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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

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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.
FactorMarineTerrestrial
WaterAlways present; salinity variesRainfall and soil moisture vary
TemperatureChanges slowlyChanges quickly
OxygenDissolved, can be limitingAbundant in air
LightDecreases with depthVaries 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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