2.8.4Additional lessons
Abiotic Factors in Marine and Terrestrial Habitats — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 44 of 142
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.
Part 1 of 5Marine Habitats
Salinity
- Salinity The salt concentration of the water affects osmosis in organisms and sets which species can live in estuaries.
Temperature
- Temperature Water temperature influences metabolism and also how much oxygen can dissolve, since warm water holds less.
Light penetration
- Light penetration Light decreases with depth, so photosynthesis occurs only in the upper, lit layers of the sea.
Dissolved oxygen
- Dissolved oxygen Aquatic animals depend on oxygen dissolved in the water, which varies with temperature and mixing.
Wave action and pH
- Wave action and pH Waves, tides and the acidity of seawater influence which organisms can attach, shelter and form shells.
Part 2 of 5Terrestrial Habitats
Terrestrial Habitats
Temperature
- Temperature Air temperature varies daily and seasonally and limits enzyme activity and growth.
Water availability
- Water availability Rainfall and soil moisture determine whether plants can obtain water for photosynthesis and support.
Light intensity
- Light intensity Shade from other plants reduces light, so ground plants must tolerate low light.
Soil factors
- Soil factors Soil pH, mineral content, drainage and texture affect plant growth and the animals that depend on them.
Wind speed
- Wind speed Strong wind increases transpiration and can physically damage plants and affect animals.
Part 3 of 5Measuring the Factors
Measuring the Factors
Temperature
- Temperature Use a thermometer or data logger probe placed in the water or soil at the sampling site.
Light
- Light Use a light meter held at the same angle and height at each position.
Salinity and pH
- Salinity and pH Use a conductivity or salinity meter and a pH meter or probe.
Wind and moisture
- Wind and moisture Use an anemometer for wind speed and a soil moisture meter for water content.
| Factor | Marine | Terrestrial |
|---|---|---|
| Water | Always present; salinity varies | Rainfall and soil moisture vary |
| Temperature | Changes slowly | Changes quickly |
| Oxygen | Dissolved, can be limiting | Abundant in air |
| Light | Decreases with depth | Varies with shade |
Part 4 of 5Using the Measurements
Using the Measurements
Comparison
- Comparison Take readings at the same time of day in each habitat so that the values can be compared fairly.
Variation
- Variation Record readings at several positions and depths, since conditions can change over a short distance.
Link
- Link Plot species abundance against each measured factor to look for patterns in distribution.
Part 5 of 5Exam Checklist & Tips
2.8.4 – Key Points for the Exam
- Salinity The concentration of dissolved salts in water.
- Dissolved oxygen Oxygen gas dissolved in water, available to aquatic organisms.
- Soil pH The acidity or alkalinity of the soil.
- Data logger A device with probes that records measurements automatically.
Common Mistakes
- Saying that oxygen is a limiting factor in air for most terrestrial species; it is plentiful in air.
- Believing that warm water holds more dissolved oxygen than cold water.
- Taking a single light reading and using it for the whole habitat.
- Measuring different abiotic factors with different units at different positions and comparing them directly.
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