2.9.2Inquiry Process
Abiotic Factors and Species Distribution — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 93 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 4Abiotic Factors and Their Effects
Non-living conditions affect every organism, and each effect can be linked to a life process.
Light intensity
- Light intensity Plants need light for photosynthesis, so shaded or deep habitats support fewer photosynthetic species than bright, open ones.
Temperature
- Temperature Temperature changes the rate of enzyme-controlled reactions, so each species can function only within a limited band of temperatures.
Water availability
- Water availability All organisms need water, and in dry habitats only species with water-saving adaptations can survive.
Soil pH and minerals
- Soil pH and minerals Different plant species need particular pH values and nutrient concentrations, which affects which plants grow in a soil.
Wind speed
- Wind speed Strong wind increases evaporation from leaves, so it raises water loss and can restrict plants to sheltered places.
Gas concentrations
- Gas concentrations Carbon dioxide is needed for photosynthesis and oxygen for aerobic respiration, so low levels of either can limit a species.
| Abiotic factor | Life process affected |
|---|---|
| Light intensity | Photosynthesis |
| Temperature | Enzyme activity and metabolic rate |
| Oxygen concentration | Aerobic respiration |
| Wind speed | Water loss by evaporation |
Section 2 of 4Limiting Factors and Tolerance
Limiting Factors and Tolerance
Limiting factor
- Limiting factor An abiotic or biotic factor that restricts the growth or numbers of organisms when it is in short supply or too extreme.
Optimum
- Optimum The level of a factor at which a species grows and reproduces best, so population size is greatest around this value.
Range of tolerance
- Range of tolerance The span of values between the lower and upper limits within which a species can survive, even if conditions are not ideal.
Critical limits
- Critical limits Below the critical minimum or above the critical maximum the species cannot survive, and the population size falls to zero.
Interaction of factors
- Interaction of factors Several abiotic factors act together, so a species distribution reflects the combined effect of all of them, not just one.
Section 3 of 4Extreme Environments
1
A species living in an extreme habitat often has an environmental optimum that is higher or lower than average, such as marram grass needing less water than most plants.
2
Mangrove trees grow best at moderate salinity, roughly 3 to 27 parts per thousand, yet can survive in fresh water and up to about 75 parts per thousand.
3
Species with a wide tolerance can live where others cannot, and they face little competition in these harsh places.
4
The same specialist species may do poorly in moderate habitats, because competitors with an average optimum outcompete them there.
5
Distribution therefore depends on abiotic tolerance and also on biotic factors such as competition.
Section 4 of 4Exam Checklist & Tips
2.9.2 – Key Points for the Exam
- Limiting factor A factor that restricts the growth or distribution of organisms.
- Range of tolerance The range of values of an environmental factor within which a species can survive.
- Optimum The value of a factor at which a species performs best.
- Distribution Where a species is found within an ecosystem.
Common Mistakes
- Writing that organisms can survive only at their optimum; they survive across a whole range of tolerance.
- Stating that a species is absent from a place only because of competition; abiotic limits can exclude it too.
- Treating each abiotic factor as acting alone when in reality the factors interact.
- Forgetting to name the process affected, such as photosynthesis or respiration, when explaining an effect.
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