonin levels in sleep-deprived individuals?
37. To what extent do different brands of antibacterial soap affect skin microbiota diversity?
38. How does soil compaction affect earthworm burrowing behavior?
39. To what extent does CO₂ enrichment affect stomatal density in bean leaves?
40. How does the leaf wax composition of plants change in drought vs. well-watered conditions?
41. How does artificial vs. natural lighting affect root growth direction (gravitropism)?
42. How does sound frequency affect seedling growth of Phaseolus vulgaris?
43. To what extent does plastic mulch influence soil temperature and microbial respiration?
44. How does the genetic diversity of dandelion populations vary in urban vs. rural zones?
45. To what extent does vitamin C content differ between freshly squeezed and bottled orange juice over time?
46. How does the presence of pollutants in tap water (e.g. fluoride) affect yeast growth rate?
47. How does the human microbiome diversity change before and after a short-term antibiotic course?
48. To what extent does the scent of essential oils inhibit mold growth on bread?
49. How does human touch frequency affect microbial colonization on phone screens?
50. To what extent does leaf texture (smooth vs. hairy) influence water retention under wind exposure?

🟥 25 Complex and Challenging Questions for IB Bio EE

(for ambitious students using secondary data, simulations, or advanced biology)

51. How does gene expression of photosystem II-related proteins vary with light intensity in Arabidopsis thaliana?
52. To what extent does mitochondrial DNA mutation correlate with aging in human muscle tissue (secondary data)?
53. How does genome size correlate with developmental rate across amphibians?
54. To what extent can CRISPR-Cas9 be used to suppress disease vectors in Aedes aegypti mosquitoes?
55. How do invasive plant species alter nitrogen cycling in temperate forest ecosystems?
56. How does antibiotic resistance gene expression differ between hospital and environmental E. coli strains?
57. To what extent do stress-induced hormones affect immune system gene regulation in mice?
58. How do neural synapse densities vary across species with differing memory capacity?
59. To what extent do genetic polymorphisms influence lactose intolerance in different ethnic groups?
60. How do climate variables affect coral bleaching events on a molecular signaling level?
61. How do telomere shortening rates differ among cell types with high vs. low proliferation rates?
62. How does prion protein misfolding lead to neurodegeneration in Creutzfeldt-Jakob disease (CJD)?
63. How does simulated microgravity affect gene expression in Drosophila melanogaster larvae?
64. To what extent does leaf nitrogen content correlate with photosynthetic rate across C₃ and C₄ plants?
65. How does environmental stress affect epigenetic methylation patterns in plants?
66. How do differences in transposable element density affect genome evolution in maize vs. wheat?
67. To what extent can computational models predict protein folding in sickle-cell hemoglobin?
68. How does viral load correlate with symptom severity in SARS-CoV-2 case data (2020–2023)?
69. How does the surface area of alveoli change in smokers vs. non-smokers (lung histology datasets)?
70. To what extent does habitat fragmentation impact gene flow in red fox (Vulpes vulpes) populations?
71. How do mycorrhizal symbioses differ in nutrient uptake between monocots and dicots?
72. To what extent can population bottlenecks be detected through mitochondrial DNA analysis?
73. How do plant circadian rhythms adapt under constant darkness in Arctic plant species?
74. To what extent does endocrine disruption by BPA affect reproductive success in aquatic organisms?
75. How do transgenic crops affect insect herbivory and predator populations in agroecosystems?

🟨 25 IB Biology EE Current and Up-to-Date Questions

(using modern challenges, biotechnology, environment, pandemics, etc.)

76. How does air pollution affect stomatal density in urban vs. rural plant samples?
77. How does the microbial diversity of hand sanitizers change after repeated use during the COVID-19 pandemic?
78. To what extent do different mask materials affect bacterial growth on the skin?
79. How does microplastic ingestion affect feeding behavior in aquatic invertebrates?
80. How does COVID-19 lockdown affect daily circadian rhythms in adolescents?
81. To what extent does glyphosate exposure affect root elongation in model plants?
82. How does urban heat island effect influence transpiration rates in city trees?
83. How does temperature fluctuation affect the rate of COVID-19 transmission (correlation study)?
84. How do wearable fitness trackers affect heart rate variability measurements compared to ECG?
85. How does the presence of PFAS chemicals affect soil microbial activity?
86. How does overuse of hand sanitizer affect the human skin microbiome?
87. How does simulated drought affect carbon allocation between roots and shoots in wheat seedlings?
88. How do different brands of plant-based meat affect gut bacterial fermentation (in vitro fermentation models)?
89. To what extent does the composition of biodegradable plastics affect microbial decomposition rate?
90. How do varying CO₂ concentrations affect chloroplast development in Arabidopsis?
91. How does diet diversity affect gut microbial composition in humans (review/meta-analysis)?
92. How do algae-based biofuels affect oxygen levels in aquatic tanks during growth?
93. How does the rate of mutation in viruses like influenza correlate with host immunity over time?
94. To what extent does sunscreen runoff impact phytoplankton photosynthesis?
95. How does the level of atmospheric ozone affect UV penetration in skin cancer models (secondary)?
96. To what extent do probiotics alter intestinal flora diversity after antibiotic use?
97. How does artificial light exposure at night affect melatonin production in rodents (model-based)?
98. How do CRISPR-edited crops affect pest resistance in maize fields (data-based)?
99. How does temperature shock affect cell membrane permeability in yeast cells?
100. To what extent does caffeine-based fertilizer affect plant growth rate and leaf morphology?

🟪 10 Fun and Unusual Questions for Your Biology Extended Essay

(playful, quirky, and scientifically valid)

101. To what extent do horror movies increase adrenaline levels (measurable via heart rate)?
102. How does chewing different flavors of gum affect concentration in students (test-based)?
103. To what extent does playing video games affect pupil dilation and reaction time?
104. How does music genre affect the plant growth rate (light/sound-controlled chamber)?
105. How do different shoe types affect bacterial growth on insoles after running?
106. To what extent do “emotional support plants” reduce stress hormone levels in students?
107. How does mobile phone usage affect eye-blinking rate and eye strain symptoms?
108. To what extent do facial bacteria differ between makeup users and non-users?
109. How does sugar content in soft drinks affect the rate of tooth enamel softening (with eggshells as proxy)?
110. How does posture (slouching vs. upright) affect respiratory rate and lung capacity?